U.S. patent application number 09/921358 was filed with the patent office on 2002-10-31 for flexible metal-clad laminate and process for preparing the same.
Invention is credited to Inukai, Chyuji, Kurita, Tomoharu.
Application Number | 20020160211 09/921358 |
Document ID | / |
Family ID | 18729259 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020160211 |
Kind Code |
A1 |
Kurita, Tomoharu ; et
al. |
October 31, 2002 |
Flexible metal-clad laminate and process for preparing the same
Abstract
Disclosed are a flexible metal-clad laminate comprising a metal
foil and a heat-resistant resin film layer formed on one side of
the metal foil, the heat-resistant resin film layer comprising a
crosslinked condensation polymer and having an
N-methyl-2-pyrrolidone-insolule content of at least 1%, and a
method for producing the flexible metal-clad laminate comprising
the steps of applying a heat-resistant resin solution to a metal
foil; predrying the metal foil until the heat-resistant resin layer
has an residual solvent content of 10 to 40% by weight; and
carrying out solvent removal and heat-treatment while controlling
the crosslinking reaction of the resin.
Inventors: |
Kurita, Tomoharu; (Otsu-shi,
JP) ; Inukai, Chyuji; (Otsu-shi, JP) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
TWO PRUDENTIAL PLAZA, SUITE 4900
180 NORTH STETSON AVENUE
CHICAGO
IL
60601-6780
US
|
Family ID: |
18729259 |
Appl. No.: |
09/921358 |
Filed: |
August 2, 2001 |
Current U.S.
Class: |
428/458 ;
427/388.2 |
Current CPC
Class: |
Y10T 428/31681 20150401;
Y10T 428/24355 20150115; Y10T 428/31721 20150401; H05K 1/0346
20130101; Y10T 428/31678 20150401; B32B 15/08 20130101; H05K 3/002
20130101; C08G 73/10 20130101; C08G 73/14 20130101 |
Class at
Publication: |
428/458 ;
427/388.2 |
International
Class: |
B32B 015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2000 |
JP |
237389/2000 |
Claims
1. A flexible metal-clad laminate comprising a metal foil and a
heat-resistant resin film layer formed on one side of the metal
foil, the heat-resistant resin film layer comprising a crosslinked
condensation polymer and having an N-methyl-2-pyrrolidone-insolule
content of at least 1%, particularly 1 to 99%.
2. The flexible metal-clad laminate according to claim 1, wherein
the heat resistant resin film layer is formed by converting an
organic solvent-soluble condensation polymer by crosslinking into
an organic solvent-insoluble form.
3. The flexible metal-clad laminate according to claim 1, wherein
the heat-resistant resin film layer is formed by applying to the
metal foil a solution prepared by dissolving an organic
solvent-soluble condensation polymer in the organic solvent and
subjecting the coated metal foil to a predrying step, and a
heat-treatment and solvent removal step.
4. The flexible metal-clad laminate according to claim 1, wherein
the heat-resistant resin film layer has an initiation tear strength
(film thickness: 20 .mu.m) of at least 15 kg and has a thermal
gradient dimensional change of not more than 0.1% when heated at
200.degree. C. for 30 minutes.
5. The flexible metal-clad laminate according to claim 1, which has
a solder heat resistance of at least 350.degree. C., an adhesion
between the metal foil and the heat-resistant resin film of at
least 80 g/mm and a radius of curvature of at least 15 cm.
6. The flexible metal-clad laminate according to claim 1, wherein
the average surface roughness of the surface of the heat-resistant
resin film layer which is in contact with the metal foil is not
more than 0.4 .mu.m.
7. The flexible metal-clad laminate according to claim 1, wherein
the elastic modulus retentivity of the heat-resistant resin film
after being immersed in an aqueous solution of sodium hydroxide
(40% by weight) at 25.degree. C. for 100 hours is at least 40%.
8. The flexible metal-clad laminate according to claim 1, wherein
the condensation polymer comprises the unit represented by formula
(1) 7wherein R.sup.1 and R.sup.2 are the same or different and each
represents hydrogen or an alkyl or alkoxy group having 1 to 4
carbons atoms and/or the unit represented by formula (2) 8
9. A method for producing the flexible metal-clad laminate as set
forth in claim 1, the method comprising the steps of (A) applying
to the metal foil a solution prepared by dissolving a
heat-resistant resin containing an organic solvent-soluble
condensation polymer in the organic solvent, predrying the
resulting coating film until the coating has a residual solvent
content of 10 to 40% by weight to obtain a predried laminate
comprising the predried heat-resistant resin layer and the metal
foil, and (C) heat-treating the above predried laminate.
10. The method according to claim 9, which further comprises step
(B) of winding up, in the form of a roll, the predried laminate
obtained in step (A) in such a manner that its coated surface does
not come into contact with its uncoated surface.
11. The method according to claim 9, wherein the predrying in step
(A) is carried out at a temperature 70.degree. C. to 130.degree. C.
lower than the boiling point of the solvent used for preparing the
heat-resistant resin solution.
12. The method according to claim 9, wherein the heat-treating in
step (C) is carried out under reduced pressure and/or in an inert
gas atmosphere, while removing the solvent such that the
heat-resistant resin layer has an insoluble content of 1% to
99%.
13. The method according to claim 9, wherein in step (C), the
predried laminate is dried under reduced pressure at 200 to
400.degree. C. to reduce the residual solvent content to 5% by
weight or lower and then heating the laminate in an inert gas at
200 to 400.degree. C. for 1 to 30 hours.
14. The method according to claim 10, wherein step (A) comprises
applying the heat-resistant resin solution to the metal foil to
leave the lengthwise borders on either edge uncoated, predrying the
applied resin solution to obtain a predried laminate comprising the
predried heat-resistant resin layer and the metal foil and step (B)
comprises placing a tape made of a material different from that of
the laminate on the uncoated portions of the predried laminate or
covering both lengthwise edges of the predried laminate with the
tape, when winding up the metal foil.
15. The method according to claim 9, wherein the heat-resistant
resin is an organic solvent-soluble polyimide and/or
polyamide-imide.
16. The method according to claim 9, wherein the heat-resistant
resin comprises the unit represented by formula (1) 9wherein
R.sup.1 and R.sup.2 are the same or different and each represents
hydrogen or an alkyl or alkoxy group having 1 to 4 carbon atoms
and/or the unit represented by formula (2) 10
17. A flexible metal-clad laminate which is produced by the method
according to any one of claims 9 to 16.
18. A flexible printed wiring board which is obtainable from the
flexible metal-clad laminate according to any one of claims 1 to 8.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a flexible metal-clad
laminate which is for use in flexible printed boards and has high
dimensional stability, heat resistance, chemical resistance
(especially alkali resistance), adhesion and the like, and to a
method for producing the same. More specifically, the present
invention relates to a flexible metal-clad laminate produced by
continuously applying a heat-resistant resin solution to a metal
foil and then subjecting the laminate to predrying and
heat-treatment, the metal-clad laminate having high dimensional
stability, heat resistance, chemical resistance and adhesion, and
to a method for producing the same.
[0002] In the present specification and claims, the term "flexible
metal-clad laminate" means a laminate comprising a metal foil and a
resin layer, for example, a laminate which is useful for producing
flexible printed wiring boards and the like.
PRIOR ART
[0003] Conventional flexible metal-clad laminates for flexible
printed boards comprise a polyimide film and a metal foil bonded by
an epoxy resin, acrylic resin or like thermosetting adhesive. These
flexible printed boards bonded by a thermosetting adhesive, which
have thermal characteristics much lower than those of polyimide
films, have the problems of limited application to chip-on-flex and
blisters, peeling and other problems associated with soldering.
Such flexible printed boards also have the drawback of curling and
twisting in the boards caused by the thermal hysteresis resulting
from processing such as thermocompression bonding. This curing and
twisting makes the punching process to be carried out afterward
difficult.
[0004] In order to solve these problems, techniques to form a metal
foil directly on an insulating substrate without using an adhesive
have been developed. For example, some patent publications suggest
forming a metal layer on a polyimide film by sputtering (Japanese
Unexamined Patent Publication No. 1990-98994), by vacuum
evaporation (No. 1987-181488), or by ion plating (No. 1982-18357),
and then forming circuit patterns thereon. However, all of these
methods have the problem of high production costs and insufficient
adhesion between the polyimide film and conductor. Specifically,
such methods are disadvantageous in that electroplating on patterns
to increase their strength may tear them off and exposure to heat
at about 100.degree. C. may lower the adhesion between the
conductor and polyimide film.
