Aqueous Epoxy Resins for Electrical Reinforced Plastics Industry

6 Aqueous Epoxy Resins for Electrical Reinforced Plastics Industry TERRY L. ANDERSON, JAMES H . M E L L O A N , K A T H L E E N L. POWELL, ROLAND R. McCLAIN, J. BRANDON SIMONS, ROBIN L. CONWAY, and DAVID A. SHIMP

Downloaded by CORNELL UNIV on October 8, 2016 | http://pubs.acs.org Publication Date: December 3, 1979 | doi: 10.1021/bk-1979-0114.ch006

Celanese Polymer Specialties Co., 9800 E. Bluegrass Parkway, Jeffersontown, KY 40299

The electrical reinforced plastics industry is undergoing changes as the requirements of printed circuit boards become more complex. This complexity is compounded by the requirements that the processes be more environmentally acceptable. EPA acceptable resins will ultimately be required of the resin producers. The purpose of this paper is to present a new water based epoxy resin system which will meet the current requirements of the industry. In addition, an experimental system will be presented which will approach the emerging requirements of the industry.

GENERAL TECHNOLOGY AND RESIN REQUIREMENTS Prior to discussing the new water based system, let us review the basic processes used in making the laminate. Figure I gives a flow diagram of the typical laminate process. Figure II gives a typical resin and curing agent varnish formula which would be used to make the finished laminate.

0-8412-0525-6/79/47-114-077$05.00/0 © 1979 American Chemical Society

Bauer; Epoxy Resin Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

78

EPOXY RESIN CHEMISTRY

Figure I I TYPICAL ORGANIC SOLVENT VARNISH FORMULA Epoxy r e s i n @ 80% NVM i n organic s o l v e n t Dicyandiamide

4 parts

Organic Solvent

45 parts

Cure A c c e l e r a t o r Downloaded by CORNELL UNIV on October 8, 2016 | http://pubs.acs.org Publication Date: December 3, 1979 | doi: 10.1021/bk-1979-0114.ch006

125 parts

0.2 parts

As can be seen in Figures I and II, the processing involves impregnating the fiberglass with the uncured epoxy resin solution, and finally fully curing layers of the prepreg with copper foil into a finished laminate. From this point the laminate is fabricated into a finished printed circuit board. The epoxy r e s i n s o l u t i o n i s t y p i c a l l y a halogenated epoxy r e s i n d i s s o l v e d i n a v o l a t i l e s o l v e n t such as acetone. Various p r o p r i e t a r y r e s i n parameters c o n t r o l such p r o p e r t i e s as cure speed, w e t t i n g o f the g l a s s , and cured s t a t e T g . NEW WATER BASED SYSTEM (ED-24574) The above b r i e f d i s c u s s i o n i s not intended to be a comprehens i v e review o f the processes used but i s intended as an overview. Figure I I I shows the v a r n i s h formula f o r the new water based system. The key feature o f t h i s v a r n i s h system i s t h a t no organic s o l v e n t e x i s t s i n the e n t i r e formula. Figure I I I WATER BASED VARNISH FORMULA Water Based Epoxy @ 60% NVM

167 parts

Dicyandiamide

3.2 parts

Water Accelerator

22 parts 0.3 parts

Several basic problems can e x i s t w i t h a water based r e s i n when manufacturing prepreg m a t e r i a l . The f i r s t problem i s a r e a c t i v i t y problem. E a r l y attempts at preparing water based systems encountered very slow r e a c t i v i t y o f the dicyandiamide w i t h the epoxy r e s i n . This caused very slow l i n e speeds f o r the l a m i n a t o r . This problem has been resolved w i t h ED24574 and the cure response o f the system i s equal to organic s o l v e n t based standards. The second problem which can plague a water based system i s one o f foaming o f the r e s i n . The foaming tendency i s considered common t o a l l water based d i s p e r s i o n s and i s a t t r i b u t e d to the



6.

ANDERSON ET AL.

