U.S. patent application number 09/769260 was filed with the patent office on 2001-06-14 for connecting member of a circuit substrate and method of manufacturing multilayer circuit substrates by using the same.
Invention is credited to Hatakeyama, Akihito, Kawakita, Kouji, Kojima, Tamao, Nakatani, Seiichi, Ogawa, Tatsuo, Sogou, Hiroshi.
Application Number | 20010003610 09/769260 |
Document ID | / |
Family ID | 26531606 |
Filed Date | 2001-06-14 |
United States Patent
Application |
20010003610 |
Kind Code |
A1 |
Nakatani, Seiichi ; et
al. |
June 14, 2001 |
Connecting member of a circuit substrate and method of
manufacturing multilayer circuit substrates by using the same
Abstract
A connecting member of circuit substrates includes an organic
porous base material provided with tackfree films on both sides,
through-holes disposed at requested places which are filled with
conductive resin compound up to the surface of the tackfree films.
This structure enables inner-via-hole connection and can therefore
attain a connecting member of circuit substrates and an electrical
connector of high reliability and high quality. By using a
connecting member of circuit substrates including the organic
porous base material provided with tackfree films on both sides and
through-holes disposed at requested places which are filled with
conductive resin compound up to the surface of the tackfree films,
it is possible to form a high-multilayer substrate easily from
double sided boards or four-layer substrates which can be
manufactured rather stably. In addition to that, since the
conductive paste is filled up to the surface of the tackfree films,
the conductive paste sticks out from the surface of the organic
porous base material when the tackfree films are separated. As a
result, the filled amount of the conductive substance increases
after the lamination, and thus, the connection resistance is
reduced considerably.
Inventors: |
Nakatani, Seiichi; (Osaka,
JP) ; Hatakeyama, Akihito; (Osaka, JP) ;
Kawakita, Kouji; (Kyoto, JP) ; Sogou, Hiroshi;
(Hyoga, JP) ; Ogawa, Tatsuo; (Hyogo, JP) ;
Kojima, Tamao; (Osaka, JP) |
Correspondence
Address: |
Barry E. Bretschneider
Morrison & Foerster LLP
Suite 5500
2000 Pennsylvania Avenue, N.W.
Washington
DC
20006-1888
US
|
Family ID: |
26531606 |
Appl. No.: |
09/769260 |
Filed: |
January 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09769260 |
Jan 26, 2001 |
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09259966 |
Mar 1, 1999 |
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09259966 |
Mar 1, 1999 |
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08582930 |
Jan 4, 1996 |
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6108903 |
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08582930 |
Jan 4, 1996 |
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08308982 |
Sep 20, 1994 |
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5484647 |
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Current U.S.
Class: |
428/131 ;
428/137; 442/117; 442/394 |
Current CPC
Class: |
Y10S 428/901 20130101;
Y10T 428/24917 20150115; Y10T 442/674 20150401; H05K 2201/0355
20130101; H05K 2203/0191 20130101; H05K 2203/1461 20130101; H05K
3/4623 20130101; Y10T 428/24322 20150115; H05K 2201/10378 20130101;
H05K 3/4069 20130101; Y10T 29/49165 20150115; H01R 12/523 20130101;
Y10T 29/49126 20150115; H05K 3/4652 20130101; Y10T 29/49155
20150115; Y10T 428/249994 20150401; H05K 3/462 20130101; Y10T
428/24273 20150115; H05K 2201/09536 20130101; Y10T 442/2475
20150401; H05K 2201/0116 20130101; Y10T 428/249996 20150401 |
Class at
Publication: |
428/131 ;
442/394; 442/117; 428/137 |
International
Class: |
B32B 003/10; B32B
005/02; B32B 027/04; B32B 027/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 1993 |
JP |
5-234519 |
Sep 29, 1993 |
JP |
5-242450 |
Claims
What is claimed is:
1. A connecting member of a circuit substrate comprising an organic
porous base material provided with tackfree films on both sides,
wherein said connecting member of circuit substrates has
through-holes, and said through-holes are filled with conductive
resin compound up to the surface of said tackfree films.
2. The connecting member of circuit substrates as in claim 1,
wherein said organic porous base material is a composite material
which comprises a nonwoven heat-resisting synthetic fiber fabric
impregnated with an uncured thermosetting resin.
3. The connecting member of a circuit substrate as in claim 2,
wherein said nonwoven heat-resisting synthetic fiber fabrics
comprise aramid resin, while said uncured thermosetting resin is
epoxy resin.
4. The connecting member of a circuit substrate as in claim 2,
wherein said nonwoven heat-resisting synthetic fiber fabric
comprises paper, and said uncured thermosetting resin is selected
from the group consisting of phenol resin and epoxy resin.
5. The connecting member of circuit substrates as in claim 1,
wherein a conductive substance contained in said conductive resin
compound is at least one metallic powder selected from the group
consisting of silver, nickel, copper, silver alloy, nickel alloy,
and copper alloy.
6. The connecting member of circuit substrates as in claim 2,
wherein a resin component contained in said conductive resin
compound is the same as the thermosetting resin in said organic
porous base material.
7. The connecting member of circuit substrates as in claim 1,
wherein said through-holes are formed by laser irradiation.
8. The connecting member of a circuit substrate as in claim 1,
wherein said through-holes filled with the conductive resin
compound have a diameter of 50 .mu.m to 1 mm.
9. The connecting member of a circuit substrate as in claim 1,
wherein said through-holes filled with the conductive resin
compound have a pitch of 50 .mu.m or more.
10. The connecting member of circuit substrates as in claim 1,
wherein said through-holes filled with the conductive resin
compound have an electrical resistance of 0.05 to 5.0 m.OMEGA..
11. The connecting member of circuit substrates as in claim 1,
wherein said porous base material has a porosity of from 2 to
35%.
12. A method of manufacturing a multilayer circuit substrate
comprising the steps of: (a) providing a multilayer circuit
substrate having at least two layers of circuit patterns, a circuit
substrate having at least one layer of circuit pattern, and said
connecting member for circuit substrates consisting of an organic
porous base material provided with tackfree films on both sides
which is disposed with through-holes filled with conductive resin
compound up to the surface of said tackfree films; (b) separating
said tackfree films from said connecting member of circuit
substrates; (c) positioning said connecting member of circuit
substrates between the multilayer circuit substrate and the circuit
substrate; and (d) heating and pressurizing.
13. The method of manufacturing a multilayer circuit substrate as
in claim 12, wherein said organic porous base material is a
composite material which comprises a nonwoven heat- resisting
synthetic fiber fabric impregnated with uncured thermosetting
resin.
14. The method of manufacturing a multilayer circuit substrate as
in claim 13, wherein said nonwoven heat-resisting synthetic fiber
fabric comprises aramid resin, and said uncured thermosetting resin
is epoxy resin.
15. The method of manufacturing a multilayer circuit substrate in
claim 12, wherein said nonwoven heat-resisting synthetic fiber
fabric comprises paper, and said uncured thermosetting resin is
selected from the group consisting of phenol resin and epoxy
resin.
16. The method of manufacturing a multilayer circuit substrate as
in claim 12, wherein a conductive substance contained in said
conductive resin compound is at least one metallic powder selected
from the group consisting of silver, nickel, copper, silver alloy,
nickel alloy, and copper alloy.
17. The method of manufacturing a multilayer circuit substrate as
in claim 12, wherein a resin component contained in said conductive
resin compound is the same as the thermosetting resin in said
organic porous base material.
18. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 12,
wherein said multilayer circuit substrate having at least two
layers of circuit patterns and said circuit substrate having at
least one layer of circuit pattern comprise glass-epoxy substrates
having copper foil wirings and copper-plated through-holes.
19. The method of manufacturing a multilayer circuit substrate as
in claim 12, wherein said multilayer circuit substrate having at
least two layers of circuit patterns and said circuit substrate
having at least one layer of circuit pattern comprise aramid
nonwoven fabrics and thermosetting epoxy resin.
20. The method of manufacturing a multilayer circuit substrate as
in claim 12, wherein said through-holes are formed by laser
irradiation.
21. The method of manufacturing a multilayer circuit substrate as
in claim 12, wherein said through-holes filled with the conductive
resin compound have a diameter of 50 .mu.m to 1 mm.
22. The method of manufacturing a multilayer circuit substrate by
using the connecting member of a circuit substrate as in claim 12,
wherein said through-holes filled with the conductive resin
compound have a pitch of 50 .mu.m or more.
23. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 12,
wherein said through-holes filled with the conductive resin
compound have an electrical resistance of 0.05 to 5.0 m.OMEGA..
24. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 12,
wherein said porous base material has a porosity of from 2 to
35%.
25. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 12,
wherein the heating is carried out at a temperature of from 170 to
260.degree. C.
26. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 12,
wherein the pressurization is carried out at a pressure of from 20
to 80 kg/cm.sup.2.
27. A method of manufacturing a multilayer circuit substrate
comprising the steps of: (a) providing a multilayer circuit
substrate having at least two layers of circuit patterns and two
pieces of said connecting member of a circuit substrate consisting
of an organic porous base material provided with tackfree films on
both sides which is disposed with through-holes filled with
conductive resin compound up to the surface of said tackfree films;
(b) separating said tackfree films from said connecting members of
circuit substrates; (c) positioning said multilayer circuit
substrate between the two connecting members of circuit substrates;
(d) applying a metal foil on both sides; and (e) heating and
pressurizing, and forming circuit patterns on said metal foils.
28. The method of manufacturing a multilayer circuit substrate as
in claim 27, wherein said organic porous base material is a
composite material which comprises a nonwoven heat-resisting
synthetic fiber fabric impregnated with an uncured thermosetting
resin.
29. The method of manufacturing a multilayer circuit substrate by
using the connecting member of a circuit substrate as in claim 28,
wherein said nonwoven heat-resisting synthetic fiber fabrics
comprise aramid resin, and said uncured thermosetting resin is
epoxy resin.
30. The method of manufacturing a multilayer circuit substrate as
in claim 28, wherein said nonwoven heat-resisting synthetic fiber
fabric comprises paper, and said uncured thermosetting resin is
selected from the group consisting of phenol resin and epoxy
resin.
31. The method of manufacturing a multilayer circuit substrate as
in claim 27, wherein a conductive substance contained in said
conductive resin compound is at least one metallic powder selected
from the group consisting of silver, nickel, copper, silver alloy,
nickel alloy, and copper alloy.
32. The method of manufacturing a multilayer circuit substrate as
in claim 27, wherein a resin component contained in said conductive
resin compound is the same as the thermosetting resin in said
organic porous base material.
33. The method of manufacturing a multilayer circuit substrate as
in claim 27, wherein said multilayer circuit substrate having at
least two layers of circuit patterns comprises glass-epoxy
multilayer circuit substrates having copper foil wirings and
copper-plated through-holes.
34. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 27,
wherein said multilayer circuit substrate having at least two
layers of circuit patterns comprises an aramid nonwoven fabric and
a thermosetting epoxy resin.
35. The method of manufacturing a multilayer circuit substrate as
in claim 27, wherein said through-holes are formed by laser
irradiation.
36. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 27,
wherein said through-holes filled with the conductive resin
compound have a diameter of 50 .mu.m to 1 mm.
37. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 27,
wherein said through-holes filled with the conductive resin
compound have a pitch of 50 .mu.g m or more.
38. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 27,
wherein said through-holes filled with the conductive resin
compound have an electrical resistance of 0.05 to 5.0 m.OMEGA..
39. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 27,
wherein said porous base material has a porosity of from 2 to
35%.
40. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 27,
wherein the heating is carried out at a temperature of from 170 to
260.degree.C.
41. The method of manufacturing a multilayer circuit substrate by
using the connecting member of circuit substrates as in claim 27,
wherein the pressurization is carried out at a pressure of from 20
to 80 kg/cm.sup.2.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a connecting member of a circuit
substrate which connects circuit substrates electrically and
mechanically, and further relates to a simple method of
manufacturing multilayer circuit substrates by using the connecting
member of a circuit substrate.
BACKGROUND OF THE INVENTION
[0002] Recently, following the tendency of electronic devices
toward becoming smaller and lighter, a mounting substrate which is
a part of these devices is required to perform higher mounting
density. The mounting technique itself has become one of the major
elements in the field of development of new electronic devices.
This mounting technique can be divided into two components: 1.
surface mounting components such as semiconductors or chip
components, and 2. substrates for mounting and connecting these
components electrically including its mounting method. It is widely
known that semiconductors have increasingly more chip sizes and
terminals for attaining higher integration density and functional
improvements. Therefore, the terminal pitch is tending toward
becoming narrower For example, terminal pitch is 0.3 mm at present,
whereas the pitch was 0.5 mm in the past. If the pitch were
narrower than 0.3 mm, it would be difficult to apply a conventional
solder method for mounting. The chip on board (COB) technique,
which mounts semiconductors directly on substrates, will be
considered more important in the future than the well-known
"package". Therefore, the COB technique has been researched in
various fields. Furthermore, the tendency toward smaller chip
components has developed so far that nowadays 1005 chip
(1.0.times.0.5 mm) is used daily. Similar to the case with
semiconductors, it would be difficult to produce smaller chip
components than this size since the mounting method causes a limit
on size reduction. In addition, mounting costs would be
significantly higher.
[0003] On the other hand, the dominant current in electronic
devices is moving toward digitalized circuits which are accompanied
by higher frequency and acceleration. As a result, mounting
substrates can no longer sidestep the noise and heat problems. In
order to cope with this problem of higher frequency and
acceleration, a usual method which is practiced at present is to
manufacture a prototype first, and then to modify it again, if any
problem should occur. Therefore, a great amount of time has been
spent for the development of electronic devices, and this method
prolongs the development period. It is desired in the future that
the development of substrates is conducted in such a way that a
simulation of heat, transmission lines, and noise takes place at
the planning stage, and that the results of that simulation are fed
back to the substrate planning so that one prototype is enough for
completing the process. However, this substrate planning system is
still a long way from perfect operation. Thus, a designing method
in which know-how from past experience is used is still considered
to be in the main stream at the moment. In any case,
counter-methods to combat the current toward higher frequency are
surely to be based on substrates and mounting forms which have
shorter wirings.
[0004] As described above, the surface mounting components as well
as the substrate techniques are important aspects for attaining
electronic devices with high mounting density in the future. At
present, one high-density mounting substrate used generally is a
glass-epoxy substrate. This substrate is made of glass woven
fabrics which are impregnated with epoxy resin to form an
insulating substrate material. Glass-epoxy multilayer substrates
had been developed for use with computers in the past, but nowadays
they are widely applied for consumer use. A method of manufacturing
a glass-epoxy multilayer substrate comprises the steps of:
[0005] (1) adhering a Cu foil by heat-pressing the above-mentioned
material which was made of glass woven fabrics impregnated with
epoxy (this is called a prepreg);
[0006] (2) patterning the Cu foil by a photolithographic technique
to form wiring for an internal layer;
[0007] (3) forming a multilayer laminate by further heat-pressing
with the use of another prepreg and a Cu foil;
[0008] (4) drilling through-holes into the laminate and forming a
Cu electrode on the inner wall of the through-holes by an
electrolytic plating method, thereby connecting the layers
electrically; and
[0009] (5) etching the Cu surface into patterns.
[0010] FIG. 6 is a schematic view of this glass-epoxy multilayer
substrate. Referring to FIG. 6, reference numeral 500 denotes an
insulating base material made of glass woven fabrics impregnated
with epoxy resin; 501, Cu wirings in internal layers; 502, drilled
holes made after being formed into a laminated multilayer; 503, a
Cu layer on inner walls formed by a plating method; and 504,
circuit patterns on the upper most layer. This drill process and
the Cu-plated through-holes were established through the
development of techniques in which this kind of glass-epoxy base
material is used to connect internal layers to outside layers
electrically. This method is also widely acknowledged in the
world.
[0011] However, in view of the demand for higher density in the
future as mentioned above, this method can not be considered
satisfactory. The reason is that a usual glass-epoxy multilayer
substrate is disposed with through-holes which consequently reduce
the wiring space. And thus, when high-density wirings are
performed, the necessary wirings must take a round about way
thereby lengthening the wirings. In addition, it is difficult to
conduct an automatic wiring by CAD (computer aided design) because
there is not enough space for wiring. Furthermore, following the
present tendency of forming smaller holes, the drill processing can
not be applied so easily. In fact, this tendency raises the cost
ratio of the drill processing within the entire costs. Not only
that, the Cu-plating process which is necessary for through-holes
is problematic from an environmental point of view.
[0012] In order to solve the above-mentioned problems, a number of
new multilayer substrates have been developed in the field of
multilayer substrates. First, as a technique which applies the
method of forming substrates with Cu-plated through-holes by a
drill is to form SVH (Semi-Buried Via Hole) multilayer substrates.
This method of forming SVH substrates is conducted by means of via
connection consisting of not only through-holes, but also via
connections on the surface which enables more high-density wirings
than with the through-hole-type substrate. Via parts on the surface
are filled with insulating resin which are then Cu-plated thereon
in order to form mounting pads for components on top of the via
parts. According to this method, through-holes for insert
components are only present on the surface, and therefore,
components can be mounted with high-density. But this method is an
improved technique of forming the above-mentioned glass-epoxy
multilayer so that it still suffers from the same problem with the
difficulty in drill processing and the necessity for
Cu-plating.
