U.S. patent application number 16/984942 was filed with the patent office on 2020-11-26 for thermoplastic liquid crystal polymer film, circuit board, and methods respectively for manufacturing said film and said circuit board.
This patent application is currently assigned to KURARAY CO., LTD.. The applicant listed for this patent is KURARAY CO., LTD.. Invention is credited to Takahiro NAKASHIMA, Minoru ONODERA, Takeshi TAKAHASHI.
Application Number | 20200375030 16/984942 |
Document ID | / |
Family ID | 1000005004535 |
Filed Date | 2020-11-26 |
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United States Patent
Application |
20200375030 |
Kind Code |
A1 |
NAKASHIMA; Takahiro ; et
al. |
November 26, 2020 |
THERMOPLASTIC LIQUID CRYSTAL POLYMER FILM, CIRCUIT BOARD, AND
METHODS RESPECTIVELY FOR MANUFACTURING SAID FILM AND SAID CIRCUIT
BOARD
Abstract
Provided are a thermoplastic liquid crystal polymer film having
an improved thermo-adhesive property, a circuit board, and methods
respectively for producing the same. The thermoplastic liquid
crystal polymer film has a segment orientation ratio SOR of 0.8 to
1.4 and a moisture content of 300 ppm or less. The circuit board
contains a plurality of circuit board materials wherein the circuit
board materials are at least one member selected from the group
consisting of an insulating substrate having a conductor layer on
at least one surface, a bonding sheet, and a coverlay. At least one
of the circuit board materials includes a thermoplastic liquid
crystal polymer film. The circuit board shows a solder heat
resistance when the circuit board is placed in a solder bath at
290.degree. C. for 60 seconds in accordance with JIS C 5012.
Inventors: |
NAKASHIMA; Takahiro;
(Kamisu-shi, JP) ; TAKAHASHI; Takeshi;
(Kamisu-shi, JP) ; ONODERA; Minoru;
(Kurashiki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KURARAY CO., LTD. |
Kurashiki-shi |
|
JP |
|
|
Assignee: |
KURARAY CO., LTD.
Kurashiki-shi
JP
|
Family ID: |
1000005004535 |
Appl. No.: |
16/984942 |
Filed: |
August 4, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15084554 |
Mar 30, 2016 |
10765001 |
|
|
16984942 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 5/18 20130101; H05K
3/4611 20130101; C09K 19/3809 20130101; H05K 1/036 20130101; B32B
27/08 20130101; B32B 27/36 20130101; C08J 2367/04 20130101; B32B
15/20 20130101; H05K 1/0298 20130101; H05K 2201/0141 20130101; B32B
2307/50 20130101; H05K 3/4632 20130101; H05K 2201/0129 20130101;
B32B 3/04 20130101; B32B 2457/08 20130101; B32B 7/05 20190101; H05K
1/0326 20130101; B32B 15/08 20130101; B32B 2307/306 20130101 |
International
Class: |
H05K 1/03 20060101
H05K001/03; B32B 15/08 20060101 B32B015/08; B32B 27/08 20060101
B32B027/08; B32B 15/20 20060101 B32B015/20; H05K 3/46 20060101
H05K003/46; C08J 5/18 20060101 C08J005/18; B32B 3/04 20060101
B32B003/04; B32B 7/05 20060101 B32B007/05; C09K 19/38 20060101
C09K019/38; H05K 1/02 20060101 H05K001/02 |
Claims
1-17. (canceled)
18. A method for producing a thermoplastic liquid crystal polymer
film, the method at least comprising: preparing a thermoplastic
liquid crystal polymer film being capable of forming an optical
anisotropic melt phase and having a segment orientation ratio SOR
of 0.8 to 1.4, and degassing the thermoplastic liquid crystal
polymer film by degassing the film (i) under vacuum of 1500 Pa or
lower for 30 minutes or more, by degassing the film (ii) under
heating at a temperature ranging from 100.degree. C. to 200.degree.
C., or by degassing the film under the above (i) and (ii)
simultaneously or separately, so as to produce a thermoplastic
liquid crystal polymer film having a segment orientation ratio SOR
of 0.8 to 1.4 and a moisture content in accordance with Karl
Fischer method of 300 ppm or less.
19. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the degassing of the film is
performed by a process comprising: a first degassing of the
prepared thermoplastic liquid crystal polymer film under heating at
a temperature ranging from 100.degree. C. to 200.degree. C. for a
predetermined period of time, and a second degassing of the
thermoplastic liquid crystal polymer film after the first degassing
under vacuum of 1500 Pa or lower for a predetermined period of
time.
20. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the degassing under vacuum (i)
is carried out while heating the film at a temperature ranging from
80.degree. C. to 200.degree. C. under vacuum of 1500 Pa or
lower.
21. The method for producing a thermoplastic liquid crystal polymer
film according to claim 19, wherein the second degassing process is
carried out while heating the film at a temperature ranging from
80.degree. C. to 200.degree. C. under vacuum of 1500 Pa or
lower.
22. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film has a film thickness of 10 to 200 .mu.m.
23. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film after degassing has a skin layer.
24. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film after degassing is used as an insulating
substrate having a conductor layer on at least one surface.
25. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film after degassing is used as a bonding
sheet.
26. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film after degassing is used as a coverlay.
27. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film to be subjected to degassing is in a sheet
form or a roll form.
28. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film to be subjected to degassing is in a roll form
having a winding thickness of 1000 mm or smaller.
29. The method for producing a thermoplastic liquid crystal polymer
film according to claim 18, wherein the thermoplastic liquid
crystal polymer film after degassing is wrapped with a packaging
material having a gas barrier property.
30. A method for producing a circuit board at least comprising:
preparing a plurality of circuit board materials; stacking the
prepared circuit board materials in accordance with a predetermined
structure of a circuit board to obtain a stacked material, followed
by conducting thermo-compression bonding of the stacked material by
heating under a predetermined compression pressure; wherein the
prepared circuit board materials are at least one member selected
from the group consisting of an insulating substrate having an
conductor layer on at least one surface, a bonding sheet, and a
coverlay, and (I) at least one of the prepared circuit board
materials comprises a degassed thermoplastic liquid crystal polymer
film subjected to degassing as recited in claim 18, (II) at least
one of the prepared circuit board materials comprises a
non-degassed thermoplastic liquid crystal polymer film, and the
degassing process as recited in claim 18 is conducted after the
preparation of the circuit board materials and before the
thermo-compression bonding, or (III) at least one of the prepared
circuit board materials comprises a degassed thermoplastic liquid
crystal polymer film subjected to degassing as recited in claim 18
and the degassing process as recited in claim 18 is conducted after
the preparation of the circuit board materials and before the
thermo-compression bonding.
31. The method for producing a circuit board according to claim 30,
wherein the thermo-compression bonding of the circuit board
materials is performed by heating the materials while compressing
the materials under a compression pressure of 5 MPa or lower.
32. The method for producing a circuit board according to claim 31,
wherein the thermo-compression bonding of the circuit board
materials is performed by heating the materials while compressing
the materials under a compression pressure of 0.5 to 2.5 MPa.
33. The method for producing a circuit board according to claim 30,
wherein the circuit board materials are heated at a temperature
ranging from (Tm-60).degree. C. to (Tm+40).degree. C. during the
thermocompression bonding, where Tm is the melting point of the
thermoplastic liquid crystal polymer film subjected to the
thermocompression bonding.
Description
CROSS REFERENCE TO THE RELATED APPLICATION
[0001] This application is a continuation application, under 35
U.S.C. .sctn. 111(a), of international application No.
PCT/JP2014/075875, filed Sep. 29, 2014, which claims priority to
Japanese patent applications No. 2013-208209 filed Oct. 3, 2013,
No. 2014-065751 filed Mar. 27, 2014, and No. 2014-119850 filed Jun.
10, 2014, the entire disclosures of which are herein incorporated
by reference as a part of this application.
FIELD OF THE INVENTION
[0002] The present invention relates to a film of a thermoplastic
liquid crystal polymer capable of forming an optically anisotropic
melt phase (hereinafter may be referred to as a thermoplastic
liquid crystal polymer film, or TLCP film, or simply abbreviated as
a liquid crystal polymer film, or LCP film) having an improved
thermo-adhesive property, and a method for producing the same, and
to a circuit board and a method for producing the same.
BACKGROUND ART
[0003] Electronics such as information processing devices and
communication equipment generally include circuit boards inside. A
circuit board typically includes an insulating-material substrate
and a conductive-material layer on the substrate, and the
conductive-material layer includes circuits to form a predetermined
circuit pattern. Various electronic components can be mounted on
the circuit board by means of processing such as soldering.
Recently a multilayer circuit board having a plurality of conductor
layers has come to be widely used.
[0004] There has been known a conventional circuit board including
a polyimide as an insulating material, for example, a circuit board
that comprises (i) a wiring substrate comprising a polyimide film
and a circuit formed from a conductor layer on the polyimide film
and (ii) a coverlay comprising a polyimide film and an adhesive
layer to be bonded to the wiring substrate.
[0005] However, such a circuit board sometimes has poor heat
resistance, especially poor solder heat resistance, due to usage of
an adhesive. Further, some circuit boards contain residual solvent
originated from the adhesive. The presence of the solvent in the
circuit boards may cause defects in the circuit board after
multi-layering process, resulting in deterioration of reliability
of the circuit boards. Accordingly, a technique for forming a
circuit board without using an adhesive has been desired.
[0006] In recent years, there have been remarkable developments in
the field of information processing, such as personal computers, as
well as in the field communication equipment, such as mobile
phones. Such electronics and communication equipment have come to
be operated at higher frequencies of gigahertz region. In the high
frequency band, however, it is known that the electronics and
communication equipment generally have increased in transmission
loss.
[0007] Circuit boards have been conventionally known as one
comprising a wiring substrate in which a conductor circuit is
formed on a polyimide film, and a coverlay film bonded on the
wiring substrate, the coverlay film comprising a polyimide film and
an adhesive layer.
[0008] However, such a circuit board sometimes has poor heat
resistance, especially poor solder heat resistance, due to adhesive
usage. Further, some circuit boards contain residual solvent
originated from the adhesive. The presence of the solvent in the
circuit boards may cause defects in the circuit board after
multi-layering process, resulting in deterioration of reliability
of the circuit boards. Accordingly, a technique for forming a
circuit board without using an adhesive has been desired.
[0009] On the other hand, TLCP films have attracted attention as
substrate materials for forming circuit boards without using an
adhesive. The TLCP film, however, contains rigid skin layers on the
surfaces, the skin layers generated during extrusion. Where the
TLCP films are heat-bonded with each other, the skin layers
sometimes interrupt sufficient interlayer adhesion between the TLCP
films.
[0010] In order to improve adhesive property, for example, Patent
Document 1 (JP Laid-open Patent Publication No. 2010-103269)
discloses a method for producing a multilayer circuit board
including: extruding a thermoplastic liquid crystal polymer (TLCP)
capable of forming an optically anisotropic melt phase to form a
TLCP film, softening at least one surface of the TLCP film by
physical grinding or UV radiation to render the film surface to
have a hardness of 0.01 to 0.1 GPa measured in accordance with the
nanoindentation method so as to form an adhesive surface, and
counterposing the adhesive surface on a circuit surface of a wiring
substrate comprising a conductor circuit on at least one surface of
a TLCP film capable of forming an optically anisotropic melt phase
and carrying out a thermo-compression bonding of the entire
components.
[0011] In the meanwhile, where a circuit board is produced without
usage of an adhesive by laminating a conductor layer of a metal
such as copper to be bonded to a LCP layer, a process for
accomplishing an improved peel strength (strength against peeling)
has been carried out by forming an uneven surface on the conductor
layer to enhance compressive adhesion between the conductor layer
and the insulating layer by an anchoring effect of the uneven
surface. The optimization of the uneven structure has been
studied.
[0012] For example, Patent Document 2 (WO 2012/020818) discloses a
metal-clad laminate having a metal foil on one or both surfaces of
a liquid crystal polymer layer, wherein the metal foil has
projections on a surface layer portion on a side to be in contact
with the LCP layer, the projection being formed by roughening the
metal foil surface; the projections have an aspect ratio (H/L) of a
projection height H with respect to a projection bottom width L in
a range of 3 to 20; the projection height is in a range of 0.1 to 2
.mu.m; and the LCP layer has a thickness of 10 to 2000 .mu.m and a
thickness tolerance of less than 6%.
SUMMARY OF THE INVENTION
[0013] Patent Document 1 achieves the enhanced interlayer adhesion
between liquid crystal polymer films by carrying out the softening
treatment of the skin layers by physical polishing or ultraviolet
radiation. Patent Document 1, however, fails to disclose or suggest
improvement in interlayer adhesion between liquid crystal polymer
films without causing damage to the skin layer.
[0014] Patent Document 2 describes that the roughening treatment of
the metal foil improves interlayer adhesion between the liquid
crystal polymer film and the metal foil, but does not recognize
improvement in interlayer adhesion between liquid crystal polymer
films by carrying out a specific treatment on the liquid crystal
polymer films. Further, the invention described in this document
has not been studied disadvantages caused by existence of
projections on the metal foil against the liquid crystal
polymer.
[0015] An object of the present invention is to provide a liquid
crystal polymer film having an improved thermo-adhesive property
and making possible to improve interlayer adhesion between the film
and an adherend, and a method producing the same.
[0016] Another object of the present invention is to provide a
circuit board having an improved interlayer adhesion and a method
producing the same.
[0017] Based on the result of intensive studies to achieve the
above objects, the inventors of the present invention have found
the following aspects of the present invention.
[0018] That is, a first aspect of the present invention relates to
a method for producing a TLCP film at least including:
[0019] preparing a TLCP film being capable of forming an optical
anisotropic melt phase and having a segment orientation ratio SOR
of 0.8 to 1.4, degassing the TLCP film by degassing the film (i)
under vacuum of 1500 Pa or lower for 30 minutes or more, and/or by
degassing the film (ii) under heating at a temperature ranging from
100.degree. C. to 200.degree. C., and thereby producing a TLCP film
having a segment orientation ratio SOR of 0.8 to 1.4 and a moisture
content of 300 ppm or less.
[0020] In the above production method, the degassing process may
include:
[0021] a first degassing of the TLCP film by heating the prepared
TLCP film under heating at a temperature ranging from 100.degree.
C. to 200.degree. C. for a predetermined period of time, and
[0022] a second degassing of the first-degassed TLCP film by
further degassing the TLCP film after the first degassing under
vacuum of 1500 Pa or lower for a predetermined period of time.
Preferably, the degassing under vacuum (i) or the second degassing
process may be carried out under heating the film at a temperature
ranging from 80.degree. C. to 200.degree. C. under vacuum of 1500
Pa or lower.
[0023] Further, the TLCP film to be subjected to degassing may be
preferably in roll form.
[0024] A second aspect of the present invention embraces a TLCP
film having an improved thermo-adhesive property
(thermo-adhesion-improved TLCP film). Such a TLCP film has a
segment orientation ratio SOR of 0.8 to 1.4 and a moisture content
of 300 ppm or less. Further, the TLCP film may have a film
thickness of about 10 to 200 .mu.m. The TLCP film may be produced
by the above-described production method. The TLCP film may be a
TLCP film wrapped with a packaging material having a gas barrier
property (gas-barrier packaging material).
[0025] It should be noted that the present invention might embrace
a packaged TLCP film product comprising a TLCP film having
thermo-adhesive property and a packaging material having gas
barrier property.
[0026] In the packaging structure, the gas barrier packaging
material may have an oxygen permeability of, for example, 10
mL/m.sup.2dayMPa or less. Further, the gas barrier packaging
material may have a moisture permeability of, for example, 10
g/m.sup.2/day or less.
[0027] A third aspect of the present invention relates to a method
for producing a circuit board at least including:
[0028] preparing a plurality of circuit board materials;
[0029] stacking the prepared circuit board materials in accordance
with a predetermined structure of a circuit board to obtain a
stacked material, followed by conducting thermo-compression bonding
of the stacked material by heating the stacked material under a
predetermined compression pressure; wherein
[0030] the prepared circuit board materials are at least one member
selected from the group consisting of an insulating substrate
having a conductor layer on at least one surface, a bonding sheet,
and a coverlay, and
[0031] (I) at least one of the prepared circuit board materials
comprises a degassed TLCP film having an improved thermo-adhesive
property, the TLCP film being subjected to degassing as recited
above and/or
[0032] (II) at least one of the prepared circuit board materials
comprises a non-degassed TLCP film, and the degassing process as
recited above is conducted after the preparation of the circuit
board materials and before the thermo-compression bonding.
[0033] In the production method, at least one of the circuit board
materials may comprise a TLCP film having an improved
thermo-adhesive property.
