Thermal Degradation of Polymers for Molded Integrated Circuit (IC

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The Effect of a Flame Retardant R. M . LUM and L. G . F E I N S T E I N

1

Bell Laboratories, Allen town, P A 18103

This paper reports the results of a molecular-level investigation of the effects of flame retardant additives on the thermal dedomposition of thermoset molding compounds used for encapsulation of IC devices, and their implications to the r e l i a b i l i t y of devices in molded plastic packages. In particular, semiconductor grade novolac epoxy and silicone-epoxy based resins and an e l e c t r i c a l grade novolac epoxy formulation are compared. This work is an extension of a previous study1 of an epoxy encapsulant to flame retarded and non-flame retarded sample pairs of novolac epoxy and silicone-epoxy compounds. The results of this work are correlated with separate studies on device aging2,3, where appropriate. Materials Three classes of polymer encapsulant materials were studied. These are listed in Table I and include novolac epoxy and silicone-epoxy compounds. A pure silicone formulation served as a control for comparison of the thermal degradion properties

A.

1

TABLE I Sample Pairs Compared in this Study Electrical/Electronic Grade Novolac Epoxy Sample A: commercial composition -FR Sample B: experimental lot -1/2 FR Sample C: experimental lot -non FR

B.

Semiconductor Grade Silicone-Epoxy Sample D: commercial comppsition Sample E: identical to above

C.

Semiconductor Grade Novolac Epoxies Sample F: commercial composition F -FR Sample G: commercial composition G -non FR (except for FR, compositions G and F are similar)

-FR -non FR

Current address: INMOS Co., Colorado Springs, CO. 0097-6156/82/0184-0213 $ 0 5 . 0 0 / 0 © 1982 American Chemical Society

Feit and Wilkins; Polymer Materials for Electronic Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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o f t h e silicone-epoxy compounds. To i m p r o v e their m e c h a n i c a l and t h e r m a l properties, t h e e p o x y a n d silicne-epoxy m o l d i n g compounds contain u p to 7 5 % b y w e i g h t o f a s i l i c a f i l l e r , plus various sabilizer and processing additives. Investigations o f t h e epoxy a n d silicone-epoxy materials a r e r e p o r t e d f o r compound f o r m u l a t i o n s b o t h w i t h and w i t h o u t t h e f l a m e retardant, a tetrabromobisphenol-A and Sb2O3 c o m b i n a t i o n . N o v o l a c epoxy r e s i n s a r e produced by r e a c t i o n o f n o v o l a c , a p h e n o l f o r m a l d e h y d e r e s i n , w i t h e p i c h l o r o h y r i n and a b a s e ^ . A d e t a i l e d d i s c u s s i o n o f t h e c h e m i s t r y , p r o d u c t i o n and p h y s i c a l p r o p e r t i e s o f epoxy r e s i n s i n terms o f t h e i r a p p l i c a t i o n t o m o l d i n g compounds h a s r e c e n t l y been g i v e n b y H e l f a n d a n d V i l l a n i . The s i l c o n e r e s i n i s a p o l y ( m e t h y l p h e n y l s i l o x a n e ) synthesi z e d f r o m m e t h y l c h l o r o s i l a n e s and p h e n y l s i l a n e s ^ . Incorporation of phenyl groups improves the thermal s t a b i l i t y o f t h e s i l i c o n e resin. E p o x i d a t i o n o f t h e r e s i n i s most l i k e l y accomplished through s u b s t i t u t i o n of t h eoxirane r i n g a t v a r i o u phenyl group s i t e s , y e i l d i n g an e p o x i d e / s i l o x a n e r a t i o near u n i t y . The epoxy a n d s i l i c o n e - e p o x y r e s i n s were m o l d e d i n t o 37--mm d i a m e t e r b y 4-mm t h i c k d i s c s . T h e s e were g r o u n d i n a SPEX m o d e l 8004 c a r b i d e l i n e d t w o - b a l l g r i n d e r , a n d t h e r e s u l t i n g powder s i e v e d t o p r o v i d e c o n t r o l l e d sample c o n f i g u r a t i o n s f o r laboratory analyses. Apparatus Evolved g a s a n a l y s i s (EGA). T e m p e r a t u r e programmed ( 5 ° C / m i n ) mass s p e c t r o m e t r i c (MS) techniques^-»' were u s e d t o a n a l y z e t h e v o l a t i l e p r o d u c t s f o r m e d d u r i n g sample h e a t i n g . The p o l y m e r sample (35 mg) was p y r o l y z e d i n a q u a r t z c e l l w h i c h was d i r e c t l y a t t a c h e d t o t h e i n l e t f l a n g e o f a q u a d r u p o l e mass spectrometer. G a s e s e v o l v e d f r o m t h e p o l y m e r compound were d y n a m i c a l l y sampled v i a a 1.0-mm d i a m e t e r o r i f i c e , f o r m e d i n t o a m o d u l a t e d m o l e c u l a r beam, a n d mass a n a l y z e d . I n f o r m a t i o n was o b t a i n e d on t h e t o t a l y i e l d o f v o l a t i l e p r o d u c t s , p r o d u c t c o m p o s i t i o n , and i n d i v i d u a l p r o d u c t y i e l d s a s a f u n c t i o n o f temperature. D i f f e r e n t i a l S c a n n i n g C a l o r i m e t r y (DSC) . A DuPont 990 t h e r m a l a n a l y z e r e q u i p p e d w i t h a DSC c e l l was employed t o r e c o r d t h e endothermic and exothermic r e a c t i o n s which o c c u r r e d d u r i n g temperature-programmed (10°C/min) h e a t i n g o f t h e polymer samples. Sample w e i g h t s were 15 mg, a n d t h e a m b i e n t a t m o s p h e r e was e i t h e r p r e p u r i f i e d n i t r o g e n o r l i n e a i r . Elemental A n a l y s i s . A P h i l l i p s PW 1410/70 X - r a y f l u o r e s c e n c e s p e c t r o m e t e r w i t h C r r a d i a t i o n was u s e d t o m e a s u r e t h e r e l a t i v e q u a n t i t i e s o f B r i n t h e molded polymer samples. E x t r a c t a b l e b r o m i d e and c h l o r i d e i o n s w e r e d e t e c t e d w i t h s p e c i f i c i o n e l e c t r o d e s a f t e r a 4 8 - h o u r , 1 2 0 ° C steam bomb e x t r a c t i o n .


