U.S. patent application number 09/835080 was filed with the patent office on 2002-07-04 for laminate for electronic circuit.
Invention is credited to Sakayori, Katsuya.
Application Number | 20020086171 09/835080 |
Document ID | / |
Family ID | 18630395 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020086171 |
Kind Code |
A1 |
Sakayori, Katsuya |
July 4, 2002 |
Laminate for electronic circuit
Abstract
The present invention is directed to a laminate having a layer
construction of metal-insulating layer-metal or a layer
construction of metal-insulating layer, which laminate meets
conditions for developing large adhesive strength between the
insulating layer and the metal, as well as to an insulating film
and an electronic circuit using the laminate. The laminate has a
layer construction of first metal layer/insulating layer/second
metal layer or a layer construction of metal layer/insulating
layer. The insulating layer 1 has a multilayer structure of two or
more layers. The layers on the side of the adhesive interface with
each metal layer (a copper foil 3 and an SUS foil 4), out of the
layers constituting the insulating layer 1, each are a
thermoplastic resin layer 2. The minimum value of the storage
modulus at a temperature at or above Tg of the thermoplastic resin
layer 2 is not more than 10.sup.6 Pa.
Inventors: |
Sakayori, Katsuya;
(Tokyo-to, JP) |
Correspondence
Address: |
PARKHURST & WENDEL, L.L.P.
Suite 210
1421 Prince Street
Alexandria
VA
22314-2805
US
|
Family ID: |
18630395 |
Appl. No.: |
09/835080 |
Filed: |
April 16, 2001 |
Current U.S.
Class: |
428/458 |
Current CPC
Class: |
B32B 2311/30 20130101;
H05K 3/386 20130101; H05K 1/036 20130101; Y10T 156/1092 20150115;
B32B 15/08 20130101; B32B 2250/40 20130101; B32B 2309/02 20130101;
B32B 37/10 20130101; H05K 2201/0355 20130101; Y10T 428/31721
20150401; H05K 2201/0129 20130101; Y10T 428/31681 20150401; H05K
2201/0154 20130101; B32B 2311/12 20130101; Y10T 428/24355
20150115 |
Class at
Publication: |
428/458 |
International
Class: |
B32B 015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2000 |
JP |
2000-119418 |
Claims
What is claimed is:
1. A laminate comprising a combination of a metal layer with an
insulating layer, said laminate having a layer construction of
first metal layer/insulating layer/second metal layer or a layer
construction of metal layer/insulating layer, wherein said
insulating layer has a multilayer structure of two or more layers,
the layer on the side of the adhesive interface with the metal
layer, out of the layers constituting the insulating layer, is a
thermoplastic resin layer, and the minimum value of the storage
modulus at a temperature at or above Tg of the thermoplastic resin
layer is not more than 10.sup.6 Pa.
2. The laminate according to claim 1, wherein at least one layer
constituting the insulating layer is formed of a polyimide resin or
is a polyimide film.
3. The laminate according to claim 1, wherein all the layers
constituting the insulating layer each are formed of a polyimide
resin or are a polyimide film.
4. The laminate according to claim 1, wherein the metal layers each
are formed of a material selected from the group consisting of
copper alloy, copper, and stainless steel and the material
constituting the first metal layer is the same as or different from
the material constituting the second metal layer.
5. An electronic circuit produced by using the laminate according
to any one of claims 1 to 4.
6. An insulating film comprising: a resin film or a resin layer as
an insulating layer; and, provided on both sides or one side of the
insulating layer, a thermoplastic resin layer having a minimum
value of the storage modulus of not more than 10.sup.6 Pa at a
temperature at or above Tg of the thermoplastic resin layer.
7. The insulating film according to claim 6, wherein at least one
layer constituting the insulating layer is a polyimide film or is
formed of a polyimide resin.
8. The insulating film according to claim 6, wherein all the layers
constituting the insulating layer each are a polyimide film or are
formed of a polyimide resin.
9. A laminate comprising a metal and an insulating film, said
laminate being produced by using the insulating film according to
claim 6.
10. An electronic circuit produced by using the laminate according
to claim 9.