[0005] In order to more economically produce a flexible printed
board without an adhesive layer, Japanese Unexamined Patent
Publications No. 1982-50670, 1982-66690, etc., propose applying a
polyimide-based solution directly to a metal foil.
[0006] However, the flexible metal-clad laminates produced by such
methods are problematic because a decrease in the volume of the
solvents or a difference between the coefficients of thermal
expansion of the resin and the copper foil, etc., induce internal
stress which makes the metal-clad laminate curl toward the resin
layer side. Japanese Unexamined Patent Publications Nos.
1980-75289, 1979-111673, 1979-31480, etc., discloses straightening
such curled laminates by heat treatment at a high temperature, by
stretching them during drying and curing step, or by heat treatment
after winding them around a cylindrical drum, among other methods.
However, none of these methods can straighten the curled laminates
satisfactorily. These methods also have the problem that the films
obtained by etching the metal foil curl. In addition, continuous
production of the laminates entails lower productivity or require
expensive equipment, and thus these methods have the problem of
high production costs.
[0007] Further, a laminate produced by the above method comprising
directly applying a polyimide-based solution onto a substrate and
drying it has insufficient alkali resistance. Accordingly, in
various applications, such laminates are not suitable for producing
flexible printed wiring boards for use in products which involve
the use of alkaline substances, such as ink jet printers (which
usually use alkaline inks).
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to solve the
above-mentioned problems by applying a heat-resistant resin
solution directly to a metal foil and drying the solution to
economically produce a flexible metal-clad laminate for flexible
printed boards, the laminate having high heat resistance,
dimensional stability, adhesion, chemical resistance, alkali
resistance, etc., and having no curling.
[0009] The inventors of the present invention conducted extensive
research to achieve the above object. Consequently, they found the
following:
[0010] (a) A condensation polymer layer having an
N-methyl-2-pyrrolidone-i- nsoluble content of at least 1% can be
obtained by continuously applying to a metal foil a solution
prepared by dissolving an organic solvent-soluble heat-resistant
condensation polymer in the organic solvent, predrying the
resulting coating film so as to leave at least a certain amount of
the solvent, and heat-treating the predried coating film under
specific conditions to effect a controlled crosslinking reaction of
the condensation polymer.
[0011] (b) The thus obtained crosslinked condensation polymer layer
has excellent characteristics such as high heat resistance,
dimensional stability, chemical resistance, adhesion, etc., as well
as high alkali resistance.
[0012] (c) Since internal stress is inhibited or reduced in the
resulting metal-clad laminate, the flexible metal-clad laminate
does not curl and a heat-resistant resin film obtained by etching
and removing the metal foil from the flexible metal-clad laminate
does not curl either. Therefore, a flexible metal-clad laminate
from which circuit patterns are formed by etching the unnecessary
metal foil does not curl. Thus, a flexible metal-clad laminate can
be produced economically.
[0013] The present invention was accomplished based on the above
finding and further consideration. The present invention provides
the following flexible metal-clad laminates and their production
methods.
[0014] (1) A flexible metal-clad laminate comprising a metal foil
and a heat-resistant resin film layer formed on one side of the
metal foil, the heat-resistant resin film layer comprising a
crosslinked condensation polymer and having an
N-methyl-2-pyrrolidone-insolule content of at least 1%,
particularly 1 to 99%.
[0015] (2) The flexible metal-clad laminate according to item (1),
wherein the heat resistant resin film layer is formed by converting
an organic solvent-soluble condensation polymer by crosslinking
into an organic solvent-insoluble form.
[0016] (3) The flexible metal-clad laminate according to item (1),
wherein the heat-resistant resin film layer is formed by applying
to the metal foil a solution prepared by dissolving an organic
solvent-soluble condensation polymer in the organic solvent and
subjecting the coated metal foil to a predrying step and a
heat-treatment and solvent removal step.
[0017] (4) The flexible metal-clad laminate according to any one of
items (1) to (3), wherein the heat-resistant resin film has an
initiation tear strength (film thickness: 20 .mu.m) of at least 15
kg and has a thermal gradient dimensional change of not more than
0.1% when heated at 200.degree. C. for 30 minutes.
[0018] (5) The flexible metal-clad laminate according to any one of
items (1) to (4), which has a solder heat resistance of at least
350.degree. C., an adhesion between the metal foil and the
heat-resistant resin film of at least 80 g/mm and a radius of
curvature of at least 15 cm.
[0019] (6) The flexible metal-clad laminate according to any one of
items (1) to (5), wherein the average surface roughness Ra of the
surface of the heat-resistant resin film layer which is in contact
with the metal foil is not more than 0.4 .mu.m.
[0020] (7) The flexible metal-clad laminate according to any one of
items (1) to (6), wherein the elastic modulus retentivity of the
heat-resistant resin film after being immersed in an aqueous
solution of sodium hydroxide (concentration: 40% by weight) at
25.degree. C. for 100 hours is at least 40%.
[0021] (8) The flexible metal-clad laminate according to any one of
items (1) to (7), wherein the condensation polymer contains the
unit represented by formula (1) 1
[0022] wherein R.sup.1 and R.sup.2 are the same or different and
each represents hydrogen or an alkyl or alkoxy group having 1 to 4
carbons atoms and/or the unit represented by formula (2) 2
[0023] (9) A method for producing the flexible metal-clad laminate
as set forth in any one of items (1) to (8), the method comprising
the steps (A) and (C):
[0024] (A) applying to the metal foil a solution prepared by
dissolving a heat-resistant resin comprising an organic
solvent-soluble condensation polymer in the organic solvent,
predrying the resulting coating film until the coating film has a
residual solvent content of 10 to 40% by weight to obtain a
predried laminate comprising the predried heat-resistant resin
layer and the metal foil, and
[0025] (C) heat-treating the above predried laminate.
[0026] (10) The method according to item (9), which further
comprises step (B) of winding up, in the form of a roll, the
predried laminate obtained in step (A) in such a manner that its
coated surface does not come into contact with its uncoated
surface.
[0027] (11) The method according to items (9) or (10), wherein the
predrying in step (A) is carried out at a temperature 70.degree. C.
to 130.degree. C. lower than the boiling point of the solvent used
for preparing the heat-resistant resin solution.
[0028] (12) The method according to any of item (9), wherein the
heat-treating in step (C) is carried out under reduced pressure
and/or in an inert gas atmosphere, while removing the solvent such
that the heat-resistant resin layer has an insoluble content of 1%
to 99%.
[0029] (13) The method according to any one of items (9) to (11),
wherein in step (C), the predried laminate is dried under reduced
pressure at 200 to 400.degree. C. to reduce the residual solvent
content to 5% by weight or lower and then heating the laminate in
an inert gas at 200 to 400.degree. C. for 1 to 30 hours.
[0030] (14) The method according to item (10), wherein step (A)
comprises applying the heat-resistant resin solution to the metal
foil to leave the lengthwise borders on either edge uncoated,
predrying the applied resin solution (heat-resistant resin layer)
to obtain a predried laminate comprising the predried
heat-resistant resin layer and the metal foil and step (B)
comprises placing a tape made of a material different from that of
the laminate on the uncoated portions of the predried laminate or
covering both lengthwise edges of the predried laminate with the
tape, when winding up the metal foil.
[0031] (15) The method according to any one of items (9) to (14),
wherein the heat-resistant resin is an organic solvent-soluble
polyimide and/or polyamide-imide.
[0032] (16) The method according to items (9) to (15), wherein the
heat-resistant resin comprises the unit represented by formula (1)
3
[0033] wherein R.sup.1 and R.sup.2 are the same or different and
each represents hydrogen or an alkyl or alkoxy group having 1 to 4
carbon atoms and/or the unit represented by formula (2) 4
[0034] (17) A flexible metal-clad laminate which is produced by the
method according to any one of items (9) to (16).
[0035] (18) A flexible printed wiring board which is obtainable
from the flexible metal-clad laminate according to any one of items
(1) to (8).
BRIEF DESCRIPTION OF DRAWINGS
[0036] FIG. 1 is a schematic diagram showing an embodiment of the
metal foil on which a heat-resistant resin solution is applied
leaving lengthwise borders on either edge uncoated.
[0037] FIG. 2 is a schematic diagram showing an embodiment of the
predried laminate in which tape is placed between the uncoated
portions of the laminate.
