U.S. patent application number 12/750945 was filed with the patent office on 2010-07-29 for polyamideimide resin for flexible printed circuit boards; metal-clad laminate, coverlay, and flexible printed circuit board that use this resin; and resin composition.
This patent application is currently assigned to Arisawa Mfg. Co., Ltd.. Invention is credited to Shu Dobashi, Makoto Tai.
Application Number | 20100186998 12/750945 |
Document ID | / |
Family ID | 38263527 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100186998 |
Kind Code |
A1 |
Tai; Makoto ; et
al. |
July 29, 2010 |
POLYAMIDEIMIDE RESIN FOR FLEXIBLE PRINTED CIRCUIT BOARDS;
METAL-CLAD LAMINATE, COVERLAY, AND FLEXIBLE PRINTED CIRCUIT BOARD
THAT USE THIS RESIN; AND RESIN COMPOSITION
Abstract
The present invention provides a polyamideimide resin for
flexible printed circuit boards that prior to curing exhibits an
excellent solubility, processability, and handling characteristics,
and that after curing exhibits flame retardancy, solder heat
resistance, circuit embeddability, and flexibility and further has
a high glass-transition temperature and is able to maintain a high
adhesive strength. The present invention provides a polyamideimide
resin for flexible printed circuit boards, which is obtained by the
polymerization reaction of an acid component comprising at least a
monoanhydride and an aromatic dicarboxylic acid with a diisocyanate
compound or diamine compound in an approximately equimolar amount
with respect to the total molar amount of the acid component,
wherein the molar amount of the monoanhydride is 0.4 to 0.8 taking
the total molar amount of the acid component as 1.
Inventors: |
Tai; Makoto; (Joetsu-shi,
JP) ; Dobashi; Shu; (Joetsu-shi, JP) |
Correspondence
Address: |
DRINKER BIDDLE & REATH LLP;ATTN: PATENT DOCKET DEPT.
191 N. WACKER DRIVE, SUITE 3700
CHICAGO
IL
60606
US
|
Assignee: |
Arisawa Mfg. Co., Ltd.
Joetsu-shi
JP
|
Family ID: |
38263527 |
Appl. No.: |
12/750945 |
Filed: |
March 31, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11652462 |
Jan 11, 2007 |
|
|
|
12750945 |
|
|
|
|
Current U.S.
Class: |
174/254 ;
428/458; 528/59 |
Current CPC
Class: |
B32B 2457/08 20130101;
B32B 15/20 20130101; B32B 2309/12 20130101; H05K 1/0393 20130101;
Y10T 428/31681 20150401; B32B 2309/04 20130101; H05K 2201/0154
20130101; B32B 2379/08 20130101; B32B 27/34 20130101; B32B 15/088
20130101; H05K 1/0346 20130101; C08G 73/14 20130101; B32B 15/08
20130101; B32B 2307/3065 20130101; B32B 2375/00 20130101; B32B
2037/1253 20130101; B32B 2309/02 20130101; B32B 2398/10 20130101;
B32B 2309/105 20130101; B32B 27/281 20130101 |
Class at
Publication: |
174/254 ;
428/458; 528/59 |
International
Class: |
H05K 1/02 20060101
H05K001/02; B32B 15/088 20060101 B32B015/088; C08G 18/72 20060101
C08G018/72 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2006 |
JP |
2006-010346 |
Claims
1. A polyamideimide resin for flexible printed circuit boards,
which is obtained by the polymerization reaction of an acid
component comprising at least a monoanhydride and an aromatic
dicarboxylic acid with a diisocyanate compound or diamine compound
in an approximately equimolar amount with respect to the total
molar amount of the acid component, wherein the molar amount of the
monoanhydride is 0.4 to 0.8 and the molar amount of the aromatic
dicarboxylic acid is 0.2 to 0.6 taking the total molar amount of
the acid component as 1.
2. A metal-clad laminate, in which the polyamideimide resin for
flexible printed circuit boards according to claim 1 is formed as a
layer on a metal foil.
3. A coverlay in which the polyamideimide resin for flexible
printed circuit boards according to claim 1 is formed as a
film.
4. A flexible printed circuit board comprising the coverlay
according to claim 1 disposed on a metal foil that has been formed
into a circuit.
5. A resin composition comprising the polyamideimide resin for
flexible printed circuit boards according to claim 1.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/652,462, filed Jan. 11, 2007, which claims priority to
Japanese Patent Application No. 2006-010346, filed Jan. 18, 2006,
the entire contents of which are incorporated herein by
reference.
BACKGROUND
[0002] The present invention relates to a polyamideimide resin for
flexible printed circuit boards; a metal-clad laminate, a coverlay,
and a flexible printed circuit board that employ this resin; and a
resin composition that contains this resin.