11. A process for producing a laminate, comprising the step of
thermocompression bonding a core insulating layer, a thermoplastic
resin layer, which is disposed on both sides or one side (z-plane)
of the core insulating layer, has an adhesive property and has a
minimum value of the storage modulus of not more than 10.sup.6 Pa
at a temperature at or above Tg of the thermoplastic resin layer,
and a metal layer disposed on the surface of the thermoplastic
resin layer to one another at a temperature of Tg or above.
12. The process for producing the laminate according to claim 11,
wherein the thermocompression bonding is carried out under
temperature conditions such that the storage modulus of the
thermoplastic resin is minimum.
Description
TECHNICAL FIELD
[0001] The present invention relates to a laminate having a layer
construction of metal-insulating layer-metal and/or a layer
construction of metal-insulating layer, and a film consisting of
only an insulating layer having a multilayer structure of two or
more layers, and a substrate for use mainly in the formation of a
circuit on an electronic component, particularly on an insulating
layer, by taking advantage of the insulating properties of the
laminate.
BACKGROUND ART
[0002] In recent years, rapid development of semiconductor
technology has led to rapid progress of a reduction in size of
semiconductor packages, the adoption of multipin, the adoption of
fine pitch, minimization of electronic components and the like.
That is, the semiconductor field has entered the so-called "age of
high density packaging." Regarding printed wiring boards, this has
also led to a change from single side wiring to double side wiring
and, in addition, the adoption of a multilayer structure and a
thickness reduction (Iwata and Harazono, "Denshi Zairyo (Electronic
Material)," 35 (10), 53 (1996)).
[0003] Pattern formation methods used in the formation of such
wiring and circuits include: a method which comprises the steps of:
etching a metal, provided on a substrate having a layer
construction of metal-insulating layer-metal, with an acidic
solution, such as a ferric chloride solution, to form wirings, then
subjecting the insulating layer, for example, to plasma etching,
wet etching, or laser etching, to remove the insulating layer to
form a desired shape, and connecting the wirings to each other, for
example, through plating or electrically conductive paste; and a
method (Proceedings of the 7th Symposium of Japan Institute of
Electronics Packaging) which comprises the steps of: providing an
insulating layer in a desired form using a photosensitive polyimide
(Japanese Patent Laid-Open No. 168441/1992) or the like; and then
plating gaps to form wiring.
[0004] A tendency toward downsizing of electric products in recent
years has led to a reduction in thickness of each layer
constituting metal conductor layer-polymeric insulating layer, and
these layers each are in many cases used in a thickness of not more
than 100 Am. When wiring has been formed of such thin layer, a
warpage disadvantageously takes place in wiring due to a difference
in coefficient of thermal expansion between the metal conductor
layer and the polymeric insulating layer. Further, in the case of
metal conductor layer-polymeric insulating layer-metal conductor
layer, the formation of a circuit formation pattern or the like
renders the area of the upper metal conductor layer different from
the area of the lower metal conductor layer, and, in this case,
here again a warpage takes place in wiring.
[0005] When the thermal properties of the insulating layer and the
conductor layer are known, the warpage of this substrate can be
calculated according to the following equation (Miyaaki and Miki,
NITTO TECHNICAL REPORT, 35 (3), 1 (1997)). 1 = 31 E 1 E 2 2 h ( E 1
2 + 14 E 1 E 2 2 ) T
[0006] wherein
[0007] E1: modulus of the metal,
[0008] E2: modulus of the insulating layer,
[0009] .DELTA..alpha.: difference in coefficient of thermal
expansion between the metal and the insulating layer,
[0010] .DELTA.T: temperature difference, and
[0011] h: layer thickness 1: wiring length.
[0012] According to this equation, the following two methods are
considered effective for reducing the warpage of wiring:
[0013] 1. a reduction in modulus of insulating layer; and
[0014] 2. a reduction in the difference in coefficient of thermal
expansion between the insulating layer and the metal wiring
layer.