[0038] FIG. 3 is a schematic diagram showing an embodiment of the
predried laminate in which both lengthwise edges are covered with
tape.
[0039] FIG. 4 is a schematic diagram showing an embodiment of the
flexible metal-clad laminate of the present invention.
[0040] FIG. 5 is a schematic diagram showing a curled flexible
metal-clad laminate.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Metal Foil
[0042] The metal foil for use in the present invention may be a
copper foil, an aluminium foil, a steel foil, a nickel foil or the
like, a composite metal foil comprising these metal foils or a
metal foil treated with zinc, a chromium compound or other metals.
The thickness of the metal foil is not particularly limited. For
example, a metal foil having a thickness ranging from 3 to 50 .mu.m
is favorably used.
[0043] The metal foil is usually in the form of a ribbon, and its
length is not particularly limited. The width is not particularly
limited either, but is generally about 25 to 300 cm, particularly
preferably about 50 to 150 cm.
[0044] Heat-Resistant Resin
[0045] The heat-resistant resin used in the present invention may
be basically any resin which has a coefficient of thermal expansion
as high as the metal foil and high heat resistance. The
heat-resistant resin is preferably a condensation polymer, in
particular, an aromatic polyimide and/or aromatic polyamide-imide
obtained by a polycondensation reaction. The aromatic polyimide and
aromatic polyamide-imide can be synthesized by conventional
methods, for example, the isocyanate method, the acid chloride
method, the low-temperature solution polymerization method, the
room-temperature solution polymerization method, among others.
[0046] <(A) Aromatic Polyimide>
[0047] Examples of raw materials (acid component and amine
component) for the aromatic polyimide include the following.
[0048] Examples of useful acid components include monoanhydrides,
dianhydrides, esterified compounds, etc., of pyromellitic acid,
benzophenone-3,3',4,4'-tetracarboxylic acid,
biphenyl-3,3',4'-tetracarbox- ylic acid, diphenylsulfone
3,3',4,4'-tetracarboxylic acid,
diphenylether-3,3',4,4'-tetracarboxylic acid,
naphthalene-2,3,6,7-tetraca- rboxylic acid,
naphthalene-1,2,4,5-tetracarboxylic acid,
naphthalene-1,4,5,8-tetracarboxylic acid and the like. These
substances may be used singly or as mixtures of two or more
species.
[0049] Examples of amine components include p-phenylenediamine,
m-phenylenediamine, 3,4'-diaminodiphenylether,
4,4'-diaminodiphenylether, 4,4'-diaminodiphenylsulfone,
3,3'-diaminodiphenylsulfone, 3,4'-diaminobiphenyl,
3,3'-diaminobiphenyl, 3,3'-diaminobenzanilide,
4,4'-diaminobenzanilide, 4,4'-diaminobenzophenone,
3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone,
2,6-tolylenediamine, 2,4-tolylene-diamine,
4,4'-diaminodiphenylsulfide, 3,3'-diamino-diphenylsulfide,
4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane,
4,4'-diaminodiphenylhexafluoro-propane,
3,3'-diaminodiphenylhexafluoropropane, 3,3'-diaminodiphenylmethane,
4,4'-diaminodiphenylmethane,
4,4'-diaminodiphenylhexafluoroisopropylidene- , p-xylenediamine,
m-xylenediamine, 1,4-naphthalenediamine, 1,5-naphthalene-diamine,
2,6-naphthalenediamine, 2,7-naphthalenediamine, o-tolidine,
2,2'-bis(4-aminophenyl)propane, 2,2'-bis(4-aminophenyl)hexafl-
uoropropane, 1,3-bis(3-aminophenoxy)-benzene,
1,3-bis(4-aminophenoxy)benze- ne, 1,4-bis(4-aminophenoxy)benzene,
2,2-bis[4-(4-aminophenoxy)phenyl]-prop- ane,
bis[4-(4-aminophenoxy)phenyl]sulfone,
bis[4-(3-aminophenoxy)phenyl]su- lfone,
bis[4-(3-aminophenoxy)-phenyl]propane,
bis[4-(3-aminophenoxy)phenyl- ]hexafluoro-propane,
4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl,
2,2-bis[4-(4-aminophenoxy)phenyl]-hexaf- luoropropane, and the
diisocyanates corresponding to these compounds, among others. These
components may be used singly or as mixtures of two or more
species.
[0050] Further, resins prepared by polymerization of any
combinations of these acid components and amine components may also
be used as blended.
[0051] <(B) Aromatic Polyamide-imide>
[0052] Examples of raw materials used for the aromatic
polyamide-imide include the following acid components and amine
components.
[0053] The acid components include trimellitic anhydride,
diphenylether-3,3',4'-tricarboxylic anhydride,
diphenylsulfone-3,3',4'-tr- icarboxylic anhydride,
benzophenone-3,3',4'-tricarboxylic anhydride, naphthalene
1,2,4-tricarboxylic anhydride and like tricarboxylic anhydrides.
These substances may be used singly or as mixtures.
[0054] Examples of the amine components include the diamines and
diisocyanates which are mentioned as examples in item "(A) aromatic
polyimide" above, and these substances may be used singly or as a
mixture.
[0055] Further, resins prepared by polymerization of any
combinations of these acid components and amine components may also
be used as blended.
[0056] Particularly preferable heat-resistant resins in terms of
heat resistance, chemical resistance, alkali resistance,
coefficient of thermal expansion (thermal gradient dimensional
change), processability in the form of a roll, production cost,
etc. are aromatic polyimides and aromatic polyamide-imides which
are soluble in an organic solvent. More preferable are aromatic
polyamide-imides containing the unit represented by formula (1) or
(2). 5
[0057] wherein R.sup.1 and R.sup.2 may be the same or different and
each represents hydrogen or an alkyl or alkoxy group having 1 to 4
carbons atoms. 6
[0058] The heat-resistant resin for use in the present invention
preferably has a molecular weight corresponding to an inherent
viscosity in N-methyl-2-pyrrolidone (polymer density: 0.5 g/dl) at
30.degree. C. of 0.3 to 2.5 dl/g, more preferably 1.0 to 2.0 dl/g.
A resin with an inherent viscosity not higher than 0.3 dl/g has
insufficient mechanical characteristics such as bendability and
initiation tear strength of the laminate. On the other hand, an
inherent viscosity not lower than 2.0 dl/g results in reduced
adhesion and increased solution viscosity, making forming and
processing difficult.
[0059] In the preparation of aromatic polyimide and aromatic
polyamide-imide for use in the present invention, other substances
may be used insofar as heat resistance and coefficient of thermal
expansion are not deteriorated. Such other substances include acid
components such as adipic acid, azelaic acid, sebacic acid,
cyclohexane-4,4,'-dicarboxylic acid, butane-1,2,4-tricarboxylic
acid, butane-1,2,3,4-tetracarboxylic acid,
cyclopentane-1,2,3,4-tetracarboxylic acid and like aliphatic and
alicyclic dicarboxylic acids, polycarboxylic acids and
monoanhydrides, dianhydrides and esterified compounds of these
substances; amine components such as tetramethylenediamine,
hexamethylenediamine, isophorone diamine,
4,4'-dicyclohexylmethanediamine, cyclohexane-1,4-diamine,
diaminosiloxane and like aliphatic and alicyclic diamines and
diisocyanates corresponding to these substances. The aliphatic and
alicyclic diamines and diisocyanates may be used singly or as
mixtures of two or more species. Resins prepared by combining and
polymerizing any of these acid components and amine components may
also be used as blended.
[0060] Method for Producing Flexible Metal-Clad Laminate
[0061] In the present invention, the heat-resistant resin film can
be produced by a method comprising the steps of, for example, (A)
applying a heat-resistant resin solution to the above metal foil,
predrying the coating film (hereinafter referred to as "predrying
step") and (C) heat-treating and drying the resulting laminate
comprising the metal foil and the predried coating film obtained in
the above step (A) (hereinafter referred to as "heat-treating and
solvent removing step"). Thus, the flexible metal-clad laminate of
the invention is produced. If necessary, step (B) may be employed,
in which a laminate of the metal foil and the predried coating film
obtained in the above step (A) is wound up in the form of a roll in
such a manner that the coated surface and the uncoated surface of
the laminate do not contact.
