U.S. patent application number 09/730805 was filed with the patent office on 2001-06-21 for flexible printed substrate.
This patent application is currently assigned to Sony Chemicals Corp.. Invention is credited to Kudo, Noriaki, Nagashima, Minoru.
Application Number | 20010004496 09/730805 |
Document ID | / |
Family ID | 18474976 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004496 |
Kind Code |
A1 |
Kudo, Noriaki ; et
al. |
June 21, 2001 |
Flexible printed substrate
Abstract
A flexible printed substrate is constituted of metallic foil and
provided thereon a polyimide layer which is produced by forming a
film of a polyamic acid varnish on the metallic foil, followed by
imidating. The polyimide layer has a linear expansion coefficient
of 10.times.10.sup.-6 to 30.times.10.sup.-6 (1/K) and a softening
point not more than the imidation temperature.
Inventors: |
Kudo, Noriaki; (Kanuma-shi,
JP) ; Nagashima, Minoru; (Kanuma-shi, JP) |
Correspondence
Address: |
Oliff & Berridge PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Sony Chemicals Corp.
|
Family ID: |
18474976 |
Appl. No.: |
09/730805 |
Filed: |
December 7, 2000 |
Current U.S.
Class: |
428/458 ;
428/473.5 |
Current CPC
Class: |
Y10T 428/24917 20150115;
Y10T 428/31721 20150401; H05K 1/0346 20130101; C08G 73/1085
20130101; Y10T 428/31681 20150401; Y10S 428/901 20130101 |
Class at
Publication: |
428/458 ;
428/473.5 |
International
Class: |
H05K 001/03; B32B
015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 1999 |
JP |
11-361821 |
Claims
What is claimed is:
1. A flexible printed substrate, comprising metallic foil and
provided thereon a polyimide layer which is produced by forming a
film of a polyamic acid varnish on the metallic foil, followed by
imidating, wherein the polyimide layer has a linear expansion
coefficient of 10.times.10.sup.-6 to 30.times.10.sup.-6 (1/K) and a
softening point not more than the imidation temperature.
2. The flexible printed substrate according to claim 1, wherein the
metallic foil is copper foil and the linear expansion coefficient
of the polyimide layer is 18.times.10.sup.-6 to 23.times.10.sup.-6
(1/K).
3. The flexible printed substrate according to claim 1, wherein the
imidation temperature is 300 to 400.degree. C.
4. The flexible printed substrate according to claim 1, wherein the
polyimide layer is formed from the polyamic acid varnish to which
imidazolyl-diamino azine has been externally added.
5. The flexible printed substrate according to claim 4, wherein the
imidazolyl-diamino azine is selected from the group consisting of:
2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-s-triazine;
2,4-diamino-6-[2-(2-ethyl-1-imidazolyl)ethyl]-s-triazine;
2,4-diamino-6-[1-(2-undecyl-1-imidazolyl)ethyl-s-triazine;
2,4-diamino-6-[2-(2-imidazolyl)ethyl]-s-triazine;
2,4-diamino-6-[2-(1-imi- dazolyl)ethyl]-s-triazine;
2,4-diamino-6-(2-ethyl-4-imidazolyl)-s-triazine- ;
2,4-diamino-6-[2-(4-methyl-1-imidazolyl)ethyl]-s-triazine;
2,4-diamino-6-(2-ethyl-5-methyl-4-imidazolyl)-s-triazine;
2,4-diamino-6-(4-ethyl-2-methyl-1-imidazolyl)-s-triazine;
2,4-diamino-6-[3-(2-methyl-1-imidazolyl)propyl])-s-triazine;
2,4-diamino-6-[4-(2-imidazolyl)butyl]-s-triazine;
2,4-diamino-6-[2-(2-met- hyl-1-imidazolyl)propyl]-s-triazine;
2,4-diamino-6-[1-methyl-2-(2-methyl-1-
-imidazolyl)ethyl]-s-triazine;
2,4-diamino-6-[2-(2,5-dimethyl-1-imidazolyl- )ethyl]-s-triazine;
2,4-diamino-6-[2-(2,4-dimethyl-1-imidazolyl)ethyl]-s-t- riazine;
and 2,4-diamino-6-[2-(2-ethyl-4-methyl-1-imidazolyl)ethyl]-s-tria-
zine.