[0015] Regarding the wiring formation method, in the substrate used
in the method for the formation of wiring through etching of a
metal in the laminate having layer construction of metal-insulating
layer-metal or a layer construction of metal-insulating layer, in
order to reduce the warpage of the substrate, a low-expansion
polyimide is used as the insulating layer from the viewpoint of the
necessity of rendering the coefficient of thermal expansion of the
metal identical to the coefficient of thermal expansion of the
insulating layer (U.S. Pat. No. 4,543, 295, Japanese Patent
Laid-Open Nos. 18426/1980 and 25267/1977). Since, however, the
low-expansion polyimide is not generally thermoplastic, the
adhesion to metals is poor making it difficult to provide adhesive
strength high enough to withstand practical use. To overcome this
problem, a thermoplastic polyimide resin or epoxy resin having good
adhesion to the metal is used as an adhesive layer between the
metal and the low-expansion polyimide.
[0016] At the present time, rapid expansion of production of
personal computers has lead to increased production of hard disks
incorporated in the personal computers. A component, in the hard
disk, called a "suspension," which supports a head for reading
magnetism, is being shifted in its main products from one, wherein
copper wiring is connected to a stainless steel plate spring, to
one called a "wireless suspension" comprising copper wiring which
has been connected directly to a stainless steel plate spring, from
the viewpoint of coping with the size reduction.
[0017] The wireless suspension is mainly formed of a material
having a three-layer structure. The material has a layer
construction comprising an insulating layer, a copper alloy foil
provided on one side of the insulating layer, and a stainless steel
foil provided on the other side of the insulating layer. Since
scanning on a disk being rotated at a high speed is carried out,
fine vibration is applied to the member. Therefore, the adhesive
strength of the wiring is very important. This requires satisfying
severe specifications. The adhesive strength of the wiring depends
greatly upon the material having a three-layer structure in its
adhesive layer portion, and the ability of the adhesive layer as
such determines the adhesive strength as the product.
[0018] A polyimide or similar resin, which has good insulating
properties even in a thin layer thickness, is used as the resin for
the insulating layer in the laminate having a layer construction of
metal-insulating layer-metal or a layer construction of
metal-insulating layer, particularly in the field of electronic
members where long-term reliability is required. In order to impart
adhesive properties to the polyimide resin, it is common practice
to impart thermoplasticity. However, there is few specific studies
on the relationship between the adhesive strength of the polyimide
resin and the properties of adhesives. The present situation is,
for example, such that, when the adhesive strength of the polyimide
resin is examined, actual contact bonding followed by a peel test
is necessary, that is, very troublesome work should be carried
out.
DISCLOSURE OF THE INVENTION
[0019] Accordingly, it is an object of the present invention to
provide a laminate having a layer construction of metal-insulating
layer-metal or a layer construction of metal-insulating layer,
which laminate meets conditions for developing large adhesive
strength between the insulating layer and the metal, as well as to
provide an insulating film and an electronic circuit using the
laminate.
[0020] In order to solve the above problems of the prior art, the
present inventor has made extensive and intensive studies on the
properties and adhesive strength of the polyimide resin. As a
result, the present inventor has found that the influence of the
viscoelastic behavior at the contact bonding temperature on the
adhesive strength is much more significant than that of the
composition of the resin on the adhesive strength. This has led to
the completion of the present invention.
[0021] Maximizing the anchor effect created by biting of the resin
into concaves and convexes on the surface of an adherend is
considered contributable to enhanced adhesive strength. To this
end, the contact bonding is preferably carried out at a temperature
of Tg, in which the thermoplastic resin beings to develop fluidity,
or above. In this case, however, the storage modulus at a
temperature of Tg or above varies according to a difference in
structure of the resin. Therefore, even in the case of contact
bonding at a temperature of Tg (glass transition point) or above,
the created adhesive strength varies depending upon the structure
of the resin. The present inventor has directed attention to
storage modulus as a measure of the fluidity of the resin and has
made studies on the relationship between the storage modulus and
the adhesive strength for thermoplastic resins having various
different compositions. As a result, the present inventor has found
a correlation such that the adhesive properties improve with
lowering the storage modulus at a temperature at or above Tg. The
present inventor has further found that resins particularly having
a storage modulus of not more than 10.sup.6 Pa have good adhesion
to adherends independently of resin composition.