[0034] In the production method, among the circuit board materials
selected from the group consisting of an insulating substrate, a
bonding sheet, and a coverlay, at least two circuit board materials
may comprise a first LCP film having a higher melting point and
higher heat resistance and a second LCP film having a lower melting
point and lower heat resistance than the first LCP film. The
difference in melting point between the first and second LCP films
may be within 70.degree. C.
[0035] In the method for producing the circuit board, the
thermo-compression bonding process may include a thermo-compression
bonding conducted under a compression pressure of 5 MPa or lower
(preferably 0.5 to 2.5 MPa). For example, the circuit board
materials may be subjected to thermo-compression bonding by heating
the materials at a temperature ranging from (Tm-60).degree. C. to
(Tm+40).degree. C., where Tm is the melting point of the TLCP film
subjected to the thermo-compression bonding.
[0036] A fourth aspect of the present invention embraces a circuit
board comprising a plurality of circuit board materials,
wherein:
[0037] the circuit board materials are at least one member selected
from the group consisting of an insulating substrate having a
conductor layer on at least one surface, a bonding sheet, and a
coverlay;
[0038] at least one of the circuit board materials comprises a TLCP
film; and
[0039] the circuit board shows a solder heat resistance when the
circuit board is placed in a solder bath at a temperature of
290.degree. C. for 60 seconds in accordance with a method of JIS C
5012. The circuit board may be a circuit board produced by the
above-described production method.
[0040] Preferably, the circuit board may have a bonding strength
between the TLCP film and a circuit board material in contact with
the TLCP film, in a value measured in accordance with JIS
C5016-1994, of
[0041] 0.8 kN/m or higher where the circuit board material is an
insulating substrate material (e.g., TLCP film), or
[0042] 0.3 kN/m or higher where the circuit board material is a
conductor layer.
[0043] It should be noted that where circuit board material has a
conductive material portion, bonding strength is determined
depending on the surface area ratio of the conductive material
portion in contact with the TLCP film. The surface area ratio may
be determined as existing ratio of conductive material as
follows:
Existin g ratio of conductive material = ( Surface area of circuit
patterns on circuit board unit in contact with the target LCP film
) / ( Surface area of entire circuit board unit ) .times. 100
##EQU00001##
[0044] Where the ratio is 30% or more, the bonding strength is
measured as a bonding strength between the LCP film and a conductor
layer. Where the ratio is less than 30%, the bonding strength is
measured as a bonding strength between the LCP film and an
insulating substrate material.
[0045] Preferably, the circuit board may have a favorably isotropic
bonding strength. For example, where the TLCP film and the circuit
board material are peeled off along a first direction (A direction)
or along a second direction (B direction) perpendicular to the
first direction to measure the bonding strength between the TLCP
film and the circuit board material in accordance with JIS
C5016-1994,
[0046] the minimum value of bonding strength in four directions of
a forward A direction, an adverse A direction, a forward B
direction, and an adverse B direction may be:
[0047] (i) 0.5 kN/m or higher where the circuit board material is
an insulating substrate material, or
[0048] (ii) 0.25 kN/m or higher where the circuit board material is
a conductor layer.
[0049] In the circuit board, at least two circuit board materials
may be TLCP films. In the circuit board, a conductor layer may be
interposed between a first TLCP film and a second TLCP film. The
difference in melting point between the first TLCP film and the
second TLCP film may be in a range from 0.degree. C. to 70.degree.
C.
[0050] All of the circuit board materials selected from the group
consisting of an insulating substrate, a bonding sheet, and a
coverlay may comprise TLCP films. An insulating substrate may be
bonded to another insulating substrate without a bonding sheet. An
insulating substrate may be bonded to a coverlay without a bonding
sheet.
[0051] Preferably, the circuit board may have a conductor layer
with a smooth surface. For example, at least one surface of the
conductor layer may have a surface roughness (Rz.sub.JIS) of 1.25
.mu.m or less as an average value of ten-points measured according
to a method conforming to ISO4287-1997.
[0052] As an indicator to show reduction in thickness of the
circuit board, for example, a circuit board may have (n+1) layers
of TLCP film layers and n layers of conductor circuit layers, each
of the conductor circuit layer being interposed between TLCP film
layers. In this case, the circuit board may comprise TLCP films to
be adhered with each other in a state interposing the conductor
circuit layers without using a bonding sheet.
[0053] An L2/L1 ratio may be used as an indication of the degree of
subduction of the circuit board, where L1 denotes the thickness of
the insulating substrate portion at which the conductor circuit is
not formed, and L2 denotes the thickness of the insulating
substrate portion at which the conductor circuit is formed. Where
the subduction of the conductor circuit in the circuit board is
suppressed, the L2/L1 ratio in percentage may be from 80 to
100%.
[0054] The circuit board may be a circuit board comprising a
conductor circuit having a strip line structure or a micro-strip
line structure.
[0055] The present invention may encompass a circuit board produced
by the above-described production method. The circuit board of the
present invention may be either a single-layer circuit board having
one layer of conductor layer or a multi-layer circuit board having
a plurality of conductor layers as described above.
[0056] The present invention, as another aspect, may also encompass
inventions as described below.
[0057] A fifth aspect of the present invention may be a method of
producing a circuit board, the method comprising:
[0058] preparing at least one unit circuit board and at least one
TLCP film as a circuit board material to be adhered to the unit
circuit board,
[0059] the unit circuit board comprising a TLCP film and a
conductor layer formed on one or the both surfaces of the
thermoplastic liquid crystal polymer film, and
[0060] the circuit board material being adhered to the surface of
the conductor layer;
[0061] performing a first degassing of the unit circuit board(s)
and the circuit board material(s) under heating at a temperature
ranging from 100.degree. C. to 200.degree. C. for a predetermined
period of time, for example, under the ambient pressure;
[0062] performing a second degassing the of the unit circuit
board(s) and the circuit board material(s) under vacuum of 1500 Pa
or lower;
[0063] performing integration of a stacked material formed by
stacking the at least one circuit board material and the at least
one unit circuit board by thermo-compression bonding by application
of heat and pressure to the stacked material,
[0064] wherein the surface of the conductor layer in contact with
the circuit board material has a surface roughness (Rz.sub.JIS) of
1.25 .mu.m or less as an average value of ten-points measured
according to a method conforming to ISO 4287-1997.
[0065] The second degassing may be carried out at a temperature in
a range from 80.degree. C. to 200.degree. C. The second degassing
may be performed substantially without applying compression
pressure. The circuit board material may be at least one selected
from the group consisting of a bonding sheet and a coverlay.
[0066] Also, the preparation process of the unit circuit board may
comprise:
[0067] thermo-compression bonding of a metal foil(s) to a TLCP film
on one or both surfaces of the TLCP film; and
[0068] forming an oxidation-resistant coat on the metal surface of
the thermo-compressed metal foil(s).
[0069] The conductor layer may preferably include a copper layer
made of a copper foil. The conductor layer may preferably include
an alloy layer containing copper as an oxidation-resistant
coating.
[0070] The preparation process of the unit circuit board may
further comprise applying a silane-coupling agent on the conductor
layer surface.
[0071] A sixth aspect of the present invention may be a circuit
board produced by the above method.
[0072] In the sixth aspect of the present invention, the circuit
board may be a circuit board comprising one or more unit circuit
boards and one or more circuit board materials to be bonded to the
unit circuit board(s), wherein [0073] at least one of the unit
circuit boards comprises a TLCP film and a conductor layer(s)
formed on one or both sides of the TLCP film surface, the conductor
layer(s) having a surface roughness (Rz.sub.JIS) of 1.25 .mu.m or
less as an average value of ten points measured in accordance with
ISO 4287-1997 on the surface bonded to the circuit board material,
[0074] at least one of the circuit board materials comprises a TLCP
film, and [0075] the circuit board shows a solder heat resistance
when the circuit board is placed in a solder bath at a temperature
of 290.degree. C. for 60 seconds in accordance with the method
conforming to JIS C 5012.
[0076] According to the first aspect of the present invention, a
specific degassing process can improve thermo-adhesive property of
a TLCP film, while maintaining an isotropic property of the TLCP
film. As a result, even without an adhesive agent, interlayer
adhesion of the circuit board comprising a LCP film(s) can be
enhanced.
[0077] Further, by packing the TLCP film subjected to a specific
degassing process with a gas barrier packaging material, the TLCP
film can be transported or conveyed as a packaged product
containing the TLCP film while maintaining a degassed
condition.
[0078] According to the method for producing the TLCP film
according to the second aspect, the TLCP film having improved
adhesion property can be efficiently produced.
[0079] The circuit board according to the third aspect of the
present invention can suppress local adhesion failure by enhancing
the interlayer adhesive property of the circuit board even using a
TLCP film(s). The circuit board can inhibit occurrence of blisters
on the circuit board during a high temperature treatment such as a
reflow process for mounting electronic components on the circuit
board. Further, interlayer adhesion without adhesive usage enables
to enhance reliability of the circuit board.
[0080] According to the fourth aspect of the present invention, a
method for producing a circuit board can achieve production of such
a circuit board in an efficient way.
BRIEF DESCRIPTION OF THE DRAWINGS
[0081] In any event, the present invention will become more clearly
understood from the following description of preferred embodiments
thereof, when taken in conjunction with the accompanying drawings.
However, the embodiments and the drawings are given only for the
purpose of illustration and explanation, and are not to be taken as
limiting the scope of the present invention in any way whatsoever,
which scope is to be determined by the appended claims, and:
[0082] FIG. 1 is a schematic cross-sectional view for illustrating
a shape of the rolled material formed of a TLCP film according to
one embodiment of the present invention;
[0083] FIGS. 2A and 2B are schematic cross-sectional views for
explaining a production process of a circuit board according to an
embodiment of the present invention, and show states before and
after lamination, respectively;
[0084] FIGS. 3A and 3B are schematic cross-sectional views for
explaining a production process of a circuit board according to
another embodiment of the present invention, and show states before
and after lamination, respectively;
[0085] FIG. 4 is a schematic cross-sectional view for explaining a
structure of one embodiment of the present invention comprising n
layers of the conductor layers and (n+1) layers of the insulating
layer containing the conductor layers inside;
[0086] FIG. 5A is a schematic cross-sectional view showing a
laminate comprising a conductor circuit and two sheets of liquid
crystal polymer film sandwiching the conductor circuit for
explaining a subduction amount of the conductor layer into the
circuit board according to an embodiment of the present
invention;
[0087] FIG. 5B is a schematic cross-sectional view showing a
laminate further comprising a ground conductor on both surfaces of
the laminate of FIG. 5A in the circuit board according to an
embodiment of the present invention; and
[0088] FIGS. 6A, 6B and 6C show cross sectional SEM images of
Examples 4 and 5 and Comparative Example 4, respectively. Scale
width in the image is 100 .mu.m, and the SEM images have the same
magnification with each other.
DESCRIPTION OF EMBODIMENTS
[0089] The first aspect of the present invention is based on the
findings as described below. That is, (i) TLCP films have the
highest level of gas barrier properties among various organic
materials, probably because of having a rigid mesogenic groups.
This is a great advantage of TLCP films in comparison with other
organic materials. Accordingly, the necessity of degassing of TLCP
films has never been conceived in the past. (ii) However, for
reasons that are uncertain, the presence of gasifiable components
such as moisture contained in thermoplastic liquid crystal polymer,
and/or moisture adsorbed on the surface of the TLCP film and/or air
existing on the surface of the TLCP film may cause deterioration in
interlayer adhesion between the film and an adherend, and it has
been assumed that such gasifiable components may cause blisters in
the circuit board provided with the TLCP film at a high
temperature. (iii) Based on the above assumption, the inventors of
the present invention have found that where a specific degassing
process is carried out to a TLCP film, surprisingly, the degassed
TLCP film can achieve improved adhesive property with maintaining
isotropic property of the film so as to enhance interlayer adhesion
between the film and an adherend as well as to suppress the
occurrence of blisters on the circuit board even exposed to a high
temperature condition.
[0090] Production Method of TLCP Film
[0091] One embodiment of the present invention is a method for
producing a TLCP film, the method at least includes:
[0092] preparing a TLCP film being capable of forming an optical
anisotropic melt phase and having a segment orientation ratio SOR
of 0.8 to 1.4, and
[0093] degassing the TLCP film by degassing the TLCP film (i) under
vacuum of 1500 Pa or lower for 30 minutes or more, and/or by
degassing the TLCP film (ii) under heating at a temperature ranging
from 100.degree. C. to 200.degree. C., so as to produce a TLCP film
having a segment orientation ratio SOR of 0.8 to 1.4 and a moisture
content of 300 ppm or less.
[0094] Preparation Step of TLCP Film
[0095] The TLCP film to be prepared is formed from a
melt-processable liquid crystalline polymer. In particular,
chemical formulation of the thermoplastic liquid crystal polymer is
not particularly limited to a specific one as long as it is a
liquid crystalline polymer that can be melt-processable, and
examples thereof may include a thermoplastic liquid crystal
polyester, or a thermoplastic liquid crystal polyester amide
obtained by introducing an amide bond thereto.
[0096] Furthermore, the thermoplastic liquid crystal polymer may be
a polymer obtained by further introducing, to an aromatic polyester
or an aromatic polyester amide, an imide bond, a carbonate bond, a
carbodiimide bond, or an isocyanate-derived bond such as an
isocyanurate bond.
[0097] Specific examples of the thermoplastic liquid crystal
polymer used in the present invention may include known
thermoplastic liquid crystal polyesters and thermoplastic liquid
crystal polyester amides obtained from compounds classified as (1)
to (4) as exemplified in the following, and derivatives thereof.
However, it is needless to say that, in order to form a polymer
capable of forming an optically anisotropic melt phase, there is a
suitable range regarding the combination of various raw-material
compounds.
[0098] (1) Aromatic or Aliphatic Dihydroxy Compounds (See Table 1
for Representative Examples)
TABLE-US-00001 TABLE 1 Chemical structural formulae of
representative examples of aromatic or aliphatic dihydroxyl
compounds ##STR00001## ##STR00002## ##STR00003## ##STR00004##
##STR00005## ##STR00006## ##STR00007## HO(CH.sub.2).sub.nOH n is an
integer of 2 to 12
[0099] (2) Aromatic or Aliphatic Dicarboxylic Acids (See Table 2
for Representative Examples)
TABLE-US-00002 TABLE 2 Chemical structural formulae of
representative examples of aromatic or aliphatic dicarboxylic acids
##STR00008## ##STR00009## ##STR00010## ##STR00011## ##STR00012##
##STR00013## ##STR00014## ##STR00015## HOOC(CH.sub.2).sub.nCOOH n
is an integer of 2 to 12
[0100] (3) Aromatic Hydroxycarboxylic Acids (See Table 3 for
Representative Examples)
TABLE-US-00003 TABLE 3 Chemical structural formulae of
representative examples of aromatic or aliphatic hydroxycarboxylic
acids ##STR00016## ##STR00017## ##STR00018## ##STR00019##
[0101] (4) Aromatic Diamines, Aromatic Hydroxy Amines, and Aromatic
Aminocarboxylic Acids See Table 4 for Representative Examples)
TABLE-US-00004 TABLE 4 Chemical structural formulae of
representative examples of aromatic diamines, aromatic hydroxy
amines, or aromatic aminocarboxylic acids ##STR00020## ##STR00021##
##STR00022##
[0102] Representative examples of liquid crystal polymers obtained
from these raw-material compounds may include copolymers having
structural units shown in Tables 5 and 6.
TABLE-US-00005 TABLE 5 Representative examples (1) of a
thermoplastic liquid crystal polymer ##STR00023## (A) ##STR00024##
##STR00025## (B) ##STR00026## ##STR00027## (C) ##STR00028##
##STR00029## ##STR00030## (D) ##STR00031## ##STR00032##
##STR00033## ##STR00034## (E) ##STR00035## ##STR00036##
##STR00037## (F) ##STR00038## ##STR00039##
TABLE-US-00006 TABLE 6 Representative examples (2) of thermoplastic
liquid crystal polymer ##STR00040## ##STR00041## (G) ##STR00042##
##STR00043## ##STR00044## (H) ##STR00045## ##STR00046##
##STR00047## (I) ##STR00048## ##STR00049## ##STR00050## (J)
##STR00051##
[0103] Of these copolymers, polymers including at least
p-hydroxybenzoic acid and/or 6-hydroxy-2-naphthoic acid as
repeating units are preferable; and particularly preferred polymers
include:
[0104] a polymer (i) having repeating units of p-hydroxybenzoic
acid and 6-hydroxy-2-naphthoic acid, and
[0105] a polymer (ii) having repeating units of [0106] at least one
aromatic hydroxycarboxylic acid selected from a group consisting of
p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, [0107] at
least one aromatic diol selected from a group consisting of
4,4'-dihydroxybiphenyl and hydroquinone, and [0108] at least one
aromatic dicarboxylic acid selected from a group consisting of
terephthalic acid, isophthalic acid, and 2,6-naphthalene
dicarboxylic acid.