6. The flexible printed substrate according to claim 4, wherein the
imidazolyl-diamino azine is used in an amount of 0.1 to 10 parts by
weight per 100 parts by weight polyamic acid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention pertains to flexible printed
substrates with insulating layers and cover layers formed from a
polyamic acid varnish.
[0003] 2. Description of the Related Art
[0004] Flexible printed substrates, wherein as insulating layers or
cover layers polyimide layers are formed directly on metallic foil
such as copper foil without using an adhesive, are made by applying
a polyamic acid varnish, which is obtained by
addition-polymerization of an aromatic diamine such as
para-phenylene diamine and an aromatic acid dianhydride such as
pyromellitic dianhydride in a solvent such as
N-methyl-2-pyrrolidone, to copper foil and drying to make a
polyamic acid layer (polyimide precursor layer), followed by
imidating this layer by heating to 300 to 400.degree. C. to form a
polyimide layer.
[0005] However, there is a problem in that residual stress is
generated in conventional flexible printed substrates during film
formation with the polyamic acid varnish and there is a difference
in the linear expansion coefficient between the metallic foil (for
instance, copper foil) and the polyimide layer and, therefore, the
substrate curls.
[0006] Therefore, attempts have also been made to produce flexible
printed substrates that do not curl by forming a polyimide layer
with a low linear expansion coefficient using varnish containing
polyamic acid with a specific structure (Japanese Patent
Application Laid-Open No. Sho 60-157286).
[0007] Nevertheless, when a polyimide layer with a low linear
expansion coefficient is formed using varnish containing polyamic
acid with a specific structure, there are problems in that it
cannot be said that the adhesive strength between the polyimide
layer and metallic foil, such as copper foil, is sufficient, and
when the copper foil is patterned by etching, the substrate curls
to the copper foil side and as a result, there is a marked drop in
productivity during subsequent finishing processes.
SUMMARY OF THE INVENTION
[0008] A object of the present invention is to solve the
above-mentioned problems with prior art. Specifically it is to
provide a flexible printed substrate having a polyimide layer with
good adhesive strength to the metallic foil and with which there is
no curling before or after etching of the metallic foil.
[0009] The present inventors completed the present invention upon
discovering that the above-mentioned object can be accomplished by
using a polyimide layer with a linear expansion coefficient within
a specific range and a softening point not more than the imidation
temperature as the polyimide layer of a flexible printed substrate
in which this polyimide layer is provided as the insulating layer
or cover layer on metallic foil.
[0010] That is, the present invention provides a flexible printed
substrate, comprising metallic foil and provided thereon a
polyimide layer which is produced by forming a film of a polyamic
acid varnish on the metallic foil, followed by imidating, wherein
the polyimide layer has a linear expansion coefficient of
10.times.10.sup.-6 to 30.times.10.sup.-6 (1/K) and a softening
point not more than the imidation temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The flexible printed substrate of the present invention has
a structure in which a polyimide layer is provided on metallic
foil, the polyimide layer being formed by forming a film of a
polyamic acid varnish, followed by imidating.
[0012] The polyimide layer of the present invention must have a
linear expansion coefficient of 10.times.10.sup.-6 to
30.times.10.sup.-6 (1/K). As a result, the range of the linear
expansion coefficient of the polyimide layer can correspond with
the range of the linear expansion coefficient of the metallic foil
and curling of the flexible printed substrate can be easily
prevented. Taking into consideration the fact that the copper foil
is generally used as the metallic foil, the linear expansion
coefficient of the polyimide layer is preferably set at
18.times.10.sup.-6 to 23.times.10.sup.-6 (1/K).
[0013] Furthermore, the softening temperature of the polyimide
layer must be not more than the imidation temperature upon
imidation of a film of a polyamic acid varnish (usually 300 to
400.degree. C., preferably 330 to 370.degree. C.). As a result,
residual stress upon film formation of the polyamic acid varnish
can be alleviated.