[0022] These demonstrate that the use of thermoplastic resins
having a storage modulus of not more than 10.sup.6 Pa at a
temperature at or above Tg can provide laminates having good
adhesive strength. More preferably, the storage modulus in the
range of 10.sup.6 Pa to 10.sup.2 Pa can provide laminates having
better adhesive strength. The storage modulus of not less than
10.sup.6 Pa at a temperature at or above Tg is unfavorable. The
reason for this is that the fluidity is low at the time of contact
bonding in the preparation of the laminate and, thus, the resin is
less likely to bite into the concaves and convexes on the surface
of the adherend and this makes it difficult to develop anchor
effect. On the other hand, the storage modulus of not more than
10.sup.2 Pa at a temperature at or above Tg poses a problem such
that, although the adhesive property can be exhibited, the fluidity
of the adhesive layer is excessively large and, consequently, the
adhesive layer is squeezed out from the bonded surface in the step
of contact bonding in the preparation of the laminate.
[0023] Thus, according to one aspect of the present invention,
there is provided a laminate having a layer construction of first
metal layer-insulating layer-second metal layer or a layer
construction of metal layer-insulating layer, wherein
[0024] said insulating layer has a multilayer structure of two or
more layers,
[0025] the layer on the side of the adhesive interface with the
metal layer, out of the layers constituting the insulating layer,
is a thermoplastic resin layer, and
[0026] the minimum value of the storage modulus at a temperature at
or above Tg of the thermoplastic resin layer is not more than
10.sup.6 Pa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a diagram showing one embodiment of the layer
construction of the laminate according to the present
invention;
[0028] FIGS. 2A to 2D are diagrams showing one embodiment of a flow
sheet of the production process of a laminate according to the
present invention;
[0029] FIGS. 3A to 3D are diagrams showing another embodiment of a
flow sheet of the production process of a laminate according to the
present invention; and
[0030] FIG. 4 is a graph showing the relationship between the
storage modulus and the adhesive strength (g/cm) based on the
results shown in Table 1, wherein the abscissa represents the
storage modulus (Pa) and the ordinate the adhesive strength.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] The present invention will be explained in detail.
[0032] The adhesive strength between the adhesive and the metal is
mainly determined by two factors, one of which is the affinity of
the molecular structure of the adhesive for the surface of the
metal and the formation of a bond with the metal and the other is
the anchor effect attained by biting of the adhesive into concaves
and convexes on the surface of the metal.
[0033] The affinity for the surface of the metal embraces generally
considerable affinity and bond, such as chemical bond or
coordination bond to the surface of the metal and intermolecular
interaction (interaction between atoms).
[0034] As a result of extensive and intensive studies, the present
inventor has found that the adhesive strength at the interface of
the metal and adhesive bonded by contact bonding is influenced more
significantly by the anchor effect than the bond between the
molecular structure and the metal and the affinity, and has also
found the relationship between the properties of the fluidity of
the adhesive layer and the adhesive strength.
[0035] It is generally said that, when a resin having higher
fluidity is used as an adhesive, the anchor effect is more likely
to occur. In fact, however, there is no report about detailed
studies on the fluidity of the adhesive layer, and the principle of
the present invention is very useful for the preparation of
laminates having good adhesive strength.
[0036] Metals or films as the adherend are not particularly
limited. However, adherends having certain concaves and convexes
formed, for example, by hydrophobilization of the surface are
likely to develop adhesive strength by the anchor effect. In this
case, it should be noted that when the thickness of the adhesive
layer is lower than the height of the concaves and convexes of the
adherend, a space is formed between the adherend and the adhesive
layer, leading to lowered adhesive strength.