[0003] Coverlays and flexible printed circuit boards (FPCs), for
example, metal-clad laminates, comprising suitable combinations of,
for example, an electrically insulating resin layer, e.g., of
polyimide film or polyamide film, an adhesive layer in which the
main component is epoxy resin or polyimide resin, and an
electroconductive metal foil layer, e.g., of copper foil, silver
foil, or aluminum foil, are already in use.
[0004] FPCs have been made lighter and thinner in recent years
accompanying the trend toward lighter and thinner electronic and
electric devices.
[0005] For example, metal-clad laminates are undergoing a
conversion from three-layer substrate structures comprising a resin
film layer, adhesive layer, and metal foil layer, to two-layer
substrate structures comprising a resin film layer and a metal foil
layer.
[0006] In the case of coverlays, on the other hand, there are
limits on the pursuit of weight and thickness reductions while
still maintaining the properties since coverlays comprise only a
resin layer and an adhesive layer.
[0007] With regard to methods for solving the aforementioned
problem of making coverlays lighter and thinner, for example, a
printed circuit board is known in which a resin composition layer
comprising polyamideimide resin and/or polyimide resin is laminated
without an interposed adhesive layer on a metal foil layer that has
already been formed into circuitry (for example, Japanese Patent
Application Laid-open No. H3-253340).
[0008] It is also known that a polyamideimide paint obtained by the
reaction of trimellitic anhydride and aliphatic dicarboxylic acid
(molar ratio=1:2 to 2:1) with a diisocyanate compound in an amount
approximately equimolar with these two components can be utilized
as a dielectric layer for dielectric wires (for example, Japanese
Patent Application Laid-open No. H7-37438).
[0009] Moreover, it is known that a polyamideimide resin
composition containing repeat units from naphthalenediisocyanate
and, for example, monoanhydride, dianhydride, or dicarboxylic acid,
at respective specific molar ratios can be used in metal-clad
laminates (for example, Japanese Patent Application Laid-open No.
2005-325329).
SUMMARY
[0010] In the case of the printed circuit board of Japanese Patent
Application Laid-open No. H3-253340, however, there are
restrictions on factors such as the viscosity and thickness of the
resin composition layer comprising polyamideimide resin and/or
polyimide resin, and, while a satisfactory adhesive strength is
obtained, the flame retardancy and solder heat resistance are
poor.
[0011] While polyamideimide paint obtained from trimellitic
anhydride and aliphatic dicarboxylic acid as in Japanese Patent
Application Laid-open No. H7-37438 does provide a satisfactory heat
resistance when used as a dielectric layer for dielectric wires,
the flame retardancy and solder heat resistance are poor.
[0012] While heat resistance is obtained when the polyamideimide
resin composition of Japanese Patent Application Laid-open No.
2005-325329 is used as a precursor material for FPCs such as
metal-clad laminates, satisfactory handling properties and a
satisfactory adhesiveness are not obtained. Moreover, the
compatibility (solubility) is reduced due to the presence of large
amounts of the naphthalene skeleton in the main chain, making it
difficult to apply a desired thickness due to the reduced
composition concentration that accompanies this.
[0013] Accordingly, an object of the present invention is to
provide a polyamideimide resin for flexible printed circuit boards,
that prior to curing exhibits an excellent solubility,
processability, and handling characteristics, and that after curing
exhibits flame retardancy, solder heat resistance, circuit
embeddability, and flexibility and further has a high
glass-transition temperature (Tg) and is able to maintain a high
adhesive strength. An additional object of the present invention is
to provide a resin composition that contains this polyamideimide
resin for flexible printed circuit boards.
[0014] Additional objects of the present invention are to provide
an excellent coverlay, metal-clad laminate, and flexible printed
circuit board that in each case use the aforementioned
polyamideimide resin for flexible printed circuit boards.
[0015] The present invention provides (1) a polyamideimide resin
for flexible printed circuit boards, which is obtained by the
polymerization reaction of an acid component comprising at least a
monoanhydride and an aromatic dicarboxylic acid with a diisocyanate
compound or diamine compound in an approximately equimolar amount
with respect to the total molar amount of the acid component,
wherein the molar amount of the monoanhydride is 0.4 to 0.8 taking
the total molar amount of the acid component as 1; (2) a
polyamideimide resin for flexible printed circuit boards, which is
obtained by the polymerization reaction of an acid component
comprising at least a monoanhydride, an aromatic dicarboxylic acid,
and an aliphatic dicarboxylic acid with a diisocyanate compound or
a diamine compound in an approximately equimolar amount with
respect to the total molar amount of the acid component, wherein,
taking the total molar amount of the acid component as 1, the molar
amount of the monoanhydride is 0.5 to 0.8, the molar amount of the
aromatic dicarboxylic acid is 0.1 to 0.4, and the molar amount of
the aliphatic dicarboxylic acid is 0.05 to 0.2; (3) a
polyamideimide resin for flexible printed circuit boards, which is
obtained by the polymerization reaction of an acid component
comprising at least a dianhydride and an aromatic dicarboxylic acid
with a diisocyanate compound or diamine compound in an
approximately equimolar amount with respect to the total molar
amount of the acid component, wherein the molar amount of the
dianhydride is 0.2 to 0.4 taking the total molar amount of the acid
component as 1; (4) the polyamideimide resin for flexible printed
circuit boards according to (3), wherein the acid component further
contains an aliphatic dicarboxylic acid; (5) a metal-clad laminate
in which the polyamideimide resin for flexible printed circuit
boards according to any of (1) to (4) is formed as a layer on a
metal foil; (6) a coverlay in which the polyamideimide resin for
flexible printed circuit boards according to any of (1) to (4) is
formed as a film; (7) a flexible printed circuit board comprising
the coverlay according to (6) disposed on a metal foil that has
been formed into a circuit; and (8) a resin composition comprising
the polyamideimide resin for flexible printed circuit boards
according to any of (1) to (4).