[0013] On the other hand, new multilayer substrates having a
perfect inner-via-hole (IVH: Interstitional Via Hole) structure are
disclosed, for example, in a SLC (Surface Laminated Circuit,
registered trademark of IBM) substrate and a multilayer substrate
using thermoplastic resin. A method of manufacturing SLC substrates
comprises the steps of providing a double sided substrate having
usual Cu-patterned layers, coating the surface of this substrate
with resin as an insulating material, forming via holes by a
photolithographic method, adding Cu-plating on the entire surface,
and connecting a bottom conductor, a via hole part, and wiring on a
surface layer. Then, by applying the same photolithographic method,
patterns are formed. This process is repeated to form a multilayer.
At present, this method is especially watched with keen interest
because it can form highly accurate wirings at an extremely low
cost. The problems with this method is that the adhesion strength
between the insulating material and the Cu-electrode is low, and
substrates can warp easily due to the difference in thermal
expansion between the core substrate and the resin.
[0014] A multilayer substrate using thermoplastic resin is
manufactured by first disposing holes in a thermoplastic sheet-type
base material, and printing patterns on the surface of the sheet
with conductive resin paste made of silver, and then, by
heat-pressing another sheet formed separately on top to form a
multilayer substrate. The problem in this case is that the
thermoplastic resin does not have heat resistance. In addition, the
conductive resin paste has high wiring resistance, and it is also
difficult to solder the surface part. Nevertheless, both methods
are attracting attention since they have the big advantage of
forming multilayer substrates having a perfect inner-via-hole (IVH)
structure.
[0015] Another technique is disclosed in Laid-open Japanese patent
application No. (Tokkai Sho) 50-94495 and in U.S. Pat. No.
3,620,873 in which an electrical connector (rubber connector) was
used to connect NESA glass made of liquid-crystal elements and a
flexible printed substrate (FPC). This connector is in the form of
laminated layers which are piled up such that layers of silicon
rubber mixed with carbon black and layers without carbon black are
present as alternating layers.
[0016] However, the above-mentioned conventional methods have the
following problems. First, the conventional structure does not
allow the processing of through-holes easily once the substrate is
laminated into a multilayer substrate. This constitution presents
difficulties for coping with the tendency toward high-density
wiring. Namely, it is necessary to process even smaller holes, and
it is also difficult to process holes to match the wirings in the
internal layers. As for the processing of more minute holes, the
diameter of the drill is required to be smaller and smaller, and
the costs for processing this kind of drill become significant. It
is also anticipated that accurate holes can not be formed in the
thickness direction with minute drills. Furthermore, although the
accuracy in positioning wirings in an internal layer against
wirings on external layers needs to be higher and higher, it is
becoming even more and more difficult to process holes at exact
places due to a size gap or elongation of substrate materials. It
is still a big problem to position internal layers to each other
exactly in the present current toward higher build-up layers.
[0017] As a result of the problems mentioned above, the
conventional substrates used for circuits have a limit in the
number of through-hole connections which can be performed per unit
area and also in the density of circuit patterns. Therefore, the
conventional method presents major difficulties for obtaining
multilayer substrates used for high-density mounting which will be
more and more in demand.
[0018] Furthermore, the rubber connector disclosed in the
above-mentioned Laid-open Japanese patent application No. (Tokkai
Sho) 50-94495 and in U.S. Pat. No. 3,620,873 had the problem of
having high electrical resistance of several k.OMEGA./mm.sup.2
because carbon black is mixed in the silicone rubber.
SUMMARY OF THE INVENTION
[0019] An object of this invention is to solve the above problems
by providing a connecting member of circuit substrates which
enables inner-via-hole connection and has high reliability and high
quality. Another object of this invention is to provide a
multilayer circuit substrate composed of the above-noted connecting
member of circuit substrates. A further object of this invention is
to provide a connecting member of circuit substrates which is
suitable for an electrical connector of low electrical
resistance.
[0020] In order to accomplish these and other objects and
advantages, a connecting member of circuit substrates in the first
embodiment in this invention comprises an organic porous base
material provided with tackfree films on both sides, wherein the
connecting member of circuit substrates has a plurality of
through-holes at desired places, and the through-holes are filled
with conductive resin compound up to the surface of the tackfree
films.
[0021] A second embodiment of this invention is a method of
manufacturing a multilayer circuit substrate comprising the steps
of: providing a multilayer circuit substrate having at least two
layers of circuit patterns, a circuit substrate having at least one
layer of circuit pattern, and a connecting member of circuit
substrates comprising an organic porous base material provided with
tackfree films on both sides, wherein the connecting member has a
plurality of through-holes, and the through-holes are filled with
conductive resin compound up to the surface of the tackfree films
from which the tackfree films are separated, positioning the
connecting member of circuit substrates between the multilayer
circuit substrate and the circuit substrate, and heating and
pressurizing.
[0022] A third embodiment of this invention is a method of
manufacturing a multilayer circuit substrate comprising the steps
of: providing a multilayer circuit substrate having at least two
layers of circuit patterns and two pieces of a connecting member of
circuit substrates comprising an organic porous base material
provided with tackfree films on both sides, wherein the connecting
member has a plurality of through-holes, and the through-holes are
filled with conductive resin compound up to the surface of the
tackfree films from which the tackfree films are separated,
positioning the multilayer circuit substrate between the two
connecting members of circuit substrates, applying a metal foil on
both sides, heating and pressurizing and forming circuit patterns
on the metal foils.
[0023] It is preferable that the organic porous base material
comprises a composite material comprised of nonwoven heat-resisting
synthetic fiber fabrics impregnated with thermosetting resin.
[0024] Furthermore, it is preferable that the nonwoven
heat-resisting synthetic fiber fabrics comprise aramid resin, and
that the thermosetting resin is epoxy resin.
[0025] It is also preferable that the nonwoven heat-resisting
synthetic fiber fabrics comprise paper, and that the thermosetting
resin is one compound selected from the group consisting of phenol
resin and epoxy resin.
[0026] Furthermore, it is preferable that a conductive substance
contained in the conductive resin compound is at least one metallic
powder selected from the group consisting of silver, nickel, copper
and an alloy thereof.
[0027] It is preferable that a resin component contained in the
conductive resin compound is the same as the thermosetting resin in
the organic porous base material. In other words, it is preferable
to use, for example, epoxy resin with epoxy resin.
[0028] In addition, it is preferable that the multilayer circuit
substrate having at least two layers of circuit patterns and the
circuit substrate having at least one layer of circuit pattern each
comprise glass-epoxy multilayer circuit substrates having copper
foil wirings and copper-plated through-holes.
[0029] Furthermore, it is preferable that the multilayer circuit
substrate having at least two layers of circuit patterns and the
circuit substrate having at least one layer of circuit pattern each
comprise aramid nonwoven fabrics and multilayer circuit substrates
of thermosetting epoxy resin.
[0030] It is preferable that the through-holes are formed by laser
irradiation.
[0031] Furthermore, it is preferable that the through-holes filled
with the conductive resin compound have a diameter of 50 .mu.m to 1
mm.
[0032] It is preferable that the through-holes filled with the
conductive resin compound have a pitch of 50 .mu.m or more.
[0033] It is also preferable that the through-holes filled with the
conductive resin compound have an electrical resistance of 0.05 to
5.0 m.OMEGA..
[0034] Furthermore, it is preferable that the porous base material
has a porosity of from 2 to 35%.
[0035] It is also preferable that the heating is carried out at a
temperature of from 170 to 260.degree. C.
[0036] In addition, it is preferable that the pressurization is
carried out at a pressure of from 20 to 80 kg/cm.sup.2.
[0037] According to the above-mentioned embodiment of this
invention, a connecting member of circuit substrates comprises an
organic porous base material provided with tackfree films on both
sides, wherein the connecting member of circuit substrates has
through-holes at requested places, and the through-holes are filled
with conductive resin compound up to the surface of the tackfree
films. This structure enables inner-via-hole connection, and thus,
a connecting member of circuit substrates of high reliability and
high quality can be attained. Furthermore, it is easy to determine
fine pitchs at the conductive parts, and at the same time, this
connecting member of circuit substrates is suitable for an
electrical connector of low electrical resistance. In other words,
this connecting member of circuit substrates is composed of a
porous base material having compressibility resistance which
comprises a composite material of nonwoven fabrics and
thermosetting resin, and the porous base material has holes which
are filled with conductive paste up to the surface of the tackfree
films.
[0038] According to this constitution, it is possible to
manufacture connecting members of circuit substrates stably and of
high reliability with an ability to determine fine pitchs easily.