[0037] Thermoplastic Resin
[0038] According to the present invention, the insulating layer on
the side of the adhesive interface with the metal layer is formed
of a thermoplastic resin. Polyimides, which have low coefficient of
thermal expansion and are highly heat resistant, or resins having
properties similar to the polyimides are preferred as the
insulating layer from the viewpoint of the necessity of rendering
the coefficient of thermal expansion of the metal identical to that
of the insulating layer. The term "thermoplastic resin" as used
herein refers to resins having a clear glass transition point. The
resin, however, is not particularly limited and is independently of
the presence or absence of the imide bond, so far as the resin has
heat resistance and insulating property. Thermoplastic resins
preferably usable in the present invention include, but are not
particularly limited to, resins having an imide bond in the
molecule thereof, such as polyimides, polyamide-imides,
polyether-imides, and maleimide-modified resins, and resins having
a relatively high glass transition point, such as aromatic
polyesters and aromatic polyamides.
[0039] There is a tendency of a correlation such that the adhesive
strength increases with lowering the storage modulus at a
temperature at or above Tg of the thermoplastic resin. The
preparation of resins so as to lower the storage modulus generally
results in a tendency toward the formation of thermoplastic resins
having lower Tg.
[0040] The term "storage modulus" as used herein refers to the
storage modulus of the thermoplastic resin as the adhesive at the
time of bonding between the insulating layer and the adherend, for
example, by contact bonding. In this connection, it should be noted
that, in some cases, the state of the material having a three layer
structure as the final form is different from the state of the
bonding step, for example, in molecular structure due to heat
history. Therefore, the storage modulus does not refer to the
storage modulus in the changed state.
[0041] In general, the weight average molecular weight of the
thermoplastic resin according to the present invention is
preferably 6000 to 500000, particularly preferably 8000 to 80000,
although the weight average molecular weight varies depending upon
the molecular structure. When the molecular weight is not less than
500000, it is difficult to provide homogeneous coating. Further,
the larger the storage modulus at a temperature at or above Tg, the
lower the fluidity and the lower the tendency of the attainment of
the anchor effect. In general, in the case of resins having the
same chemical composition, the lower the molecular weight, the
lower the Tg (glass transition point) and the lower the storage
modulus at a temperature at or above Tg. When the molecular weight
is not more than 6000, the film forming property is poor making it
difficult to provide a homogeneous coating of a thermoplastic resin
layer.
[0042] The thermoplastic resin as the adhesive may be coated in a
solution form, or alternatively may be applied by a different
method, for example, in a film form. Further, a method may also be
used which comprises applying a precursor or a derivative of the
thermoplastic resin, performing molding and then processing the
molded product to convert the chemical structure to a desired
chemical structure.
[0043] Laminate
[0044] FIG. 1 shows one embodiment of the layer construction of the
laminate according to the present invention. Numeral 1 designates
an insulating layer. A thermoplastic resin layer 2 is stacked on
both sides of the insulating layer 1. A copper foil 3 or an alloy
foil is stacked as a metal layer on one of the thermoplastic resin
layers 2, and an SUS foil (a stainless steel foil) 4 is stacked as
a metal layer on the other thermoplastic resin layer 2.
[0045] At least one layer constituting the insulating layer may be
formed of a polyimide resin or may be a polyimide film.
Alternatively, all the layers constituting the insulating layer may
be formed of a polyimide resin or may be a polyimide film.
[0046] Each metal layer is preferably formed of a material selected
from the group consisting of copper alloy, copper, and stainless
steel. The first metal layer may be formed of a material which is
the same as or different from that constituting the second metal
layer.
[0047] Insulating Film
[0048] An insulating film comprising a resin film or a resin layer
as an insulating layer and a thermoplastic resin layer, having a
minimum value of storage modulus of not more than 10.sup.6 Pa at a
temperature at or above Tg, provided on both sides or one side of
the insulating layer may be used as an intermediate material for
the production of the laminate according to the present invention.
At least one resin layer constituting the insulating layer may be a
polyimide film or may be formed of a polyimide resin.
Alternatively, all the layers constituting the insulating layer may
be formed of a polyimide resin or may be a polyimide film.
[0049] Production Process of Laminate
[0050] A film coating process and a metal coating process will be
described as a production process of a laminate having layer
construction of first metal layer-insulating layer-second metal
layer as an example of the laminate composed of a metal layer and
an insulating layer. The production process is not particularly
limited to these only. The production process of the laminate
according to the present invention will be described by taking, as
an example, the use of a polyimide film as an insulating layer.