[0014] Determination of the "linear expansion coefficient" and
"softening point" of the polyimide layer in the present invention
can be performed using a thermomechanical analyzer (TMA, Seiko
Denshi Co., Ltd.) For instance, TMA properties are determined
within a temperature range of 30.degree. C. to 400.degree. C. under
conditions of a temperature elevation speed of 5.degree. C./minute
in tensile mode under a 5 g load using a polyimide film with a
thickness of 20 .mu.m, width of 4 mm, and length of 20 mm as the
sample, and the linear expansion coefficient can be found from the
TMA curve that has been obtained. Moreover, it is possible to
extend the almost straight part of the TMA curve on the
low-temperature side to the high-temperature side and extend the
tangent of the part of the curve, where at the part the changing
rate of the TMA curve is increased due to softening, to the
low-temperature side and find the point of intersection between
these extensions as the "softening point" (in accordance with the
method of finding needle temperature of JIS K7196).
[0015] Examples of a specific measure for obtaining a polyimide
film having a linear expansion coefficient of 10.times.10.sup.-6 to
30.times.10.sup.-6 (1/K) and a softening point not more than the
imidation temperature includes a measure in which
imidazolyl-diamino azine is externally added to a polyamic acid
varnish used for the formation of polyimide layers (that is, a
mixture containing polyamic acid obtained by addition
polymerization of aromatic diamine and aromatic acid dianhydride in
a solvent); and a measure in which the the types and mixture ratios
of the aromatic diamine component and aromatic acid dianhydride
component constituting the polyamic acid are selected. These two
measures can also be combined.
[0016] Those represented by general formula (1) 1
[0017] (where A is an imidazolyl group represented by formula (1a),
(1b), or (1c) 2
[0018] R.sup.1 is an alkylene group and m is 0 or 1. R.sup.2 is an
alkyl group and n is 0, 1 or 2. R.sup.3 and R.sup.4 are alkylene
groups and p and q are each 0 or 1. B is an azine residue, diazine
residue, or triazine residue.) are given as examples of
imidazolyl-diamino azines that can be used in the present
invention.
[0019] Furthermore, when m is 0 in the imidazolyl-diamino azine of
formula (1), the alkylene group of R.sup.1 is not present and the
azine residue, diazine residue or traizine residue is directly
bonded to the imidazole ring. Methylene, ethylene, propylene and
the like can be given as examples of alkylene groups of R.sup.1
when m is 1.
[0020] When n is 0, the alkyl group of R.sup.2 is not present and
the hydrogen atom is bonded with the imidazole ring. Methyl, ethyl,
can be given as examples of alkyl groups of R.sup.2 when n is 1.
Two R.sup.2 groups are bonded to the imidazole ring when n is 2 and
methyl, ethyl and the like can be given independently as examples
of alkyl groups of each R.sup.2. Furthermore, depending on the
case, R.sup.2 may also be directly bonded with the nitrogen atoms
of the imidazole ring.
[0021] When p is 0, the alkylene group of R.sup.3 is not present
and the amino group is bonded directly with the azine residue,
diazine residue, or triazine residue. Methylene, ethylene and the
like can be given as examples of the alkylene group of R.sup.3 when
p is 1.
[0022] When q is 0, the alkylene group of R.sup.4 is not present
and the amino group is directly bonded to the azine residue,
diazine residue, or triazine residue. Methylene, ethylene and the
like can be given as examples of the alkylene group of R.sup.4 when
q is 1.
[0023] B is an azine residue, diazine residue or triazine residue.
Of these, diamines with triazine residues are preferred because
they can be easily synthesized or easily procured industrially.