Therefore, it is possible to form a high-layered substrate from a
double sided substrate or a four-layer substrate without
complications. In addition, the conductive resin compound is filled
up to the surface of the tackfree films so that the conductive
paste sticks out from the surface of the organic porous base
material when the tackfree films are separated. If this connecting
member is used for an electrical connector, these stick-out parts
work favorably for electrical connection because electrical
connection can take place easily through the stick-out parts.
[0039] Next, according to the embodiment of the first manufacturing
method of a multilayer circuit substrate in this invention, the
connecting member of circuit substrates is held between a
multilayer circuit substrate having at least two layers of circuit
patterns and a circuit substrate having at least one layer of
circuit pattern in which the tackfree films of the connecting
member are already separated. And then, the whole assembly is
provided with heat and pressure. The organic porous base material
used has compressibility resistance and comprises a composite
material of nonwoven fabrics and uncured thermosetting resin, and
therefore, when the porous base material is compressed by heating
and pressurization, the adhesion between the circuit substrates
occurs strongly through the the thermosetting reaction within the
above-mentioned connecting member of circuit substrates, and at the
same time, the conductive paste is also compressed in this process.
At this moment, a binder component is pressed out between the
conductive substances, thereby strengthening the binding between
the conductive substance to each other and between the conductive
substance and the metal foils. Thus, the conductive substance
contained in the conductive paste becomes dense. In addition, since
the conductive paste is filled up to the surface of the tackfree
films, the conductive paste sticks out from the surface of the
organic porous base material when the tackfree films are separated.
Accordingly, the filled amount of the conductive substance
increases after the lamination, and thus, the connection resistance
is reduced considerably.
[0040] Furthermore, by using a porous base material having
compressibility resistance, the binder component of the conductive
paste filled into the through-holes penetrates into the porous base
material side. This reduces the filled amount so that the
conductive paste does not intrude between the porous base material
and the metal foil applied on both sides any more, and accordingly,
short-circuits can be prevented from occurring between the
adjoining circuit patterns. Furthermore, by using a porous base
material having compressibility resistance and comprising the
composite material of the nonwoven fabrics and the thermosetting
resin, it is not only possible to connect the circuit substrates to
each other, but the metal foils for the wirings on the upper most
layers are also adhered strongly by heating and pressurization. It
is also favorable to the environment that the plating processing is
no longer necessary in the manufacturing process of multilayer
circuit substrates.
[0041] Subsequently, according to the embodiment of the second
manufacturing method of a multilayer circuit substrate in this
invention, the multilayer circuit substrate is positioned between
the two connecting members of circuit substrates from which the
tackfree films are already separated. After a metal foil is applied
on both sides, it is heated and pressurized, and then, the metal
foils are formed into circuit patterns. In this way, multilayer
circuit substrates are manufactured efficiently as in the case with
the first manufacturing method.
[0042] It is preferable that the organic porous base material
comprises a composite material which is composed of nonwoven
heat-resisting synthetic fiber fabrics impregnated with
thermosetting resin. Thus, the multilayer circuit substrate is
excellent in thermal and mechanical strength.
[0043] Furthermore, it is preferable that the nonwoven
heat-resisting synthetic fiber fabrics comprise aramid resin, while
the thermosetting resin is epoxy resin. Thus, the multilayer
circuit substrate is even more excellent in thermal and mechanical
strength.
[0044] It is also preferable that the nonwoven heat-resisting
synthetic fiber fabrics comprise paper, while the thermosetting
resin is selected from the group consisting of phenol resin and
epoxy resin. Accordingly, the multilayer circuit substrate is even
more excellent in thermal and mechanical strength.
[0045] Furthermore, it is preferable that the conductive substance
contained in the conductive resin compound is at least one metallic
powder selected from the group consisting of silver, nickel, copper
and an alloy thereof. As a result, the multilayer circuit substrate
is excellent in electrical conductivity.
[0046] In addition, it is preferable that the resin component
contained in the conductive resin compound is the same as the
thermosetting resin in the organic porous base material. Thus, the
conductive resin compound has excellent adhesion to the organic
porous base material.
[0047] Furthermore, it is preferable that the multilayer circuit
substrate having at least two layers of circuit patterns and the
circuit substrate having at least one layer of circuit pattern
comprise glass-epoxy multilayer circuit substrates having copper
foil wirings and copper-plated through-holes. As a result, it can
be used in combination with conventional glass-epoxy multilayer
circuit substrates.
[0048] It is preferable that the multilayer circuit substrate
having at least two layers of circuit patterns and the circuit
substrate having at least one layer of circuit pattern comprise
aramid nonwoven fabrics and multilayer circuit substrates of
thermosetting epoxy resin, thereby forming multilayer substrates
easily.
[0049] Furthermore, it is preferable that the through-holes are
formed by laser irradiation. This method is more suitable for
forming fine-pitched holes than by a drill. In addition, there is
no dust created in this process.
[0050] It is also preferable that the through-holes filled with the
conductive resin compound have a diameter of 50 .mu.m to 1 mm,
thereby forming the conductive part with a desirable diameter. An
even more preferable diameter is from 100 to 300 .mu.m.
[0051] Furthermore, it is preferable that the through-holes filled
with the conductive resin compound have a pitch (a distance between
the filled parts) of 50 .mu.m or more. As a result, the filled
parts are completely insulated from each other.
[0052] Additionally, it is preferable that the through-holes filled
with the conductive resin compound have an electrical resistance of
0.05 to 5.0 m.OMEGA.. This resistance provides good continuity for
practical use as a circuit substrate or as a connector. A more
preferable range is 0.1 to 0.8 m.OMEGA..
[0053] Furthermore, it is preferable that the porous base material
has a porosity of from 2 to 35%. This is practical since an
"anchor" effect with the conductive paste can be attained.
[0054] It is also preferable that the heating is carried out at a
temperature of from 170 to 260.degree. C . When a thermosetting
resin is used, a hardening reaction can be effectively
conducted.
[0055] In addition, it is preferable that the pressurization is
carried out at a pressure of from 20 to 80 kg/cm.sup.2. The
substrate has effective properties by substantially diminishing air
holes inside the substrate.
[0056] As described above, by using the connecting member of
circuit substrates comprising the porous base material having
compressibility resistance and consisting of a composite material
of heat-resisting organic reinforcement and uncured thermosetting
resin in which the holes are filled with the conductive paste up to
the surface of the tackfree films, it is possible to connect double
sided substrates or four-layer substrates to each other
electrically and mechanically without any problems, particularly in
manufacturing. Therefore, double sided substrates can be easily
formed into multilayer substrates having an inner via
structure.
[0057] As for the porous base material having compressibility
resistance, a composite material can be used which is composed of
organic reinforcement and uncured thermosetting resin. Therefore,
when the porous base material is compressed by heating and
pressurization, the conductive paste is also compressed in this
process. The organic binder component, pressed out between the
conductive substances, hardens and strengthens the binding between
the conductive substances and between the conductive substance and
the metal foil. Accordingly, the conductive substance within the
conductive paste becomes dense. This leads to via connection of
extremely low resistance. In addition, since the conductive paste
is filled up to the surface of the tackfree films, the conductive
paste sticks out from the surface of the organic porous base
material when the tackfree films are separated. As a result, the
filled amount of the conductive substance increases after the
lamination, and thus, the connection resistance is reduced
considerably.
[0058] In addition, by using a porous base material having
compressibility resistance, the binder component of the conductive
paste filled into the through-holes penetrates into the porous base
material side. This reduces the filled amount so that the
conductive paste does not intrude between the porous base material
and the metal foil applied on both sides. As a result,
short-circuits can be prevented from occurring between adjoining
circuit patterns. Furthermore, by using a thermosetting resin of
the porous base material having compressibility resistance and
comprising the composite material of an organic reinforcement and
thermosetting resin, it is not only possible to connect the circuit
substrates to each other, but the wirings of metal foils can be
connected electrically by heating and pressurization.
[0059] It is also favorable to the environment that plating
processing is no longer necessary in manufacturing multilayer
circuit substrates. As mentioned above, the connecting member of
circuit substrates of this invention is suitable for connecting
circuit substrates to each other. This connecting member is also
effective for connecting circuit substrates to devices electrically
and mechanically.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] FIGS. 1(a)-(c) are cross-sectional views showing a method of
manufacturing a connecting member of circuit substrates of a first
embodiment to a fourth embodiment of this invention. FIG. 1(a)
shows a step in which tackfree films are disposed on both sides of
an organic porous base material. FIG. 1(b) shows a step in which
through-holes are formed. FIG. 1(c) shows a step in which
conductive paste is filled into the through-holes.