[0051] 1) Film Coating Process
[0052] FIG. 2 is an embodiment of a flow sheet showing a production
process of the laminate according to the present invention.
According to this embodiment, as shown in FIGS. 2A to 2D, a
polyimide film is provided as an insulating layer 1 (FIG. 2A). A
thermoplastic polyimide solution is coated on both sides of the
polyimide film, and the coated polyimide film is dried to remove
the solvent to form a thermoplastic resin layer 2 as an adhesive
layer (FIG. 2B). Next, as shown in FIG. 2C, a copper foil 3 and an
SUS foil (a stainless steel foil) 4 are brought into intimate
contact with respective both sides of the polyimide film through
the respective thermoplastic resin layers 2, that is, the copper
foil 3 is formed on one of the thermoplastic resin layers 2, while
the SUS foil 4 is formed on the other thermoplastic resin layer 2.
Thereafter, as shown in FIG. 2D, thermocompression bonding is
carried out at a temperature at or above the softening point (Tg)
of polyimide in the thermoplastic resin layer 2 while applying high
pressure.
[0053] 2) Metal Coating Process
[0054] FIG. 3 is another embodiment of a flow sheet showing a
production process of the laminate according to the present
invention. As shown in FIGS. 3A to 3D, a copper foil 3 and an SUS
foil (a stainless steel foil) 4 are provided (FIG. 3A). A polyimide
solution is coated on one side of each of the copper foil 3 and the
SUS foil 4, and the coated copper foil 3 and the coated SUS foil 4
are dried to remove the solvent to form a thermoplastic resin layer
2 on the copper foil 3 and on the SUS foil 4 (FIG. 3B). A polyimide
film as an insulating layer 1 is sandwiched between the copper foil
3 with the thermoplastic resin layer 2 formed thereon and the SUS
foil (stainless steel foil) 4 with the thermoplastic resin layer 2
formed thereon so that the thermoplastic resin layers 2 face each
other, followed by intimate contact (FIG. 3C). Thereafter,
thermocompression bonding is carried out at a temperature at or
above the softening point (Tg) of the thermoplastic resin layer 2
while applying high pressure (FIG. 3D).
[0055] For each coating process, the thermocompression bonding is
preferably carried out at a temperature such that exhibits the
minimum value of the storage modulus of the thermoplastic resin.
This is because the fluidity of the thermoplastic resin is best and
the anchor effect attained by biting of the thermoplastic resin
into the concaves and convexes on the surface of the adherend is
maximized to enhance the adhesive strength between the metal layer
and the core insulating layer.
[0056] Electronic Circuit
[0057] An electronic circuit can be generally formed by the
following method.
[0058] At the outset, a photosensitive resin layer is coated or
laminated on the surface of a metal on its side where the formation
of a circuit is desired. A mask with a desired pattern image formed
thereon is brought into intimate contact with the photosensitive
resin layer, followed by exposure to an electromagnetic wave with
wavelength to which the photosensitive resin is sensitive.
Thereafter, when the photosensitive resin is of a positive-working
type, the exposed area is developed with a predetermined developing
solution. On the other hand, when the photosensitive resin is of a
negative-working type, the unexposed area is eluted with a
predetermined developing solution. Thus, a desired circuit image is
formed on the metal. The metal with the circuit image formed
thereon is then immersed in a solution capable of dissolving the
metal, such as an aqueous ferric chloride solution. Alternatively,
this solution may be sprayed on the substrate. Thus, the metal
exposed on the surface is eluted, and the photosensitive resin is
then peeled off by a predetermined peeling solution to form a
circuit.
[0059] When etching of the insulating layer is necessary, a desired
pattern may be formed on the circuit prepared in the above manner,
followed by patterning of the insulating layer by a dry or wet
process.