[0024] The following compounds where both p and q are 0 can be
given as preferred specific examples of the imidazolyl-diamino
azines of formula (1):
[0025]
2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-s-triazine;
[0026]
2,4-diamino-6-[2-(2-ethyl-1-imidazolyl)ethyl]-s-triazine;
[0027]
2,4-diamino-6-[1-(2-undecyl-1-imidazolyl)ethyl-s-triazine;
[0028] 2,4-diamino-6-[2-(2-imidazolyl)ethyl]-s-triazine;
[0029] 2,4-diamino-6-[2-(1-imidazolyl)ethyl]-s-triazine;
[0030] 2,4-diamino-6-(2-ethyl-4-imidazolyl)-s-triazine;
[0031]
2,4-diamino-6-[2-(4-methyl-1-imidazolyl)ethyl]-s-triazine;
[0032]
2,4-diamino-6-(2-ethyl-5-methyl-4-imidazolyl)-s-triazine;
[0033]
2,4-diamino-6-(4-ethyl-2-methyl-1-imidazolyl)-s-triazine;
[0034]
2,4-diamino-6-[3-(2-methyl-1-imidazolyl)propyl]-s-triazine;
[0035] 2,4-diamino-6-[4-(2-imidazolyl)butyl]-s-triazine;
[0036]
2,4-diamino-6-[2-(2-methyl-1-imidazolyl)propyl]-s-triazine;
[0037]
2,4-diamino-6-[1-methyl-2-(2-methyl-1-imidazolyl)ethyl]-s-triazine;
[0038]
2,4-diamino-6-[2-(2,5-dimethyl-1-imidazolyl)ethyl]-s-triazine;
[0039]
2,4-diamino-6-[2-(2,4-dimethyl-1-imidazolyl)ethyl]-s-triazine;
or
[0040]
2,4-diamino-6-[2-(2-ethyl-4-methyl-1-imidazolyl)ethyl]-s-triazine.
[0041] Of these, the following compounds are preferred:
[0042]
2,4-diamino-6-[2[(2-ethyl-4-methyl-1-imidazolyl)ethyl]-s-triazine;
[0043] 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-s-triazine;
or
[0044]
2,4-diamino-6-[1-(2-undecyl-1-imidazolyl)ethyl]-s-triazine.
[0045] If the amount of imidazolyl-diamino azine of formula (1)
mixed in the polyamic acid varnish is too little or too much, the
adhesive strength of the polyimide layer will be insufficient,
while if it is too much, there will be a reduction in mechanical
strength and heat resistance. Therefore, it should be preferably
0.1 to 10 parts by weight, more preferably 0.1 to 5 parts by
weight, per 100 parts by weight polyamic acid, which is the solid
content.
[0046] Conventionally, well known aromatic diamine components can
be used as the aromatic diamine component of the polyamic acid.
Aromatic diamines selected from 4,4'-diaminophenyl ether,
para-phenylene diamine, 4,4'-diaminobenzanilide,
4,4'-bis(p-aminophenoxy)diphenylsulfone and
2,2-bis[4-(4-aminophenoxy)phenyl propane can be given as preferred
examples.
[0047] Furthermore, of these aromatic diamines, simultaneous use of
para-phenylene diamine is preferred in order to reduce
thermoexpansivity of the polyimide. Moreover, simultaneous use of
4,4-diaminodiphenyl ether is preferred in order to increase
thermoexpansivity of the polyimide.
[0048] Moreover, conventionally well-known aromatic acid
dianhydrides can be used as the aromatic acid dianhydride for the
polyamic acid. For instance, aromatic dianhydrides selected from
pyromellitic dianhydride (PMDA), 3,4,3',4'-biphenyl tetracarboxylic
dianhydride (BPDA), 3,4,3',4'-benzophenonetetracarboxylic
dianhydride (BTDA), or 3,4,3',4'-diphenylsulfonetetracarboxylic
dianhydride (DSDA) can be given as preferred examples.
[0049] Although the percentages of aromatic diamine component and
aromatic acid dianhydride component constituting the polyamic acid
can be such that there is excess aromatic diamine or excess
aromatic acid dianhydride, it is preferred that they are used at
the equimolar ratio.
[0050] A solvent that is conventionally used for a polyamic acid
varnish can be used as the solvent in the polyamic acid varnish,
and N-methyl-2-pyrrolidone can be given as a preferred example.
[0051] There are no particular restrictions to the amount of
solvent that is used and it can be set as needed in accordance with
viscosity of the polyamic acid varnish.
[0052] Conventionally well-known additives may be mixed as needed
in accordance with the polyamic acid varnish used by the present
invention.
[0053] Furthermore, although there are no particular restrictions
to the thickness of the polyimide layer that is used, it is
normally 10 to 50 .mu.m.