[0016] The present invention can provide a polyamideimide resin for
flexible printed circuit boards, that prior to curing exhibits an
excellent solubility, processability, and handling characteristics,
and that after curing exhibits an excellent flame retardancy,
solder heat resistance, circuit embeddability, and flexibility and
further has a high glass-transition temperature and is able to
maintain a high adhesive strength.
[0017] In addition, the polyamideimide resin according to the
present invention for flexible printed circuit boards is well
adapted for application to metal-clad laminates, coverlays, and
flexible printed circuit boards.
DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a schematic cross section that shows an embodiment
of a metal-clad laminate (single-sided metal-clad laminate)
according to the present invention;
[0019] FIG. 2 is a schematic cross section that shows an embodiment
of a coverlay according to the present invention;
[0020] FIG. 3 is a schematic cross section that shows an embodiment
of a single-sided copper-clad laminate according to the present
invention;
[0021] FIG. 4 is a plan view that shows the circuit pattern formed
in the metal foil plane of a single-sided copper-clad laminate used
in property evaluation testing; and
[0022] FIG. 5 is a plan view that shows the circuit pattern formed
in the metal foil plane of a single-sided copper-clad laminate used
in property evaluation testing.
DETAILED DESCRIPTION
[0023] Embodiments of the present invention are described below.
The following embodiments are provided as examples to describe the
present invention, but it should not be construed that the present
invention is limited only to these embodiments. The present
invention can be executed in a variety of embodiments within the
scope of its essential features.
The Polyamideimide Resin for Flexible Printed Circuit Boards
[0024] The polyamideimide resin for flexible printed circuit boards
according to the first invention is a polyamideimide resin for
flexible printed circuit boards that is obtained by the
polymerization reaction of an acid component comprising at least a
monoanhydride and aromatic dicarboxylic acid with a diisocyanate
compound or diamine compound in an approximately equimolar amount
with respect to the total molar amount of the acid component,
wherein the molar amount of the monoanhydride is 0.4 to 0.8 taking
the total molar amount of the acid component as 1.
[0025] That is, the ratio between the molar amount of the
monoanhydride and the molar amount of the aromatic dicarboxylic
acid (molar amount of the monoanhydride/molar amount of the
aromatic dicarboxylic acid) is in the range of 0.4/0.8 to
0.6/0.2.
[0026] Due to this composition, the polyamideimide resin according
to the present invention prior to curing exhibits an excellent
solubility, processability, and handling characteristics; after
curing exhibits an excellent flame retardancy, solder heat
resistance, circuit embeddability, and flexibility and further has
a high glass-transition temperature and is able to maintain a high
adhesive strength; and is useful for application as a flexible
printed circuit board.
[0027] In particular, since at least a certain amount of imide
component can be ensured by setting the molar amount of the
monoanhydride at greater than or equal to 0.4 taking the total
molar amount of the acid component as 1, a high Tg and a good flame
retardancy can be maintained; in addition, a good solder heat
resistance and dimensional stability are obtained because moisture
absorption can be inhibited.
[0028] In addition, since at least a certain amount of amide
component can be ensured by setting the molar amount of the
monoanhydride at no more than 0.8 taking the total molar amount of
the acid component as 1, a high adhesiveness is obtained and a good
circuit embeddability is obtained in application as a coverlay.
[0029] The molar amount of the monoanhydride is more preferably 0.5
to 0.8 taking the total molar amount of the acid component as
1.
[0030] The polyamideimide resin for flexible printed circuit boards
according to the second invention is a polyamideimide resin for
flexible printed circuit boards obtained by the polymerization
reaction of an acid component comprising at least a monoanhydride,
an aromatic dicarboxylic acid, and an aliphatic dicarboxylic acid
with a diisocyanate compound or a diamine compound in an
approximately equimolar amount with respect to the total molar
amount of the acid component, wherein, taking the total molar
amount of the acid component as 1, the molar amount of the
monoanhydride is 0.5 to 0.8, the molar amount of the aromatic
dicarboxylic acid is 0.1 to 0.4, and the molar amount of the
aliphatic dicarboxylic acid is 0.05 to 0.2.