EXAMPLES
[0060] Dynamic Viscoelastic Test
[0061] Resins, i.e., polyamic acid varnish [PAA-A (tradename)
manufactured by Mitsui Chemicals Inc.] as a precursor-type
polyimide; polyamide-imide varnish [N 8020 (tradename) manufactured
by Toyobo Co., Ltd.] as a polyamide-imide; and polyimide varnish
[SN-20 (tradename), PN-20 (tradename), and EN-20 (tradename),
manufactured by New Japan Chemical Co., Ltd.] as solvent-soluble,
ring-closing-type polyimide, were used in a dynamic viscoelastic
test. Metal foils, i.e., a rolled copper foil [18 .mu.m (layer
thickness), RCF-T5B (tradename) manufactured by FUKUDA METAL FOIL
& POWDER CORPORATION] and a stainless steel foil [20 .mu.m
(layer thickness), SUS 304 H-TA foil (tradename) manufactured by
Nippon Steel Corp.], were provided as a substrate and used in an
adhesive property test. Further, a polyimide film [75 .mu.m (layer
thickness), APIKAL NPI film (tradename) manufactured by Kanegafuchi
Chemical Ind. Co., Ltd.] was used for studies on adhesion to the
resins.
[0062] Each resin was coated on each substrate having a size of 10
cm.times.10 cm and a layer thickness of 12 .mu.m, and all the
coated substrates except for PAA-A (tradename) were dried in an
oven at 180.degree. C. for 30 min. For PAA-A (tradename) which is
an amic acid varnish, the solvent was removed by drying at
120.degree. C. for 15 min, and the coated substrate was then
subjected to a predetermined procedure to perform thermal
imidation, thereby preparing a polyimide. After the formation of
the coating in a thickness of about 20 .mu.m, etching of the
substrates was carried out in 45 Baume ferric chloride having a
liquid temperature of 50.degree. C. to prepare coating substrates.
These coating substrates were taken off to obtain test pieces
having a size of about 1.5 cm in length.times.5 mm in width. These
coating substrates were measured for storage modulus at each
temperature by means of a viscoelastic measuring apparatus RSA-II
(tradename) manufactured by Rheometric Scientific under conditions
of sample length 8 mm, sample width 5 mm, temperature rise rate
5.degree. C./min, frequency 3.0 Hz, and temperature rise from room
temperature to 400.degree. C.
[0063] Evaluation of Adhesive Property
[0064] Concaves and convexes were intentionally provided on the
surface of the substrate so that separation does not take place
between the adhesive layer and the substrate and interfacial
peeling between the adherend and the adhesive layer or cohesive
failure of the adhesive layer necessarily takes place. The surface
of a 100 .mu.m-thick SUS 304 plate was roughened by means of a wet
blasting machine manufactured by MACOHO using #1000 alumina as an
abrasive under conditions of pressure 0.7 kg/cm.sup.2 and scanning
speed 10 mm/sec, and the surface was then ultrasonically washed
with pure water for 30 min to remove the abrasive deposited on the
surface. In this case, both sides of the plate were roughened
because roughening of only one side causes warpage of the SUS 304
plate. Thereafter, a 2 to 3 .mu.m-thick coating was spin coated on
the surface, and the coating was dried or imidated under the
above-described consitions to form an adhesive layer on the SUS 304
plate. Desired metals and films were stacked on the assemblies,
followed by vacuum contact bonding at a temperature, which renders
the storage modulus of each sample lowest, at a surface pressure of
1 MPa for 10 min to preape samples. Here the peak of Tan .delta. as
obtained from the measurement of viscoelasticity was regarded as
Tg.
[0065] The samples were cut with a hand push cutter into a size of
1 cm in width, followed by a 90-degree peel test at a tensile speed
of 500 mm/min by means of a material tester (type 5565)
manufactured by Instron. The test results on the adhesive property,
Tg, and the lowest value of the storage modulus are shown in Table
1.
1 TABLE 1 Min. value of storage modulus Substrate Tg at temp. of Tg
or above RCF-TSB SUS 304 H-TA APIKAL NPI Thermo- PAA-A 205.degree.