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E l e c t r i c a l / E l e c t r o n i c Grade Novolac Epoxy Results TGA. Weight-loss measurements f o r the e l e c t r i c a l - e l e c t r o n i c grade novolac epoxy were reported i n our e a r l i e r work . For samples heated i n N2 to 350°C>no d i f f e r e n c e s a t t r i b u t a b l e to the presence of FR were observed. Isothermal measurements i n d i c a t e d a 20% weight l o s s f o r the u n f i l l e d molding compound a f t e r 12-days at 220°C. EGA. A d e t a i l e d d i s c u s s i o n of the evolved gas measurements f o r the e l e c t r i c a l grade epoxy compound was given i n our e a r l i e r work!. Several sources were found to c o n t r i b u t e to the observed outgassing: decomposition of the epoxy polymer s t r u c t u r e ; r e r e l e a s e of trapped impurity or r e s i d u a l species from the p o l y m e r i z a t i o n process; and breakdown of the brominated flame r e t a r d a n t . E v o l u t i o n of v o l a t i l e species from each source, however, occurred i n d i f f e r e n t temperature regimes. Aromatic species and c h l o r i d e products remaining from polymer synthesis dominated the i n i t i a l outgassing (100-225°C). The major r e l e a s e of bromine products form the flame retardant d i d not occur u n t i l higher temperatures (275-350°C). This i s w e l l above the range employed i n d e v i c e t e s t i n g . The EGA data i n d i c a t e d that the flame retardant had l i t t l e e f f e c t on the composition or formation k i n e t i c s of the v o l a t i l e decomposition products. The major species released from the FR was HBr. A small amount of CI^Br was a l s o d e t e c t e d . I n d i v i d u a l p r o f i l e s of the i o n s i g n a l s c h a r a c t e r i s t i c of the HBr and CI^Br flame retardant products are shown i n Figure 1 f o r sample A ( s o l i d curves), and compared with the corresponding ion s i g n a l i n t e n s i t i e s observed f o r sample C (dashed c u r v e s ) . Release of HBr from sample A i s shown i n Figure l c , superimposed on an i n c r e a s i n g background s i g n a l . The temperature of maximum HBr e v o l u t i o n , 325QC, i s i n good agreement with that p r e v i o u s l y observed i n t h i s l a b o r a t o r y f o r polycarbonate samples c o n t a i n i n g tetrabromobisphenol-A, and w i t h recent weight l o s s measurements on the flame retardant compound i t s e l f . The observed background at the component s i g n a l s used to c h a r a c t e r i z e HBr (m/e=79, 80, 81 and 82) a r i s e s from fragmentation of aromatic species produced during chain s c i s s i o n of the epoxy polymer backbone. Ion s i g n a l s f o r the CH 9Br+ (m/e=94) and CH3 Br (m/e=96) i s o t o p i c components are presented separately i n Figures l a and l b , because of the i n t e r f e r e n c e of the m/e=94 phenol s i g n a l . Barely d e t e c t a b l e s i g n a l l e v e l s are observed f o r these ions below 300° from sample C, while the p r o f i l e s from sample A provide c l e a r evidence f o r the r e l e a s e of methyl bromide from the flame r e t a r d a n t . T h i s r e l e a s e occurs i n two stages, with the s i g n a l i n t e n s i t i e s i n the high temperature stage C290°C) approximately twice those observed at the low temperature peak (190°). However, at 190°C methyl c h l o r i d e i s the dominant v o l a t i l e component, as shown i n Figure Id, exceeding e v o l u t i o n 8

