CA1063006A - Composite material of a polyparabanic acid film and base substrate - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Polyparabanic acid and metal composite laminates are obtained by adhering polyparabanic acid film and copper foil without intermediate adhesive layer except with small amount of solvent which will dissolve polyparabanic acid such as DMF, NMP, DMSO, etc. The laminates are useful for preparing flexible printed circuits which will withstand high soldering temperatures without distortion or delamination.

Description

L ~

1o63006 1 This invention relates to a novel composite

2 material and a method of producing it9 the said composite

3 material comprising polyparabanic acid (which will

4 hereinafter be referred to as PPA) and a base substrate.
More particularly, the invention is concerned with a method 6 of producing a composite material suita~le for use as 7 flexible printed circuits (which will hereinafter be 8 referred to as FPC) and other electrical insulating mater-9 ials.
In the field of printed circuits of the prior ll art, copper laminate for printed circuits, using thermo-12 setting resins such as phenol resins and epoxy resins as 13 a base substrate, have been used, but, with the progress 14 of the electronic industry, requirements have also risen for rendering printed circuits flexible. In the field 16 using connectors needing no solderingg as laminates for 17 FPC, a copper foil and base substrate of thermoplastic 18 resin such as polyethylene terephthalateJ have been used.
19 Of late, requirements for laminates for FPC
which can be soldered at a high temperature and high 21 speed have risen and, accordingly, there has arisen need 22 for a base substrate fo~ FPC which is re~is~ant to a 23 solder bath at high temperature. However, no completely 24 heat-resistant FPC plate has hitherto been found except a copper laminate using a polyimide (Trade Mark: Kapton) 26 a~ a ba8e sub~trate, which is sold by-DuPont.
~7 Inventor8 have been interested in ~he excellent 28 heat resistance of a PPA film under such circumstance and -~ . - . ~; -',' ~

'. 10630061 have attcmpted to make a copper laminate for FPC using 2 various adhesives. However, use of such copper lamInates 3 has resulted in various drawbacks due to the adhesives 4 used. That is to say, the adhesives must have excellent adhesiveness, dimensional stability, and chemical sta-6 bility at soldering temperatures and resistance to the 7 solder bath at 260C or higher~ which are not affected 8 by humidity. However, there have hitherto been found no 9 adhesives capable of satisfying these cond~tions.
The present invention provides an excellent FPC
11 free from the above mentioned disadvantages comprising a 12 metal plate such as copper plate or heat resistant resin 13 plate, and a PPA film and a composite plate of PPA -l~ copper that can be soldered. Su¢h a compo~ite article can be prepared without using special adhesives by causing a 16 thin layer of PPA solution to be present between a PPA
17 film and copper plate when hot. For example, a composite 18 material of PPA and copper is obtained by sub3ecting to 19 thermo~compression bonding to a copper foil, a PPA film immediately after preparation thereof by the solution ;, . .
21 casting method, before the film is dried completely and 22 contains s~me a~ount of the solvent, thereby forming a 23 small amount of PPA solution to act as a strong adhesive 24 between the copper foil and PPA. A copper laminate of PPA can be prepared during the process of protucing a 26 PPA film and, therefore, this process is favorably com-27 pared in simplicity of process with the process of obtain-28 ing a copper laminate of PPA using adhesives. As compared .

1 with a laminate obtained by spreading a concentrated solu-2 tion of PPA directly on a copper foil followed by drying, 3 the curling is reduced and the worka~ility such as printing is increased 80 as to be suited for practical use.
Moreover, the method of the present inventi~n csn 6 also be applied to la~ination with a solvent-free fil~. In 7 this case, a composite material of PPA and base ~ubstrate 8 can be obtained by coating a base substrate such as copper - 9 foil or a PPA film thinly with a solvent and then hot pressing them to form a small amount of adhesive thin layer 11 of PPA solution therebetween, or by causing a solution of ~2 polyparabanic acid or a film or powder of polyparabanic 13 acid containing a solvent of polyparabanic acid, i.e. non-1~ dried polyparabsnic acid to be present between a base sub-strate snd PPA film and then hotpressing them. When a 16 composite material of PPA and base substrate obtained by 17 one of these methods is dried completely~ a high perforo }8 msnce composlte material of PPA and base substrate, for 19 example, PPA and copper foil laminate for FPC is provided which is resistsnt to a solder bath at a high te~pera~ure.
21 In addition, it is confirmed that this composite material 22 is not affected by the smbient humidity even when sllowed 23 to stsnd for a long time.
24 A PPA useful in the present invention i8 a homo-2~ polymer or copolymer having a repeating unit represented 26 by the gener~l fonmula, ~ , .. . . .