[0061] FIGS. 2(a)-(d) are cross-sectional views showing a method of
manufacturing a multilayer circuit substrate by means of a
connecting member of circuit substrates of a fifth embodiment to a
eighth embodiment of this invention. FIG. 2(a) shows a connecting
member of circuit substrates. FIG. 2(b) shows a step in which a
copper foil is applied on both sides of uncured circuit substrate
materials. FIG. 2(c) shows a step after being heat-pressed. FIG.
2(d) shows a step after being etched.
[0062] FIG. 3 is a cross-sectional view of a multilayer circuit
substrate using a connecting member of circuit substrates of a
ninth embodiment to a twelfth embodiment of this invention.
[0063] FIG. 4 is a cross-sectional view of a multilayer circuit
substrate using a connecting member of circuit substrates of a
thirteenth embodiment to a sixteenth embodiment of this
invention.
[0064] FIG. 5(a) is a perspective view and FIG. 5(b) is a
cross-sectional view of an electrical connector using a connecting
member of circuit substrates in a seventeenth embodiment of this
invention.
[0065] FIG. 6 is a cross-sectional view showing a glass-epoxy
multilayer substrate manufactured in a conventional method.
DETAILED DESCRIPTION OF THE INVENTION
[0066] This invention will be described by referring to the
following illustrative examples and attached figures.
[0067] A connecting member of circuit substrates and a method of
manufacturing a multilayer circuit substrate by using the
connecting member will be explained in one embodiment of this
invention.
[0068] (A) Conductive paste
[0069] (a) Filler
[0070] The conductive paste of this embodiment is composed of a
metallic filler, thermosetting resin, and a hardener. First, the
conductive filler will be explained. According to the main object
of this conductive filler, it should be contained in the conductive
compound in high concentration. The reason for this is that, as
mentioned above, conductive reliability must be maintained by
raising the contact probability of the conductive fillers to each
other even if the substrates are distorted due to lower resistance
of connected via holes or due to thermal and mechanical stress. In
order to disperse the conductive fillers with high concentration,
an average particle size of the conductive filler should be
preferably from 0.2 to 20 .mu.m, and should also have as small
specific surface as possible. The average diameter can be measured
by using a microscopic method or a light scattering method. A
preferred value for the average particle size is from 0.1 to 1.5
m.sup.2/g, and more preferably, from 0.1 to 1.0 m.sup.2/g. Silver,
copper or nickel are illustrative examples of conductive fillers,
and it is also possible to use two different kinds or more of these
metals simultaneously. As long as the conductive filler has the
characteristics mentioned above, it can be a spherical shape or of
a flaked form etc. It is especially desirable to use copper powder
as the conductive filler in view of migration control, economic
supply, and price stability. But in general, copper powder is
easily oxidised, and this oxidation of copper powder can obstruct
conductivity when it is used for filling via holes in the
connecting member of circuit substrates of this invention.
Therefore, the adhesion process by heating and pressurization is
preferably conducted in an atmosphere in which the oxygen content
is 1.0% or less.
[0071] (b) Epoxy resin
[0072] Next, epoxy resin of specific characteristics will be
explained. As mentioned above, the connecting member of circuit
substrates of this invention is formed by heating and
pressurization in a closed state in order to connect the metal
foils electrically. Therefore, it is inconvenient to include a
volatile constituent such as solvent because it can lead to causing
internal blisters. In order to form the conductive compound in one
non-solvent type liquid, it is basically necessary to have a liquid
resin as the epoxy resin. For the dispersion of the above-mentioned
conductive fillers in high concentration, viscosity of the epoxy
resin must be 15 Pa.s or less. If epoxy resin with higher viscosity
than this value is used, the viscosity of the paste made from the
conductive compound will be extremely high. As a result, the via
hole filling process can not take place any more when the paste
viscosity is 2,000 Pa.s or higher.
[0073] On the other hand, the volatile constituent in this compound
should preferably be controlled to prevent the volatile constituent
from volatilizing and causing voids and blisters within the
structure of the via hole filling or to prevent the prepreg from
separating when this compound is heat-compressed after being filled
into the via holes. The volatile amount is preferably as small as
possible, but the above-noted inconveniences can be avoided when
the amount is 2.0 percent by weight or less.
[0074] Examples of suitable epoxy resins are liquid-type epoxy
resin including two or more epoxy radicals, for example, bisphenol
A-type epoxy resin, bisphenol F-type epoxy resin, alicyclic epoxy
resin, and amine epoxy resin etc. It is also possible to use
liquid-type epoxy resin processed by molecular distillation to
reduce the volatile constituent.
[0075] With regard to hardeners, any ordinary hardener can be used.
Generally used hardeners include amine hardeners, e.g.
dicyandiamide and carboxylic acid hydrazide, urea hardeners, e.g.
3-(3,4-dichlorophenyl)-1,- 1-dimethyl urea, acid anhydride
hardeners, e.g. phthalic anhydride, phromellitic acid anhydride,
and hexahydro phthalic acid anhydride, and aromatic amine
hardeners, e.g. diamide diphenylmethane, diamide diphenylsulfonic
acid (amine adduct). It is preferable to use solid-type subclinical
hardener powder, particularly in view of stability and
workability.
[0076] (B) Tackfree film
[0077] Tackfree films in the connecting member of circuit
substrates function as pollution control films during the processes
of forming holes and filling the conductive paste, but also during
transportation. The films are separated when circuit substrates are
connected, and therefore, they must have enough adhesion strength
until they are used, while they are to be separated easily in
use.
[0078] Furthermore, the tackfree films are preferably to be adhered
in a heated environment at a temperature that the thermosetting
resin of the porous base material does not begin to cure. At the
same time, the films are preferably of
non-heat-contraction-type.
[0079] A plastic sheet of about 10 .mu.m in thickness which is
applied with a Si-type lubricant on one side was used in this
example. For example, polyethylene terephthalate (hereinafter
abbreviated as PET sheet) and PP can be used here.
[0080] (C) Prepreg
[0081] The base material used in the connecting member of circuit
substrates of this embodiment is at least an organic porous base
material. However, if this base material is combined with another
base material to form a multilayer substrate, a well-known
laminated base material can be used. Generally, a laminated base
material used for circuit substrates is a composite material of
inorganic or organic reinforcement and thermosetting resin. The
reinforcement has the functions of strengthening the circuit
substrate itself and controlling the warp caused by the heat when
parts are mounted on the substrate.
[0082] Examples of inorganic reinforcement are glass woven fabrics
containing woven glass fibers and nonwoven fabrics consisting of
glass fibers cut to a length of several mm to several 10 mm. The
glass cloth is made by weaving filaments of 5 to 15 .mu.m in
diameter as warps and twines (yarn) bonding several hundreds pieces
as wefts together. The glass which is generally used for printed
substrates is composed mainly of SiO.sub.2. CaO, Al.sub.2O.sub.3,
and B.sub.2O.sub.3 which are called E-glass. The glass nonwoven
fabrics are mainly glass nonwoven paper which is produced by
cutting the above-noted glass fibers into paper and adhering them
together with water dispersible epoxy resin. Occasionally, an
inorganic filler is added for the purpose of improving the
dimensional stability.
[0083] On the other hand, examples of organic reinforcement are
woven or nonwoven fabrics (e.g. commodity name "THERMOUNT"
manufactured by E. I. Dupont) made of paper or aromatic polyamide
fibers (e.g. commodity name "KEVLAR" manufactured by E. I. Dupont).
THERMOUNT (Trademark) used here is produced by first cutting the
above-noted KEVLAR fabrics of para-type aramid at a length of about
6.7 mm, adding about 10 to 15% by weight of filmed meta-type aramid
to form paper, and calendering under high temperature and high
pressure after being dried (e.g. U.S. Pat. No. 4,729,921).
[0084] Substrates using aramid are attracting attention for their
use in MCM because of the excellent heat resistance and small
coefficient of thermal expansion (e.g. IEEE TRANSACTIONS OF
COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, VOL. 13, NO. 3,
SEPTEMBER 1990, PP.570-PP.575).
[0085] A prepreg is a composite material consisting of
reinforcement and uncured resin in which the above-described
reinforcement is impregnated with thermosetting resin from which
the solvent is removed. Usually, they are in the form of a glass
epoxy prepreg or an aramid epoxy prepreg in which the former
prepreg consists of glass woven fabrics and epoxy resin and the
latter consists of aramid reinforcement and epoxy resin. The
expression "prepreg" is used for expressing the step up to the
point where resin cures through heating and pressurization when
double sided substrates and multilayer substrates are
manufactured.