7

81

3


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TEMP < ° C ) Figure 1.

TEMP C°C)

Ion profiles representative of HBr and CH Br flame retardant species. Key: , Sample A(FR) and , Sample C(no FR). 3


16.


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of methyl bromide from the flame r e t a r d a n t approximately ten.

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DSC. F l a m e r e t a r d a n t e f f e c t s on t h e d e c o m p o s i t i o n c h e m i s t r y o f m o l d i n g compounds c a n a l s o be d e t e c t e d f r o m DSC m e a s u r e m e n t s of the heat r e l e a s e d d u r i n g exothermic r e a c t i o n s o f c o n s t i t u e n t s of t h e polymer b l e n d . The DSC d a t a c h a r a c t e r i s t i c o f t h e e l e c t r i c a l grade epoxy samples has been d i s c u s s e d i n d e t a i l p r e v i o u s l y ^ , and i s r e p r o d u c e d i n F i g u r e 2 f o r c o m p a r i s o n w i t h t h e o t h e r sample p a i r s . The e f f e c t o f t h e f l a m e r e t a r d a n t i s e v i d e n c e d by t h e e x o t h e r m a t a p p r o x i m a t e l y 3 5 0 ° C w h i c h i n c r e a s e s w i t h i n c r e a s i n g FR c o n t e n t . Elemental Analyses. X - r a y f l u o r e s c e n c e measurements o f t h e m o l d e d e p o x y d i s c s a r e summarized i n T a b l e I I . H a l i d e c o n c e n t r a t i o n s were d e t e r m i n e d by a q u e o u s e x t r a c t i o n and a r e presented i n Table I I I . Semiconductor

Grade S i l i c o n e - E p o x y R e s u l t s

TGA. Weight l o s s measurements f o r t h e s e m i c o n d u c t o r grade s i l i c o n e - e p o x y f o r m u l a t i o n s w i t h and w i t h o u t FR a r e p r e s e n t e d i n F i g u r e 3. F o r t e m p e r a t u r e s up t o a t l e a s t 3 2 5 ° C , no d i f f e r e n c e s a t t r i b u t a b l e t o t h e FR a r e o b s e r v e d . F u r t h e r m o r e , below 2 7 5 ° , t h e r e i s no d i f f e r e n c e f o r s a m p l e s h e a t e d i n a i r o r n i t r o gen. D a t a were a l s o o b t a i n e d f o r a p u r e s i l i c o n e m o l d i n g com— pound and a r e p r e s e n t e d i n F i g u r e 3 f o r c o m p a r i s o n . Isothermal w e i g h t l o s s m e a s u r e m e n t s r e v e a l e d no d i f f e r e n c e b e t w e e n FR and non-FR s i l i c o n e - e p o x y compounds. A f t e r 1 2 - d a y s a t 2 2 0 ° , a 20% w e i g h t l o s s was o b s e r v e d f o r t h e u n f i l l e d p o l y m e r , s i m i l a r t o t h e e l e c t r i c a l g r a d e n o v o l a c epoxy i s o t h e r m a l r e s u l t s . TABLE I I X-RAY FLUORESCENCE MEASUREMENTS R e l a t i v e T o t a l Br C o n c e n t r a t i o n Sample Designation

Izpe

R e l a t i v e Br Concentration

Electrical Grade Epoxy

A(FR) B ( l / 2 FR) C(no-FR)

1.0 0.6 0.0

SiliconeEpoxy

D(FR) E(no-FR)

1.1 0.0

Semiconductor Epoxies

F(FR) G(no-FR)

1.6 0.0

^uncorrected

for attenuation

i n t h e compounds.