-`` 1063006 2 r 4 ~ c 6 in which Ar represents an arylene group, as disclosed in US
7 Patents 3,547,897 issued December 15, 1970 and 3,591,562 8 issued July 6, 1971 both to Tad L. Patton and ACS Polymer g Preprints 12 (No. 1) p 162 (1971). Examples of Ar (arylene group) in the above mentioned general formula are as follows:

11 ~ CH2 ~ (diphenylmethane-4~4~-diyl) 12 ~ CH2 ~ (diphenylmethane-393~diyl) 13 ~ 0 ~ (diphenylether~494~-diyl) 14 ~ S2 ~ (diphenylsulfone-4~4~diyl) :~ 15 ~ (naphthylene) ~ (phenylene) 16 A polymer or copolymer having an inherent viscosity (DMF, 25 17 C) of0.4-2.5 is desirable and one having an inherent vis-18 cosity of 0.6-1.2 is particularly desirable to obtain a 19 highly flexible composite ma,erial.
.. . .
As the solvent of the invention there may be used :~ 21 any materiAls capable of dissolving PPA, in particular, ~: -22 dimethylfor~amite ~DMF), N-methylpyrrolidone (NMP), dimethyl 23 ulfoxide (DMS0) and dimethyl acetamide (DMAC). Cresols and 24 cyclohexanone can be used and the use of a low boiling point . 25 801vent such as 1~3-dioxolane can shorten the time for ~6 re~oving the solvent.

- 5 -. .

. 10 6 3C~D6 1 A method for carrying out the termocompression 2 bonding of a PPA film and a base substrate, for example, 3 metal plate in.the presence of a solvent of PPA will now be 4 illustrated as one embodiment of the inventionO In general, production of a PPA film is carried out by the so~called

6 solution casting method wherein a PPA dope i8 firstly ~pread

7 on a support such as stainless steel belt, dried to remove

8 the solvent at least to such an extent that the film i8

9 self-supporting and then the completely dried film is peeled from the metal support, followed by drying under severe 11- conditions to remove the reQidual solvent completely. In 12 the present invention, the completely dried film or non-13 dried film i8 peeled and sub~ected to continuous thermo~
14 compression bonding to a base substrate such as copper plate by calendering rolls befcre the second drying and then 16 completely dried. That is to say, the feature of the in-17 vention i8 insertion of the thermocompression bonding step 18 between the first drying ~nd second dryingO In this case, 19 the film obtained in the step of the first drying can be taken up, stored for a long time and then bonded to a base 21 substrate, for example, copper foil by continuous thermo-22 compression bonding u~ing calendering rollsO The thermo-23 compression bonding conditions9 for example, to a copper 24 foil vary mainly with the kind or content of the residual solvent and, when using DMF as the solvent, for example, a 2~ t-~perature of 130 -250C and a pressure such as not to crack 27 the copper foll,.in general, a pressure of 5-30 kg/cm2 are - . . . , . . - ~. ~

' 1063006 desirable.
In general, temperatures of 50 to 250 C., time periods of 2 to 10 minutes and pressures of 5 to 40 kilograms per square centimeterare employed for the compressîon bonding and temperatures of 50 to 290C for 40 to 60 minutes are employed for complete drying of the composite.
In the method of coating a solvent or PPA solution onto the surface of a completely dried film, the thermo-compression bonding is preferably carried out at a temperature of not more than the boiling point of the solvent in order to prevent formation of blisters in the film and the pressure is preferably 5-30 kg/cm . The drying conditions for removing the solvent are also such that the temperature is only slight-ly higher than the boiling point of the solvent in order to prevent formation of blisters. When using a PPA solution, it is not always necessary to specify the concentration and - molecular weight of PPA dissolved therein but a uniform sur-face is difficult to obtain where the solution has a remar-: kably high viscosity. Furthermore, the thermocompression bonding can be carried out in the presence of a coating of PPA solution from which most of the solvent has been removed or a thin layer PPA film or PPA powder containing a solvent.
for PPA.
In cases where the copper laminate of PPA of the invention is used as FPC, it is desirable to effect the .: I . . .
solvent removing as completely as possible, since the performance as FPC improves as the residual quantity of , ~: ~ 7 . . ,; , ...
, .
.,. . , . , ~ ;
. . , : . .

the solvent in the laminate becomes less. Therefore, the thus obtained composite material of a PPA film and base substrate is preferably dried at a relatively high tempera-ture~

In particular, the method of the invention i8 suitable for the production of a copper~to-PPA laminate ' :~ .