C. 1.2 .times. 10.sup.4 Pa 1250 g/cm 1300 g/cm 920 g/cm plastic N
8020 315.degree. C. 1.0 .times. 10.sup.8 Pa 190 g/cm 10 g/cm 270
g/cm resin SN-20 305.degree. C. 1.0 .times. 10.sup.7 Pa 250 g/cm 70
g/cm 200 g/cm PN-20 285.degree. C. 1.5 .times. 10.sup.6 Pa 300 g/cm
200 g/cm 360 g/cm EN-20 160.degree. C. 1.0 .times. 10.sup.4 Pa 1250
g/cm 820 g/cm 1600 g/cm
[0066] FIG. 4 is a graph showing the relationship between the
storage modulus and the adhesive strength based on the results
shown in Table 1, wherein the abscissa represents the storage
modulus (Pa) and the ordinate the adhesive strength. In FIG. 4,
.diamond-solid. represents data on RCF-T5B foil (tradename)
manufactured by FUKUDA METAL FOIL & POWDER CORPORATION,
.box-solid. represents data on SUS 304 H-TA foil (tradename)
manufactured by Nippon Steel Corp., and .tangle-solidup. represents
data on APIKAL NPI film (tradename) manufactured by Kanegafuchi
Chemical Ind. Co., Ltd. As is apparent from the graph shown in FIG.
4, lower storage modulus at temperatures of Tg or above provides
better adhesion to each substrate.
[0067] Production of Laminate
[0068] An APIKAL NPI film (tradename, manufactured by Kanegafuchi
Chemical Ind. Co., Ltd.) having a thickness of 12.5 .mu.m (layer
thickness) was applied as a polyimide core film to a 100
.mu.m-thick SUS 304 plate. A thermoplastic polyimide varnish EN-20
manufactured by New Japan Chemical Co., Ltd. was spin coated on one
side of the polyimide film applied onto the substrate to a final
layer thickness of about 2 .mu.m, and the coating was dried at
180.degree. C. for 30 min in the air to remove the solvent.
Thereafter, the film was separated from the substrate, and the
substrate was turned over. The film was again applied to the
substrate, and an adhesive layer was formed in the same manner as
described above. The film with an adhesive layer formed on both
sides thereof was sandwiched between a 20 .mu.m thick SUS 304 HTA
and a rolled copper foil RCF-T5B manufactured by FUKUDA METAL FOIL
& POWDER CORPORATION (thickness 18 .mu.m), and vacuum contact
bonding was carried out under conditions of 300.degree. C., 1 MPa,
and 10 min.
[0069] For various samples, laminates were prepared in the same
manner as described above, and circuits were formed by the
following method. The temperature, at which contact bonding to the
laminate was carried out, was the temperature at which the lowest
storage modulus was provided in the dynamic viscoelasticity test,
and the pressure and the time were 1 MPa and 10 min for all the
cases. For the polyamic acid varnish [PAA-A (tradename)
manufactured by Mitsui Chemicals Inc.] which is a precursor
varnish, a tack-free precursor layer was formed on both sides of
the film, and the polyamic acid varnish on both sides of the film
was simultaneously thermally imidated by a predetermined method to
prepare a film provided with an adhesive layer, followed by
stacking.
[0070] Circuits were prepared as follows. An assembly composed of
SUNFORT AQ 5038 (a negative-working dry film manufactured by Asahi
Chemical Industry Co, Ltd.) laminated onto the copper side of the
three-layer material was exposed by a contact exposure system
through a predetermined mask. The exposed assembly was developed
with a 1% aqueous sodium carbonate solution, was immersed in a 45
Baume aqueous ferric chloride solution to remove the exposed
copper, and was then immersed in a 3% aqueous sodium hydroxide
solution of 50.degree. C. for one min to remove the dry film.
[0071] The circuit prepared from the three-layer material had a
desired shape.
[0072] According to the present invention, the interposition, as an
adhesive layer, of a thermoplastic resin having a minimum value of
storage modulus of not more than 106 Pa at a temperature at or
above Tg of the thermoplastic resin layer at the interface between
the metal layer and the insulating layer can provide laminates
having good adhesive strength between the metal layer and the
insulating layer.
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