[0031] Due to this composition, the polyamideimide resin according
to the present invention prior to curing exhibits an excellent
solubility, processability, and handling characteristics; after
curing exhibits an excellent flame retardancy, solder heat
resistance, circuit embeddability, and flexibility and further has
a high glass-transition temperature and is able to maintain a high
adhesive strength; and is useful for application as a flexible
printed circuit board.
[0032] When the aforementioned acid component comprises at least
monoanhydride, aromatic dicarboxylic acid, and aliphatic
dicarboxylic acid, the addition of at least 0.1 aromatic
dicarboxylic acid, taking the total molar amount of the acid
component as 1, is preferred from the standpoint of maintaining the
post-cure Tg. In addition, the addition of at least 0.05 aliphatic
dicarboxylic acid, taking the total molar amount of the acid
component as 1, is preferred from the standpoint of maintaining the
post-cure adhesiveness.
[0033] The ratio between the molar amounts of the aromatic
dicarboxylic acid and the aliphatic dicarboxylic acid
(former/latter) is preferably 70/30 to 50/50 when the
polyamideimide resin according to the present invention is used for
a coverlay.
[0034] The ratio between the molar amounts of the aromatic
dicarboxylic acid and the aliphatic dicarboxylic acid
(former/latter) is preferably 80/20 to 70/30 when the
polyamideimide resin according to the present invention is used for
a substrate.
[0035] The polyamideimide resin for flexible printed circuit boards
according to the third invention is a polyamideimide resin for
flexible printed circuit boards obtained by the polymerization
reaction of an acid component comprising at least a dianhydride and
an aromatic dicarboxylic acid with a diisocyanate compound or
diamine compound in an approximately equimolar amount with respect
to the total molar amount of the acid component, wherein the molar
amount of the dianhydride is 0.2 to 0.4 taking the total molar
amount of the acid component as 1.
[0036] Due to this composition, the polyamideimide resin according
to the present invention prior to curing exhibits an excellent
solubility, processability, and handling characteristics; after
curing exhibits an excellent flame retardancy, solder heat
resistance, circuit embeddability, and flexibility and further has
a high glass-transition temperature and is able to maintain a high
adhesive strength; and is useful for application as a flexible
printed circuit board.
[0037] The acid component in this polyamideimide resin may also
contain an aliphatic dicarboxylic acid in addition to the
dianhydride and the aromatic dicarboxylic acid.
[0038] The monoanhydride used by the present invention can be
exemplified by the anhydride of terephthalic acid, isophthalic
acid, trimellitic acid, 4,4'-biphenyldicarboxylic acid, sebacic
acid, maleic acid, fumaric acid, and dimer acid.
[0039] The dianhydride can be exemplified by the anhydride of
diphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic
acid, pyromellitic acid, naphthalenetetracarboxylic acid,
diphenyltetracarboxylic acid, bis(dicarboxyphenyl)propane,
bis(dicarboxyphenyl)sulfone, and bis(dicarboxyphenyl)ether.
[0040] A monoanhydride containing a plurality of aromatic rings in
its structure, such as the anhydride of terephthalic acid or
4,4'-biphenyldicarboxylic acid, may be used with the goal of
raising the Tg, insofar as this does not influence the
compatibility (solubility).
[0041] The aromatic dicarboxylic acid can be exemplified by
terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic
acid, and naphthalenedicarboxylic acid, wherein terephthalic acid
is preferred from a cost standpoint. Two or more aromatic
dicarboxylic acids may also be used in combination.
[0042] The aliphatic dicarboxylic acid is not specifically limited
and preferably a saturated dicarboxylic acid and also can be
exemplified by adipic acid, sebacic acid, maleic acid, fumaric
acid, decanedioic acid, dodecanedioic acid, and dimer acid, wherein
adipic acid is preferred from a cost standpoint. Two or more
aliphatic dicarboxylic acids may also be used in combination.
[0043] The diisocyanate compounds and diamine compounds generally
used in FPC applications can be used with no particular limitation
as the diisocyanate compound and diamine compound used in the
present invention; however, aromatic diisocyanate compounds and
diamine compounds having an aromatic ring in the main chain are
preferred.
[0044] In addition, a structure that does not influence the
compatibility (solubility) is preferred from a processability
standpoint. With regard to whether a diisocyanate compound or
diamine compound is to be used, an appropriate selection can be
made based on the method of production and conditions. Combinations
of both types of compounds may also be used.
[0045] 4,4'-diphenyl ether diisocyanate, tolylenediisocyanate
(TDI), 4,4'-diphenylmethanediisocyanate, and
1,5-naphthalenediisocyanate are preferred for the diisocyanate
compound because they satisfy the properties required of FPC
precursor materials from the standpoints of reactivity and
processability.