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1 0 63UDCH~

1 for FPC. In this case~ a copper foil9 proce~sed particular-2 ly for a printed circuit, having a thickness of 35 microns - 3 (1 ounce/ft2) or 75 microns (2 ounce~/ft2) is favorably used 4 with good results. However other metal plates such as alu-minum, tin and stainless steel plates, as well as inorganic 6 fibrous materials such as glass cloth and films9 fibers, 7 woven cloth and unwcven cloths of heat resistant resins such 8 as polyimides~ polyamides~ polyamideimides, PPA and their 9 miYtures can be used in similar manner. Composite materials of PPA and these inorganic materials or heat resistant 11 resins provite composite materials excellent in mechanical 12 and electrical properties. Films, woven cloths or unwoven 13 cloths of polyimides~ polyamides and polyamideimides can be-; 14 thermocompression bonded to the PPA side of a~composite materisl of a PPA film and metal plate acccrding to the ~ 16 method of the invention and the thus resulting composite j 17 material has particularly excellent mechanical and electri-18 cal properties. -- -19 ; According to the present invention, a heat re-sistance composite material of a PPA film can be produced 1 21 without using the so-called adhesives by using a solvent 22 for PPA in an e$fective but simple manner. The composite 23 material of the invention, in particular, using a copper 24 foil holds a high performance as a FPC plate for a long ~`~ 25 time, for exa~ple, a peel strengtb of 1.5 kg/cm at a temper-26 ature of 150C or hlgher and a heat re~i~tance of 270~C or 27 higher ln a 801der resistance test according to JIS C 6481, 28 which are hardly affected by humidity. ~-- 8 ~

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1 The present invention will be illustrated in 2 detail by the following exsmples~ in which measurements of 3 the peel strength and solder resistance are carried cut 4 according to JIS C 6481D the angle of peel being 180 in the peel strength, and measurements of the tensile strength 6 or tensile modulus of elasticity, tear strength9 dielectric 7 constant~ dielectric breakdown voltage and volume resistlv-8 ity are carried out respectively according to ASTM Do882, 9 ASTM D~1922, ASTM DolSO~ ASTM D-149 and ASTM D~2570 Example 1 11 According to US Patent 295479897, PPA having an 12 ~ DMF
13 inherent viscosity of l~inh ~ lolO and corresponding to the foregoing general formula where~n Ar ~ diphenylmethane-16 4,4'-diyl group was synthesized. The synthesized PPA powter 17 was dissolved in DMF to prepare a 20% by weight solution, 18 defoamed in vacuum, spread on a glass sheet and dried at 19 150C for 10 minutes~ Thereafter, the resulting PPA film was peeled from the glass sheet to obtain a film of 60 21 microns in thicknes~, having a residual solvent quantity 22 of 20% by weight therein. This film was put upon a copper 23 foil having a thickness of 35 microns, processed for print-24 ed circuit8, (manufactured by Fukuda Kinzoku C0.9 Ltd., Trade Mark: CF3T5), hot pressed for 5 minutes at a temper-26 ature of 200C and a pressure of 30 kg/cm2 and driet at 27 250-280C for 40 minutes to remove the solvent, thus ob-~ ~Jlning a composite material having a residual solvent 29 content of 0.1% by weight or less.

_ g O - .