[0062] <Heat-Resistant Resin Solution>
[0063] A useful solvent for preparing the above heat-resistant
resin solution for use in the present invention is an organic
solvent which can dissolve the above heat-resistant resin. Typical
examples of such an organic solvent include N-methyl-2-pyrrolidone,
N,N'-dimethylformamide, N,N'-dimethylacetamide,
1,3-dimethyl-2-imidazolidinone, tetramethylurea, sulfolane,
dimethylsulfoxide, .gamma.-butyrolactone, cyclohexanone,
cyclopentanone and the like. Among these, N-methyl-2-pyrrolidone is
preferable. When any of these solvents is used as a polymerization
solvent, it can be used as it is.
[0064] Part of these solvents can be substituted by toluene, xylene
and like hydrocarbon-based organic solvents, diglyme, triglyme,
tetrahydrofuran and like ether-based organic solvents, methyl ethyl
ketone, methyl isobutyl ketone and like ketone-based organic
solvents.
[0065] In order to improve various characteristics of the flexible
metal-clad laminate, e.g., mechanical characteristics, electrical
characteristics, slippage, flame-resistance and other
characteristics, the heat-resistant resin solution of the invention
may contain, or may be used after being reacted with, other resins,
organic compounds and/or inorganic compounds, if necessary.
Examples thereof include lubricants (silica, talc, silicone, etc.),
adhesion promoters, flame retardants (phosphorus-based compounds,
triazine-based compounds, aluminum hydroxide, etc.), stabilizers
(antioxidants, ultraviolet absorbers, polymerization inhibitors,
etc.), electroplating activators, organic and inorganic fillers
(talc, titanium oxide, fine particles of fluorine-containing
polymers, pigments, dyes, calcium carbide, etc.), silicone
compounds, fluorine compounds, isocyanate compounds, block
isocyanate compounds, acrylic resins, urethane resins, polyester
resins, polyamide resins, epoxy resins, phenol resins and like
resins and organic compounds, curing agents of these resins,
silicon oxides, titanium oxides, calcium carbonate, iron oxides and
like inorganic compounds. These compounds may be used as long as
they do not adversely affect the object of the present
invention.
[0066] The concentration of the heat-resistant resin in the thus
obtained heat-resistant resin solution may be selected from a wide
range, but preferably is about 5 to 40% by weight, particularly
about 8 to 20% by weight. When the concentration is outside the
above range, the coating property of the resin is likely to
decrease. When the concentration is lower than 5% by weight,
curling in resulting laminate tends to be greater.
[0067] <(A) Predrying Step>
[0068] In the predrying step (A) of the present invention, the
above heat-resistant resin solution is applied to the metal foil,
and the coating is dried.
[0069] The method for applying the solution is not particularly
limited and may be any conventionally known method. For example, a
coating solution, i.e., a heat-resistant resin solution, adjusted
to a suitable viscosity, can be applied with a roll coater, knife
coater, doctor, blade coater, gravure coater, die coater, reverse
coater or the like, directly to the metal foil.
[0070] Suitable solution viscosity ranges from 1 to 1000 Poise in
Brookfield viscosity at 25.degree. C. In the application of the
solution, to increase the processability of rolling up the laminate
in step (B), which will be explained below, both lengthwise edges 2
and 2' of the metal foil 1 are preferably left uncoated, as shown
in FIG. 1. In FIG. 1, an applied resin solution (heat-resistant
resin layer) is shown at 3.
[0071] In the present invention, the residual solvent content in
the predried heat-resistant resin layer or the residual solvent
content in the heat-resistant resin layer immediately before being
subjected to heat-treatment and solvent removal need to be at least
10% by weight. The higher the residual solvent content is, the less
curling occurs in the resulting flexible printed wiring board.
[0072] In the present specification, the term "residual solvent
content" means the amount of solvent in a resin system containing
solvent after the predrying step. The residual solvent content is
calculated by equation (3) in Examples.
[0073] When the residual solvent content is lower than 10% by
weight, internal stress caused by a decrease in the volume of
solvent cannot be reduced under the treatment conditions of the
invention. Therefore, reducing curling in the metal-clad laminate
is generally made difficult and heat-resistant resin film obtained
by removing the metal foil by etching tends to curl, making circuit
processing difficult. Although a higher residual solvent content
causes less curling in a metal-clad laminate, excessively high
residual solvent content is not favorable since the resin layer
formed by coating may undergo sagging and becomes adherent and thus
the processability in the form of a roll is lowered. Although the
residual solvent content after the predrying varies depending on
the type of the resin, it is at most 40% by weight, preferably 30%
or less by weight.
[0074] The predrying is preferably carried out at a temperature
70.degree. C. to 130.degree. C. lower than the boiling point (Tb
(.degree. C.)) of the solvent used for the heat-resistant resin
solution. A drying temperature higher than (Tb-70).degree. C.
increases the unevenness of the remaining solvent in the direction
of the thickness of the resin layer even when the residual solvent
content is 10% by weight or higher. In particular, since the
residual solvent content in the resin surface layer is reduced, the
reduction of internal stress in later steps becomes insufficient
and thus curling is likely to occur in the metal-clad laminate. A
drying temperature lower than (Tb-130).degree. C. prolongs the
drying time and thus may lower productivity. The drying temperature
required can be varied depending on the type of the solvent, but is
generally about 60 to 150.degree. C., particularly about 80 to
120.degree. C.
[0075] The time required for predrying may be any period of time
effective for achieving the above-specified residual solvent
content under the above temperature conditions. The predrying time
is generally about 1 to 30 minutes, particularly about 2 to 15
minutes.
[0076] The predrying may be conducted by a conventional method such
as the roll support system, floating system, among others. In this
manner, the predried laminate comprising the predried
heat-resistant resin coating film and a metal foil is obtained.
[0077] <(C) Heat-Treating and Solvent Removing Step>
[0078] The heat-treating and solvent removing step in the present
invention is carried out by any of the following methods: (I)
heating under reduced pressure the predried laminate obtained in
the above predrying step; (II) heating the predried laminate in an
inert gas atmosphere; (III) heating the predried laminate under
reduced pressure and in an inert gas atmosphere; and other methods.
Examples of the inert gas include nitrogen, carbon dioxide, helium,
argon, etc. Among these, nitrogen is favorable because it is
readily available.
[0079] Conducting the above heat-treating and solvent removing step
in air causes deterioration of the resin layer and/or excessive
crosslinking, which increases curling in the substrate and lowers
the mechanical characteristics of the resin layer. In addition,
when the heat treatment is carried out in air or in an atmosphere
containing oxygen while a solvent such as N-methyl-2-pyrrolidone is
present in the above-specified amount, not only the mechanical
characteristics of the resin layer but also the adhesion between
the resin layer and metal foil is lowered.
[0080] The above heat-treating and solvent removing step is
preferably carried out by heating under reduced pressure, or more
preferably by preliminarily reducing the residual solvent content
to 5% by weight or lower under reduced pressure and then heating in
an inert gas atmosphere.
[0081] Particularly, when preliminarily reducing the residual
solvent content to 5% by weight or lower under reduced pressure and
heating in an inert gas atmosphere, a flexible metal-clad laminate
that does not curl and high heat resistance can be obtained by
conducting step (C) in the following 2 steps: (i) reducing the
residual solvent content to 5% by weight or lower under reduced
pressure while keeping the insoluble content of the solvent-removed
predried resin to 20% or lower, and then (ii) further carrying out
heating at a high temperature in an inert gas atmosphere.
[0082] In the present specification, the terms "insoluble content"
and "N-methyl-2-pyrrolidone-insoluble content" mean insoluble
content of the resin layer of the laminate, which is determined by
removing the metal foil from the laminate, after heat-treatment and
solvent removal, to leave the resin layer only, and adding the
resin layer to N-methyl-2-pyrrolidone in an attempt to prepare a
solution having a concentration of 0.5 weight % and maintaining the
solution at 100.degree. C. for 2 hours. The "insoluble content" and
"N-methyl-2-pyrrolidone-insol- uble content" are calculated by the
equation (4) in Examples.
[0083] The heat-treating and solvent removing are conducted under
such temperature and time conditions that the insoluble content of
the coated resin layer becomes 1% to 99%, preferably 5% to 85%,
after finishing the heat-treating and solvent removing step. When
the insoluble content is lower than 1%, solder heat resistance and
like heat resistance and chemical resistance, especially alkali
resistance become insufficient. When the insoluble content is
higher than 99%, the metal-clad laminate has increased curling and
lower flexibility. More specifically, the heat-treating and solvent
removing step is carried out at (Tg-250).degree. C. to
(Tg+50).degree. C. Herein, the term "Tg" means the glass transition
temperature of the heat-resistant resin expressed in Celsius.