[0086] (D) Thermosetting resin
[0087] Thermosetting resin is an insoluble and infusible
macromolecule having a three-dimensional knitting structure of
molecules which melt, undergo propagation reaction and crosslinking
reaction by heat. A thermosetting resin for printed substrates is
selected in view of heat resistance and solvent resistance.
Examples include epoxy, phenol, melamine, and polyester. By adding
a sub-material, such as a hardener, a modifier or a filler,
thermosetting resins of various reaction temperatures can be
obtained.
[0088] The most generally applied resin is epoxy resin. Epoxy resin
is most widely used among different kinds of thermosetting resins
and is characterized by excellent mechanical, electrical, and
chemical properties. Recently, ordinary epoxy resin is modified in
various ways to meet the needs toward higher mounting density and
higher heat resistance.
[0089] There is also novolak epoxy resin in which novolak-type
phenol is used for the purpose of enhancing heat resistance. In
some cases, a flame retarder is added to attain not only heat
resistance, but also flame resistance.
[0090] (E) Copper foil
[0091] A conductor used for metal foil in this example is copper in
the form of foil. Thicknesses of 18 to 70 microns are used widely
as the copper foils, and they are usually electrolytic copper
foils. Copper foil suitable for use in the connecting member of
circuit substrates in this invention is placed such that the
treated copper foil side is generally used for the electrical
connecting surface in view of via connection through the conductive
paste. The reason for this is that the treated degree is important
with respect to reliability of connection. In other words, the
rougher the surface is treated, the better results can be attained
in the connection resistance, electrical strength and
reliability.
[0092] When a multilayer substrate is manufactured by using a
connecting member of circuit substrates of this invention, a copper
foil which is treated by oxiding treatment can not be used for
electrical connecting parts of circuit substrates to be connected.
This is due to the fact that the oxide treated side forms a oxide
copper layer which is insulated electrically. Therefore, no
connection can be achieved. It is preferable that the surface part
of copper foil on the substrates to be connected is treated copper
foil as mentioned above.
[0093] The following embodiments are evaluated by methods shown
below.
[0094] (1) Via connection resistance
[0095] The evaluation method of via connection resistance in a
circuit substrate manufactured by the connecting member of circuit
substrates of this invention is to measure two different
resistances, namely, to measure connection resistance per each via
and to measure connection resistance when 500 via connections are
chained in line for wirings.
[0096] The connection resistance per each via is measured by a
four-terminal resistance measurement conducted at both ends of
metal wirings of both via ends. The serial resistance of 500 pieces
can be evaluated in a method which is mainly used for reliability
tests. This method is conducted by first adding the resistance for
500 pieces and the resistance of metallic wirings by the
above-noted four-terminal measurement method, and then, subtracting
the initial resistance amount from the measured amount after the
experiment. In other words, this method determines the amount of
change in via resistance of 500 pieces.
[0097] (2) Various kinds of reliability test in via connection
[0098] {circle over (1)}Heat cycle test
[0099] A heat cycle test is based on the amount of change in via
connection resistance after 30 minutes at -55.degree. C. in vapor
phase, and then, after 30 minutes at +125.degree. C. a thousand
times. The evaluation standard is that the amount of change in via
serial substrate of 500 pieces is 250 m.OMEGA. or less. This is
equivalent to a change in 0.5 m.OMEGA. or less per each via.
[0100] {circle over (2)}Solder dipping test
[0101] A solder dipping test is conducted by first dipping for 10
seconds in a solder vessel heated and dissolved at 230.degree. C.,
and then measuring the amount of change in via connection
resistance in the same manner as mentioned above. The evaluation
standard is the same as above.
[0102] {circle over (3)}Oil-dipping test
[0103] An oil-dipping test is a heat cycle test conducted in the
oil part of a liquid phase. A sample substrate is dipped 10 seconds
in the oil which is heated up to 260.degree. C., maintained 10
seconds at room temperature, and further dipped 10 seconds in the
oil at 20.degree. C. The evaluation takes place after this heat
cycle is repeated 200 times. At this time, it is measured whether
the resistance shows no breakage during 200 times when it is dipped
in the higher and lower temperature sides. At the same time, the
amount of change in resistance is measured and evaluated according
to the same evaluation standard mentioned above.
[0104] Embodiments will be specifically described in the following
illustrative examples.
Examples 1 to 4
[0105] A connecting member of circuit substrates and a method of
manufacturing a multilayer circuit substrate by using the
connecting member of circuit substrates will be explained by
referring to the attached figures in one embodiment of this
invention.
[0106] In the first place, prepregs used for the connecting member
of circuit substrates are shown in Prepreg 1 to 4.
[0107] (1) Prepreg 1
[0108] Glass woven fabrics as inorganic reinforcement were used in
which E-glass of 4.6 micron in filament diameter was twined 4.4
pieces per one inch. As thermosetting resin, epoxy resin with high
glass transition point was used which was in this case Shell EPON
1151B60 of 180.degree. C. in the glass transition point. This resin
was impregnated by using methylethylketone (MEK) as a deluent
solvent. This prepreg line could be dried for both resin
impregnation and solvent removal consecutively. The amount of resin
after being dried was about 30 wt % against the glass cloth. The
thickness of the prepreg after being dried was 120 .mu.m.
[0109] (2) Prepreg 2
[0110] Glass nonwoven fabrics were also used as inorganic
reinforcement, and the impregnated resin was the same with in
Prepreg 1. The glass unwoven fabrics used were made into glass
nonwoven paper by cutting the above-mentioned glass fabrics to
paper and by adhering them together with water dispersible epoxy
resin. An inorganic filler of alumina powder was added to improve
the dimensional stability. The amount of impregnated resin was
about 40 wt % against the glass woven fabrics, and the thickness of
the prepreg was 140 .mu.m.
[0111] (3) Prepreg 3
[0112] Nonwoven fabric paper of aromatic polyamid was used as an
organic reinforcement which was in this case "THERMOUNT"
manufactured by E. I. Dupont of 72 g/m.sup.2 in basis weight and
0.5 g/cc in paper density. The impregnated resin was epoxy resin of
Dow DER 532A80, and the glass transition point was 140.degree. C.
The resin impregnation and the drying process took place in the
same method as in Prepreg 1. The amount of impregnated resin was 52
wt %, and the thickness of the prepreg was 150 .mu.m.
[0113] (4) Prepreg 4
[0114] Paper as an organic reinforcement was also used here which
was in this case paper phenol prepreg. The paper used was kraft
paper of 70 g/m.sup.2 in basis weight. Thermosetting resin was
modified resin added with alkyl phenol group. The amount of resin
was 48 wt % against the kraft paper, and the thickness of the
prepreg was 145 .mu.m.
[0115] (5) Conductive paste
[0116] Composition of the conductive paste of this invention is
shown in TABLE 1. Metallic fillers of silver, copper and nickel
were used in a spherical and flake form. The resin compound was
bisphenol A-type epoxy resin (EPICOAT 828 manufactured by Yuka
Shell Epoxy Co., Ltd.), and the harder used was Amineadduct (MY-24
manufactured by Ajinomoto Co., Ltd.).
[0117] Three roles of the above-described compound were kneaded and
mixed into paste. TABLE 1 shows the form of the metal particle, the
average size of the particle, the mixed amount (% by weight), and
the viscosity of the paste of 0.5 rpm in an E-type viscometer at
room temperature.
1 TABLE 1 Metal Resin Compound Par- Amount Amount Amount ticle of
of of Vis- Paste size metal resin hardener cosity No. Metal Form
(.mu.m) (wt %) (wt %) (wt %) (Pa .multidot. s) P-1 Cu spherical 2
85 12 3 120 P-2 Cu spherical 2 87.5 10 2.5 340 P-3 Ni spherical 1.2
85 12 3 300 P-4 Ni spherical 1.2 87.5 10 2.5 550 P-5 Ag flake 1.8
85 12 3 220 P-6 Ag flake 1.8 87.5 10 2.5 475
[0118] FIGS. 1(a) to (c) are cross-sectional views showing a method
of manufacturing a connecting member of circuit substrates in the
embodiment of this invention by using the above-mentioned Prepregs
1 to 4. As shown in FIG. 1(a), a porous base material 102 (Prepreg
3) was prepared which was provided with tackfree films 101
(thickness of about 12 .mu.m) made of polyester on both sides. The
method of applying the tackfree films is to position the above
prepreg between the tackfree films, and to position it further
between stainless steel plates. After that, it is heated four
minutes at a temperature of 110.degree. C. and pressurized with 20
Kg/cm.sup.2. At this moment, the prepreg is compressed by the
heating and pressurization so that internal pores 102a
decrease.