. .. . . . -t 1063006 When the resulting composite material was sub-2 ~ected to tests, the solder resistance was 1 mi~ute or 3 longer at 270C and the peel strength was 1.6 kg/cm, which 4 were held for 2 weeks at room temperature. When the com-5 posite material was allowed to stand in an atmosphere at 6 40C and 100% relative humidity for 1 day, the solder re-7 si~tance was reduced to 1 minute or longer at 250Co 8 Example 2 9 In a manner analogous to Example 19 the PPA
, 10 synthesized in ~xample 1 was flowed and spread on a glass 11 sheet, dried at 150C for 15 minutes, peeled from the glass 12 sheet and dried at 250-280C for 20 minutes to obtain a - -13 film having a thickness of 50 microns and a residual solvent ~ -14 content of 1% or less.
To prepare ~n FPC ~e surface of the resulting PPA
16 film was coated with DMF, placed on a copper foil having a 17 thickness of 3S microns, (made by Fukuda Kinzoku Co.9 Ltd, 18 Trade Mark: CF3T5), hot pressed at 130C and 10 kglcm2 19 for 2 minutes and then dried at 170C for 30 ~inutes and at 20 250-280C ~or 20 minutes to remove the: solvent, thus ob-21 taining a composite materiai having a residual DMF content 22 of 0.1% by weight or less, measured by the pyrolysis gas 23 chromatograph.
24 When this composite material was sub3ected to 2S property test as FPC, the peel strength was 1.6 kg/cm and 26 th ~older resistance was 1 milwte or longer at 270C. When 27 this material was tested for storage in a room for a long 28 time snd for isture absorptionJ the results similar to A~ - lo ~, ... . ~ . . : . --: . ~ .- . . .. .

. .
. .~ . , .

1(~63006 1 tho~e of Example 1 were obtained.
2 Example 3 3 According to US Patent 3,547,897, PPA having an inherent viscosity of ~ inh - 0.95 and corresponding to the 6 ~ 25C
7 foregoing general formula wherein Ar - diphenylether-4,4'-8 diyl group was synthesized. This PPA was sub~ected to film 9 making to obtain a film of 50 mic~ons in thicknes~. The 80 obtained PPA film was coated with NMP, placed on the copper 11- foil used in Example 1, hot pressed at 180C and 10 kg/cm2 12 for 2 minutes and dried at 200~220C for 30 minutes and at 13 270-290C for 20 minutes to remove the solvent, thus obtain-` 14 ing a composite material having a residual solvent content of '! 15 0.1% by weight or less.
16 When the resulting composite material was sub-17 ~ected to testing as FPC, the peel strength was 1.5 kg/cm 18 and the solder resistance was 1 minute or longer at 270C, 1 1~ which were not deteriorated even after storage in a room ii 20 for 2 weeks.
~i 21 ~ Example 4 22 A powder of PPA obtained in Example 1 was dis-2~ solved in NMP to prepare a 1% by weight solution, coated on-24 -to the same copper foil as used in Example 1, combined with . ~
2S the PPA film obtained in Exa~ple 2, hot pressed at 180C and `~ 26 10 kg/cm2 for 2 minutes and dried at 200-220C for 30 min-.. ~
27 utes and at 270-290C for 20 minutes, thus obtaining a com-28 posite materia? capable of resisting for 1 minut- or longer 29 on a solder bath at 270C nd having a peel stren8th of 1.5 ~; 30 ~g/cm. The residual ~olvent content in th fllm was 0.1%
~ .
, - 11 - ' ~: ` ' . ~ . . , ~063W6 1 by weight or less. Even after the storage in a room for a 2 long time, these properties were not changed with the pass-3 age of time.
4 Example 5 The PPA film obtained in Example 2 was coated 6 with 1,3-dioxane, put upon Aromatic Nylon sold by Du Pont 7 (Trade Marko Nomex Paper), pressed under a pressure of 40 8 kg/cm2 at 50~C for 5 minutes and dried at 50~70C for 20 9 minutes and at 150C for 20 minutes to obtain a PPA-Nomex composite article whereby a composite article having eleco 11 trical properties better than those of Nomex and tear 12 strength better than that of PPA wns obtained.
13 PPA_ Nomex PPA-Nomex 14 Thickness (~ 50 50 100 Tensile Strength (kg/cm2) 16 Machine Direction1200 1100 1300 17 Transverse Direction1200 500 900 18 Tear Strength (g/dl) -19 Nachine Direction 7.0 53 - 26 20 Transverse Direc-tion8.0 ~ 68 ~3~
. ~ ;
21 Dlelectric Breakdow~
22 Voltage (V/mil) 4000 800 3000 23~ D~e1ectric Constant 24 at 50 Hz ~ 3.8 4.7 3.4 25 Dielectric Loss Tangent 26 at 50 Hz 0.003 0.012 0.007 27 Volume Re8istlvity 28~ cm 3.9 x 1016 5.1 x 10151.6 x 1016 ..} ~;, . ~ , ,,~. ~:. ~ ' , .
. ~ , -.
~ A~ -12 -, , , ;, , , , , , ~ " , ;, . . . , ., ,.. . ..... . ;. .
.