Aqueous Epoxy Resins

79

decrease i n s u r f a c e t e n s i o n caused by the d i s p e r s a n t . Foaming manifests i t s e l f when the g l a s s c l o t h i s p u l l e d c o n t i n u o u s l y through the r e s i n d i s p e r s i o n . S i n c e l a r g e volumes o f a i r a r e introduced i n t o the g l a s s / r e s i n i n t e r f a c e a s u b s t a n t i a l amount o f foaming can occur. Wetting problems a r e then introduced i n t o the prepreg and u l t i m a t e l y i n t o the f i n i s h e d laminate. Unique a t t e n t i o n t o r e s i n composition has s o l v e d the foaming problem f o r ED24574. I t does not generate foam and the subsequent wetting problems i n the f i n i s h e d laminate. The t h i r d problem a s s o c i a t e d with water based varnishes i s poor e l e c t r i c a l i n s u l a t i o n p r o p e r t i e s o f the laminate a f t e r moisture c o n d i t i o n i n g . T h i s problem i s probably the most c r i t i c a l problem because i n s u l a t i o n f a i l u r e s o f the laminate can l e a d t o e l e c t r i c a l f a i l u r e o f the f i n i s h e d p r i n t e d c i r c u i t board. T h i s property i s measured by c o n d i t i o n i n g t h e f i n i s h e d laminate i n a high moisture environment and then t e s t i n g the d i e l e c t r i c breakdown s t r e n g t h . ED24574 has e x c e l l e n t i n s u l a t i o n r e s i s t a n c e . T h i s was achieved by a p r o p r i e t a r y r e s i n composition. S o l u t i o n o f the above problems has allowed the ED24574 system to run on commercial t r e a t e r l i n e s t o produce laminates which w i l l pass NEMA FR4 requirements. PROPERTIES OF ED24574 Figure IV gives the general p r o p e r t i e s o f the new water based r e s i n ED24574. The key p r o p e r t i e s t o note a r e the e l e c t r i c prop e r t i e s . S p e c i f i c a l l y , t h e d i e l e c t r i c breakdown v o l t a g e i s a s a f e margin above the minimum requirements. The remainder o f the e l e c t r i c a l p r o p e r t i e s a r e a l s o well above the requirements. Recently i n the i n d u s t r y , requirements on cured s t a t e Tg and r e l a t e d phenomena have begun t o be requested o f the r e s i n supp l i e r s . One o f two types o f t e s t s has been added over t h e NEMA FR4 requirements l i s t e d i n F i g u r e IV. T h i s t e s t i s e i t h e r a measurement o f the cured s t a t e Tg o r a pressure cooker J e s t . The Tg requirement has i n c r e a s e d from about 115-120 C. t o a l e v e l o f 120-130 C. f o r the cured laminate. The pressure cooker t e s t i s run by s u b j e c t i n g the t e s t laminate t o 15 p s i steam i n a conventional pressure cooker f o r 20-40 minutes. The t e s t l a m i nate i s removed from the pressure cooker, c o n d i t i o n e d one hour a t room temperature and immediately placed i n a hot s o l d e r bath (about 500 F . ) . The laminate i s then t e s t e d f o r water b l i s t e r i n g between the laminate p l i e s . Any v i s i b l e b l i s t e r i n g i s considered a failure. Figure V presents data which compares the ED24574 system with a standard o r g a n i c s o l v e n t based r e s i n system. As can be seen i n F i g u r e V the ED24574 f o r m u l a t i o n does not pass t h e emerging Tg o r pressure cooker requirements o f the i n d u s t r y .



D i e l e c t r i c Breakdown (KV) p a r a l l e l to lamination F l a m m a b i l i t y , per UL94V Burning Time (seconds)

D i s s i p a t i o n Factor @ 1 megacycle

D i e l e c t r i c Constant @ 1 megacycle

Surface R e s i s t i v i t y (megohms)

Volume R e s i s t i v i t y (megohm-cm)

Resin Content (wt. %) F l e x u r a l Strength ( p s i ) Lengthwise Crosswise Lengthwise Izod Impact ( f t . - l b s . / i n . notch) Lengthwise Crosswise Peel Strength ( l b . inch width) 1 o z . copper Water Absorption (%)

V

10 5.0 5.1 0.016 0.017 > 60 52 7

_

7

9

10 min. 5.2 max. 5.4 max. 0.025 max. 0.035 45 min. 40 min.

10

10

8 min. 0.20 max.

20 sec. s o l d e r d i p 24 h r s . @ 23°C. 1 hr. @ B o i l , 96 h r s . @ 35°C. & 90% RH 96 h r s . 0 35°C. & 90% RH 2 3 ° C , 50% RH 24 h r s . θ 23°C. i n water 2 3 ° C , 50% RH 24^hrs. @ 23°C. in water 23°C. 50% Ry 48 h r s . @ 50 C. i n water

min.

11.4 0.06 0.21

7.0 min. 5.5 min.