[0119] Accordingly, an aramid-epoxy sheet having tackfree films is
obtained. Next, through-holes 103 (diameter of about 250 .mu.m)
were formed into aramid-epoxy sheet 102 (thickness of about 130
.mu.g m) at predetermined places by a carbon dioxide laser, as
shown in FIG. 1(b). Subsequently, as shown in FIG. 1(c), conductive
paste 104 is filled into through-holes 103 to form the connecting
member of circuit substrates of this invention. Regarding the
filling method of conductive paste 104, aramid-epoxy sheet 102
having through-holes 103 was placed on a table of a printing
machine (not shown), and conductive paste 104 was printed directly
from above on tackfree films 101. Tackfree film 101 on the upper
surface serves as a printing mask and also prevents the surface of
aramid-epoxy sheet 102 from soiling.
Examples 5 to 8
[0120] A method of manufacturing a double sided printed circuit
substrate by using the connecting members of circuit substrates
will be explained which are manufactured according to Examples 1 to
4.
[0121] FIG. 2(a) shows the above-noted connecting member of circuit
substrates. Tackfree films 101 were separated from both sides of
the connecting member of circuit substrates. Besides, three sheets
of uncured substrate material filled with the conductive paste at
the same places were prepared and laminated by positioning them by
means of a basic pin (not shown).
[0122] As shown in FIG. 2(b), the uncured circuit substrate
materials were laminated, and further, copper foil 105 of 35 .mu.m
in thickness each having one treated side which faces inside was
applied. By heating and pressurization about one hour at a
temperature of 170.degree. C. with 40 Kg/cm.sup.2 in vacuum by
heat-pressing, the substrates were cured and adhered to the copper
foils. Reference numeral 107 shows conductive resin compount after
being cured. FIG. 2(c) shows a state after being laminated. After
that, circuit patterns 106 on the upper most layer were formed by
means of a photolithography method. This process can be more
precisely described as follows. Dry films were applied on both
sides of the above-mentioned laminated substrate by a heat roll,
and patterns were exposed through ultraviolet in order to harden
only the parts where the copper foil is to remain. Thereafter,
uncured parts were eliminated in a developing process, and then,
the foils were etched in a copper chloride solution. Further,
excessive dry films were seperated, and circuit patterns were
formed in a usual method. FIG. 2(d) is a completed view of the
double sided circuit substrate of this embodiment. Evaluation
results of the double sided circuit substrate manufactured in this
manner are shown in TABLE 2.
2 TABLE 2 Via connection reliability (.DELTA.R m.OMEGA./500 via)
Heat Solder Oil- cycle dipping dipping Pre- Conductive Via after
after after Example preg paste resistance 1000 10 200 No. No. No.
m.OMEGA./via cycles seconds cycles 5a 1 P-1 12.8 22 45 155 5b 1 P-2
6.1 15 23 87 5c 1 P-3 35.9 -103 -55 11 5d 1 P-4 17.5 -45 -15 57 5e
1 P-5 12.3 155 187 205 5f 1 P-6 14.3 88 122 117 6a 1 P-1 10.8 33 35
53 6b 1 P-2 7.2 25 18 53 6c 1 P-3 25.3 3 -21 -21 6d 1 P-4 18.2 -5
-19 33 6e 1 P-5 9.1 198 215 198 6f 1 P-6 4.3 76 113 112 7a 1 P-1
1.8 56 24 76 7b 1 P-2 1.2 37 13 34 7c 1 P-3 15.3 -99 -12 89 7d 1
P-4 7.2 -76 -11 122 7e 1 P-5 2.1 19 112 198 7f 1 P-6 1.3 22 62 109
8a 1 P-1 3.8 78 47 97 8b 1 P-2 2.9 7 63 23 8c 1 P-3 31.3 -203 22 11
8d 1 P-4 22.1 -134 5 98 8e 1 P-5 15.1 285 85 101 8f 1 P-6 9.6 118
45 61
[0123] Each connection resistance of the through-holes in the
double sided substrates showed an extremely low amount of about 1.2
m.OMEGA. to 35.9 m.OMEGA. per each through-hole. Furthermore, as a
result of several reliability tests conducted to the double sided
circuit substrates, the rates of resistance change were 250
m.OMEGA. or less in both oil-dipping and solder dipping tests
(230.degree. C., 10 seconds), and there was no breakage in the
oil-dipping test. Therefore, results can be valued as satisfactory
in all cases.
Examples 9 to 12
[0124] Next is a description of a method of manufacturing a
multilayer circuit substrate by using the connecting member of
circuit substrates of this invention. Circuit substrates to be
combined were two pairs of double sided board comprising
glass-epoxy substrate. This glass-epoxy double sided boards were
produced from glass woven fabrics laminated with four sheets of
prepreg (thickness of about 100 .mu.m) which is impregnated with
thermosetting resin equivalent to FR-4, as in the above-mentioned
case. Then, a copper foil which was treated on both sides was
laminated with a thickness of 35 .mu.m on both sides of the
substrates. By heating and pressurizing about one hour at a
temperature of 170.degree. C. and with 40 Kg/cm.sup.2 in vacuum by
heat-pressing, the substrates were cured and adhered to the copper
foils. The substrates manufactured in this manner were disposed
with holes of 0.6 mm in diameter at predetermined places by using a
drill machine, and the substrates were further processed by a
copper-plating method to form copper-plated films on the inner wall
of the through-holes and on the entire upper surface. After that,
circuit patterns were formed by means of a photolithography method
to form wirings on the upper layers. The glass epoxy double sided
board manufactured in this way and another glass epoxy double sided
board with different patterns manufactured in the same way were
used to position the connecting member of circuit substrates of the
above-mentioned first to the fourth embodiments from which the
tackfree films had been separated on both sides. They were
positioned for lamination and subjected to heat and pressurization
by heat-pressing under the same conditions as mentioned above. FIG.
3 shows a cross-sectional view of this embodiment before being
laminated. Referring to FIG. 3, reference numeral 305 is a
glass-epoxy substrate; 307, drilled holes; 308, a copper-plated
inner wall; and 306, circuit patterns of copper. Connecting member
of circuit substrates 309 is placed between the above-mentioned
double sided boards.
[0125] In this structure, the above-noted double sided boards have
a connecting land at places to be connected electrically, and the
land part is positioned to meet conductive paste 304 of the
connecting member of circuit substrates mentioned above. It is
therefore necessary to be arranged in such a way that the drilled
through-hole parts do not come in contact with the conductive paste
part of the above-mentioned connecting member of circuit
substrates. The multilayer member manufactured in this manner is a
four-layer substrate having four layers of circuit patterns in
which the epoxy resin of the above-mentioned connecting member of
circuit substrates flowed into the through- hole parts of the
above-noted double sided board, thereby forming a complete closed
structure. This four-layer substrate was tested and the results of
different reliability tests are shown in TABLE 3.
3 TABLE 3 Via connection reliability (.DELTA.R m.OMEGA./500 via)
Circuit Heat Solder Oil- connect- Conduc- Via cycle dipping dipping
ing tive resis- after after after Example member paste tance 1000
10 200 No. No. No. m.OMEGA./via cycles seconds cycles 9 5b P-2 0.51
16 21 89 10 6b P-2 0.45 9 14 55 11 7b P-2 0.44 -3 5 33 12 8b P-2
0.45 -15 2 71
[0126] As shown in TABLE 3, the results of the heat cycle test,
solder dipping test, and oil-dipping test indicated satisfactory in
all cases.
[0127] In this manufacturing method of multilayer substrates, the
aramid-epoxy double sided substrate (Example 7) manufactured by the
connecting member of circuit substrates was also used instead of
the glass-epoxy double sided circuit substrate held between the
above-mentioned connecting members of circuit substrates with the
same satisfactory properties being achieved
Examples 13 to 16
[0128] The connecting member of circuit substrates will be
explained in this embodiment of the invention. The same connecting
member of circuit substrates was used as in the first embodiment to
the fourth embodiment.
[0129] FIG. 4 is a cross-sectional view of a multilayer circuit
substrate before being laminated in one embodiment of this
invention, and the description follows by referring to the figure.
A circuit substrate to be combined was a four-layer substrate
consisting of a glass-epoxy substrate. This four-layer substrate
was manufactured from glass woven fabrics laminated with four
sheets of the prepreg (thickness of about 100 .mu.m) impregnated
with thermosetting resin as in the case mentioned above. Then, a
copper foil which was treated on one side was applied with a
thickness of 35 .mu.m on both sides of the substrates. By heating
and pressurizing about one hour at the temperature of 170.degree.