[0054] Moreover, various metallic foils can be used as the metallic
foil for the flexible printed substrate of the present invention,
and aluminum foil, copper foil, gold foil, are preferred. Mat
treatment, plating treatment, aluminum alcoholate treatment,
aluminum chelate treatment, silane coupling agent treatment, can be
performed on these metallic foils as needed.
[0055] There are no particular restrictions to thickness of the
metallic foil, but it is normally 5 to 35 .mu.m.
[0056] The flexible printed substrate of the present invention can
be produced as described below:
[0057] First, aromatic diamine and aromatic acid dianhydride are
addition-polymerized in a solvent. The conditions of
addition-polymerization can be set as needed in accordance with the
conditions of conventional addition-polymerization of polyamic
acid. Specifically, the aromatic diamine is first heated and
dissolved in a solvent (for instance, N-methyl-2-pyrrolidone) and
acid dianhydride is gradually added at 0 to 90.degree. C.,
preferably 5 to 50.degree. C., under an inert ambient atmosphere,
such as nitrogen gas. Then addition-polymerization is performed for
several hours. As a result, polyamic acid is obtained in a state of
dissolution in a solvent. The polyamic acid varnish is obtained by
adding imidazolyl-diamino azine of formula (1) to this solution and
mixing to dissolution.
[0058] Next, the a polyamic acid varnish to which
imidazolyl-diamino azine has been externally added is applied to
the metallic foil using a comma coater, and dried to obtain a
polyamic acid layer as the polyimide precursor layer. Upon the
drying, it is preferable that a residual volatile amount in the
polyamic acid film (content of "remaining solvent undried and water
generated upon by imidation") is 70% or less so that foaming will
not occur during imidation of the following process.
[0059] Imidation of the polyamic acid layer that has been obtained
is performed by heating to 300 to 400.degree. C. under an inert
ambient atmosphere (for instance, nitrogen ambient atmosphere) to
form the polyimide layer. As a result, a flexible printed substrate
is obtained, Incidentally, it appears that the imidazolyl-diamino
azine that has been externally added reacts with the polyamic acid
and part [of this] is taken up inside the polyimide molecules.
[0060] The flexible printed substrate obtained in this way has good
adhesive strength between the metallic foil (copper foil) and
polyimide layer. Moreover, curling will not occur before and after
etching of the metallic foil. In addition, imidazol residues that
show rust-proofing effects are present in the polyimide layer and
therefore, no corrosion or discoloration of the surface (surface
where polyimide is formed) of the metallic foil, such as copper
foil, and no electric migration by copper ions, even when the
flexible printed substrate is a circuit board, can be expected.
EXAMPLES
[0061] The present invention will be explained in specific terms
below:
Example 1 and Comparative Examples 1.about.2
[0062] First, in a 5 liter reaction vessel with a jacket, 83.3 g
(0.77 mole) para-phenylene diamine (PDA, Daishin Kasei Co., Ltd.)
and 46.0 g (0.23 mole) 4,4'-diaminodiphenyl ether (DPE, Wakayama
Seika Co., Ltd.) were dissolved in approximately 3 kg solvent
N-methyl-2-pyrrolidone (NMP, Mitsubishi Kagaku Co., Ltd.) under a
nitrogen gas ambient atmosphere and kept at 50.degree. C. Then they
were reacted for 3 hours as 297.1 g (1.01 moles) 3,4,3',4'-biphenyl
tetracarboxylic dianhydride (BPDA, Mitsubishi Kagaku Co., Ltd.)
were gradually added.
[0063] Next, in the polyamic acid solution thus obtained, 21.3 g (5
parts by weight per 100 parts by weight polyamic acid)
2,4-diamino-6-[2-(2-ethy- l-4-methyl-1-imidazolyl)ether]-s-triazine
were added and dissolved as the imidazolyl-diamino azine of formula
(1) to obtain a polyamic acid varnish.
[0064] The same polyamic acid varnish as in comparative Examples 1
and 2 were obtained by repeating the same procedure as in Example
1, with the exception that imidazolyl-diamino azine was not
used.