1 Example 6 2 The PPA films obtained in Example 2 were coated 3 with DMSO, between which a glass cloth of 50 microns in 4 thickness (manufactured by Nippon Glass Fibers Co., Ltd.) was sandwiched, pressed at 140C under a pressure of 100 6 kg/cm for 10 minutes and dried at 150-200C for 30 minutes 7 and at 250-280C for 30 minutes, thus obtaining a PPA com-8 posite material having a high mechanical strength at a high 9 temperature as shown in the following tableo PPA (50~ PPA/Glass Cloth/PPA
11 - (135 12 Tensile Strength Ckg/cm2) 16 Tensile Modulus of Elasticity (kg/cm2) .. - . ..
. . -

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for preparing a flexible composite structure of polyparabanic acid and a substrate which comprises preparing a polyparabanic acid film by solution casting, placing the polyparabanic acid film so formed on the substrate which is selected from copper, aluminum, tin, and stainless steel plates, inorganic fibrous materials, films, fibers, woven cloth and unwoven cloth of heat resistant resins and PPA and their mixtures, causing a thin layer of PPA
solution to be present between the PPA film and the substrate and subjecting the composite so formed to thermocompression bonding at a temperature of 50 to 250°C. for a period of 2 to 10 minutes and pressures of 5 to 50 kilograms per square centimeter and then completely drying the composite at temperatures of 50 to 290°C. for 40 to 60 minutes.

2. A method for preparing a flexible composite material of a polyparabanic acid film and a base substrate which comprises preparing a polyparabanic acid film by solution casting, placing the non-dried polyparabanic acid film so formed which contains a solvent for a polyparabanic acid selected from dimethyl formamide, N-methyl pyrrolidane, dimethyl sulfoxide, dimethyl acetamide, cresols, cyclohexanone or 1,3-dioxolane, upon a base substrate selected from copper, aluminum, tin and stainless steel plates, inorganic fibrous materials, films, fibers, woven cloth and unwoven cloth of heat resistant resins and PPA and their mixtures and then subjecting the composite to thermocompression bonding at a temperature of 50 to 250°C., a pressure of 5 to 40 kilograms per square centimeter, for a period of 2 to 10 minutes and then completely drying the composite at temperatures of 50 to 290°C. for 40 to 60 minutes.

3. A method for preparing a flexible composite structure of polyparabanic acid and a substrate which comprises preparing a polyparabanic acid film by solution casting, drying the film, placing the so formed polyparabanic acid film on the substrate selected from copper, aluminum, tin and stainless steel plates, inorganic fibrous materials, films, fibers, woven cloth and unwoven cloth of heat resistant resins and PPA and their mixtures, placing a solution of polyparabanic acid therebetween, said solution including a solvent selected from dimethyl formamide, N-methyl pyrrolidane, dimethyl sulfoxide, dimethyl acetamide, cresols, cyclohexanone and 1,3-dioxolane, and subjecting the composites so formed to thermocompression bonding at a temper-ature not more than the boiling point of the solvent at a pressure of 5 to 40 kilograms per square centimeter for a period of 2 to 10 minutes and then drying the composite completely at 50 to 290°C.
for 40 to 60 minutes.

4. A method for preparing a flexible composite struc-ture of polyparabanic acid and a substrate which comprises pre-paring a polyparabanic acid film by solution casting, placing the polyparabanic acid film so formed on the substrate which is selected from copper, aluminum, tin and stainless steel plates, inorganic fibrous materials, films, fibers, woven cloth and un-woven cloth of heat resistant resins and PPA and their mixtures, placing polyparabanic acid, containing a solvent therefor selected from dimethyl formamide, N-methyl pyrrolidane, dimethyl sulfoxide, dimethyl acetamide, cresols, cyclohexanone and 1,3-dioxolane, between the film and the substrate and subjecting the composite so formed to thermocompression bonding at a temperature of 50 to 250°C. for a period of 2 to 10 minutes and pressures of 5 to 50 kilograms per square centimeter and then completely drying the composite at temperatures of 50 to 290°C. for 40 to 60 minutes.