[0084] One of the goals of the present invention is to completely
remove the solvent from a laminate, optionally in the form of a
roll, while reducing the internal stress caused by the decrease in
the volume of the solvent. Heat treatment at a higher temperature,
preferably at a temperature higher than the glass transition
temperature of the heat-resistant resin containing no solvent,
effectively reduces stress. However, an excessively high
temperature induces excessive crosslinking and degradation in the
resin. This increases internal strain and curling in the metal-clad
laminate. This temperature may vary depending on the long-term heat
resistance of the heat-resistant resin. In the present invention,
the temperature needs to be (Tg+50).degree. C. or lower. Further,
when the heat-treating and solvent removing temperature is lower
than (Tg-250).degree. C., it takes a long time to carry out the
crosslinking reaction to correct the curl in the laminate and to
increase the insoluble content, lowering productivity.
[0085] Considering the above, when the heat-treating and solvent
removing step is carried out by heating under reduced pressure
(method (I) above), it is advantageously carried out under a
pressure of about 10.sup.-5 to 10.sup.3 Pa, preferably about
10.sup.-1 to 200 Pa, at a heating temperature of about 250 to
450.degree. C., preferably about 300 to 400.degree. C., and for
about 1 to 30 hours, preferably about 10 to 20 hours.
[0086] In addition, when the heat-treating and solvent removing
step is performed by heating in an inert gas atmosphere (method
(II) above), it is advantageously performed under a pressure of
about 10.sup.4 to 2.times.10.sup.4 Pa, preferably about 10.sup.4 to
1.1.times.10.sup.4 Pa, at a heating temperature of about 200 to
400.degree. C., preferably about 250 to 350.degree. C., and for
about 1 to 30 hours, preferably about 1 to 10 hours.
[0087] When the heat-treating and solvent removing step is carried
out by preliminarily reducing the residual solvent content to 5% by
weight or lower under reduced pressure, followed by heating in an
inert gas atmosphere (method (III) above), it is advantageously
carried out in the following manner. In the above step (i), i.e.,
the step in which residual solvent content is reduced to 5% by
weight or lower while keeping the insoluble content of the coated
resin layer at 20% or lower, it is preferable to heat the coated
resin layer under a pressure of, for example, about 10.sup.-5 to
1000 Pa, particularly about 10.sup.-1 to 200 Pa, at a temperature
of about 200 to 400.degree. C., particularly about 200 to
300.degree. C., for about 1 to 30 hours, particularly about 10 to
20 hours. In the above step (ii), i.e., the step in which further
heating is conducted in an inert gas atmosphere, the heating
condition varies depending on the type, molecular weight, Tg,
residual solvent content after the above step (i), etc., of the
heat-resistant resin. In general, it is preferable that the heating
temperature is about 200 to 400.degree. C., particularly about 250
to 350.degree. C., and that the heating time is about 1 to 30
hours, particularly about 1 to 10 hours. The pressure of the inert
gas atmosphere may be selected from a wide range, and generally is
about 10000 to 20000 Pa, preferably about 10000 to 11000 Pa.
[0088] <(B) Winding Step>
[0089] In the present invention, the metal foil (predried laminate)
which has a resin layer produced by applying a resin solution and
predrying the laminate to leave therein the above-specified amount
of solvent in the above step (A) may optionally be wound up in the
form of a roll. The winding is done in such a manner that the
surface coated with the resin solution and the surface not coated
with the resin solution do not come into contact, and then the
predried laminate is subjected to step (C).
[0090] When the winding step is conducted, the diameter of the roll
is about 1 to 30 inches, preferably about 3 to 10 inches. The
diameter of the roll, however, is not limited to this range. It is
generally preferable to make the diameter of the roll small when
the heat-resistant resin layer is thick after a thorough-drying and
to make the diameter large when the heat-resistant resin layer is
thin after a thorough-drying.
[0091] In order to prevent the coated surface and uncoated surface
from coming into contact, various methods can be employed. For
example, the laminate may be loosely wound; a tape made of a
material different from that of the laminate can be placed between
the layers of the predried laminate; etc.
[0092] The placement of the tape is not particularly limited. A
preferable example of a method for placing the tape is, as shown in
FIG. 2, applying a predried product 30 of the heat-resistant resin
solution to a metal foil 10 avoiding both lengthwise edges 20 and
20' of the metal foil 10, and placing tapes 40 and 40' on the
portions 20 and 20' of the coated surface where no resin solution
has been applied. The tapes 40 and 40' may be placed before or
after the heat-resistant resin solution applied forms the predried
product 30. The tapes are preferably placed during the winding step
after the predried product 30 is formed.
[0093] More preferably, as shown in FIG. 3, both sides of a
predried laminate 500 comprising a metal foil 100 and a predried
heat-resistant resin layer 300 are covered with tapes 400 and 400'
and the laminate is wound. In FIG. 3, the predried laminate 500 has
uncoated portions 200 and 200'. However, the heat-resistant resin
layer 300 may be formed across the entire width of the metal foil
100 without leaving the uncoated portions 200 and 200'.
[0094] Materials for the tape may be selected from substances which
do not deform by shrinking, softening or melting at the
heat-treating and solvent removing temperature. Preferably, the
tape comprises a woven fabric or a nonwoven fabric, made of
cellulose, glass, carbon, aramid, etc., among others.
[0095] The thickness of the tape needs to be greater than or equal
to that of the coated resin solution. Otherwise, especially when
the residual solvent content is high, the coated surface and
uncoated surface will come into contact, thereby lowering
productivity. A width of the tape is about 5 to 100 mm. The width
of 5 mm or less lowers workability, particularly when covering the
laminate with the tape. The width of 100 mm or more lowers the
efficiency of solvent removal and degrades the appearance of the
coated surface since the area which contacts the coated surface
increases (or a wider uncoated surface is required). This results
in a lowered yield.
[0096] In the above winding step (B), when using tape, after the
completion of step (C), the portion which is covered with tape is
cut off and the reminder is wound onto a paper tube to prepare the
final product. The paper tube preferably has a large diameter
ranging from about 3 to 10 inches in order to avoid curling that
would otherwise be caused by the winding.
[0097] Flexible Metal-Clad Laminate
[0098] As shown in FIG. 4, the flexible metal-clad laminate of the
present invention produced by a method comprising the above steps
(A) and (C) or a method comprising the above steps (A), (B) and (C)
is characterized in that it comprises the metal foil 11 and the
heat-resistant resin film 31 comprising a condensation polymer and
formed on one side of the metal foil, the heat-resistant resin film
11 having an N-methyl-2-pyrrolidone-i- nsolule content of 1% or
higher, particularly 1 to 99%.
[0099] The flexible metal-clad laminate of the present invention is
characterized in that it is produced by laminating (e.g., by
applying a solution containing an organic solvent and a
condensation polymer to a metal foil and drying the laminate) the
metal foil 11 and the heat-resistant resin film 31 comprising an
organic solvent-soluble condensation polymer and formed on one side
of the metal foil. The flexible metal-clad laminate is also
characterized in that the heat-resistant resin film 11 contains the
above crosslinked condensation polymer and that the heat-resistant
resin film has an N-methyl-2-pyrrolidone-insolule content of at
least 1% after being laminated.
[0100] The heat-resistant resin film of the flexible metal foil
laminate of the present invention has initiation tear strength
(film thickness: 20 .mu.m) of 15 kg or more and a thermal gradient
dimensional change when heated at 200.degree. C. for 30 minutes of
0.1% or lower.
[0101] The flexible metal foil laminate of the invention has solder
heat resistance of 350.degree. C. or higher, adhesion between the
metal layer and heat-resistant resin film of 80 g/mm or higher and
radius of curvature of 15 cm or greater.
[0102] Further, the heat-resistant resin film has elastic modulus
retentivity of 40% or higher when immersed in an aqueous solution
of sodium hydroxide (concentration: 40% by weight) at 25.degree. C.
for 100 hours.
[0103] The above initiation tear strength, solder heat resistance,
adhesion, radius of curvature of a curl and elastic modulus
retentivity are measured by the methods described below in
Examples.