[0065] Furthermore, the compounds in Table 1 are listed below:
[0066] (Aromatic acid dianhydride)
[0067] BPDA: 3,4,3',4'-biphenyl tetracarboxylic dianhydride
[0068] PMDA: pyromellitic dianhydride
[0069] (Aromatic diamine)
[0070] PDA: para-phenylene diamine
[0071] DPE: 4,4'-diaminodiphenyl ether
1 TABLE 1 Example Comparative Example 1 1 2 Acid dianhydride BPDA
PMDA PMDA Diamine (a) PDA PDA PDA (b) DPE DPE DABA Molar ratio
(a)/(b) 75/25 75/25 50/50 Compound of formula (1) 2.5 wt parts --
--
[0072] Next, the above-mentioned polyamic acid varnishes were
applied to a roughed surface of a copper foil (Furukawa Circuit
Foil Co., Ltd.) and dried step by step so that foaming would not
occur. Then imidation was performed under a nitrogen gas ambient
temperature of 350.degree. C. (15 minutes) to obtain a flexible
printed substrate having a polyimide layer with a thickness of 25
.mu.m. Peeling strength (kg/cm) was determined as the adhesive
strength at 23.degree. C. of the polyimide layer of the flexible
printed substrate that was obtained in accordance with JIS C6471
(peeled at a width of 1.59 mm and at a 90.degree. angle). The
results thus obtained are shown in Table 2.
[0073] Determination of the "linear expansion coefficient" and
"softening point" in the polyimide layer of the present invention
was from the TMA curve, which is the result of determining TMA
properties under conditions of a temperature elevation speed of
5.degree. C./minute within a temperature range of 30.degree. C. to
400.degree. C. in tensile mode under a 5 g load using a
thermomechanical analyzer (TMA, Seiko Denshi Co., Ltd.) and a
polyimide film with a thickness of 20 .mu.m, width of 4 mm, and
length of 20 mm. The linear expansion coefficient and softening
point are shown in Table 2.
[0074] In addition, the entire surface of the copper foil of the
flexible printed substrate that was made in the same way was etched
with cuprous chloride etching solution to obtain polyimide film
only and the curled status of the flexible printed substrate before
etching and the polyimide film obtained after etching was
investigated. Specifically, the flexible printed substrate and
polyimide film were placed on a flat plate under conditions of
23.degree. C. and 60% Rh, and average distance beween the surface
of the flat plane and each of four corners of the surface of the
films was determined. The results are shown in Table 2.
2 TABLE 2 Example Comparative Example 1 1 2 Adhesive strength
(kg/cm) 1.43 0.74 0.82 Linear expansion 21 35 24 coefficient
(.times.10.sup.-6 (1/K)) Softening point (.degree. C.) 310-320
350-360 <400 Curling: (mm) Substrate 4.0 Tubular curling Tubular
curling Film 0.75 Tubular curling Tubular curling
[0075] From the results in Table 2, the flexible printed substrate
having a polyimide layer formed from a polyamic acid varnish
containing a specific imidazolyl-diamino azine as external additive
(Example 1) has a linear expansion coefficient of the polyimide
layer of 21.times.10.sup.-6 (1/K), which is within the range of
10.times.10.sup.-6 to 30.times.10.sup.-6 (1/K) and it begins to
show a softening point at 310 to 320.degree. C., which is less than
the imidation temperature (400.degree. C.). Therefore, it is clear
that it has good adhesive strength between the polyimide layer and
copper foil and there is very little curling before and after
etching.
[0076] On the other hand, the flexible printed substrates having a
polyimide layer formed from a polyamic acid varnish that did not
contain a specific imidazolyl-diamino azine as external additive
(Comparative Examples 1 and 2) either had a linear expansion
coefficient of the polyamide layer outside the range of
10.times.10.sup.-6 to 30.times.10.sup.-6 (1/K) or a softening point
more than the imidation temperature (400.degree. C.), and
therefore, adhesive strength between the polyimide layer and copper
foil was poor and there was remarkable curling before and after
etching.
[0077] The flexible printed substrate of the present invention
shows good adhesive strength of its polyimide layer to the metallic
foil and curling before and after etching is kept to a level that
does not pose a problem in terms of practical use.
[0078] The entire disclosure of the specification, claims and
abstract of Japanese Patent Application No. 11-361821 filed Dec.
20, 1999 is hereby incorporated by reference.
* * * * *