[0109] For example, in the case where the polymer (i) comprises a
thermoplastic liquid crystal polymer having repeating units of at
least p-hydroxybenzoic acid (A) and 6-hydroxy-2-naphthoic acid (B),
the liquid crystal polymer may have a mole ratio (A)/(B) of
preferably about (A)/(B)=10/90 to 90/10, more preferably about
(A)/(B)=50/50 to 85/15, and further preferably about (A)/(B)=60/40
to 80/20.
[0110] Furthermore, in the case where the polymer (ii) comprises a
liquid crystal polymer having repeating units of at least one
aromatic hydroxycarboxylic acid (C) selected from a group
consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid,
at least one aromatic diol (D) selected from a group consisting of
4,4'-dihydroxybiphenyl and hydroquinone, and at least one aromatic
dicarboxylic acid (E) selected from a group consisting of
terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic
acid, the liquid crystal polymer may have a mole ratio of aromatic
hydroxycarboxylic acid (C):aromatic diol (D):aromatic dicarboxylic
acid (E)=30 to 80:35 to 10:35 to 10, more preferably about
(C):(D):(E)=35 to 75:32.5 to 12.5:32.5 to 12.5, and further
preferably about (C):(D):(E)=40 to 70:30 to 15:30 to 15.
[0111] Furthermore, the liquid crystal polymer may have a mole
ratio of a repeating structural unit derived from an aromatic
dicarboxylic acid relative to a repeating structural unit derived
from an aromatic diol of preferably (D)/(E)=95/100 to 100/95.
Deviation from this range may tend to result in a low degree of
polymerization and deterioration in mechanical strength.
[0112] It should be noted that, in the present invention, optical
anisotropy in a molten state can be determined by, for example,
placing a sample on a hot stage, heating the sample with an
elevating temperature under nitrogen atmosphere, and observing
light transmitted through the sample.
[0113] Preferred thermoplastic liquid crystal polymer has a melting
point (hereinafter, referred to as Tm.sub.0) in a range from
260.degree. C. to 360.degree. C., and more preferably from
270.degree. C. to 350.degree. C. The melting point is determined by
measuring the temperature at which the main endothermic peak
appears using a differential scanning calorimeter (Shimadzu
Corporation DSC).
[0114] As long as the advantageous effect of the present invention
is not deteriorated, to the thermoplastic liquid crystal polymer,
may be added any thermoplastic polymer such as a polyethylene
terephthalate, a modified polyethylene terephthalate, a polyolefin,
a polycarbonate, a polyarylate, a polyamide, a polyphenylene
sulfide, a polyether ether ketone, and a fluorine resin; and/or
various additives. If necessary, a filler may be added to the
thermoplastic liquid crystal polymer.
[0115] The TLCP film used in the present invention can be obtained
by extruding a thermoplastic liquid crystal polymer. As long as the
direction of rigid rod-like molecules of the thermoplastic liquid
crystal polymer can be controlled, any extrusion method may be
applied. In particular, well-known methods such as a T-die method,
a laminate-stretching method, and an inflation method (tubular
blown film extrusion method) are industrially advantageous. In
particular, the inflation method or the laminate-stretching method
can apply stresses not only in a machine direction of the film (or
the machine processing direction, hereinafter referred to as MD
direction), but also in a transverse direction (hereinafter,
abbreviated as TD direction) perpendicular to the MD direction.
Accordingly, the inflation method or the laminate-stretching method
can be advantageously used to obtain a film having controlled
properties such as molecular orientation and dielectric
characteristics in both the MD and TD directions.
[0116] The extrusion molding is preferably accompanied by a
stretching treatment in order to control the orientation. For
example, in the extrusion molding using a T-die method, a molten
polymer sheet extruded from a T-die may be stretched in the MD
direction and the TD direction at the same time, alternatively a
molten polymer sheet extruded from a T-die may be stretched in
sequence, first in the MD direction and then the TD direction.
[0117] Also, in the extrusion molding using an inflation method, a
tubular sheet being melt-extruded from an annular die may be drawn
with a predetermined draw ratio (corresponding to a stretching
ratio in the MD direction) and a predetermined blow ratio
(corresponding to a stretching ratio in the TD direction).
[0118] The stretching ratios carried out in such extrusion molding
may be, as a stretching ratio in the MD direction (or draw ratio),
for example, about 1.0 to 10, preferably about 1.2 to 7, and more
preferably 1.3 to 7; and/or as a stretching ratio in the TD
direction (or blow ratio), for example, about 1.5 to 20, preferably
2 to about 15, and still more preferably about 2.5 to 14.
[0119] The ratio of the TD direction-stretching ratio relative to
the MD direction-stretching ratio (TD direction/MD direction), may
be, for example, 2.6 or less, preferably about 0.4 to 2.5.
[0120] If necessary, the extrusion-molded TLCP film may be
subjected to further stretching. The stretching method itself is
known, and either biaxial stretching or uniaxial stretching may be
employed. From the viewpoint of easy control of molecular
orientation, biaxial stretching is preferable. The stretching may
be carried out using a known machine such as a uniaxial stretching
machine, a simultaneous biaxial stretching machine, and a
sequential biaxial stretching machine.
[0121] If necessary, a known or conventional heat treatment may be
carried out in order to control a melting point and/or thermal
expansion coefficient of the TLCP film. Heat treatment conditions
can be set appropriately depending on the purpose. The heat
treatment may be carried out by heating for hours at a temperature
of, for example, (Tm.sub.0-10).degree. C. or higher, wherein
Tm.sub.0 denotes a melting point of a liquid crystal polymer, for
example, about (Tm.sub.0-10).degree. C. to (Tm.sub.0+30).degree.
C., and preferably about Tm.sub.0.degree. C. to
(Tm.sub.0+20).degree. C. to increase a melting point (Tm) of the
TLCP film.
[0122] Thus-obtained TLCP film according to the present invention
has improved properties such as dielectric properties, gas barrier
properties and low moisture absorption, thus the TLCP film can be
suitably used as a circuit board material.
[0123] In view of desired heat resistance and processability of the
film, the melting point (Tm) of the TLCP film may be selected in a
range from about 200.degree. C. to 400.degree. C., preferably about
250.degree. C. to 360.degree. C., more preferably about 260.degree.
C. to 350.degree. C. (for example, 260.degree. C. to 340.degree.
C.). It should be noted that the melting point of the film can be
determined by observing the thermal behavior of the film using a
differential scanning calorimeter. That is, a test film is heated
at a rate of 20.degree. C./min to completely melt the film, and the
melt is rapidly cooled or quenched to 50.degree. C. at a rate of
50.degree. C./min. Subsequently, the quenched material is reheated
at a heating rate of 20.degree. C./min., and a position of an
endothermic peak appearing in the reheating process may be recorded
as a melting point of the film.
[0124] The TLCP film used in the present invention may have any
thickness. Where the TLCP film is used in a high-frequency
transmission line, the TLCP film may have a thickness as thick as
possible because usage of a thicker film can reduce transmission
loss. Where a TLCP film is used as an electrically insulating
layer, the film may preferably have a thickness in a range from 10
to 500 .mu.m, and more preferably in a range from 15 to 200 .mu.m.
Since a film having too small thickness has small rigidity and poor
strength, it is possible to achieve a desired thickness by
laminating the films having a thickness in a range from 10 to 200
.mu.m.
[0125] Degassing Process
[0126] Thus-obtained TLCP films are subjected to a degassing
process for removing air or moisture present in and/or on the
film.
[0127] Degassing process may be carried out in the production of a
TLCP film having improved thermo-adhesiveness, and/or may be
carried out as one of the processes during the production of a
circuit board.
[0128] Degassing process enables to improve the thermo-adhesiveness
of the TLCP film, and also enables to enhance interlayer adhesion
between the TLCP film and an adherend.
[0129] The TLCP film subjected to the degassing process may have
any shape as long as degassing of the TLCP film is possible. For
example, in the degassing process, the TLCP film may be prepared as
a sheet material that may be provided with a conductor layer; as a
multi-layer laminate (for example, a multi-layer laminate
comprising a plurality of film layers each of which may be provided
with a conductor layer); or as a product in roll form.
[0130] For example, where a product in roll form is used, the
product in roll form may be prepared by winding a film onto a
tubular core in a known or conventional manner. FIG. 1 is a
schematic view for explaining a product in roll form comprising a
TLCP film. As shown in FIG. 1, a rolled product 1 is formed by
winding a TLCP film 3 onto a tubular core 2.
[0131] The product in roll form, for example, as shown in FIG. 1,
may have a winding thickness (W) of 1000 mm or smaller, for
example, about 10 to 900 mm, preferably 800 mm or smaller, and more
preferably 600 mm or smaller.
[0132] The degassing of the TLCP film can be carried out by
degassing the TLCP film under a certain vacuum condition (for
example, a vacuum drying) and/or degassing under heat condition
(for example, a heat drying) to reduce air and moisture on and/or
in the TLCP film to an extremely low level. As a result,
surprisingly, the TLCP film that has undergone such a degassing
process can improve the thermo-adhesive property.
[0133] For example, although the present invention does not exclude
the softening process, such TLCP films can achieve enhanced
adhesive property even without softening treatment such as
destruction of the skin layer in the TLCP film. If desired, a
surface treatment such as softening treatment may be carried out
for TLCP films.
[0134] In the degassing process, degassing of the TLCP film can be
carried out (i) by degassing under vacuum of 1500 Pa or lower for
30 minutes or more, and/or (ii) by degassing under heating at a
temperature ranging from 100.degree. C. to 200.degree. C.
[0135] The degassing process may be carried out in a condition
satisfying either degassing (i) under vacuum, or degassing (ii)
under heating, preferably in a condition satisfying both (i) and
(ii).
[0136] The degassing condition where both (i) and (ii) are
satisfied may be a condition where both (i) and (ii) are satisfied
at the same time, i.e., degassing a TLCP film by heating at a
specific temperature under a specific vacuum degree (vacuum
pressure). Alternatively, the degassing condition where both (i)
and (ii) are satisfied may be a condition where (i) and (ii) are
carried out separately, i.e., degassing a TLCP film in the order of
from (i) to (ii) or in the order of from (ii) to (i).
[0137] It should be noted that where degassing process (i) and (ii)
are carried out separately, another process might be inserted
within a range not adversely affecting the film, between the
degassing (i) and (ii) or between the degassing (ii) and (i).
[0138] Moreover, from the viewpoint of improving degassing
efficacy, degassing may be carried out without substantial
pressurization (under pressure release). For example, degassing may
be carried out under a minimum pressure or pressure-released state
(for example, under a compression pressure of about 0 to 0.7 MPa,
preferably under a compression pressure of about 0 to 0.5 MPa).
[0139] Degassing under vacuum (i) may be carried out at a vacuum
degree of 1500 Pa or lower, preferably 1300 Pa or lower, and more
preferably 1100 Pa or lower.
[0140] Where degassing under vacuum is performed independently,
degassing may be carried out at an ambient temperature (for
example, from 10.degree. C. to 50.degree. C., preferably from
15.degree. C. to 45.degree. C.). In view of enhancing the degassing
efficiency, degassing may be carried out under heating, for
example, at a heating temperature ranging from 50.degree. C. to
200.degree. C. (for example, from 50.degree. C. to 150.degree. C.),
preferably from 80.degree. C. to 200.degree. C., and more
preferably from about 90.degree. C. to about 190.degree. C.
[0141] Degassing under heating (ii) may be carried out in a range
from 100.degree. C. to 200.degree. C., preferably from 105.degree.
C. to 190.degree. C., and more preferably from 110.degree. C. to
180.degree. C.
[0142] Degassing temperature under heating may be set in a
predetermined temperature range with respect to a melting point
(Tm) of the TLCP film. Degassing may be carried out by heating at a
temperature ranging from (Tm-235).degree. C. to (Tm-50).degree. C.
[e.g., from (Tm-200).degree. C. to (Tm-50).degree. C.], preferably,
from (Tm-225).degree. C. to (Tm-60).degree. C. [e.g., from
(Tm-190).degree. C. to (Tm-60).degree. C.], and more preferably
from (Tm-215).degree. C. to (Tm-70).degree. C. [e.g., from
(Tm-180).degree. C. to (Tm-70).degree. C.].
[0143] By heating the TLCP film in a specific temperature range as
described above, while suppressing rapid moisture generation from
the film, the moisture in the film (for example, inside or on a
surface of the film) can be degassed as water vapor, or the air on
the surface of the film can be degassed by enhancing kinetic energy
of the air.
[0144] It should be noted that where degassing under heating is
carried out independently, the degassing might be carried out under
a condition that does not contain the vacuum condition of 1500 Pa
or lower. For example, degassing may be carried out by heating
under an atmospheric pressure (or ambient pressure) where the
pressure is not specifically adjusted. Alternatively, if necessary,
degassing may be carried out by heating under a reduced pressure
from the atmospheric pressure (for example, beyond 1500 Pa and less
than 100000 Pa, preferably about 3000 to 50000 Pa).
[0145] The period of time required for degassing procedure may be
suitably set depending on various conditions such as a state of the
TLCP film, a vacuum degree, and/or a heating temperature. In view
of removing moisture and air from the entire TLCP film, the period
for degassing for the degassing process (i) and/or the degassing
process (ii) (i.e., under vacuum, under heating, under vacuum while
heating) may be same or different. The degassing period may be 30
minutes or more, 40 minutes or more, or 50 minutes or more. The
degassing period may be 6 hours or less, 4 hours or less, 3 hours
or less, 2 hours or less, or 1.5 hours or less.
[0146] Alternatively, the degassing period may be set appropriately
depending on the moisture content in the TLCP film, for example,
may be carried out until the TLCP film has a desired moisture
content range to be described later (for example, 300 ppm or less,
or 200 ppm or less).
[0147] As described above, where degassing under vacuum (i) and
degassing under heating (ii) are carried out in combination to the
extent that thermo-adhesiveness of the TLCP film is capable of
being increased, the degassing processes (i) and (ii) may be
carried out in any order, preferably carried out by degassing under
heating (ii) as a first degassing, followed by degassing under
vacuum (i) as a second degassing.
[0148] Specifically, for example, degassing process may comprise a
first degassing process in which degassing of the circuit board
materials is carried out under heating at a temperature ranging
from 100.degree. C. to 200.degree. C. for a predetermined time, and
a second degassing process in which degassing of the circuit board
materials is carried out under vacuum of 1500 Pa or lower for
another predetermined time. These degassing processes may be
appropriately carried out by combining the above-mentioned
conditions.
[0149] TLCP Film Having Improved Thermo-Adhesiveness
[0150] By carrying out such a degassing process, surprisingly, a
TLCP film having enhanced thermo-adhesive property can be obtained.
Although the reason for this achievement is not clear, the
following mechanism is presumed. Since the TLCP film is excellent
in gas barrier property, there is a possibility that the TLCP film
itself may suppress escape of moisture from the film once the
moisture is contained inside, as well as may suppress escape of air
from the film where the TLCP film absorbs the air on the
surface.
[0151] Further, there is another possibility described as follows.
The main component of the gas released from the resin is water
vapor in general. The water vapor volume becomes several thousand
times when water is converted to vapor. In the meantime, as the
vacuum status proceeds, moisture can be hardly released from inside
of the film after reaching equilibrium of the emission amount from
the resin and the emission amount of the vacuum pump. Accordingly,
where thermo-compression bonding is carried out under vacuum, the
water molecules contained inside of the film may be hardly
released.
[0152] Where the film itself is a source for generating the air and
the moisture, local adhesion failure (local delamination) between
bonded layers may occur due to the air and the moisture remained in
the film or on the surface of the film in the lamination process
for the circuit board production.
[0153] Further, the TLCP film obtained by a specific degassing
method can achieve an extremely low moisture content while
maintaining isotropic property of the polymer.
[0154] The TLCP film obtained by the degassing process has a
Segment Orientation Ratio SOR of 0.8 to 1.4, and a moisture content
of 300 ppm or less.
[0155] The moisture content may be preferably 200 ppm or less, more
preferably 180 ppm or less, and even more preferably 150 ppm or
less. Here, the moisture content indicates a value measured by the
method described in Examples below.
[0156] The Segment Orientation Ratio SOR as an indicator of
isotropic property of the film is 0.8 to 1.4, and may be preferably
0.9 to 1.3, more preferably 1.0 to 1.2, and particularly preferably
1.0 to 1.1.