[0104] In the present invention, the average surface roughness (Ra)
of the area of the heat-resistant resin film layer which contacts
the metal foil on which it is formed is preferably 0.4 .mu.m or
less. When the average surface roughness is greater than 0.4 .mu.m,
the resin film layer after the metal foil is removed by etching
curls, thereby making circuit processing difficult. In the present
specification, average surface roughness Ra is measured according
to the method of JIS B0601.
[0105] The average surface roughness Ra of a heat-resistant resin
film layer can be lowered by using a metal foil having a coated
surface with low surface roughness (particularly Ra is 0.6 .mu.m or
lower, particularly about 0.1 to 0.4 .mu.m) and/or by adjusting the
viscosity of the coating solution and drying conditions, especially
predrying conditions. In the latter case, it is preferable that the
viscosity of the coating solution be adjusted to about 10 to 500
Poise and that the drying is carried out as quickly as possible,
particularly at (Tb-70).degree. C. to (Tb-100).degree. C. for about
2 to 15 minutes.
[0106] In the flexible metal-clad laminate of the invention
comprising the heat-resistant resin film layer and metal foil, the
thickness of the heat-resistant resin film layer may be selected
from a wide range. The thickness is generally about 5 to 100 .mu.m,
preferably about 10 to 50 .mu.m after a thorough-drying. When the
thickness is less than 5 .mu.m, mechanical properties such as film
strength and handling properties are lowered. On the other hand,
when the thickness is greater than 100 .mu.m, flexibility and like
characteristics and processability (drying property, coating
property) and the like are likely to be lowered.
[0107] Flexible Printed Wiring Board
[0108] Using the above flexible metal-clad laminate of the
invention, for example, a flexible printed wiring board can be
produced by the subtractive process and like conventional methods.
The thus obtained printed wiring board of the present invention is
advantageous in that it curls less, that peeling and blistering in
the circuit patterns are inhibited since the printed wiring board
has limited curling and high solder heat resistance and that the
adhesion of circuit patterns is high, etc. Therefore, the flexible
metal-clad laminate of the invention is considerably advantageous
in industry.
EXAMPLES
[0109] The present invention will be explained below in further
detail with Examples. However, the present invention is not limited
to the embdiments described in Examples. The following methods of
evaluation are used in Examples.
[0110] Inherent Viscosity
[0111] A condensation polymer was dissolved in
N-methyl-2-pyrrolidone so as to attain a polymer concentration of
0.5 g/dl. The solution viscosity and solvent viscosity of the
resulting solution at 30.degree. C. were measured with an
Ubbelohde's viscometer, and the inherent viscosity was calculated
according to the following equation.
Inherent viscosity (dl/g)=[1n(V.sub.1/V.sub.2)]/V.sub.3 (1)
[0112] In the above equation, V.sub.1 represents the solution
viscosity measured with an Ubbelohde's viscometer, and V.sub.2
represents the solvent viscosity measured with an Ubbelohde's
viscometer. V.sub.1 and V.sub.2 were determined based on the time
taken for the polymer solution and the solvent
(N-methyl-2-pyrrolidone) to pass through the capillary of the
viscometer. V.sub.3 is a polymer concentration (g/dl).
[0113] Glass Transition Temperature
[0114] A resin film layer was obtained by removing the metal foil
of a flexible metal-clad laminate of the present invention by
etching. The glass transition temperature of the resin film layer
was measured by the tension mode using a TMA (thermomechanical
analyzer/manufactured by RIGAKU DENKI Co., Ltd.). The conditions
for the measurement are as shown below. The measured film was
heated in a nitrogen environment to point of inflection at a
heating rate of 10.degree. C./min., and then was cooled to room
temperature before being tested.
[0115] Load: 1 g
[0116] Sample size: 4 (width).times.20 (length) mm
[0117] Heating rate: 10.degree. C./min.
[0118] Atmosphere: nitrogen
[0119] Residual Solvent Content
[0120] The residual solvent content in a predried laminate
(comprising a predried coating film of a heat-resistant resin
solution and a metal foil) or a flexible metal-clad laminate
obtained as the final product (in connection with this item,
predried laminates and flexible metal-clad laminates are
collectively referred to as "metal-clad laminates") was determined
according to JIS K5400 under the drying conditions of 250.degree.
C. for 1 hour. The residual solvent content was calculated by the
equation (3) below.
[0121] More specifically, the metal-clad laminate was thoroughly
dried at 250.degree. C. for 1 hr. Then the weight of the metal foil
was determined by removing the metal foil by etching. The weight of
the metal foil was subtracted from the weight of the metal-clad
laminate before the thorough-drying to determine the weight of
<resin+solvent>. The weight of the solvent was determined
from the change in the weight of the metal-clad laminate before and
after the thorough-drying. The residual solvent content was
calculated by equation (3).
Residual solvent content (%)=[(RSM-RM)/(RSM-M)].times.100 (3)
[0122] where RSM represents the weight (g) of the metal-clad
laminate before the thorough-drying, RM represents the weight (g)
of the metal-clad laminate after the thorough-drying, and M
represents the weight (g) of the metal foil.
[0123] Measurement of Insoluble Content
[0124] A flexible metal-clad laminate was immersed in ferric
chloride at 40.degree. C. (concentration: 35% by weight) to etch
and remove the metal foil therefrom. The obtained resin film was
dissolved in N-methyl-2-pyrrolidone, giving a 0.5% by weight
solution of the resin film layer in N-methyl-2-pyrrolidone. The
solution was prepared using a 100 ml Erlenmeyer flask.
[0125] Subsequently, this solution was heat-treated at 1.degree. C.
(by immersing the Erlenmeyer flask in an oil bath at 100.degree.
C.) for 2 hours. The Erlenmeyer flask was cooled to room
temperature. The insolubles in the Erlenmeyer flask was collected
by filtration using a glass filter (No. 3G-2) while being washed
with 100 ml of N-methyl-2-pyrrolidone.
[0126] Thereafter, the glass filter with the insolubles was dried
in vacuum at 200.degree. C. for 20 hours. The weight of the dried
glass filter was measured. From this weight was subtracted the
original weight of the glass filter which had been preliminarily
measured, thereby determining the weight of the insolubles. The
insoluble content was calculated from the weight of the insolubles
(Mi) and the weight of the resin film (Mf) by the following
equation.
Insoluble content (%)=[Mi/Mf].times.100 (4)
[0127] where Mi represents the weight (g) of the insolubles, and Mf
represents the weight (g) of the resin film.
[0128] Curling
[0129] As shown in FIG. 5, a flexible metal-clad laminate (sample
size: 10 cm.times.10 cm) or a heat-resistant resin film (sample
size: 10 cm.times.10 cm) obtained by etching the metal foil from a
flexible metal-clad laminate was left in a free state (the state
that weight is not applied in the direction of curling). The
distance (R) between the ends 102 and 102' which do not lie in the
vertical plane S due to curling of the sample 100 and the distance
h between the vertical plane S and each of the ends 102 and 102'
were measured. The radius of curvature r was calculated by the
following equation.
Radius of curvature (r)=(h/2)+(1/8).times.(R.sup.2/h)
[0130] Solder Heat Resistance
[0131] Circuit patterns (1 mm in width) were formed by etching the
metal foil of the flexible metal-clad laminate by the subtractive
process, giving a sample. This sample was exposed to a temperature
of 40.degree. C. and a humidity of 85% for 5 hours for
conditioning, subjected to flux cleaning and immersed in a wave
solder bath at 350.degree. C. for 10 seconds. The sample was then
observed with a microscope for peelings and blisters.
[0132] Thermal Gradient Dimensional Change
[0133] Thermal gradient dimensional change in the directions of MD
and TD was determined according to IPC-FC241 (IPC-TM-650, 2.2.4
(c)) under the conditions of 150.degree. C..times.30 min.,
200.degree. C..times.30 min., and 250.degree. C..times.30 min.
[0134] Adhesion
[0135] The adhesion between the circuit patterns and the
heat-resistant resin layer was determined according to IPC-FC241
(TM-650, 2.4.9 (A)) using a sample on which circuit patterns were
formed by the subtractive process.
[0136] Initiation Tear Strength
[0137] A sample (20 mm in width, 200 mm in length) was prepared
from a resin film prepared by removing the metal foil therefrom by
etching. This sample was tested according to JIS-C2318.