[0046] Other usable diisocyanate compounds can be exemplified by
xylylenediisocyanate (XDI),
3,3'-dimethyldiphenyl-4,4'-diisocyanate,
3,3'-diethyldiphenyl-4,4'-diisocyanate,
naphthylene-1,5-diisocyanate (NDI), tetramethylxylenediisocyanate
(TMXDI), isophoronediisocyanate (IPDI), hydrogenated
xylylenediisocyanate (H.sub.6XDI), dicyclohexylmethanediisocyanate
(H.sub.12MDI), hexamethylenediisocyanate (HDI), dimer acid
diisocyanate (DDI), norbornene diisocyanate (NBDI), and
trimethylhexamethylenediisocyanate (TMDI), and any two or more can
be used in combination.
[0047] p-phenylenediamine and 4,4'-diaminediphenyl ether are
preferred for the diamine compound because they fulfill the
properties required of FPC precursor materials from the standpoints
of reactivity and processability.
[0048] Other usable diamine compounds can be exemplified by
m-phenylenediamine, 4,4'-diaminodiphenyl sulfone,
4,4'-diaminobenzophenone, 2,2'-bis(4-aminophenyl)propane,
2,4-tolylenediamine, 2,6-tolylenediamine, p-xylylenediamine,
m-xylylenediamine, and hexamethylenediamine, and any two or more
can be used in combination.
The Resin Composition
[0049] The resin composition according to the present invention
contains the aforementioned polyamideimide resin for flexible
printed circuit boards.
[0050] An example of the resin composition according to the present
invention is the resin composition provided by blending the
aforementioned polyamideimide resin for flexible printed circuit
boards with a flame retardant for the purpose of obtaining an even
better flame retardancy. The flame retardant can be exemplified by
inorganic fillers such as aluminum hydroxide, silica, and barium
sulfate and by organophosphorus compounds such as phosphate esters.
These can be used individually or in combination.
[0051] The inorganic filler is preferably added at 30 to 70 weight
% with reference to the total weight of the solids fraction of the
acid component and diisocyanate or diamine.
[0052] The organophosphorus compound is preferably added at 10 to
30 weight % with reference to the total weight of the solids
fraction of the acid component and diisocyanate or diamine.
[0053] When the phosphorus content in the organophosphorus compound
is 10 to 20 weight %, the organophosphorus compound is preferably
added at 10 to 20 weight % with reference to the total weight of
the solids fraction of the acid component and diisocyanate or
diamine.
Example of a Method for Synthesizing the Polyamideimide Resin for
Flexible Printed Circuit Boards
[0054] 60 moles trimellitic anhydride is added as the acid
anhydride and 40 moles terephthalic acid is added as the
dicarboxylic acid to a reactor containing N-methyl-2-pyrrolidone.
100 moles 4,4'-diphenylmethanediisocyanate is then added as the
diisocyanate compound so as to provide an amount approximately
equimolar with the total molar amount of the acid anhydride and
dicarboxylic acid. A suitable amount of N-methyl-2-pyrrolidone is
added so as to bring the solids concentration to 45 weight %,
thereby giving a polyamideimide resin-precursor composition.
[0055] Polymerization (prepolymerization) is then carried out with
stirring under curing conditions of (1) 2 hours at 80.degree. C.,
(2) 5 hours at 120.degree. C., and (3) 1 hour at 150.degree. C.
This is followed by cooling and dilution to a solids concentration
of 25 weight % by the addition of a dilution solvent such as
dimethylformamide, N-methyl-2-pyrrolidone, or dimethylacetamide,
thus yielding a coatable polyamideimide resin.
The Metal-Clad Laminate
[0056] The metal-clad laminate according to the present invention
is a metal-clad laminate in which the aforementioned polyamideimide
resin for flexible printed circuit boards is formed as a layer on a
metal foil.
[0057] FIG. 1 is a schematic cross section that shows an embodiment
of a metal-clad laminate 100 according to the present
invention.
[0058] As shown in FIG. 1, the metal-clad laminate 100 is a
single-sided metal-clad laminate constructed from a metal foil 120
and the aforementioned polyamideimide resin 110 for flexible
printed circuit boards.
[0059] The metal foil 120 comprises a metal foil such as, for
example, copper, silver, or aluminum. The thickness of the metal
foil 120 is established as appropriate within the range of
thicknesses used in the field of electronic materials.
[0060] By virtue of the structure herein described, this metal-clad
laminate 100 exhibits an excellent flame retardancy and solder heat
resistance and can maintain a high adhesiveness and can be made
lighter and thinner than the prior art.
[0061] The metal-clad laminate 100 can be fabricated by a step in
which a coating layer is formed by coating the polyamideimide
resin-precursor composition on the surface of the metal foil 120
and a curing step in which the coating layer is cured under
prescribed curing conditions and the organic solvent present in the
coating layer is dried off, yielding the resin layer 110.
[0062] With regard to the step in which the coating layer is
formed, the thickness of the coating layer formed on the metal foil
120 will vary with the application, but is suitably established in
the range of 2 to 150 .mu.m. A suitable coating method can be used
in correspondence to the coated thickness, for example, a comma
coater, die coater, or gravure coater.