[0157] Here, the Segment Orientation Ratio SOR is an index
descriptive of a degree of molecular orientation, and represents,
unlike the standard MOR (Molecular Orientation Ratio), a value that
takes the thickness of an object into consideration.
[0158] Since the film is isotropic, the film may preferably have a
dimensional stability in the MD and TD directions of within .+-.1%,
more preferably within .+-.0.5%, and more preferably within
.+-.0.1%. Here, the dimensional stability may be a value measured
in accordance with IPC-TM-6502.2.4.
[0159] The obtained TLCP film may be used as an insulating
substrate layer of a unit circuit board comprising a conductor
layer formed on one or both sides of the insulating substrate
layer. Alternatively, the TLCP film may be used as an adhesive
material (for example, a bonding sheet and a coverlay) for bonding
to a conductor layer(s).
[0160] The TLCP film may have a dielectric loss tangent at 25 GHz
of, for example, 0.0025 or less (e.g., about 0.0001 to 0.0023), and
preferably about 0.0010 to 0.0022. The TLCP film having such a
dielectric loss tangent enables to lower power consumption as well
as to reduce noise.
[0161] The relative dielectric constant of the TLCP film varies
depending on the thickness of the film. The TLCP film may have a
relative dielectric constant at 25 GHz in the TD direction, for
example, of 3.25 or less (e.g., about 1.8 to 3.23), and preferably
about 2.5 to 3.20. It should be noted that the dielectric constant
can be generally calculated by multiplying the vacuum dielectric
constant (=8.855.times.10.sup.-12 (F/m)) to relative dielectric
constant.
[0162] For example, the dielectric constant measurement may be
carried out by a resonance perturbation method at a frequency of 10
GHz. Where a 1 GHz cavity resonator (manufactured by Kanto
Electronic Application and Development Inc.) is connected to a
network analyzer ("E8362B", manufactured by Agilent Technologies,
Inc.), and a small sample (width: 2.7 mm.times.length: 45 mm) is
inserted into the cavity resonator, the dielectric constant and the
dielectric loss tangent of the sample can be measured from the
change in resonance frequency before and after inserting the
material to expose the material to an environment at a temperature
of 20.degree. C. and a humidity of 65% (RH) for 96 hours.
[0163] The present invention may also embrace a packaged TLCP film
product. The packaged TLCP film product may comprise the TLCP film
having thermo-adhesive property and a gas barrier packaging
material packing the TLCP film inside. In this case, the TLCP film
is packed with the packaging material having a gas barrier
property.
[0164] The packaged TLCP film product makes it possible to
transport or convey a degassed TLCP film with maintaining the
degassed state since the TLCP film is packed with a gas barrier
packaging material.
[0165] The shape of the TLCP film may be any shape such as a sheet
material as described above, a multilayer laminate, and a product
in roll form (rolled product). If necessary, a conductor layer or a
conductive layer may be formed on the TLCP film.
[0166] From the viewpoint of portability, the TLCP film to be
packed in the packaged product may be preferably in roll form.
[0167] The gas barrier packaging material may have, for example, a
moisture permeability of 10 g/m.sup.2/day or less (e.g., 0.5 to 10
g/m/day), preferably 8 g/m.sup.2/day or less, and more preferably 6
g/m.sup.2/day or less.
[0168] Furthermore, the gas barrier packaging material may have,
for example, an oxygen permeability of 10 mL/m.sup.2/day/MPa or
less (for example 0.5 to 10 mL/m.sup.2/day/MPa), preferably 8
mL/m.sup.2/day/MPa or less, and more preferably 5
mL/m.sup.2/day/MPa or less.
[0169] As the gas barrier packaging material, there may be
exemplified various gas barrier films, and a laminate of a gas
barrier film with a CLAF, a paper, and/or a non-woven fabric.
[0170] Examples of the gas barrier films may include various types
of films such as an aluminum foil-laminated film, an
aluminum-evaporated film, a silica-evaporated film, a
polyvinylidene chloride-coated film and other gas barrier films.
The gas barrier film may have a substrate film such as a polyester
film, a polyethylene film, and a polypropylene film.
[0171] Furthermore, the outside of these films and/or laminates may
be further packed with a paper or others; and/or these films and/or
laminates may be housed in a carton box, a crate, a metal case, a
pedestal and others.
[0172] Method for Producing Circuit Board
[0173] As one embodiment of the present invention, there may be
mentioned a method for producing a circuit board having an improved
interlayer adhesion even without an adhesive agent.
[0174] The producing method at least includes:
[0175] preparing a plurality of circuit board materials;
[0176] stacking the prepared circuit board materials in accordance
with a predetermined structure of a circuit board to obtain a
stacked material, followed by conducting thermo-compression bonding
of the stacked material by heating under a predetermined
compression pressure; wherein
[0177] the prepared circuit board materials are at least one member
selected from the group consisting of an insulating substrate
having a conductor layer (e.g., a conductor circuit or a conductor
pattern, a conductor foil, a conductor film) on at least one
surface, a bonding sheet, and a coverlay, and
[0178] (I) at least one of the prepared circuit board materials
comprises a degassed thermoplastic liquid crystal polymer film
subjected to the above-mentioned degassing, and/or
[0179] (II) at least one of the prepared circuit board materials
comprises a non-degassed thermoplastic liquid crystal polymer film,
and the above-mentioned degassing process is conducted after the
preparation of the circuit board materials and before the
thermo-compression bonding.
[0180] That is, in the method for producing a circuit board of the
present invention, the interlayer adhesion of the circuit board can
be improved by carrying out the following process (I) and/or
process (II).
[0181] In the process (I), a degassed TLCP film is prepared as a
TLCP film in a preparation process.
[0182] In the process (II), a specific degassing process to degas a
TLCP film is carried out after preparation of the circuit board
materials and before thermo-compression bonding.
[0183] Preparation of Circuit Board Materials
[0184] In the preparation process, a plurality of circuit board
materials (or insulating substrate materials), are prepared. The
circuit board materials can comprise at least one member selected
from the group consisting of an insulating substrate, a bonding
sheet, and a coverlay, where the insulating substrate having a
conductor layer (e.g., a conductor circuit or a conductor pattern,
a conductor foil, a conductor film) on at least one surface.
[0185] In the preparation, the prepared circuit board materials may
be, for example, a plurality of insulating substrates each having a
conductor layer on at least one surface; alternatively, may be a
combination of (i) an insulating substrate having a conductor
circuit on at least one surface and (ii) at least one circuit board
material selected from the group consisting of a bonding sheet and
a coverlay.
[0186] As described above, in the process (I), at least one member
selected from the group consisting of an insulating substrate, a
bonding sheet, and coverlay may comprise a degassed TLCP film
having an improved thermo-adhesiveness. By using such a TLCP film
having an improved thermo-adhesiveness; it is possible to improve
the interlayer adhesion of the circuit board even carrying out a
conventional thermo-compression bonding process for producing a
circuit board.
[0187] As the insulating substrate, there may be mentioned various
organic materials and inorganic materials used in the conventional
circuit board. Examples of the organic materials may include a
thermoplastic liquid crystal polymer, a polyimide, a cycloolefin
polymer, a fluorine resin, an epoxy resin, a phenolic resin and an
acrylic resin, and other organic materials. Examples of the
inorganic materials may include a ceramic, and the like. These
materials may be used in the circuit board singly or in combination
of two or more. Of these, from the viewpoint of high-frequency
characteristics and dimensional stability, the TLCP insulating
substrate is preferred.
[0188] Examples of the insulating substrates each having a
conductor layer on at least one surface may include:
[0189] a unit circuit board comprising an insulating substrate and
a conductor circuit or pattern formed on one surface of the
insulating substrate;
[0190] a unit circuit board comprising an insulating substrate and
conductor circuits or patterns formed on both surfaces of the
insulating substrate;
[0191] a unit circuit board comprising an insulating substrate, a
conductor circuit or pattern formed on one surface of the
insulating substrate, and a conductor film or foil formed on the
other surface of the insulating substrate;
[0192] a conductor-clad laminate comprising an insulating substrate
and a conductor film or foil formed on one surface of the
insulating substrate; and
[0193] a conductor-clad laminate comprising an insulating substrate
and conductor films or foils formed on both surfaces of the
insulating substrate.
[0194] Conductor Layer
[0195] The conductor layer can be at least formed for example from
a conductive metal. By using a known circuit processing method, the
conductor layer may be formed into any pattern of circuits. As the
conductor for forming a conductor layer, there may be mentioned
various metals having conductivity, such as gold, silver, copper,
iron, nickel, aluminum, and an alloy metal thereof.
[0196] Any known method may be used as a method for forming a
conductor layer on an insulating substrate of a TLCP film. For
example, a metal layer may be formed by evaporation, electroless
plating, and/or electrolytic plating. Alternatively, a metal foil
(for example, copper foil) may be thermo-compression bonded on the
surface of the TLCP film.
[0197] The metal foil constituting the conductor layer may be
preferably a metal foil used in electrical connections. Examples of
the metal foils may include a copper foil, as well as various metal
foils such as gold, silver, nickel, aluminum foils, and also an
alloy foil comprising these metals in a substantial manner (for
example, 98% by weight or greater).
[0198] Of these metal foils, a copper foil can be preferably used.
The species of the copper foil is not particularly limited, and can
be any of copper foil usable in the circuit board, for example, a
rolled copper foil or an electrolytic copper foil.
[0199] From the viewpoint of improvement in solder heat resistance
and interlayer adhesion, it is preferable that the conductor layer
has a smooth surface.
[0200] Preferably, the conductor layer may have a surface roughness
(Rz.sub.JIS) of 1.25 .mu.m or less, preferably 1.2 .mu.m or less,
and more preferably 1.15 .mu.m or less as an average value of
ten-points measured according to a method conforming to
ISO4287-1997. The lower limit of Rz.sub.JIS is not particularly
limited, and for example, may be about 0.5 .mu.m.
[0201] The conductor layer may have an arithmetic mean roughness
of, for example, 0.15 .mu.m or less, or 0.14 .mu.m or less measured
according to the method conforming to ISO4287-1997 (Ra). The lower
limit of Ra is not particularly limited, and for example, may be
about 0.05 .mu.m, or may be about 0.11 .mu.m.
[0202] In the above configuration, it may be possible for a
conductive layer on the TLCP film to have a smooth surface even
where the conductive layer is not adhered to another layer in the
lamination for obtaining a laminate. It should be noted that where
the conductor layer is processed into circuits, it might be
sufficient for the remained part of the conductor layer (i.e.,
circuit part) to have a smooth surface.
[0203] The conductor layer may preferably have a thickness of, for
example, 1 to 50 .mu.m (e.g., about 5 to 50 .mu.m), and more
preferably of 8 to 35 m (e.g., 10 to 35 .mu.m).
[0204] The conductor layer may contain an oxidation-resistant coat
on the surface. The surface treatment of the conductor layer makes
it possible to form an alloy layer on the surface of the conductor
layer, the alloy layer having a higher oxidation resistance than
the conductor layer body itself. The conductor layer having such an
oxidation-resistant coat can advantageously prevent deterioration
of the conductor layer due to oxidation of the conductor surface
during the degassing process. It is also expected to achieve a
further improvement in adhesion due to the alloy layer.
[0205] For example, the preparation process of the unit circuit
board may comprise:
[0206] thermo-compression bonding of a metal foil(s) to a TLCP film
on one or both surfaces of the TLCP film; and
[0207] forming an oxidation-resistant coat on the surface of the
metal foil(s).
[0208] The preparation process of the unit circuit board may
further include applying or attaching a silane-coupling agent on
the conductor layer surface.
[0209] As the oxidation-resistant coat, there may be exemplified an
oxidation-resistant alloy layer, an oxidation-resistant plating
layer, an anticorrosive agent layer such as a benzotriazole-coating
layer, and other oxidation-resistant layer.
[0210] It should be noted that depending on the type of the
conductor layers and oxidation resistant coat, the
oxidation-resistant coat might be formed either before or after
processing circuits.
[0211] For example, if the conductor layer comprises a
thermo-compression bonded metal foil, the oxidation-resistant alloy
layer may be preferably formed from an alloy metal including at
least the metal constituting the metal foil in order to enhance
adhesive property. For example, where the metal foil constituting
the conductor layer is a copper foil, an alloy layer may be an
alloy at least containing copper. For example, an
oxidation-resistant alloy layer may be preferably formed before
processing circuits.
[0212] For example, such an alloy layer may be formed using
"FatBOND GT" manufactured by MEC Co., Ltd.
[0213] It should be noted that, there might be an alloy portion
existing apart from the copper foil, the alloy portion containing
no copper. Such an alloy portion without copper may be etched with
an etching liquid. As such an etching solution, there may be used,
for example "MEC REMOVER S-651A" (produced by MEC Co., Ltd.),
"S-BACK H-150" (produced by SASAKI CHEMICAL CO., LTD.), an aqueous
solution containing an inorganic acid such as nitric acid, and the
like.
[0214] From the viewpoint of improving adhesive property of the
conductor layer, a known or conventional silane-coupling agent may
be applied or attached to the surface of the conductor layer (in
particular the alloy layer). Application of the silane-coupling
agent to the alloy layer surface can further improve bonding
strength between the conductor layer and the TLCP film. Even
without forming uneven surface exerting an anchoring effect on the
surface of the conductor layer, it is possible to achieve a bonding
strength indicated by a high peel strength by the
thermo-compression while maintaining the smooth surface of the
conductor layer in the thermo-compression bonding.
[0215] Bonding Sheet and/or Coverlay
[0216] As an adhesive circuit board material used for adhering to
the conductor layer, one or more circuit board materials (adhesive
materials) may be prepared in addition to the unit circuit board.
The adhesive material may be preferably a TLCP film. Examples of
the adhesive materials may include at least one selected from a
bonding sheet and a coverlay. It should be noted that the coverlay
is typically used to cover the conductor layer as an outermost
layer, and that the bonding sheet is typically used to bond the
circuit board materials. The bonding sheet and/or the coverlay may
be composed of a TLCP film. Preferably, at least one selected from
the bonding sheet and the coverlay may be composed of a TLCP film
having an improved thermo-adhesive property.
[0217] For example, where a TLCP film subjected to degassing
process is referred to as an adhesion-improved LCP film, and a TLCP
film not subjected to degassing process is referred to as an
un-degassed LCP film, a combination of suitable circuit board
materials may be exemplified as follows:
[0218] (a) a circuit board including an un-degassed LCP film as an
insulating substrate and an adhesion-improved LCP film as a bonding
sheet, and optionally an un-degassed LCP film as a coverlay;
[0219] (b) a circuit board including an un-degassed LCP film as an
insulating substrate and an adhesion-improved LCP film as a bonding
sheet, and optionally an adhesion-improved LCP film as a
coverlay;
[0220] (c) a circuit board including an adhesion-improved LCP film
as an insulating substrate and an un-degassed LCP film as a bonding
sheet, and optionally an un-degassed LCP film as a coverlay;
[0221] (d) a circuit board including an adhesion-improved LCP film
as an insulating substrate and an adhesion-improved LCP film as a
bonding sheet, and optionally an un-degassed LCP film as a
coverlay;
[0222] (e) a circuit board including an adhesion-improved LCP film
as an insulating substrate and an adhesion-improved LCP film as a
bonding sheet, and optionally an adhesion-improved LCP film as a
coverlay;
[0223] (f) a circuit board including an adhesion-improved LCP film
as an insulating substrate and an un-degassed LCP film as a
coverlay;
[0224] (g) a circuit board including an un-degassed LCP film as an
insulating substrate and an adhesion-improved LCP film as a
coverlay;
[0225] (h) a circuit board including an adhesion-improved LCP film
as an insulating substrate and an adhesion-improved LCP film as a
coverlay;
[0226] (i) a circuit board including an adhesion-improved LCP film
as a first insulating substrate, an adhesion-improved LCP film as a
second insulating substrate, and optionally an un-degassed LCP film
as a coverlay;
[0227] (j) a circuit board including an adhesion-improved LCP film
as a first insulating substrate, an adhesion-improved LCP film as a
second insulating substrate, and optionally an adhesion-improved
LCP film as a coverlay; and other combinations.
[0228] Where the degassing process is carried out in the producing
process of the circuit board, since the specific degassing process
provides LCP films with improved thermo-adhesive property, an
un-degassed LCP film can be used as any of the prepared the circuit
board material such as an insulating substrate, a bonding sheet,
and a coverlay.
[0229] In the circuit board comprising the circuit board materials,
the circuit board materials may comprise at least two TLCP films
including a first TLCP film and a second TLCP film, wherein a
conductor layer is interposed between the first TLCP film and the
second TLCP film. In such a case, the difference in melting point
between the first TLCP film and the second TLCP film may be in a
range of, for example, 0.degree. C. to 70.degree. C., and
preferably about 0.degree. C. to 60.degree. C. (for example, about
10.degree. C. to 50.degree. C.).