[0138] Tensile Strength, Elongation and Elastic Modulus of Resin
Film
[0139] A resin film was obtained by removing the metal foil
therefrom by etching with an aqueous solution of ferric chloride
(concentration: 35% by weight) at 40.degree. C. A sample (10 mm in
width, 100 mm in length) was prepared from the resin film. The
sample was tested with a tensile tester (trade name "Tensilon
tensile tester", manufactured by TOYO BALDWIN CO., LTD.) under the
following conditions.
[0140] Conditioning: 40.degree. C., 85% (humidity).times.5 hrs
[0141] Drawing rate : 20 mm/min.
[0142] Distance between chucks 40 mm
[0143] Alkali Resistance Test of Resin Film
[0144] A heat-resistant resin film was prepared by removing the
metal foil therefrom by etching with an aqueous solution of ferric
chloride (concentration: 35% by weight) at 40.degree. C. The
heat-resistant resin film was immersed in 40% by weight of an
aqueous solution of sodium hydroxide for 100 hours. Thereafter, the
sample was thoroughly washed and dried. The elastic modulus of the
sample was determined under the above conditions. Subsequently, the
retentivity of elastic modulus was calculated based on the elastic
modulus before and after the immersion.
Retentivity of elastic modulus (%)=[Ea/Eb].times.100 (5)
[0145] wherein Ea represents the elastic modulus after the
immersion, and Eb represents the elastic modulus before
immersion.
[0146] Flexural Endurance
[0147] A heat-resistant resin film (10 mm in width) prepared by
etching the metal foil was tested for the number of times it could
be bent before being broken according to JIS C 5016. In the test,
the load was 500 g and the bending radius was 0.38 mm.
[0148] Measurement of Surface Roughness (Ra)
[0149] A metal foil of the produced flexible metal-clad laminate
was removed by etching with ferric chloride (concentration: 35% by
weight) at 40.degree. C., giving a resin film sample. The surface
of the thus obtained resin film which was contacting a copper foil
was traced by a surface texture and contour measuring instrument
with differential transformer type pickup (manufactured by TOKYO
SEIMITSU CO., LTD.) to determine its surface roughness. The tracing
was conducted according to the method of JIS B0601, at a rate of
0.12 mm/min. and cutoff of 0.8 mm.
Synthesis Example 1
Synthesis of Resin A
[0150] Into a reaction vessel were placed 192 g of trimellitic acid
anhydride (manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC.),
211 g (80 mol %) of 3,3'-dimethyl- 4,4'-biphenyldiisocyanate
(manufactured by NIPPON SODA CO., LTD., "O-tolidinediisocyanate"),
35 g (20 mol %) of 2,4-tolylene diisocyanate (manufactured by
NIPPON POLYURETHANE INDUSTRY CO., LTD., "Coronate T-100"), 0.5 g of
sodium methylate (manufactured by WAKO PURE CHEMICALS INDUSTRIES,
LTD.) and 2.5 kg of N-methyl-2-pyrrolidone (manufactured by
MITSUBISHI CHEMICAL CORPORATION). The mixture was heated to
150.degree. C. over 1 hour and was further reacted at 150.degree.
C. for 5 hours. The resulting polymer had an inherent viscosity of
1.6 dl/g and a glass transition temperature of 320.degree. C.
Synthesis Example 2
Synthesis of Resin B
[0151] Into a reaction vessel were placed 192 g of trimellitic acid
anhydride, 157 g (75 mol %) of 1,5-naphthalenediisocyanate
(manufactured by SUMITOMO BAYER URETHANE CO., LTD., "Desmodur 15"),
63 g (25 mol %) of 4,4'-diphenylmethanediisocyanate (manufactured
by SUMITOMO BAYER URETHANE CO., LTD.), 1 g of diazabicycloundecene
(manufactured by SAN-APRO LIMITED) and 2 kg of
N-methyl-2-pyrrolidone. The mixture was heated to 170.degree. C.
over 1 hour and further reacted at 170.degree. C. for 5 hours. The
resulting polymer had an inherent viscosity of 1.4 dl/g and a glass
transition temperature of 356.degree. C.
Synthesis Example 3
Synthesis of Resin B-1
[0152] Into a reaction vessel were placed 384 g of trimellitic acid
anhydride, 378 g (90 mol %) of 1,5-naphthalenediisocyanate, 50 g
(10 mol %) of 4,4'-diphenylmethanediisocyanate, 2.5 g of potassium
fluoride (manufactured by TOKYO KASEI KOGYO CO., LTD.) and 2 kg of
N-methyl-2-pyrrolidone. The mixture was heated to 130.degree. C.
over 1 hour, and further reacted at 130.degree. C. for 5 hours. The
resulting polymer had an inherent viscosity of 1.7 dl/g and a glass
transition temperature of 381.degree. C.
Synthesis Example 4
Synthesis of Resin B-2
[0153] Into a reaction vessel were placed 384 g of trimellitic acid
anhydride, 399 g (95 mol %) of 1,5-naphthalenediisocyanate, 25 g (5
mol %) of 4,4'-diphenylmethanediisocyanate, 2.5 g of potassium
fluoride and 2 kg of N-methyl-2-pyrrolidone. The mixture was heated
to 100.degree. C. over 1 hour, and further reacted at 100.degree.
C. for 5 hours. The resulting polymer had an inherent viscosity of
1.8 dl/g and a glass transition temperature of 390.degree. C.
Synthesis Example 5
Synthesis of Resin B-3
[0154] Into a reaction vessel were placed 384 g of trimellitic acid
anhydride, 210 g (50 mol %) of 1,5-naphthalenediisocyanate, 251 g
(50 mol %) of 4,4'-diphenylmethanediisocyanate, 2.5 g of potassium
fluoride and 1.5 kg of N-methyl-2-pyrrolidone. The mixture was
heated to 150.degree. C. over 1 hour, and further reacted at
150.degree. C. for 5 hours. The resulting polymer had an inherent
viscosity of 1.2 dl/g and a glass transition temperature of
367.degree. C.
Synthesis Example 6
Synthesis of Resin A-1
[0155] Into a reaction vessel were placed 192 g of trimellitic acid
anhydride, 251 g (95 mol %) of
3,3'-dimethyl-4,4'-biphenyldiisocyanate, 8.7 g (5 mol %) of
2,4-tolylene diisocyanate, 0.5 g of sodium methylate and 2.5 kg of
N-methyl-2-pyrrolidone. The mixture was heated to 150.degree. C.
over 1 hour, and further reacted at 150.degree. C. for 5 hours. The
resulting polymer had an inherent viscosity of 1.7 dl/g and a glass
transition temperature of 315.degree. C.
Examples 1 to 12 and Comparative Examples 1 to 5
[0156] (A) Predrying Step
[0157] Each of the resin solutions obtained in the above Synthesis
Examples was continuously applied to a copper foil with a knife
coater, leaving a 1 cm lengthwise border on both edges (uncoated)
in such a manner that the thickness of the resin layer after
removing the solvent therefrom was 20 .mu.m.
[0158] The copper foils used in Examples 1 to 12 and Comparative
Examples 1 to 4 were rolled copper foils (trade name "BHY-02-BT",
manufactured by JAPAN ENERGY CORPORATION) having a surface
roughness Ra of 0.35 .mu.m and thickness of 18 .mu.m. The copper
foil used in Comparative Example 5 was an electro-deposited copper
foil (trade name "NDP-III", manufactured by Mitsui Mining &
Smelting Co., Ltd.) having a surface roughness Ra of 0.65 .mu.m and
thickness of 18 .mu.m.
[0159] Subsequently, the coated metal foils were continuously
passed through a floating-type drying furnace which was 20 m long.
The speed of the line was adjusted so that the drying conditions
shown in Table 1 were attained. The residual solvent contents in
the resulting predried resin layers are shown in Table 1.
[0160] (B) Winding Step
[0161] In Examples 1 to 8 and Comparative Examples 1 to 5, while
both lengthwise edges of the coated surfaces of the thus obtained
ribbon-shaped laminates were covered with glass cloth tape (1 cm in
width and 200 .mu.m in thickness), the laminates were wound on
aluminum tubes (3 inches in diameter) with the coated surface
facing outward.
[0162] In Examples 9 to 11, glass cloth tape (1 cm in width and 300
.mu.m in thickness) was placed on the uncoated area at both
lengthwise edges of the ribbon-shaped laminates. The laminates were
wound on aluminum tubes (3 inches in diameter) with the coated
surface facing outward. In Example 12, as shown in FIG. 3, both
uncoated lengthwise edges of the ribbon-shaped laminate were
covered with tape. The laminates were wound on aluminum tubes (3
inches in diameter) with the coated surface facing outward.