48 h r s . @ 5 0 " C 48 h r s . θ 50°C.

6

17.6 10.3

-

-

84,000 64,000 8500

60,000 min. 50,000 min.

34

2 3 „ C , 50% RH 2 3 ° C . , 50% RH 150°C

-

Laminate P r o p e r t i e s Laminates cgnstructed from 12 pi ies of S t y l e 7628, 1-399 f i n i s h g l a s s c l o t h prepreg press cured one hour at 350 F. and 150 psi were t e s t e d versus NEMA FR-4 s p e c i f i c a t i o n l i m i t s . Resul ts are l i s t e d below: Test NEMA FR-4 Results Requirements Conditioning Laminate Property

Figure IV PROPERTI ES OF LAMINATES PREPARED FROM ED24574


6.

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81

Aqueous Epoxy Resins

Figure V COMPARISON OF LAMINATE Tg AND PRESSURE COOKER TEST RESULTS

Tg (cured laminate)

Standard Acetone S o l u t i o n Based Resin

ED24574

125°C

100°C.

Pass

Fail

20 minutes pressure


cooker b l i s t e r i n g

30 minutes pressure cooker b l i s t e r i n g Pass Fail EXPERIMENTAL SYSTEMS At present i t i s not c l e a r whether Tg or pressure cooker r e s u l t s w i l l be required o f the epoxy r e s i n s i n the e l e c t r i c a l l a m i nate i n d u s t r y . We have developed an experimental r e s i n i n the l a b o r a t o r y which w i l l pass the new Tg or pressure cooker r e q u i r e ments. The r e s u l t s of t h i s experimental system are depicted i n Figure VI and i n Figure V I I . Figure VI LAMINATE TEST RESULTS FOR EXPERIMENTAL RESIN Experimental Resin Tg

119°c.

20 minutes pressure cooker blistering

Pass

30 minutes pressure cooker blistering

Pass

As can be seen from t h i s data i n Figure VI s u b s t a n t i a l improvement over the c u r r e n t ED24574 system has o c c u r r e d . Both Tg and e l e c t r i c a l data are acceptable for t h i s i n d u s t r y . CONCLUSION A new water based epoxy r e s i n system has been developed f o r the e l e c t r i c a l r e i n f o r c e d p l a s t i c s i n d u s t r y . Key features o f the ED24574 system are i t s a b i l i t y to run on commercial t r e a t e r l i n e s without cure speed problems, no foaming or w e t t i n g problems, and f i n a l l y no i n s u l a t i o n r e s i s t a n c e problems a f t e r moisture c o n d i t i o n i n g . The ED24574 system does not pass the emerging Tg or pressure cooker requirements. However, an experimental r e s i n does pass these requirements. I t i s a n t i c i p a t e d t h a t t h i s higher Tg r e s i n w i l l a l l o w laminates to be made which w i l l pass the emerging r e quirements of the p r i n t e d c i r c u i t board i n d u s t r y .



Resin Content

(%)

F l a m m a b i l i t y , per UL94V Burning Time (seconds

D i e l e c t r i c Breakdown (KV) p a r a l l e l to laminations

D i s s i p a t i o n Factor @ 1 megacycle

D i e l e c t r i c Constant @ 1 megacycle

Surface R e s i s t i v i t y (megohms)

Volume R e s i s t i v i t y (megohm-cm)

U

96 h r s . @ 3 5 T . & 90% RH 96 h r s . 9 35°C. & 90% RH 2 3 ° C , 50% RH 24 h r s . @ 23°C. i n water 2 3 ° C , 50% RH 24 h r s . 9 23°C. 2 3 ° C , 50% RH 48 h r s . @ 50 C. i n water

1 3

1 5

38

7

.006 .007 60 56

io

10

0.025 max. 0.035 max. 45 min. 40 min.

min.

5.2 5.3

6

10 mm. 5.2 max. 5.4 max.

10

Laminate P r o p e r t i e s Laminates cgnstructed from 8 p l i e s of S t y l e 7628, 1-399 f i n i s h g l a s s c l o t h pre-preg press cured one hour at 350 F . and 150 p s i were tested versus NEMA FR-4 s p e c i f i c a t i o n l i m i t s . R e s u l t s are l i s t e d below: Test NEMA FR-4 Results Requirements Conditioning Laminate Property

PROPERTIES OF LAMINATES PREPARED FROM EXPERIMENTAL RESIN

Figure VII


Aqueous Epoxy Resins for Electrical Reinforced Plastics Industry

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