[0230] For example, the first LCP film may be a high-melting-point
LCP film having higher heat resistance, and the second LCP film may
be a low-melting-point LCP film having lower heat resistance than
the first LCP film. For example, at least two circuit board
materials selected from an insulating substrate, a bonding sheet
and a coverlay may comprise a combination of a high-melting-point
LCP film having higher heat resistance (for example, melting point
of about 300.degree. C. to 350.degree. C.) and a low-melting-point
LCP film having lower heat resistance (for example, melting point
of about 250.degree. C. to 300.degree. C.).
[0231] Further, since the circuit board according to the present
invention is excellent in interlayer adhesion, for example, the
circuit board materials adhered to each other may be composed of
high-melting-point LCP films, alternatively may be composed of
low-melting-point LCP films. In this case, the difference in
melting point between high-melting-point LCP films or between
low-melting-point LCP films may be, for example, about 0.degree. C.
to 20.degree. C., and preferably about 0.degree. C. to 10.degree.
C.
[0232] Alternatively, the adjacent circuit board materials adhered
to each other may comprise a combination of a high-melting-point
LCP film and a low-melting-point LCP film. In this case, the
difference in melting point between LCP films may be, for example,
exceeding 20.degree. C., and preferably 30.degree. C. to 70.degree.
C.
[0233] The adhesion-improved LCP film can be used as the
high-melting-point LCP film or can be used as the low-melting-point
LCP film. Among the adjacent LCP films adhered to each other (for
example, a combination of a high-melting-point LCP film and a
high-melting-point LCP film, a combination of a low-melting-point
LCP film and a low-melting-point LCP film, a combination of a
high-melting-point LCP film and a low-melting-point LCP film), at
least one LCP film in the combination may be an adhesion-improved
LCP film; preferably both of the LCP films in the combination may
be adhesion-improved LCP films. Alternatively, at least the
low-melting-point LCP film in the combination may be an
adhesion-improved LCP film.
[0234] Depending on the configuration of the circuit board, the
melting point of the LCP film used as an adhesive material may be
identical to the melting point of the substrate of the unit circuit
board. Alternatively, the LCP film used as an adhesive material may
have a lower melting point than a LCP film constituting the unit
circuit board. In that case, the difference in melting point
between the LCP films may be, for example, about 0.degree. C. to
70.degree. C., and more preferably about 0.degree. C. to 60.degree.
C.
[0235] It should be noted that within the range that does not
impair the effects of the present invention, the surface treatment
might be performed on the circuit board material (in particular on
the LCP film). The surface treatment can be carried out, for
example, by known methods such as ultraviolet irradiation, plasma
irradiation, and physical polishing.
[0236] Degassing Process
[0237] By carrying out the above-mentioned degassing process in the
production method of a circuit board, the TLCP film may have
improved adhesiveness.
[0238] The degassing process in the production method may be
carried out before the thermo-compression bonding process, or after
the preparation process and before the thermo-compression bonding
process.
[0239] Where the degassing process is carried out in the method for
producing a circuit board, preferably the degassing process may
comprise:
[0240] a first degassing of the circuit board materials under
heating at a temperature ranging from 100.degree. C. to 200.degree.
C. for a predetermined time; and
[0241] a second degassing of the circuit board materials under
vacuum of 1500 Pa or lower for another predetermined time.
[0242] Furthermore, degassing process may be carried out as a
pre-heating process prior to the thermo-compression bonding. The
pre-heating process may be carried out, for example, in a heating
temperature range from 50.degree. C. to 150.degree. C. under vacuum
of 1500 Pa or lower. The heating temperature during the pre-heating
process may be preferably about 60.degree. C. to 120.degree. C.,
and more preferably 70.degree. C. to 110.degree. C.
[0243] Such a pre-heating process makes it possible to remove air
and/or moisture on and/or in the LCP film to some extent, even if
an un-degassed film is used as the circuit board materials. As a
result, it is possible to improve the interlayer adhesion between
the LCP film and an adherend even without an adhesive agent.
[0244] The pre-heating process may be carried out under a vacuum
degree of 1500 Pa or less, preferably 1300 Pa or less, and more
preferably 1100 Pa or less.
[0245] During the pre-heating process, a compression pressure may
be applied to the circuit board material within a range that does
not inhibit the effect of the invention. The compression pressure
in the pre-heating process may be, for example, 0.8 MPa or less,
and more preferably 0.6 MPa or less. The pre-heating process may be
preferably carried out with applying a compression pressure as low
as possible, preferably substantially without applying a
compression pressure.
[0246] The pre-heating process may be carried out, for example, for
about 30 to 120 minutes, preferably about 40 to 100 minutes, and
more preferably about 45 to 75 minutes.
[0247] For example, where the first degassing process is combined
with the second degassing process, the degassing process may be
carried out as follows:
[0248] First Degassing Process: Degassing Under Heating
[0249] In order to avoid gas discharge in the lamination process
for producing a circuit board or post-process thereafter, degassing
can be carried out. Without degassing process, a gaseous compound
may be discharged from LCP films used for a circuit board material
or adhesive material, as well as from metal layer of the conductor
layer. The degassing process may be carried out by preliminarily
degassing a unit circuit board(s) as well as a LCP film(s) used for
the adhesive material under heating, for example, at atmospheric
pressure (or ambient pressure).
[0250] The heating may be carried out at a temperature ranging from
100.degree. C. to 200.degree. C., preferably of 110.degree. C. to
190.degree. C. The heating time can be adjusted appropriately
depending on the heating temperature, and may be, for example, 30
minutes to 4 hours, and preferably 1 hour to 3 hours.
[0251] The degassing under heating may be conducted under
conditions that do not contain a vacuum degree of 1500 Pa or less,
for example, may be carried out under an atmospheric pressure (or
normal pressure) without adjusting the pressure. If desired, the
degassing under heating may be conducted under a pressure reduced
from the atmospheric pressure (e.g., beyond 1500 Pa and less than
100000 Pa, preferably about 3000 to 50000 Pa).
[0252] Incidentally, in order to prevent oxidation of conductors
(such as copper foil); it is preferable to heat under an inert gas
atmosphere such as nitrogen in the first degassing process.
Alternatively, such a heating may be carried out in the state that
the conductor has an oxidation-resistant coat (e.g.,
oxidation-resistant alloy layer, oxidation resistant plating layer,
anti-rust inhibitor layer such as benzotriazole-coated layer) on
the surface.
[0253] Second Degassing Process: Enhanced or Intensified
Degassing
[0254] Subsequently, further degassing of LCP films used for the
unit circuit board and the adhesive material may be preferably
carried out under vacuum. This degassing process (second degassing
process) may be performed at a vacuum degree of 1500 Pa or less,
preferably 1300 Pa or less, and more preferably 1100 Pa or less.
The degassing period can be adjusted appropriately according to the
vacuum degree, for example 30 minutes or more, 40 minutes or more,
or 50 minutes or more. The degassing period may be 6 hours or less,
4 hours or less, and 3 hours or less, 2 hours or less, or 1.5 hours
or less.
[0255] The degassing under vacuum may be carried out at an ambient
temperature (e.g., in a range from 10.degree. C. to 50.degree. C.,
preferably 15.degree. C. to 45.degree. C.), alternatively may be
carried out under heating in view of increasing degassing
efficiency. Where heating the LCP films, the heating temperature
may be in a range from 80.degree. C. to 200.degree. C., preferably
100.degree. C. to 200.degree. C., and more preferably 115.degree.
C. to 200.degree. C. As described above, by heating the LCP film at
a certain temperature lower than the melting point of the film, it
is possible to carry out degassing water in the film as the water
vapor while suppressing the rapid moisture generation from the
film.
[0256] The second degassing process, from the viewpoint of
improving the degassing, may be carried out substantially without
pressurization (carried out under pressure release). For example,
where a circuit board is produced using a vacuum hot press
apparatus; a unit circuit board(s) and a LCP film(s) for an
adhesive material(s) are degassed in the first degassing process,
and then the unit circuit board(s) and the adhesive material(s) may
be set with stacking one another to obtain a stacked material to be
subjected to a second degassing process without pressurization.
[0257] Such a degassing process(es) makes it possible to obtain an
LCP film having extremely low moisture and air contents as the
substrate material, resulting in prevention of local adhesion
failure that is caused by air introduction in a
multilayer-laminated body due to insufficient degassing. In
particular, according to the present invention, the multilayer
circuit board, even having many layers, can avoid insufficient
degassing of a film(s) that exist(s) in the center portion of the
multilayer circuit board.
[0258] Thermo-Compression Bonding Process
[0259] In the thermo-compression bonding process, the circuit board
materials prepared in the preparation process are stacked
(overlaid) in accordance with a predetermined circuit board
structure, and the stacked circuit board materials are
thermo-compression bonded by heating at a predetermined
pressure.
[0260] The circuit board structure to be laminated is not
particularly limited, and may have appropriately determined
according to the desired structure. The circuit board materials are
usually stacked so that a conductor layer (or a conductor circuit)
is interposed between the circuit board materials.
[0261] It should be noted that the circuit board materials need
only to be in a stacked structure in the thermo-compression bonding
process. The circuit board materials may be stacked at any time,
depending on the state of the prepared circuit board materials and
work procedures, for example, may be stacked in the process such as
preparation process, degassing process, and thermo-compression
bonding process.
[0262] Stacking may be carried out, for example, by sandwiching a
bonding sheet between at least two sheets of insulating substrates
each having a conductor circuit on at least one surface, and
optionally by arranging a coverlay on an outermost surface of a
stacked body. Alternatively, stacking may be carried out by
superposing, without a bonding sheet, at least two sheets of
insulating substrates each having a conductor circuit on at least
one surface, and optionally by placing a coverlay on an outermost
surface of a stacked body. Where the insulating substrates can be
directly bonded without a bonding sheet, the thickness of the
entire circuit board can be reduced.
[0263] Thermo-compression bonding of a stacked body can be carried
out by using a vacuum hot press apparatus, a heating roll
lamination equipment, or others, depending on the type of circuit
board materials. From the viewpoint of reducing further gas from
the LCP film, it is preferable to use a vacuum hot press apparatus.
For example, the vacuum hot press may be preferably carried out by
thermo-compression bonding, while maintaining the degassed state of
the stacked structure achieved by vacuum degassing. The vacuum
degree during thermo-compression bonding may be preferably
maintained in the same degree with the vacuum degree of the second
degassing process (e.g., 1500 Pa or below).
[0264] Where using a TLCP film that has a thermo-adhesive property
enhanced by degassing process, the heating temperature in the
thermo-compression bonding may be a temperature selected from a
broad temperature range, for example, from (Tm-60).degree. C. to
(Tm+40).degree. C., preferably from (Tm-55).degree. C. to
(Tm+30).degree. C., and more preferably from (Tm-50).degree. C. to
(Tm+25).degree. C., where Tm denotes the melting point of the
adhesion-improved TLCP film to be bonded (in particular, where TLCP
films each having different melting point with each other, Tm
denotes a lower (lowest) melting point of the films). For example,
where thermo-compression bonding is carried out at a high
temperature environment, the heating temperature may be in a range
from (Tm-20).degree. C. to (Tm+40).degree. C., (e.g.,
(Tm-20).degree. C. to (Tm+20).degree. C.), preferably about
(Tm-10).degree. C. to (Tm+30).degree. C., and more preferably about
(Tm-10).degree. C. to (Tm+10).degree. C.
[0265] According to the present invention, where the degassing
processes (i) and (ii) are combined, surprisingly, it is possible
to achieve good interlayer adhesion even by heating at a
temperature lower than the melting point of the adhesion-improved
TLCP film to be adhered. The thermo-compression bonding may be
carried out at a temperature for example, (Tm-60).degree. C. or
higher and lower than (Tm-20).degree. C., (Tm-50).degree. C. or
higher and lower than (Tm-30).degree. C., and more preferably
(Tm-40).degree. C. to (Tm-32).degree. C.
[0266] Also, the pressure applied during thermo-compression bonding
can be selected, depending on the LCP film characteristics, for
example, from a wide range from 0.5 to 6 MPa. According to the
present invention, since an adhesion-improved LCP film(s) undergone
the degassing process is(are) used for bonding, good adhesion
between LCP film layers can be achieved even at a pressing pressure
of 5 MPa or less, particularly 4.5 MPa or less (for example, 0.5 to
3 MPa, preferably, 1 to 2.5 MPa), resulting in avoidance of local
adhesion failure caused by air introduction in a circuit board even
after bonding.
[0267] According to the present invention, where the degassing
process (i) and (ii) are combined, the thermo-compression bonding
process may include a thermo-compression bonding at a low pressing
pressure. For example, thermo-compression bonding process may be
carried out under a low pressure, for example, in a pressing
pressure range from 0.5 to 2.5 MPa, preferably 0.6 to 2 MPa, and
more preferably 0.7 to 1.5 MPa.
[0268] Further, according to the present invention,
thermo-compression bonding may be carried out in a single-stage
pressing, or in a multi-stage pressing such as two-stage pressing.
For example, a two-stage pressing may be carried out by pressing
under a higher compression pressure (for example, a range of beyond
2.5 MPa and less than 5 MPa) so as to conduct a temporary bonding
as a pre-process of the thermo-compression bonding, followed by
pressing under the above-described lower compression pressure.
Thermo-compression bonding under the lower compression pressure may
be carried out in a longer time than thermo-compression bonding
time of under the higher compression pressure. Thermo-compression
bonding under the low compression pressure may be carried out at a
higher temperature than the thermo-compression bonding temperature
under the higher compression pressure.
[0269] The time required for the thermo-compression bonding
(retention time under a constant temperature and pressure) is not
particularly limited as far as the circuit board can have an
improved interlayer adhesion, and for example, may be about 15 to
60 minutes, preferably about 20 to 50 minutes, and more preferably
about 20 to 40 minutes. In the case where the multi-stage pressing
is carried out, the thermo-compression bonding time may be the
total time of each of the retention times.
[0270] It should be noted that the method for producing the circuit
board might include, if necessary, various producing processes that
are known or conventional (e.g., circuit formation process,
through-connection process, inter-layer connection process).
[0271] The method for producing a circuit board according to
preferable one embodiment may include:
[0272] preparing at least one unit circuit board and at least one
TLCP film as a circuit board material to be adhered to the unit
circuit board, [0273] the unit circuit board comprising a
thermoplastic liquid crystal polymer film and a conductor layer
formed on one or the both surfaces of the thermoplastic liquid
crystal polymer film, and [0274] the circuit board material being
adhered to the surface of the conductor layer;
[0275] performing a first degassing of the unit circuit board(s)
and the circuit board material(s) under heating at a temperature
ranging from 100.degree. C. to 200.degree. C. for a predetermined
period of time, for example, under the ambient pressure;
[0276] performing a second degassing the of the unit circuit
board(s) and the circuit board material(s) under vacuum of 1500 Pa
or lower;
[0277] performing integration of a stacked material formed by
stacking the at least one circuit board material and the at least
one unit circuit board by thermo-compression bonding by application
of heat and pressure to the stacked material,
[0278] wherein the surface of the conductor layer in contact with
the circuit board material has a surface roughness (Rz.sub.JIS) of
1.25 .mu.m or less as an average value of ten-points measured
according to a method conforming to ISO 4287-1997.
[0279] Hereinafter, with reference to the drawings, as an
embodiment according to the present invention, there may be
mentioned a method for producing a circuit board (laminating
insulating substrates without a bonding sheet) as well as a method
for producing a circuit board (laminating insulating substrates
with a bonding sheet in between). It should be noted that the scope
of the present invention is not limited to these embodiments.
[0280] FIG. 2A is a schematic sectional view showing a circuit
board without a bonding sheet in a state before insulating
substrates are stacked. Here are prepared a first unit circuit
board (double-sided copper-clad laminate) 10 that comprises a first
TLCP film 5 and copper foils 4,4 cladded on both surfaces of the
film 5; and a second unit circuit board (single-sided copper-clad
laminate) 20 that comprises a second TLCP film 6 and a copper foil
4 cladded on one surface of the film 6. Here the first TLCP film 5
and the second TLCP film 6 may be made of the same material, and
may have thicknesses being identical or different with each
other.
[0281] Then a circuit processing (e.g., a strip line pattern
processing) may be carried out to a copper foil to be interposed
with the opposed unit circuit boards so as to obtain a conductor
circuit.
[0282] Then, preferably in a nitrogen gas atmosphere, the first
unit circuit board 10 and the unit circuit board 20 are heated for
a predetermined time (first degassing process). The conditions for
degassing temperature and degassing time may follow the conditions
described above.