C. and 40 Kg/cm.sup.2 in vacuum by heat-pressing, the substrate was
cured and adhered to the copper foils. After the copper foils were
adhered, a photolithography method was used to form circuit
patterns. In particular, dry films were applied on both sides by
using a laminater, and then patterns were exposed. After that, the
processes of development, etching and separation of the dry films
followed. Subsequently, the copper foil surface of the substrate
with the above patterns was treated, and further, two sheets of the
above-noted prepreg were disposed on both sides. The treated
surface of the one-side treated copper foil was placed on both
sides such that the treated surfaces face inside, and they were
laminated once more by heat-pressing. This substrate was disposed
with holes of 0.6 mm in diameter at requested places by using a
drill machine.
[0130] Then, copper-plating was applied on the inner wall of the
through-holes and the entire upper layer part to form copper-plated
films. After that, circuit patterns were formed on the upper layer
by means of a photolithography method. The four-layer glass epoxy
substrate manufactured in this manner was placed as an intermediate
layer between the connecting members of circuit substrates from
which the tackfree films had been separated on both sides. As shown
in FIG. 4, they were positioned for the lamination together with
the one-side treated copper foils and were subjected to heating and
pressurization by heat-pressing under the same conditions as
mentioned above. The copper foils on the surface of this multilayer
substrate were formed into patterns by the same photolithographic
method. Referring to FIG. 4, reference numeral 410 denoted the
above-mentioned four-layer glass-epoxy substrate; 411, drilled
holes; 412, a copper-plated inner wall; and 413, circuit patterns
of copper formed by the photolithographic method. The above-noted
four-layer glass-epoxy substrate was held between connecting
members of circuit substrates 414 and 415, which are again held
between one-side treated copper foils 416 and 417.
[0131] In this structure, the above-noted four-layer substrate and
the connecting members of circuit substrates have connecting land
419 at places to be connected electrically and conductive paste
part 418. The above-mentioned land part was positioned to meet
conductive paste 418 of the connecting members of circuit
substrates mentioned above. It is therefore necessary to position
in such a way that the drilled through-hole parts do not come in
contact with the conductive paste part of the above-mentioned
connecting members of circuit substrates. A multilayer member
manufactured in this manner is a six-layer substrate having six
layers of wirings in which the above-mentioned connecting members
of circuit substrates are filled with the epoxy resin flowed into
the through-hole parts of the above-noted double sided board,
thereby forming a complete closed structure. This multilayer
substrate was tested and the results of different reliability tests
are shown in TABLE 4.
4 TABLE 4 Via connection reliability (.DELTA.R m.OMEGA./500 via)
Circuit Heat Solder Oil- connect- Conduc- Via cycle dipping dipping
ing tive resis- after after after Example member paste tance 1000
10 200 No. No. No. m.OMEGA./via cycles seconds cycles 13 5b P-2
1.21 45 38 101 14 6b P-2 2.22 27 29 79 15 7b P-2 1.78 19 39 83 16
8b P-2 1.15 41 52 72
[0132] As shown in TABLE 4, the results of the heat cycle test,
solder dipping test, and oil-dipping test were satisfactory in all
cases.
[0133] Furthermore, it is possible to manufacture a multilayer
circuit substrate with even more layers by repeating the above
process for a needed number of times. Another method of obtaining a
substrate with multilayer circuit patterns is to prepare a
desirable number of the above-mentioned intermediate multilayer
member and the connecting member of circuit substrates and to
laminating them at once.
[0134] In this manufacturing method of multilayer substrates, the
aramid-epoxy double sided substrate (Example 7) manufactured by the
above-noted connecting member of circuit substrates was used
instead of the four-layer glass-epoxy circuit substrate held
between the connecting members of circuit substrates with the same
satisfactory properties being shown.
[0135] In the method of manufacturing multilayer circuit substrates
as described above, the circuit substrates and the connecting
members of circuit substrates used had been already checked so that
a high processing yield could be preserved at a controlled cost
increase.
[0136] In the multilayer circuit substrates manufactured according
to the method mentioned above, the first circuit substrate and the
second circuit substrate are connected to each other through the
compressibility of the connecting members of circuit substrates by
heating and pressurization. As a result, a highly laminated
substrate can be manufactured rather easily.
Example 17
[0137] The porous base material of about 150 to 170 .mu.m in
thickness which was used in the first embodiment was applied on
both sides with fluorocarbon tackfree films
(tetrafluoroethylene-ethylene copolymer manufactured by Asahi
Garasu Co., Ltd., commodity name: Aflex) of about 30 .mu.m in
thickness. Next, an excimer laser was used to form through-holes of
about 200 .mu.m in diameter. The distance (pitch) between the holes
was set at about 200 .mu.m. Subsequently, conductive paste was
filled into the through-holes. Regarding the filling method of the
conductive paste, an aramid-epoxy sheet having through-holes was
placed on a table of a printing machine (not shown), and the
conductive paste 104 was printed directly from above on tackfree
films 1. At this moment, the tackfree film on the upper surface
serves as a printing mask and also prevents the surface of the
aramid-epoxy sheet from soiling. The conductive paste used was
silver powder with an average diameter of 2 .mu.m as conductive
filler, and the resin was the same thermosetting epoxy resin
(non-solvent type) as in the above-noted substrate material. A
hardener was obtained by kneading and mixing three roles of acid
anhydride-type hardener each having 85, 12.5, and 2.5 by weight
sufficiently. After that, the substrate was subjected to heat and
pressure for one hour at a temperature of 170.degree. C. and
pressure of 40 kg/cm.sup.2 in vacuum. Then, the tackfree films were
separated, thereby obtaining an electrical connector of about 100
.mu.m in thickness. FIGS. 5(a) and (b) are examples of electrical
connectors obtained in the manner mentioned above. FIG. 5(a) is a
perspective view of an electrical connector, and FIG. 5(b) is a
cross-sectional view of the same. Referring to FIGS. 5(a) and (b),
reference numeral 102 denotes an organic porous base material
(aramid epoxy sheet); and 104, conductive resin compound part. This
electrical connector can conduct electricity only in the vertical
direction, not in the horizontal direction. Furthermore, conductive
resin compound 104 is formed with a pitch of three roles per 1 mm.
Conductive resin compound 104 sticks out about 30 .mu.m which makes
it suitable for connecting NESA glass of liquid-crystal elements
and a flexible printed substrate (FPC). Additionally, when an
adhesive is applied on surface A and surface B, it can easily stick
to other circuit substrates.
[0138] The connecting member of circuit substrates of the
above-mentioned embodiment can be used, for example, as an
electrical connector for connecting NESA glass of liquid-crystal
elements and a flexible printed substrate (FPC) or as an electrical
connector for connecting a driver circuit of electrical signal
conductor in a movable telephone and a FPC.
[0139] According to the embodiments of this invention as described
above, by using the connecting member of circuit substrates
comprising the porous base material having compressibility
resistance and consisting of a composite material of nonwoven
fabrics and thermosetting resin which are also provided with
tackfree films and holes filled with the conductive paste up to the
surface of the tackfree films, it is possible to form a
high-layered substrate easily from double sided boards or
four-layer substrates which can be manufactured rather stably. When
the connecting member of circuit substrates of the embodiments is
used, the porous base material is compressed by heating and
pressurization so that the conductive paste is also compressed.
During this process, a binder component which is pressed out
between the conductive substances strengthens the binding between
the conductive substance to each other and between the conductive
substance and the metal foil, and accordingly, the conductive
substance contained in the conductive paste becomes dense. In
addition to that, since the conductive paste is filled up to the
surface of the tackfree films, the conductive paste sticks out from
the surface of the organic porous base material when the tackfree
films are separated. As a result, the filled amount of the
conductive substance increases after the lamination, and thus, the
connection resistance is reduced considerably.
[0140] Furthermore, by using the porous base material having
compressibility resistance and comprising a composite material of
nonwoven fabrics and thermosetting resin, it is not only possible
to connect the circuit substrates to each other, but the metal foil
for wirings on the upper most layer can be also adhered strongly by
heating and pressurization. It is also favorable to the environment
that a drilling process or a plating process is not necessary any
more in the manufacturing process of multilayer circuit
substrates.
[0141] According to the above-mentioned invention, the connecting
member of circuit substrates comprises an organic porous base
material provided with tackfree films on both sides, wherein the
connecting member for circuit substrates has through-holes at
requested places, and the through-holes are filled with conductive
resin compound up to the surface of the tackfree films. This
structure enables inner-via-hole connection and can therefore
attain the connecting member of circuit substrates of high
reliability and high quality. Additionally, it is easy to determine
fine pitchs at the conductive parts, and an electrical connector of
low electrical resistance can be attained.
[0142] The invention may be embodied in other forms without
departing from the spirit or essential characteristics thereof. The
embodiments disclosed in this application are to be considered in
all respects as illustrative and not restrictive, the scope of the
invention is indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalency of the claims are intended to be
embraced therein.
* * * * *