[0063] The aforementioned curing step is preferably carried out at
a curing temperature of 160 to 220.degree. C. for a curing time of
3 to 30 hours.
[0064] The metal-clad laminate 100 can also be fabricated by the
coverlay formation method as follows.
[0065] The polyamideimide resin-precursor composition is first
coated on a release film, e.g., PET (polyethylene terephthalate)
film, PP (polypropylene) film, PE (polyethylene) film, to form a
coating layer and a resin layer is then obtained by curing and
drying under prescribed curing and drying conditions
(temperature=80 to 160.degree. C., time=1 to 30 minutes) to yield a
semi-cured state (also called the B-stage below). The ability to
release the resin layer can be improved by subjecting the surface
of the release film to a release treatment.
[0066] The metal-clad laminate is subsequently fabricated by
pasting the resin surface of the resin layer on a rough surface of
the metal foil. For example, the use of a press or lamination using
a hot roll can be employed as the pasting method. The pasting
conditions are preferably a temperature of 200 to 350.degree. C.
and a pressure of 0.5 to 5 MPa.
[0067] While the preceding description relates to a single-sided
metal-clad laminate, it can also be applied to a two-sided
metal-clad laminate (not shown) in which metal foil is placed on
both sides of the resin layer.
[0068] A two-sided metal-clad laminate can be fabricated by placing
metal foil on both sides of a resin sheet fabricated by the
aforementioned coverlay formation method and thereafter carrying
out hot-press bonding by the pasting method cited above.
The Coverlay
[0069] The coverlay according to the present invention is a
coverlay in which the aforementioned polyamideimide resin for
flexible printed circuit boards is formed as a film.
[0070] FIG. 2 is a schematic cross section that shows an embodiment
of the coverlay according to the present invention.
[0071] As shown in FIG. 2, the coverlay 200 is constructed from a
layer 210 of the aforementioned polyamide resin for flexible
printed circuit boards and a release film 220.
[0072] Due to the presence of the resin layer 210 comprising the
aforementioned polyamideimide resin, the coverlay 200 exhibits an
excellent flame retardancy, an excellent solder heat resistance,
and the excellent circuit embeddability expected of coverlays, and
can maintain a high adhesiveness and can also be made lighter and
thinner due to the integration into a single feature of the resin
layer and the adhesive layer that is a component of previous
coverlays.
[0073] In addition, the coverlay according to the present
invention, because it can be used without having to modify an
existing flexible printed circuit board fabrication process, can
also reduce production costs from an equipment standpoint.
[0074] The coverlay 200 can be fabricated by forming a resin layer
210 on a release film 220 by the previously described coverlay
formation method.
[0075] In the coverlay formation method, the resin layer 210 need
not be completely cured and is obtained by curing and drying under
prescribed curing and drying conditions (temperature=80 to
160.degree. C., time=1 to 30 minutes) to yield a semi-cured state
(B-stage). The release film 220 may be disposed on both sides of
the resin layer 210 and is peeled off at the time of
application.
The Flexible Printed Circuit Board
[0076] The flexible printed circuit board according to the present
invention is a flexible printed circuit board in which the
aforementioned coverlay is disposed on a metal foil that has been
formed into a circuit.
[0077] The thickness of the flexible printed circuit board
according to the present invention can be freely set in accordance
with its application.
[0078] The aforementioned coverlay can also function in the
flexible printed circuit board as the interlayer adhesive (bonding
sheet) that is used in a multilayer printed circuit board.
Specifically, a multilayer printed circuit board can be fabricated
by layering the coverlay on the circuit-patterned plane elaborated
in the metal foil in a flexible printed circuit board, layering a
separate flexible printed circuit board thereon, and heating and
pressing under prescribed conditions.
[0079] As a consequence, a bonding sheet is no longer required for
joining flexible printed circuit boards in which a coverlay is
disposed on the circuit-patterned side, and it then becomes
possible to make a multilayer printed circuit board that is lighter
and thinner. Higher density multilayer printed circuit boards can
also be prepared.
[0080] When lamination is carried out with the circuit-patterned
sides of flexible printed boards facing each other, the coverlay
must be thick enough that the facing circuit-patterned sides do not
come into contact with one another.
[0081] The flexible printed circuit board according to the present
invention is well adapted for application as a so-called chip-on
flexible printed circuit board for IC chip mounting.
EXAMPLES
[0082] The present invention is described in additional detail by
the examples that follow, but the present invention is not limited
by these examples. The individual skilled in the art can add and
execute various modifications, not only to the examples provided
below, and these modifications are also encompassed in the scope of
the claims.
Examples 1 to 10 and Comparative Examples 1 to 10
[0083] Polyamideimide resin-precursor compositions were first
prepared from the individual components in the proportions (unit
for the numerical values: mole) shown in Tables 1 and 2.