[0163] (C) Heat-Treating and Solvent Removing Step
[0164] Subsequently, the rolls obtained in the above winding step
were heat-treated in a vacuum dryer or an inert oven under the
conditions shown in Table 1.
[0165] In Table 1, the reduced pressure in column "solvent removing
and heat-treating condition" varied from 10 to 100 Pa because of
the volatilization of the solvent.
[0166] The solvent in the coating film of the obtained flexible
metal-clad laminate was completely removed. The characteristics of
the laminates are shown in Tables 2 and 3.
[0167] The metal foils of the flexible metal-clad laminates
obtained in Examples 1 to 12 and Comparative Example 5 were removed
by etching with an aqueous solution of ferric chloride
(concentration: 35% by weight) at 40.degree. C. The surface
roughness Ra of the surfaces of the heat-resistant resin film
layers which were contacting the metal foils was determined. The
results are shown in Table 3.
[0168] In Comparative Example 5, the heat-resistant resin film
layer curled with the surface which was contacting the copper foil
facing inward and had a radius of curvature of 3 cm. On the
contrary, the heat-resistant resin film layers obtained in Examples
1 to 12 were flat.
1TABLE 1 Residual solvent content Ex. after Comp. Ex. Resin
Predrying conditions predrying Solvent removing and heat-treating
conditions Ex. 1 A 100.degree. C. .times. 5 min. 21% 200.degree. C.
(reduced pressure) .times. 20 hr., 260.degree. C. .times. 3 hr.
(nitrogen) Ex. 2 A 100.degree. C. .times. 5 min. 19% 200.degree. C.
(reduced pressure) .times. 20 hr., 280.degree. C. .times. 3 hr.
(nitrogen) Ex. 3 A 100.degree. C. .times. 5 min. 22% 200.degree. C.
(reduced pressure) .times. 20 hr., 300.degree. C. .times. 3 hr.
(nitrogen) Ex. 4 A 80.degree. C. .times. 8 min. 28% 200.degree. C.
(reduced pressure) .times. 10 hr., 280.degree. C. .times. 3 hr.
(nitrogen) Ex. 5 A 100.degree. C. .times. 5 min. 20% 200.degree. C.
(reduced pressure) .times. 10 hr., 280.degree. C. .times. 3 hr.
(nitrogen) Ex. 6 A 110.degree. C. .times. 4 min. 18% 200.degree. C.
(reduced pressure) .times. 10 hr., 280.degree. C. .times. 3 hr.
(nitrogen) Ex. 7 A 100.degree. C. .times. 5 min. 20% 200.degree. C.
(reduced pressure) .times. 10 hr., 300.degree. C. .times. 3 hr.
(nitrogen) Ex. 8 B 100.degree. C. .times. 5 min. 20% 200.degree. C.
(reduced pressure) .times. 10 hr., 280.degree. C. .times. 3 hr.
(nitrogen) Ex. 9 B-1 100.degree. C. .times. 5 min. 21% 200.degree.
C. (reduced pressure) .times. 30 hr., 300.degree. C. .times. 4 hr.
(nitrogen) Ex. 10 B-2 100.degree. C. .times. 5 min. 19% 200.degree.
C. (reduced pressure) .times. 30 hr., 300.degree. C. .times. 4 hr.
(nitrogen) Ex. 11 B-3 100.degree. C. .times. 5 min. 19% 200.degree.
C. (reduced pressure) .times. 30 hr., 300.degree. C. .times. 4 hr.
(nitrogen) Ex. 12 A-1 100.degree. C. .times. 5 min. 20% 200.degree.
C. (reduced pressure) .times. 30 hr., 300.degree. C. .times. 4 hr.
(nitrogen) Comp. Ex. 1 A 100.degree. C. .times. 5 min. 20%
200.degree. C. (reduced pressure) .times. 20 hr. Comp. Ex. 2 A
150.degree. C. .times. 3 min. 22% 200.degree. C. (reduced pressure)
.times. 10 hr., 280.degree. C. .times. 3 hr. (nitrogen) Comp. Ex. 3
A 100.degree. C. .times. 5 min. 7% 200.degree. C. (reduced
pressure) .times. 10 hr., 280.degree. C. .times. 3 hr. (nitrogen)
200.degree. C. .times. 10 min. Comp. Ex. 4 A 100.degree. C. .times.
5 min. 20% 180.degree. C. (reduced pressure) .times. 20 hr. Comp.
Ex. 5 A 80.degree. C. .times. 8 min. 29% 200.degree. C. (reduced
pressure) .times. 20 hr., 280.degree. C. .times. 3 hr.
(nitrogen)
[0169]
2 TABLE 2 Curling in Thermal gradient Thermal gradient Thermal
gradient Insolu- metal dimensional change at dimensional change at
dimensional change at Ex. ble Solder lami- 150.degree. C. (%)
200.degree. C. (%) 250.degree. C. (%) Comp. content heat nate
Direction Direction Direction Direction Direction Direction Ex. (%)
resistance (cm) MD TD MD TD MD TD Ex. 1 2 Fine None -0.043 -0.045
-0.068 -0.073 -0.095 -0.094 2 10 Fine None -0.010 -0.029 -0.032
-0.041 -0.088 -0.084 3 76 Fine None 0.023 -0.024 -0.039 -0.040
-0.073 -0.088 4 9 Fine None -0.008 -0.001 -0.033 -0.036 -0.059
-0.066 5 10 Fine None 0.025 0.021 -0.036 -0.036 -0.093 -0.094 6 10
Fine None -0.037 0.008 -0.045 -0.052 -0.094 -0.089 7 76 Fine None
-0.039 -0.039 -0.041 -0.048 -0.088 -0.086 8 10 Fine None -0.009
-0.023 -0.036 -0.059 -0.074 -0.082 9 22 Fine None -0.008 -0.001
-0.048 -0.054 10 28 Fine None -0.022 -0.020 -0.049 -0.052 11 35
Fine None -0.030 -0.036 -0.073 -0.085 12 29 Fine None -0.029 -0.031
-0.071 -0.079 Comp. 1> Blisters, 15.0 -0.054 -0.054 -0.101
-0.123 Ex. 1 peelings 2 10 Fine 5.5 -0.049 -0.056 -0.101 -0.113 3
10 Fine 13.0 -0.063 -0.079 -0.112 -0.136 4 1> Blisters, 14.0
-0.035 -0.023 -0.105 -0.140 peelings 5 10 Fine None -0.035 -0.038
-0.044 -0.049
[0170]
3 TABLE 3 Elastic modulus Initiation retentivity Ex. tear Tensile
Elon- Elastic (after Flexural Comp. Adhesion strength strength
gation modulus immersion in endurance Ra Ex. (g/mm) (Kg)
(Kg/mm.sup.2) (%) (Kg/mm.sup.2) alkali; %) (cycle) (.mu.m) Ex. 1
114 21 43 53 728 69 10520 0.12 2 97 20 43 60 614 81 11210 0.11 3
111 21 34 45 619 91 6350 0.12 4 105 22 41 61 616 72 8820 0.15 5 91
22 36 60 621 83 8950 0.11 6 115 27 37 57 625 86 10310 0.09 7 105 19
35 53 611 91 6110 0.12 8 145 20 42 56 609 87 3470 0.12 9 89 20 24
11 483 41 6850 0.15 10 87 21 25 22 454 43 6400 0.13 11 101 23 15 39
367 48 5720 0.13 12 111 24 39 46 711 96 6920 0.12 Comp. 119 20 35
41 681 39 -- -- Ex. 1 2 -- -- -- -- -- -- -- -- 3 -- -- -- -- -- --
-- -- 4 115 20 -- -- -- -- -- -- 5 190 23 38 47 693 81 7920
0.53
Effect of the Invention
[0171] As mentioned above, since the flexible metal-clad laminate
of the present invention is prepared by (A) applying a
heat-resistant resin solution to a metal foil and drying the
solution, (B) winding the laminate (if necessary), and further (C)
heat-treating the laminate while removing the solvent therefrom,
the flexible metal-clad laminate and heat-resistant resin film
produced by removing the metal foil therefrom by etching do not
curl and are excellent in dimensional stability, heat resistance
and chemical resistance (particularly alkali resistance), hence
industrially useful.
* * * * *