[0283] Thereafter, the first unit circuit board 10 and the second
unit circuit board 20 are placed in stack in a chamber of a vacuum
hot press apparatus (not shown) so as to obtain a stacked body 30
as shown in FIG. 2B. Then, heating treatment may be carried out for
a predetermined time (second degassing process) while retaining a
vacuum degree of 1500 Pa or lower by vacuuming. The conditions for
degassing temperature and degassing time may follow the conditions
described above.
[0284] Then, while maintaining the vacuum degree of 1500 Pa or
lower, the heating temperature may be elevated to a temperature for
carrying out a thermo-compression bonding to laminate each of the
layers in the stacked body 30 under a predetermined compression
pressure. The conditions of temperature as well as period for
thermo-compression bonding may follow the conditions described
above.
[0285] Thereafter, according to a conventional process, the
conditions inside the apparatus are returned to ambient temperature
and ambient pressure so as to collect a circuit board 30 from the
apparatus.
[0286] In the above embodiment, the first unit circuit board 10 is
directly attached to the second unit circuit board 20.
Alternatively, as a modified embodiment, if necessary, a bonding
sheet may be interposed between the first unit circuit board 10 and
the second unit circuit board 20. As a further modified embodiment,
a conductive circuit is formed to have a micro-strip line pattern
and a coverlay may be used instead of the second unit circuit board
20.
[0287] Also, in the embodiment shown in FIG. 2B, the circuit board
has three conductor layers. The number of conductor layers may be
set appropriately, and may be one or more layers (for example, 2 to
10 layers).
[0288] FIG. 3A is a schematic sectional view showing a state before
lamination of a circuit board where laminating insulating
substrates and a bonding sheet. Here are prepared a first unit
circuit board (double-sided copper-clad laminate) 70 that comprises
a first TLCP film 7 and copper foils 40,40 cladded on both surfaces
of the film 7; a second unit circuit board (single-sided
copper-clad laminate) 80 that comprises a second TLCP film 8 and a
copper foil 40 cladded on one surface of the film 8; and a bonding
sheet 90 of a third TLCP film 9 (a LCP film as an adhesive
material) having a melting point lower than both of the TLCP films
7 and 8. Here, the first TLCP film 7 and the second TLCP film 8 may
be made of the same material, and may have thicknesses being
identical or different with each other.
[0289] Then after circuit-processing on the copper foil 40 of each
unit circuit board, the copper foil surface of the first unit
circuit board may be treated with FlatBOND GT (produced by MEC Co.,
Ltd.) to form an oxidation-resistant alloy layer (not shown) on the
copper foil surface, and subsequently treated with FlatBOND GC
(produced by MEC Co., Ltd.) for applying a silane-coupling agent so
as to obtain a conductor layer.
[0290] Thereafter, preferably in a nitrogen gas atmosphere, the
first unit circuit board 70, the second unit circuit board 80, and
the bonding sheet 90 are heated for a predetermined time (first
degassing process). The conditions for degassing temperature and
degassing time may follow the conditions described above.
[0291] Thereafter, the first unit circuit board 70, the second unit
circuit board 80, and the bonding sheet 90 are placed in stack in a
chamber of a vacuum hot press apparatus (not shown) so as to obtain
a stacked body 50 as shown in FIG. 3B. Then, heating treatment may
be carried out for a predetermined time (second degassing process)
while retaining a vacuum degree of 1500 Pa or lower by vacuuming.
The conditions for degassing temperature and degassing time may
follow the conditions described above.
[0292] Subsequently, while maintaining the vacuum degree of 1500 Pa
or lower, the heating temperature is elevated to a temperature
condition for carrying out a thermo-compression bonding to laminate
the layers with each other in the stacked body 50 under a
predetermined compression pressure. The conditions of temperature
as well as period for thermo-compression bonding may follow the
conditions described above.
[0293] Thereafter, according to a conventional process, the
conditions inside the apparatus are returned to ambient temperature
and ambient pressure so as to collect a circuit board 50 from the
apparatus.
[0294] In the embodiments described above, the second unit circuit
board is laminated to the first unit circuit board with or without
a bonding sheet. The first unit circuit board comprises an
insulating layer and conductor layers (copper foils) placed on both
surfaces of the insulating layer. The second unit circuit board
comprises an insulating layer and a conductor layer on one surface
(upper surface) of the insulating layer. However, the configuration
illustrated is not intended to limit the circuit board of the
present invention. For example, the circuit board may have two
conductor layers, or four or more conductor layers. The circuit
board may comprise a coverlay of a LCP film to cover the conductor
layer on the outermost layer.
[0295] Circuit Board
[0296] The circuit board (preferably a multi-layer circuit board)
according to the fourth aspect of the present invention relates to
a circuit board comprising a plurality of circuit board materials,
wherein:
[0297] the circuit board materials are at least one member selected
from the group consisting of an insulating substrate having a
conductor layer on at least one surface, a bonding sheet, and a
coverlay; and
[0298] at least one of the circuit board materials comprises a TLCP
film.
[0299] The circuit board has an improved heat resistance, and is a
circuit board showing a solder heat resistance when the circuit
board is placed in a solder bath at a temperature of 290.degree. C.
for 60 seconds conforming to a method of JIS C 5012. The solder
heat resistance may be evaluated by observing a substrate sample
that is subjected to solder float test in a solder bath at a
temperature of 290.degree. C. for 60 seconds conforming to a method
of JIS C 5012 to be determined whether the substrate sample has
blisters having a height of 100 .mu.m or higher by sight or using
an optical microscopy (5 magnifications or higher).
[0300] For example, the circuit board of the present invention may
be a circuit board having the following configuration:
[0301] (i) a circuit board (multilayer or laminated circuit board)
that comprises two or more unit circuit boards each including an
insulating layer of a TLCP film (a first TLCP film) and a conductor
layer(s) formed on one or both surfaces of the film, and a bonding
sheet(s) interposing between the unit circuit boards,
[0302] (ii) a circuit board (single layer or bilayer circuit board)
that comprises a unit circuit board including an insulating layer
of a TLCP film (a first LCP film) and a conductor layer(s) formed
on one or both surfaces of the film, and a coverlay(s) to cover the
conductor layer(s) of the unit circuit board,
[0303] (iii) a configuration combining the above (i) and (ii), for
example, a circuit board (multilayer or laminated circuit board)
that comprises a unit circuit board, a bonding sheet(s), and a
coverlay(s) to cover the conductor layer(s) of the unit circuit
board, wherein the bonding sheet(s) interposes between the unit
circuit board, and the outermost layer of the circuit board
comprises the coverlay covering the conductor layer(s) of the unit
circuit board,
[0304] (iv) a circuit board (multilayer or laminated circuit board)
that comprises two or more unit circuit boards, each including an
insulating layer of a TLCP film (a substrate layer), wherein the
unit circuit boards are directly laminated without a bonding
sheet(s), and
[0305] (v) a configuration combining the above (ii) and (iv), for
example, a circuit board (multilayer or laminated circuit board)
that comprises two or more unit circuit boards and a coverlay(s),
wherein the unit circuit boards are directly laminated without a
bonding sheet, and the outermost layer of the circuit board
comprises the coverlay covering the conductor layer(s) of the unit
circuit board.
[0306] It should be noted that, as already mentioned in the
producing method, a surface of the conductor layer on the side of
bonding to a circuit board material may have a surface roughness
(Rz.sub.JIS) of 1.25 .mu.m or less as an average value of
ten-points measured according to a method conforming to
ISO4287-1997.
[0307] Further, since the adhesive property of the TLCP film is
improved in the above circuit board, the circuit board may have an
improved bonding strength between the TLCP film and a circuit board
material in contact with the TLCP film, as a value measured in
accordance with JIS C5016-1994. Where the circuit board material is
an insulating substrate material (preferably, another TLCP film),
the bonding strength between the TLCP film and the insulating
substrate material may be 0.8 kN/m or higher (e.g., 0.8 to 3 kN/m),
preferably 0.9 kN/m or higher, more preferably 1 kN/m or higher,
and further preferably 1.1 kN/m or higher. It should be noted that
the bonding strength may be determined as a peel strength value
measured conforming to JIS C5016-1994 by peeling a TLCP film from
an adherend at a peeling angle of 90.degree. and at a peeling rate
of 50 mm per minute using a tensile tester ("Digital force gauge
FGP-2" produced by NIDEC-SHIMPO CORPORATION.).
[0308] Further, since the adhesive property of the LCP film is
improved in the above circuit board, where the circuit board
material is a conductor layer, the bonding strength in accordance
with JIS C5016-1994 between the TLCP film and the conductor layer
may be 0.3 kN/m or higher (e.g., 0.3 to 2 kN/m), and preferably 0.5
kN/m or higher.
[0309] It should be noted that upon determining interlayer
adhesion, existence of cohesive failure could be generally
determined as an evidence of good bonding. In contrast, occurrence
of interfacial separation shows poor bonding in many cases.
[0310] Preferably, the circuit board is generally improved in
bonding strength in every direction. For example, with respect to a
first direction (A direction) of a circuit board sample and a
second direction (B direction) perpendicular to the first
direction, where bonding strengths of the sample are measured in
four direction by peeling from both sides, i.e., in a forward A
direction, in an adverse A direction, in a forward B direction, and
in an adverse B direction,
[0311] (i) the minimum bonding strength in the four directions
between the TLCP film and an insulating substrate material may be
0.5 kN/m or higher (e.g., 0.5 to 3 kN/m), preferably 0.6 kN/m or
higher, more preferably 0.7 kN/m or higher, still more preferably
0.8 kN/m or higher, and particularly preferably 0.9 kN/m or higher,
and/or
[0312] (ii) the minimum bonding strength in the four directions
between the TLCP film and a conductor layer may be 0.25 kN/m or
higher (e.g., 0.25 to 2 kN/m), preferably 0.28 kN/m or higher, and
more preferably 0.5 kN/m or higher.
[0313] In the circuit board comprising the circuit board materials,
the circuit board materials may comprise at least two TLCP films
including a first TLCP film and a second TLCP film, wherein a
conductor layer is interposed between the first and the second TLCP
films. The difference in melting point between the first TLCP film
and the second TLCP film may be in the range described above. Also,
in order to enhance high frequency characteristics, all of the
circuit board materials preferably comprise TLCP films.
[0314] Moreover, depending on thermo-adhesive property of TLCP
films, the circuit board may have a configuration without a bonding
sheet, i.e., direct bonding of insulating substrates with each
other, or direct bonding of an insulating substrate and a coverlay.
For example, non-use of the bonding sheet makes it possible to
achieve a circuit board with a reduced thickness.
[0315] For example, as shown in FIG. 4, the circuit board may
comprise n layers of conductor layer 4 and n+1 layers of insulating
layer (or a TLCP film layer) 3 wherein each of the conductor layers
is interposed between the insulating layers. In this case, if
necessary, the circuit board may be provided with a conductor layer
on the outermost layer. It should be noted that where one portion
of the conductor layer is originally formed on an upper layer of an
insulating layer and another portion of the conductor layer is
originally formed on a lower layer of an insulating layer, as long
as these parts are interposed between the same insulating layers,
these parts are regarded as belonging to the same conductor
layer.
[0316] Further, since the circuit board with an adhesive-improved
TLCP film(s) makes it possible to be thermo-compression bonded at a
lower pressure (preferably, at a lower temperature and lower
pressure). As a result, the subduction (sinking) of the conductor
circuit, the subduction being caused in the thermo-compression
bonding, can be reduced, resulting in improvement in reliability of
the circuit board.
[0317] For example, FIG. 5A shows a schematic cross-sectional view
showing a laminate sample comprising a conductor circuit 4, and LCP
films 5 and 6 obtained by cutting the sample vertically to the
conductor circuit. Where L1 denotes the thickness of the LCP film 5
at which the conductor circuit 4 is not formed, and L2 denotes the
thickness of the insulating substrate at which the conductor
circuit is formed, the measured thicknesses L1 and L2 can be used
for calculating a L2/L1 ratio in percentage that an index parameter
for subduction. The ratio of L2/L1 in percentage may be 80 to 100%,
preferably 85 to 100%, and more preferably 90 to 100%. It should be
noted that where there is no subduction, the ratio is 100% because
of L1=L2. The larger the subduction amount is, the lower the
percent ratio is. The thickness L2 may be measured as a distance L2
between the lower surface of the conductor circuit 4 and the bottom
surface of the LCP film 5.
[0318] As shown in FIG. 5B, where a ground conductor 4b is formed
on the bottom surface of the LCP film, the L1 may be determined as
a distance from the boundary surface between the adjacent LCP films
to the upper surface of the ground conductor 4b. The L2 may be
determined as a distance from the lower surface of the conductor
circuit 4a to the upper surface of the ground conductor 4b in the
circuit board.
[0319] Since the circuit board according to the present invention
can employ, as an insulating material, a thermoplastic liquid
crystal polymer excellent in dielectric characteristics, the
circuit board can be used particularly suitably as a high frequency
circuit board. Examples of high frequency circuits include a
circuit for transmitting mainly (only) high frequency signals; in
addition; a circuit for a transmission line transmitting low
frequency signals, for example, a circuit for a transmission line
transmitting low frequency signals as output after converting high
frequency signals into low frequency signals, a circuit for a
transmission line supplying electronic power to drive high
frequency-corresponding parts; as well as a circuit provided with
the above circuits or transmission lines on the same plane.
[0320] For example, at a frequency of 10 GHz, the circuit board
(.epsilon..sub.r) may have a relative dielectric constant of, for
example, from 2.6 to 3.5, and more preferably from 2.6 to 3.4.
[0321] Also, for example, at a frequency of 10 GHz, the circuit
board may have a dielectric loss tangent (Tan .delta.) of, for
example, from 0.001 to 0.01, and more preferably from 0.001 to
0.008.
EXAMPLES
[0322] Hereinafter, the present invention is described in greater
detail by examples, but the invention is not limited in any way by
the present invention to this embodiment. In the following Examples
and Comparative Examples were measured for various physical
properties by the following method.
[0323] Melting Point
[0324] Melting point of a film was determined based on the
observation of thermal behavior of the film using a differential
scanning calorimeter. A test film was heated at a rate of
20.degree. C./min to completely melt the film, and the melt was
rapidly cooled to 50.degree. C. at a rate of 50.degree. C./min.
Subsequently, the quenched material was reheated at a heating rate
of 20.degree. C./minute, and a position of an endothermic peak
appearing in the reheating process was recorded as a melting point
of the film.
[0325] Moisture Content
[0326] Karl Fischer method was employed as a measuring method of
moisture content, that is, moisture content was measured by
observing change in potential difference before and after allowing
moisture absorbed in a solvent in accordance with the principle of
the Karl Fischer titration.
[0327] (1) Device name for trace moisture measurement: VA-07, CA-07
available from Mitsubishi Chemical Analytech Co., Ltd.
[0328] (2) Heating temperature: 260.degree. C.
[0329] (3) N.sub.2 purge pressure: 150 mL/min.
[0330] (4) Measurement preparation (automatic) [0331] Purge: 1
minute [0332] Pre-heat: 2 minutes for baking a sample board [0333]
Cooling: 2 minutes for cooling the sample board
[0334] (5) Measurement [0335] Time for accumulating moisture in a
measurement titration cell, i.e., time for sending moisture with
N.sub.2: 3 minutes
[0336] (6) Sample weight: 1.0 to 1.3 g
[0337] Segment Orientation Ratio (SOR)
[0338] Using a microwave type molecular orientation meter, a liquid
crystal polymer film is inserted into a microwave resonance
waveguide tube such that a propagation direction of microwave is
perpendicular to the film surface, and electric-field strength
(microwave transmission intensity) of microwave transmitting
through the film is measured. Then, based on the measured value, m
value (referred to as refractive index) is calculated from the
following formula:
m=(Zo/.DELTA.z).times.[1-.nu.max/.nu.o]
[0339] Here, Zo represents a device constant, .DELTA.z represents
an average thickness of an object subjected to the measurement,
.nu.max represents the frequency at which the maximum microwave
transmission intensity can be obtained when the frequency of the
microwave is varied, and .nu.o represents the frequency at which
the maximum microwave transmission intensity can be obtained when
the average thickness is zero, that is, when no object is
present.
[0340] Next, when the rotation angle of the object relative to the
direction of oscillation of the microwaves is 0.degree., that is,
when the direction of oscillation of the microwaves is aligned with
the direction in which molecules of the object are most oriented as
well as in which the minimum microwave transmission intensity is
exhibited, an m value obtained in such a case was represented as
m.sub.0. An m value obtained as m represents the value of the
refractive index when the angle of rotation of the object is
90.degree.. A segment orientation ratio SOR was calculated as
m.sub.0/m.sub.90.