[0084] The molar quantities shown in Tables 1 and 2 of the acid
anhydride and dicarboxylic acid were added to a reactor that
contained N-methyl-2-pyrrolidone. 100 moles of the diisocyanate
compound was then added so as to give an amount approximately
equimolar with the total moles of the acid anhydride and
dicarboxylic acid. N-methyl-2-pyrrolidone was additionally added in
an amount sufficient to bring the solids concentration to 45 weight
%, yielding the particular polyamideimide resin-precursor
composition.
TABLE-US-00001 TABLE 1 Example Example Example Example Example
Comp. Comp. Comp. Comp. Comp. 1 2 3 4 5 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.
5 components TMA 60 40 80 30 90 60 PMDA 20 40 10 50 TPA 40 60 20 80
60 70 10 90 50 ADA 40 MDI 100 100 100 100 100 100 100 100 100 100
NDI results of varnish stability OK OK OK OK OK OK OK OK OK OK
evaluation flame very good very good very poor very poor very poor
retardancy good good good good good peel strength 12 very 10 very 7
good 9 good 7 good 10 very 3 poor 11 very 5 poor 14 very good good
good good good Tg (.degree. C.) 280 260 300 280 290 240 300 245 300
190 solder heat good good good good good poor good poor good poor
resistance circuit good good good good good good poor good poor
good embeddability bendability OK OK OK OK OK OK OK OK OK OK
migration very very very very very good very good very good good
good good good good good good
TABLE-US-00002 TABLE 2 Example Example Example Example Example
Comp. Comp. Comp. Comp. Comp. 6 7 8 9 10 Ex. 6 Ex. 7 Ex. 8 Ex. 9
Ex. 10 components TMA 70 50 80 60 70 40 90 50 75 65 PMDA TPA 20 40
10 20 25 50 15 45 5 10 ADA 10 10 10 20 5 10 5 5 20 25 MDI 100 100
100 100 100 100 100 100 100 100 NDI results of varnish stability OK
OK OK OK OK OK OK OK OK OK evaluation flame very very very good
good poor good poor good good retardancy good good good peel
strength 13 very 11 very 9 good 14 very 12 very 15 very 7 good 17
very 15 very 17 very good good good good good good good good Tg
(.degree. C.) 280 270 290 260 290 115 80 130 130 130 solder heat
good good good good good poor good poor poor poor resistance
circuit good good good good good good good good good good
embeddability bendability OK OK OK OK OK OK OK OK OK OK migration
very very very very very very poor very very very good good good
good good good good good good
[0085] Details for the individual components in Tables 1 and 2 are
provided below. [0086] TMA: trimellitic anhydride (Mitsubishi Gas
Chemical Co., Ltd.) [0087] PMDA: pyromellitic anhydride (Daicel
Chemical) [0088] TPA: terephthalic acid (Mitsubishi Gas Chemical
Co., Ltd.) [0089] ADA: adipic acid (Asahi Kasei Corporation) [0090]
MDI: Cosmonet M-100 (Mitsui Takeda Fluorochemical)
(4,4'-diphenylmethanediisocyanate) [0091] NDI: Cosmonet NDI (Mitsui
Takeda Fluorochemical) (naphthalenediisocyanate)
[0092] Each of the resulting polyamideimide resin-precursor
compositions was polymerized (prepolymerization) while stirring
under curing conditions of (1) 2 hours at 80.degree. C., (2) 5
hours at 120.degree. C., and (3) 1 hour at 150.degree. C. This was
followed by cooling and dilution by the addition of
dimethylformamide so as to give a solids concentration of 25 weight
%.
[0093] Coating on a release film was then carried out so as to give
a 25-.mu.m thickness of the aforementioned dilution and a
semi-cured (B-stage) polyamideimide resin layer was obtained under
prescribed curing and drying conditions (temperature=80 to
160.degree. C., time=1 to 30 minutes). In addition, in order to
obtain the completely cured (C-stage) polyamideimide resin layer,
the B-stage polyamideimide resin layer was subjected to an
additional polymerization reaction under prescribed curing
conditions (temperature=140 to 200.degree. C., pressure=30 to 60
MPa, time=20 to 120 minutes); cooling then gave the C-stage
polyamideimide resin layer.
[0094] The following evaluation testing was carried out on each of
the obtained polyamideimide resin layers.
Flame Retardancy
[0095] Samples were fabricated (B-stage sample and a sample heated
for 168 hours at 70.degree. C.) and the flame retardancy was
evaluated in accordance with the UL94 standard in terms of whether
a V-0 grade could be met. [0096] very good: the V-0 grade of the
UL94 standard was completely met [0097] good: the V-0 grade of the
UL94 standard was almost met, no practical problems [0098] poor:
impractical, the V-0 grade of the UL94 standard could not be
met
Peel Strength
[0099] In accordance with JPCA BM-02, a sample was prepared and the
peel strength (adhesive strength) was evaluated by a 180.degree.
film (C-stage resin layer) peel. [0100] very good: peel strength at
least 10 N/cm, the adhesive strength was entirely unproblematic
from a practical standpoint [0101] good: peel strength at least 7
N/cm, but less than 10 N/cm, a practical adhesive strength was
obtained [0102] poor: peel strength less than 7 N/cm, the adhesive
strength was inadequate
The Glass-Transition Temperature: Tg
[0103] Individual semi-cured (B-stage) resin plates were prepared
in a thickness that would enable measurement by dynamic mechanical
analysis (DMA) and the Tg (.degree. C.) was measured.
Bendability
[0104] A measurement sample was fabricated and the bendability was
measured in accordance with JIS C-5016. With regard to the bending
angle, a radius R of 0.38 m was used, and a score of OK was
assigned when 1000 times was exceeded.
Migration
[0105] FIG. 3 shows the structure of the single-sided copper-clad
laminate used in the migration test. FIG. 4 shows the design of the
circuit pattern for carrying out the migration test.
[0106] As shown in FIG. 3, the single-sided copper-clad laminate
300 was constructed from a polyimide film layer 310 with a
thickness of 25 .mu.m (1 mil), a layer 320 of adhesive comprising a
known adhesive for FPC applications, and a copper foil layer 330
comprising 35-.mu.m (1 ounce) cold-rolled copper foil.
[0107] A prescribed treatment was first executed on the copper foil
layer 330 of the single-sided copper-clad laminate 300 to form the
circuit pattern 410 shown in FIG. 4. This circuit pattern 410 was
elaborated as a comb-shaped pattern with line/space=50 .mu.m/50
.mu.m.
[0108] Using the resin-precursor composition prepared for each
blend, a coverlay was fabricated in such a manner that the
semi-cured (B-stage) resin layer had a thickness of 25 .mu.m. This
coverlay was layered on the circuit pattern 410 on the single-sided
copper-clad laminate 300 and a flexible printed circuit board was
fabricated by hot-press bonding at 180.degree. C. and 40 MPa for 1
hour.
[0109] Testing was carried out on the resulting flexible printed
circuit board under prescribed conditions (voltage: DC100V,
temperature: 85.degree. C., humidity: 85% RH), and the change in
voltage was measured at a specified time (1000 hr). The migration
was evaluated based on the following scale.
[0110] very good: the resistance value over the prescribed time
period is at least 1.0.times.10.sup.9.OMEGA., the migration
behavior is excellent [0111] good: the resistance value over the
prescribed time period is at least 1.0.times.10.sup.7.OMEGA. but
less than 1.0.times.10.sup.9.OMEGA., this is a level unproblematic
from a practical standpoint [0112] poor: the resistance value over
the prescribed time period is less than 1.0.times.10.sup.7.OMEGA.,
impractical
[0113] Migration (also called copper migration) is a phenomenon in
which, when voltage is applied between copper foil conductors, the
copper ion elutes from the anode with ionic impurities in the
adhesive acting as a medium and copper eventually precipitates on
the cathode side. As this precipitated copper accumulates, the
precipitated copper undergoes dendritic growth between the
conductors. This is called a "tree", and when treeing is produced
the resistance between conductors is reduced and the insulating
properties can no longer be maintained.
Circuit Embeddability
[0114] The sample used in circuit embeddability testing was
prepared by executing a prescribed treatment on the copper foil
layer 330 of the single-sided copper-clad laminate 300 shown in
FIG. 3 to form the circuit pattern 510 shown in FIG. 5. This
circuit pattern was a straight line pattern with line/space=100
.mu.m/100 .mu.m.
[0115] Then, using the resin-precursor composition prepared for
each blend, a coverlay was fabricated in such a manner that the
semi-cured (B-stage) resin layer had a thickness of 25 .mu.m. This
coverlay was layered on the circuit pattern 510 on the single-sided
copper-clad laminate 300 and a flexible printed circuit board was
fabricated by hot-press bonding at 180.degree. C. and 40 MPa for 1
hour.
[0116] The presence/absence of voids between the lines and spaces
was investigated microscopically on the resulting flexible printed
circuit board. [0117] good: no voids [0118] poor: voids are
present
Solder Heat Resistance
[0119] The resin layer side of the single-sided copper-clad
laminate 300 shown in FIG. 3 was dipped and held in a 260.degree.
C. solder bath for 30 seconds. This was followed by an evaluation
in which the presence/absence of peeling and blistering was
determined by visual inspection. [0120] good: peeling and
blistering are absent [0121] poor: peeling and blistering occur in
some areas
Varnish Stability
[0122] Prior to heating and curing, each polyamideimide
resin-precursor composition was visually inspected for the presence
of phase separation; the absence of phase separation was scored as
OK.
[0123] As shown by the evaluation results in Tables 1 and 2, the
polyamideimide resins obtained by polymerizing the component blends
of Examples 1 to 10 gave an excellent post-cure flame retardancy,
solder heat resistance, circuit embeddability, flexibility,
adhesive strength, and migration behavior; a high Tg was also
confirmed.
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