[0341] Film Thickness
[0342] Thicknesses of an obtained film were measured at intervals
of 1 cm in the TD direction using a digital thickness meter
(manufactured by Mitutoyo Corporation), and the film thickness was
determined as an average thicknesses of 10 points arbitrarily
selected from a center portion and end portions.
[0343] Heat Resistance Test
[0344] Solder float test was carried in conformity with JIS C 5012
to examine solder heat resistance of the circuit board. The solder
heat resistance was evaluated by observing a substrate sample that
was subjected to solder float test in a solder bath of 290.degree.
C. for 60 seconds whether the substrate sample had at least one
blister having an area of 100 .mu.m.times.100 .mu.m or wider by
sight or using an optical microscopy (5 magnifications or
higher).
[0345] Specifically, from a circuit board sample having a size of
30 cm square (30 cm.times.30 cm) were derived five circuit board
samples each having a size of 5 cm square (5 cm.times.5 cm) by
randomly cutting. Each of the five circuit board samples were
subjected to the solder float test, and blister occurrence was
observed by sight or using an optical microscopy (5 magnifications
or higher). Where blister was not observed in all of the five cut
samples, the originated circuit board sample was determined as
good, i.e., showing solder heat resistance. Where blister was
observed in any one of the five cut samples, the originated circuit
board sample was determined as poor.
[0346] Method for Measuring Bonding Strength between Adjacent
Circuit Board Materials
[0347] In conformity to JIS C5016-1994, peel strength was measured
by peeling one of two bonding circuit board materials from the
other material at a peeling angle of 90.degree. and at a peeling
rate of 50 mm per minute using a tensile tester ["Digital force
gauge FGP-2" produced by NIDEC-SHIMPO CORPORATION.]. The obtained
value was regarded as bonding strength (peeling strength).
[0348] It should be noted that bonding strength was measured in
four directions with respect to a first direction (MD direction) of
a circuit board sample and a second direction (TD direction)
perpendicular to the first direction, by peeling from both sides,
i.e., in a forward MD direction (or MD-proceeding direction), in an
adverse MD direction (or MD-reversing direction), in a forward TD
direction (or rightward TD direction), and in an adverse TD
direction (or leftward TD direction). The average value in the four
directions was treated as a representative bonding strength of the
circuit board.
[0349] It should be noted that where circuit board material has a
conductive material, bonding strength is determined depending on
the surface area ratio of the conductive material portion in
contact with the TLCP film. The surface area ratio may be
determined as existing ratio of conductive material as follows:
Existin g ratio of conductive material = ( Surface area of circuit
patterns on circuit board unit in contact with the target LCP film
) / ( Surface area of entire circuit board unit ) .times. 100
##EQU00002##
[0350] Where the ratio is 30% or more, the bonding strength was
measured as a bonding strength between the LCP film and a conductor
layer. Where the ratio is less than 30%, the bonding strength was
measured as a bonding strength between the LCP film and an
insulating substrate material.
[0351] Method for Measuring Surface Roughness
[0352] A copper foil surface in a laminate (B) was subjected to
roughening treatment, and then an arithmetic mean roughness (Ra)
and a surface roughness (Rz.sub.JIS) of the treated surface were
measured using a stylus-type surface roughness tester ("SJ-201"
produced by Mitutoyo Corp.). Measurement was carried out conforming
to ISO 4287-1997. More specifically, the arithmetic mean roughness
Ra is a value that shows an average value of the absolute value of
the deviation from the mean line; the surface roughness
(Rz.sub.JIS) is an average value of ten points selected from a
roughness curve in a sampled standard length along the direction of
the average line as the sum of the average of the absolute values
of the 5 highest peak points (convex top points) and the average of
the absolute values of the 5 lowest valley points (concave bottom
points) in the sampled section, and is express in .mu.m.
[0353] Subduction
[0354] A laminate containing a conductor circuit was cut to give a
cross-sectional sample vertical to the conductor circuit. The
sample was placed on a Pt sputtering machine to form a Pt film
(thickness: 20 .ANG.) on the surface. Then, using a scanning
electron microscope ("SU-70" produced by Hitachi High-Technologies
Corporation.), secondary electron image of the laminate in the
cross section (SEM image) was obtained at an accelerating voltage
of 5 kV to observe the degree of subduction.
[0355] As shown in FIG. 5B, with respect to a laminate containing
LCP films and a ground conductor adjacent to one of the LCP film,
the L1 was determined as a distance from the boundary surface
between the adjacent LCP films to the ground conductor; the L2 was
determined as a distance from the lower surface of the conductor
circuit to the upper surface of the ground conductor in the circuit
board. After calculating a ratio of L2/L1 in percentage, subduction
of the circuit board was evaluated in accordance with the following
criteria:
[0356] Good: Ratio of L2/L1 is 80% or more.
[0357] Poor: Ratio of L2/L1 is less than 80%.
[0358] Where no subduction occurred, the ratio is 100% because of
L1=L2. The larger subduction is, the lower the percentage ratio
is.
[0359] Resin Flow
[0360] Occurrence of resin flow in 10 cm circuit board samples was
visually observed. A sample having a resin flow of 1 mm or less was
determined as good in quality; a sample having a resin flow of over
1 mm was determined as poor in quality.
Example 1
[0361] (1) Production of Adhesive-Improved LCP Film
[0362] A copolymerization product of p-hydroxybenzoic acid and
6-hydroxy-2-naphthoic acid (mole ratio: 73/27), being a
thermoplastic liquid crystal polymer having a melting point of
280.degree. C., was melted and extruded by inflation method to
obtain a rolled product (winding thickness W=600 mm) of a
thermoplastic liquid crystal polymer film having a melting point of
280.degree. C., a film thickness of 50 .mu.m, and a segment
orientation ratio SOR of 1.02. The TLCP film in the rolled product
had a moisture content of 400 ppm.
[0363] Thus obtained TLCP film rolled product was degassed by heat
treatment for 60 minutes at a temperature of 120.degree. C.
Thus-degassed TLCP film in the rolled product had a moisture
content of 200 ppm and a segment orientation ratio SOR of 1.02.
[0364] (2) Production of Unit Circuit Board
[0365] From a copolymerization product of p-hydroxybenzoic acid and
6-hydroxy-2-naphthoic acid (mole ratio: 73/27) was obtained a TLCP
film having a melting point of 280.degree. C. and a film thickness
of 50 .mu.m. The TLCP film was heat-treated under nitrogen
atmosphere at 260.degree. C. for 4 hours, and at 280.degree. C. for
another 2 hours to increase a melting point into 325.degree. C.
Onto each surface of the film, a rolled copper foil (JX Nippon
Mining & Metals Corporation, BHYX-T-12, thickness: 12 .mu.m)
was set to be laminated using a continuous heat-pressing machine
with a pair of rolls at a roll temperature of 290.degree. C., a
linear pressure of 100 kg/cm, a line speed of 2 m/min to obtain a
copper-clad laminate. The copper-clad laminate was processed to
produce a unit circuit board having a strip line structure. The
TLCP film in the unit circuit board had a moisture content of 400
ppm.
[0366] (3) Production of Multilayer Circuit Board
[0367] The adhesive-improved LCP film obtained in the process (1)
was used as a bonding sheet to be interposed between two sheets of
the unit circuit boards to obtain a stacked material. The stacked
material was placed in a vacuum heat press apparatus. Thereafter,
the stacked material was thermo-compression bonded under vacuum at
a vacuum degree of 1300 Pa and a compression pressure of 4 MPa at
300.degree. C. for 30 minutes to be bonded with each other to
obtain a circuit board having a configuration of unit circuit
board/bonding sheet/unit circuit board. The obtained circuit board
was evaluated in various physical properties. Table 7 shows
obtained properties.
Example 2
[0368] (1) Production of Circuit Board
[0369] A stacked material was prepared in the same manner with
Example 1 except for using, as a bonding sheet, a non-degassed TLCP
film having a melting point of 280.degree. C., a film thickness of
50 .mu.m, a moisture content of 400 ppm, and a segment orientation
ratio SOR of 1.02 obtained from a copolymerization product of
p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (mole ratio:
73/27). The stacked material in which the bonding sheet was
interposed between two sheets of the unit circuit boards was placed
in a vacuum heat press apparatus.
[0370] Thereafter, the stacked material was subjected to degassing
under vacuum at a vacuum degree of 1000 Pa and a compression
pressure of 0.5 MPa at 120.degree. C. for 60 minutes to be degassed
in the stacked configuration.
[0371] After degassing under vacuum, the stacked material was
subjected to thermo-compression bonding in the same way as Example
1 to be bonded with each other to obtain a circuit board having a
configuration of unit circuit board/bonding sheet/unit circuit
board. The obtained circuit board was evaluated in various physical
properties. Table 7 shows obtained properties.
Example 3
[0372] (1) Production of Circuit Board
[0373] A circuit board was prepared in the same manner with Example
2 except for using, as a bonding sheet, an adhesive-improved TLCP
film obtained in Example 1. The obtained circuit board was
evaluated in various physical properties. Table 7 shows obtained
properties.
Comparative Example 1
[0374] (1) Production of Circuit Board
[0375] A circuit board was prepared in the same manner with Example
1 except for using, as a bonding sheet, a non-degassed TLCP film
having a melting point of 280.degree. C., a film thickness of 50
.mu.m, a moisture content of 400 ppm, and a segment orientation
ratio SOR of 1.02 obtained from a copolymerization product of
p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (mole ratio:
73/27). The obtained circuit board was evaluated in various
physical properties. Table 7 shows obtained properties.
TABLE-US-00007 TABLE 7 Circuit board unit Bonding sheet Degass
under vacuum Moisture Moisture Vacuum Insulating content content
degree Temp. Pressure Period substrate (ppm) Film (ppm) SOR (Pa)
(.degree. C.) (MPa) (min) Ex. 1 LCP film 400 Adhesive-improved 200
1.02 -- -- -- -- (Tm325.degree. C.) LCP film (Tm280.degree. C.) Ex.
2 LCP film 400 LCP film 400 1.02 1000 120 0.5 60 (Tm325.degree. C.)
(Tm280.degree. C.) Ex. 3 LCP film 400 Adhesive-improved 200 1.02
1000 120 0.5 60 (Tm325.degree. C.) LCP film Com. Ex. 1 LCP film 400
LCP film 400 1.02 -- -- -- -- (Tm325.degree. C.) (Tm280.degree. C.)
Thermo-compression bonding Circuit board Vacuum Heat Bonding degree
Temp. Pressure Period resistance strength (Pa) (.degree. C.) (MPa)
(min) (290.degree. C.) (kN/m) Ex. 1 1300 300 4 30 Good 1.0 Ex. 2
1300 300 4 30 Good 1.0 Ex. 3 1300 300 4 30 Good 1.5 Com. Ex. 1 1300
300 4 30 Poor 0.5
[0376] As shown in Table 7, since each of the circuit boards in
Examples 1 and 3 uses the adhesive-improved LCP film as a bonding
sheet, the interlayer adhesion of the circuit boards can be
improved even in the conventional thermo-compression bonding
procedure. These circuit boards also have enhanced heat resistance
so that occurrence of blisters can be suppressed at high
temperatures.
[0377] Meanwhile, Example 2 does not employ the adhesive-improved
LCP film as the circuit board material. However, because of the
degassing process for the stacked material under vacuum before
thermo-compression bonding, the interlayer adhesion of the circuit
board can be also enhanced after thermo-compression bonding. The
circuit board also has enhanced heat resistance so that occurrence
of blisters can be suppressed at high temperatures.
[0378] In particular, in Example 3, usage of the adhesion-improved
LCP film as the bonding sheet in combination with the specific
degassing process makes it possible to achieve particularly
excellent interlayer adhesion.
[0379] On the other hand, Comparative Example 1, which neither
employs the adhesion-improved LCP film nor is subjected to the
degassing process, deteriorates in interlayer adhesion, showing
lower bonding strength than those in Examples. Further, some
samples in Comparative Example 1 have blisters at the high
temperature.
Example 4
[0380] (1) Production of Unit Circuit Board
[0381] Onto each surface of a TLCP film having a melting point of
335.degree. C. ("CT-Z", produced by Kuraray Co., Ltd., thickness:
25 .mu.m), a rolled copper foil ("BHYX-T-12", produced by X Nippon
Mining & Metals Corporation, thickness: 12 .mu.m) was overlaid
to obtain a stacked material. The stacked material was placed in a
vacuum heat press apparatus with heated plates at 295.degree. C.
under a compression pressure of 4 MPa for 10 minutes to be bonded
with each other to obtain a first copper-clad laminate having a
configuration of copper foil/first TLCP film/copper foil. In the
meantime, onto each surface of a TLCP film having a melting point
of 280.degree. C. ("CT-F", produced by Kuraray Co., Ltd.,
thickness: 50 .mu.m), a rolled copper foil ("BHYX-T-12", produced
by J Nippon Mining & Metals Corporation, thickness: 12 .mu.m)
was overlaid to obtain a stacked material. The stacked material was
placed in a vacuum heat press apparatus with heated plates at
275.degree. C. under a compression pressure of 4 MPa for 10 minutes
to be bonded with each other to obtain a second copper-clad
laminate having a configuration of copper foil/second TLCP
film.
[0382] Subsequently, one copper foil of the first copper-clad
laminate was processed by a chemical etching process to have a
circuit pattern of a strip line structure (existing conductive
material ratio: less than 30%) to obtain a first unit circuit
board.
[0383] The first unit circuit board and the second copper-clad
laminate were stacked so that the circuit pattern was interposed
between the first and second TLCP films to obtain a stacked
material. The stacked material was subjected to degassing under
heating at 100.degree. C. under atmospheric pressure at a pressing
pressure of 0 MPa for 1 hour (a first degassing process: degassing
under heating).
[0384] Subsequently, the stacked material of the first unit circuit
board and the second copper-clad laminate, in which the circuit
pattern was interposed between the first and second TLCP films, was
placed in a chamber of a vacuum hot press apparatus for degassing
under vacuum at a vacuum degree of 1000 Pa with heating at
100.degree. C. under a compression pressure of 0 MPa for 1 hour
(second degassing: degassing under vacuum).
[0385] Then, the stacked material was subjected to two-stage press,
i.e., first compression-bonding by means of heated plates set to
150.degree. C. under a compression pressure of 4 MPa for 5 minutes
(pre-process), followed by second compression-bonding by means of
heated plates set to 300.degree. C. under a compression pressure of
1 MPa for 30 minutes (post-process) to obtain a circuit board
having a multilayer configuration of copper foil/first TLCP
layer/circuit layer/second TLCP layer/copper foil. The obtained
circuit board was evaluated in various physical properties. Table 8
shows obtained properties.
[0386] It should be noted that FIG. 6A shows an SEM image of
thus-obtained circuit board. As shown in FIG. 6A, in which the
white portion shows liquid crystal polymer, the boundary surface
between the first TLCP layer and the second TLCP layer can be
observed. A copper stripe or the copper foil portion can be
observed as a white or high contrast part in monochrome.
Observation of FIG. 6A reveals that subduction of circuit layer
into the TLCP layer is suppressed.
Example 5
[0387] Onto each surface of a TLCP film having a melting point of
335.degree. C. ("CT-Z", produced by Kuraray Co., Ltd., thickness:
25 .mu.m), a rolled copper foil ("BHYX-T-12", produced by JX Nippon
Mining & Metals Corporation, thickness: 12 .mu.m) was overlaid
to obtain a stacked material. The stacked material was placed in a
vacuum heat press apparatus with heated plates at 295.degree. C.
under a compression pressure of 4 MPa for 10 minutes to be bonded
with each other to obtain a second copper-clad laminate having a
configuration of copper foil/second TLCP film. The circuit board
was produced in the same manner with Example 4 except for using the
second copper-clad laminate as obtained above. The obtained circuit
board was evaluated in various physical properties. Table 8 shows
obtained properties.
[0388] It should be noted that FIG. 6B shows an SEM image of
thus-obtained circuit board. Observation of FIG. 6B reveals that
subduction of circuit layer into the TLCP layer is suppressed.
Comparative Example 2
[0389] A circuit board was produced in the same manner as in
Example 4 except for carrying out neither degassing under heating
nor degassing under vacuum. The obtained circuit board was
evaluated in various physical properties. Table 8 shows obtained
properties.
Comparative Example 3
[0390] A circuit board was produced in the same manner as in
Example 5 except for carrying out neither degassing under heating
nor degassing under vacuum. The obtained circuit board was
evaluated in various physical properties. Table 8 shows obtained
properties.
Comparative Example 4
[0391] A circuit board was produced in the same manner as in
Example 5 except that neither degassing under heating nor degassing
under vacuum was carried out, and that two-stage press was carried
out in the thermo-compression bonding, i.e., in a first
compression-bonding by means of heated plates set to 150.degree. C.
under a compression pressure of 4 MPa for 5 minutes (pre-process),
followed by second compression-bonding by means of heated plates
set to 320.degree. C. under a compression pressure of 3 MPa for 30
minutes (post-process). The obtained circuit board was evaluated in
various physical properties. Table 8 shows obtained properties.
[0392] It should be noted that FIG. 6C shows an SEM image of
thus-obtained circuit board. Observation of FIG. 6C reveals that
the circuit layer is subducted into the LCP layer.
TABLE-US-00008 TABLE 8 Second Circuit board material degassing
Second First degassing Vacuum First LCP LCP Environ- Temp. Pressure
Period degree Temp. Pressure Period film film ment (.degree. C.)
(MPa) (min) (Pa) (.degree. C.) (MPa) (min) Ex. 4 CTZ-25 CTF-50
Ambient 100 0 60 1000 100 0 60 (Tm335.degree. C.) (Tm280.degree.
C.) pressure Ex. 5 CTZ-25 CTZ-50 Ambient 100 0 60 1000 100 0 60
(Tm335.degree. C.) (Tm335.degree. C.) pressure Com. Ex. 2 CTZ-25
CTF-50 -- -- -- -- -- -- -- -- (Tm335.degree. C.) (Tm280.degree.
C.) Com. Ex. 3 CTZ-25 CTZ-50 -- -- -- -- -- -- -- -- (Tm335.degree.
C.) (Tm335.degree. C.) Com. Ex. 4 CTZ-25 CTZ-50 -- -- -- -- -- --
-- -- (Tm335.degree. C.) (Tm335.degree. C.) Thermo- Bonding
strength compression LCP film/LCP Heat Compression Pressure film
(kN/m) resistance Resin Temp (.degree. C.) (MPa) Max. Min. Avg.
(290.degree. C.) flow Subduction Ex. 4 300 1.0 1.80 1.50 1.70 Good
Good Good Ex. 5 300 1.0 1.20 1.00 1.05 Good Good Good Com. Ex. 2
300 1.0 0.80 0.60 0.63 Poor Good Good Com. Ex. 3 300 1.0 0.80 0.60
0.63 Poor Good Good Com. Ex. 4 320 3.0 1.30 1.10 1.14 Poor Poor
Poor
[0393] As shown in Table 8, since each of the circuit boards in
Examples 4 and 5 uses the LCP film subjected to the specific
degassing process, the heat resistance of the circuit boards is
improved. Further, even if the post-process as the main
thermo-compression bonding is carried out under a low compression
pressure of 1 MPa, it is possible to improve interlayer adhesion in
the circuit board (between the adjacent TLCP films as well as
between the TLCP film and the conductive layer). In particular,
Examples 4 and 5 achieve satisfactory adhesion of directly bonding
between unit circuit boards even without a bonding sheet used in
Examples 1 to 3.
[0394] In addition, the production of these circuit boards under
low compression pressure of 1 MPa in the main thermo-compression
bonding process makes it possible to suppress not only resin flow
during circuit board production but also subduction of the
conductor layer into the TLCP film.
[0395] Furthermore, in Example 5, even if both of the TLCP films
are high-melting-point films, it is possible to achieve
satisfactory adhesion between the circuit board materials.
Particularly surprisingly, in Example 5, even if the
thermo-compression bonding is carried out at a temperature lower
than the melting point of these high melting point films, it is
possible to show satisfactory interlayer adhesion.
[0396] On the other hand, in Comparative Example 2 and Comparative
Example 3, because of lack in degassing process, the obtained
circuit boards are inferior in heat resistance as well as in
interlayer adhesion being reduced by about 40% compared with the
interlayer adhesion of Example 5.
[0397] In Comparative Example 4, since the production of the
circuit board was carried out at a high temperature under high
compression pressure in the main thermo-compression bonding
process, bonding strength is improved whereas heat resistance is
deteriorated. Further, resin flow is occurred during circuit board
production, and the conductor layer is subducted into the TLCP
film.
[0398] Various properties measured in the above Examples show
advantageous properties such as heat resistance and interlayer
adhesion in the combination of the insulating substrate and the
bonding film, the combination of the insulating substrate and the
coverlay, and the combination of the insulating substrate and the
insulating substrate.
[0399] Next, on the basis of Examples 6 to 8 and Comparative
Example 5, the influence of the surface roughness of the conductor
layer on the circuit board will be discussed.
Example 6
[0400] Onto each surface of a TLCP film having a melting point of
335.degree. C. ("CT-Z", produced by Kuraray Co., Ltd.), a rolled
copper foil ("BHYX-T-12", produced by JX Nippon Mining & Metals
Corporation, thickness: 12 .mu.m) was overlaid to obtain a stacked
material. The stacked material was placed in a vacuum heat press
apparatus with heated plates at 295.degree. C. under a compression
pressure of 4 MPa for 10 minutes to be bonded with each other to
obtain a first unit circuit board having a configuration of copper
foil/TLCP film/copper foil as well as a second unit circuit board
having a configuration of copper foil/TLCP film. The thicknesses of
the TLCP films in the first unit circuit board and the second unit
circuit board are 100 .mu.m and 75 .mu.m, respectively.
Subsequently, each of the copper foils was processed by a chemical
etching method (existing conductive material ratio: 30% or
more).
[0401] Subsequently, the copper foils of the first unit circuit
board were treated by a surface roughening treatment, more
specifically, a treatment carried out with "FlatBOND GT and
FlatBOND GC treatment" available from MEC Co., Ltd. Hereinafter
this treatment is referred to as FlatBOND treatment. The conductor
layer including an alloy layer had surface roughness Ra of 0.13
.mu.m and Rz.sub.JIS of 1.05 .mu.m.
[0402] The first unit circuit board, a bonding sheet (a TLCP film
"CT-F" having a melting point of 280.degree. C. and a thickness of
25 .mu.m produced by Kuraray Co., Ltd.) and the second unit circuit
board were overlaid in this order to obtain a stacked material. The
stacked material was subjected to degassing under heating at
115.degree. C. under atmospheric pressure, at a compression
pressure of 0 MPa for 2 hours (a first degassing process).
[0403] Subsequently, as shown in FIG. 3B, the stacked material of
the first unit circuit board and the second copper-clad laminate,
in which the bonding sheet was interposed between the first and
second unit circuit boards, was placed in a chamber of a vacuum hot
press apparatus for degassing under vacuum at a vacuum degree of
1000 Pa with heating at 00.degree. C. under a compression pressure
of 0 MPa for 1 hour (second degassing).
[0404] Then, the stacked material was subjected to
thermo-compression bonding by means of heated plates set to
295.degree. C. under a compression pressure of 1 MPa for 30 minutes
(pre-process) to obtain a circuit board having a multilayer
configuration of copper foil/first TLCP layer/second TLCP
layer/circuit layer/first TLCP layer/copper foil as shown in FIG.
3B.
[0405] The obtained circuit board was evaluated in heat resistance,
bonding strength, flowing property, and subduction of circuit
layer. Table 9 shows obtained properties.
Example 7
[0406] A circuit board was produced in the same manner as in
Example 6 except that the FlatBOND treatment was not carried out to
the copper foils in the first unit circuit board. The obtained
circuit board was evaluated in heat resistance, bonding strength,
flowing property, and subduction of circuit layer. Table 9 shows
obtained properties. It should be noted that the copper foil
constituting the conductor layer had surface roughness Ra of 0.14 m
and Rz.sub.JIS of 1.09 .mu.m.
Example 8
[0407] A circuit board was produced in the same manner as in
Example 6 except that the surface roughening was carried out by a
blackening treatment, which belongs to a conventional surface
roughening treatment, instead of the FlatBOND treatment, and that
the compression pressure was changed into 4 MPa. The obtained
circuit board was evaluated in heat resistance, bonding strength,
flowing property, and subduction of circuit layer. Table 9 shows
obtained properties.
[0408] It should be noted that the blackening treatment was carried
out by immersing the first unit circuit board for 2 minutes into a
blackening treatment solution (aqueous solution) containing 31 g/L
of sodium sulfite, 15 g/L of sodium hydroxide, 12 g/L of sodium
phosphate kept in a warm bath at 95.degree. C., followed by washing
the immersed first unit circuit board with water and drying. The
copper foil constituting the conductor layer had surface roughness
Ra of 0.18 .mu.m and Rz.sub.JIS of 1.31 .mu.m.
Comparative Example 5
[0409] A circuit board was produced in the same manner as in
Example 8 except for carrying out neither degassing under heating
nor degassing under vacuum. The obtained circuit board was
evaluated in various physical properties. Table 9 shows obtained
properties.
TABLE-US-00009 TABLE 9 Circuit board unit Second degassing
Conductor layer First degassing Vacuum Insulating roughness (.mu.m)
Bonding Environ- Temp. Pressure Period degree Temp. Pressure Period
substrate Ra sheet ment (.degree. C.) (MPa) (min) (Pa) (.degree.
C.) (MPa) (min) Ex. 6 LCP film 0.13 1.05 LCP film Ambient 115 0 120
1000 100 0 60 (Tm335.degree. C.) (Tm280.degree. C.) pressure Ex. 7
LCP film 0.14 1.09 LCP film Ambient 115 0 120 2000 100 0 60
(Tm335.degree. C.) (Tm280.degree. C.) pressure Ex. 8 LCP film 0.18
1.31 LCP film Ambient 115 0 120 1000 100 0 60 (Tm335.degree. C.)
(Tm280.degree. C.) pressure Com. LCP film 0.18 1.31 CCP film -- --
-- -- -- -- -- -- Ex. 5 (Tm335.degree. C.) (Tm280.degree. C.)
Thermo-compression Bonding Strength LCP Vacuum film/Conductor layer
Heat degree Temp. Pressure Period (kN/m) resistance (Pa) (.degree.
C.) (MPa) (min) Max. Min. Avg. (290.degree. C.) Subduction Ex. 6
1000 295 1 30 0.9 0.7 0.84 Good Good Good Ex. 7 1000 295 1 30 0.4
0.3 0.37 Good Good Good Ex. 8 1000 295 4 30 1 0.8 0.95 Good Poor
Poor Com. 1000 295 4 30 0.5 0.3 0.35 Poor Poor Poor Ex. 5 indicates
data missing or illegible when filed
[0410] As shown in Table 9, in any of Examples, combination of a
degassing process(es) at the specified condition makes it possible
to suppress blister occurrence in the circuit board
effectively.
[0411] In particular, in the circuit board of Example 6, since the
FlatBOND treatment capable of achieving smooth surface of the
copper foil is carried out in combination with the specific
degassing process, the obtained circuit board has not only
satisfactory heat resistance but also improved bonding strength in
the circuit board.
[0412] It should be noted that in Examples 6 and 7 obtained by
lowering the compression pressure at the time of thermo-compression
bonding, it is possible to reduce the subduction amount into the
insulating substrate; and that in Example 8 the circuit board has
larger subduction amount of circuitry layer in the insulating
substrate and is deteriorated in resin flowing because of high
pressure in the thermo-compression bonding.
[0413] Then, on the basis of Examples 10 to 11 and Comparative
Example 6, the effect of degassing process on the interlayer
bonding strength of a circuit board will be considered.
Example 9
[0414] A circuit board was produced in the same manner as in
Example 4 except that the first degassing was not carried out but
the second degassing was carried out. The obtained circuit board
was evaluated in various physical properties. Table 10 shows
obtained properties.
Example 10
[0415] A circuit board was produced in the same manner as in
Example 4 except that the first degassing was carried out but the
second degassing was not carried out. The obtained circuit board
was evaluated in various physical properties. Table 10 shows
obtained properties.
Comparative Example 6
[0416] (1) Production of Unit Circuit Board
[0417] Onto each surface of a TLCP film having a melting point of
335.degree. C. ("CT-Z", produced by Kuraray Co., Ltd., thickness:
25 .mu.m), a rolled copper foil ("BHYX-T-12", produced by JX Nippon
Mining & Metals Corporation, thickness: 12 .mu.m) was overlaid
to obtain a stacked material. The stacked material was placed in a
vacuum heat press apparatus with heated plates at 295.degree. C.
under a compression pressure of 4 MPa for 10 minutes to be bonded
with each other to obtain a first copper-clad laminate having a
configuration of copper foil/first TLCP film/copper foil. In the
meantime, onto one surface of a TLCP film having a melting point of
280.degree. C. ("CT-F", produced by Kuraray Co., Ltd., thickness:
50 .mu.m), a rolled copper foil ("BHYX-T-12", produced by JX Nippon
Mining & Metals Corporation, thickness: 12 .mu.m) was overlaid
to obtain a stacked material. The stacked material was placed in a
vacuum heat press apparatus with heated plates at 275.degree. C.
under a compression pressure of 4 MPa for 10 minutes to be bonded
with each other to obtain a second copper-clad laminate having a
configuration of copper foil/second TLCP film.
[0418] Subsequently, one copper foil of the first copper-clad
laminate was processed by a chemical etching process to have a
circuit pattern of a strip line structure (existing conductive
material ratio: less than 30%) to obtain a first unit circuit
board.
[0419] Subsequently, a stacked material of the first unit circuit
board and the second copper-clad laminate, in which the circuit
pattern was interposed between the first and second TLCP films, was
placed in a chamber of a vacuum hot press apparatus to be subjected
to two-stage press at a vacuum degree of 1000 Pa, i.e., first
compression-bonding by means of heated plates set to 150.degree. C.
under a compression pressure of 4 MPa for 5 minutes (pre-process),
followed by second compression-bonding by means of heated plates
set to 320.degree. C. under a compression pressure of 1 MPa for 30
minutes (post-process) to obtain a circuit board having a
multilayer configuration of copper foil/first TLCP layer/circuit
layer/second TLCP layer/copper foil. The obtained circuit board was
evaluated in various physical properties. Table 10 shows obtained
properties.
TABLE-US-00010 TABLE 10 Second Circuit board material degassing
Second First degassing Vacuum First LCP LCP Environ- Temp. Pressure
Period degree Temp. Pressure Period film film ment (.degree. C.)
(MPa) (min) (Pa) (.degree. C.) (MPa) (min) Ex. 9 CTZ-25 CTF-50 --
-- -- -- 1000 100 0 60 (Tm335.degree. C.) (Tm280.degree. C.) Ex. 10
CTZ-25 CTF-50 Ambient 100 0 60 -- -- -- -- (Tm335.degree. C.)
(Tm280.degree. C.) pressure Com. Ex. 6 CTZ-25 CTF-50 -- -- -- -- --
-- -- -- (Tm335.degree. C.) (Tm280.degree. C.) Thermo- Bonding
strength compression LCP film/LCP Compression Pressure film (kN/m)
Temp (.degree. C.) (MPa) Max. Min. Avg. Ex. 9 300 1.0 1.6 0.7 1.3
Ex. 10 300 1.0 1.1 0.7 0.9 Com. Ex. 6 320 1.0 0.7 0.3 0.5
[0420] As shown in Table 10, in Comparative Example 6 without being
subjected to degassing process, bonding strength values are low
with respect to not only the maximum and minimum values but also
the average value of the whole directions. In particular,
Comparative Example 6 has difficulty in improvement in bonding
strength despite employing high thermo-compression temperature of
320.degree. C. that is intended to increase the bonding strength.
For example, in comparison with Example 4, the representative
bonding strength value and the minimum bonding strength value of
Comparative Example 6 are 1/3 or less and 1/5 or less of Example 4,
respectively.
[0421] In Example 9, in which the second degassing process was
carried out, the bonding strength can be increased in all of the
maximum, minimum, and average values in comparison with Comparative
Example 6. In Example 10, in which the first degassing process was
carried out, the bonding strength can be increased in all of the
maximum, minimum, and average values in comparison with Comparative
Example 6. In these Examples 9 and 10, the bonding strengths of the
circuit boards each evaluated from the four directions can achieve
0.7 kN/m as the minimum value, that is more than twice of the
minimum bonding strength in Comparative Example 6.
INDUSTRIAL APPLICABILITY
[0422] The LCP films according to the present invention have
satisfactory thermo-adhesive property, and can be advantageously
used as various circuit board materials. Further, the circuit board
of the present invention can be used as substrates for various
electrical and electronic products. In particular, since the LCP
film has excellent dielectric characteristics at high frequency,
the circuit board according to the present invention can be
advantageously used as a high frequency circuit board or the
like.
[0423] Although the present invention has been fully described in
connection with the preferred embodiments thereof, those skilled in
the art will readily conceive numerous changes and modifications
within the framework of obviousness upon the reading of the
specification herein presented of the present invention.
Accordingly, such changes and modifications are to be construed as
included therein.
* * * * *