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EGA. An i s o m e t r i c r e p r e s e n t a t i o n o f t h e i o n p r o f i l e s c h a r a c t e r i s t i c of the gases evolved from the s i l i c o n e - e p o x y compounds a r e p r e s e n t e d i n F i g u r e s 4 and 5 f o r s a m p l e s D(FR) and E ( n o - F R ) , r e s p e c t i v e l y . From t h e s e d a t a t h e initial w e i g h t l o s s o b s e r v e d i n t h e TGA m e a s u r e m e n t s o f t h e s e s a m p l e s ( 5 0 - 1 5 0 ° C ) i s i d e n t i f i e d a s b e i n g due t o e v o l u t i o n o f b e n z e n e (m/e=78 p a r e n t i o n ; m/e39, 50, 51 and 52 f r a g m e n t i o n s ) a n d , t o a l e s s e r e x t e n t , w a t e r v a p o r (m/e=17, 1 8 ) . Contributions from o t h e r s p e c i e s a r e minor. The i s o m e t r i c i o n p l o t s o f F i g u r e s 4 and 5 i n d i c a t e t h a t e v o l u t i o n of benzene from t h e s i l i c o n e - e p o x y samples o c c u r s i n two d i s t i n c t s t a g e s , w i t h t h e l o w t e m p e r a t u r e p e a k a t t r i b u t a b l e t o r e s i d u a l s o l v e n t s p e c i e s . Above 2 0 0 ° C , t h e r m a l degradation processes i n v o l v i n g s c i s s i o n of the Si-phenyl bond o c c u r and a c c o u n t f o r t h e i n c r e a s e d f o r m a t i o n r a t e o f benzene. The o t h e r h i g h t e m p e r a t u r e v o l a t i l e p r o d u c t s a r e s i m i l a r t o t h o s e o b s e r v e d f o r t h e n o v o l a c epoxy s a m p l e s ^ , and a r e a t t r i b u t e d t o d e c o m p o s i t i o n of t h e epoxy f r a c t i o n o f s a m p l e s D and E . Comparison of t h e s i l i c o n e - e p o x y i o n p r o f i l e s i n d i c a t e s t h a t t h e p r e s e n c e o f t h e f l a m e r e t a r d a n t i n s a m p l e E has l i t t l e e f f e c t on t h e c o m p o s i t i o n o r f o r m a t i o n r a t e s o f t h e m a j o r v o l a t i l e s p e c i e s . The s p e c i f i c i o n p r o f i l e s c h a r a c t e r i s t i c o f HBr and CH^Br f r o m t h e f l a m e r e t a r d a n t i n s a m p l e E a r e s i m i l a r t o t h o s e e x h i b i t e d by t h e f l a m e - r e t a r d e d n o v o l a c epoxy ( s a m p l e A i n F i g u r e 1 ) , and c o n f i r m t h e o b s e r v a t i o n t h a t breakdown o f t h e f l a m e r e t a r d a n t has l i t t l e e f f e c t on o u t g a s s i n g below 300°C. DSC. 6 f o r the

The p r i n c i p a l f e a t u r e o f t h e DSC p l o t s i n F i g u r e FR and non-FR s i l i c o n e - e p o x i e s i s t h e o c c u r r e n c e o f TABLE I I I EXTRACTABLE HALIDES Sample Designation

Type Electrical Grade

A(FR) B(l/2

Br

CI is 650ppm 650 650

FR)

Epoxy

C(no-FR)

SiliconeEpoxy

D(FR) E(no-FR)

«25 «25

Semiconductor Epoxy

F(FR) G(no-FR)

200

*Aqueous e x t r a c t i o n f o r 4 8 - h r s . Cppm i n m o l d i n g compound).

160ppm 120

α


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an e x o t h e r m j u s t b e l o w 4 0 0 ° C . As was o b s e r v e d f o r t h e e l e c t r i c a l g r a d e epoxy s a m p l e s , t h e e x o t h e r m i s g r e a t e r f o r t h e FR compound. A n i t r o g e n a m b i e n t was u s e d t o e l i m i n a t e p o s s i b l e i n t e r f e r e n c e s i n t h e d e c o m p o s i t i o n e x o t h e r m s by exothermic o x i d a t i o n r e a c t i o n s . In runs at higher s e n s i t i v i t y , no d i f f e r e n c e s were o b s e r v e d i n t h e DSC d a t a f o r t e m p e r a t u r e s b e l o w 300OC. E l e m e n t a l A n a l y s e s . X - r a y f l u o r e s c e n c e measurements ( T a b l e I I ) i n d i c a t e no m a j o r d i f f e r e n c e between t h e t o t a l B r c o n t e n t i n t h e FR s i l i c o n e - e p o x y ( s a m p l e A ) . However, extractable halide concentrations, l i s t e d i n Table I I I , are much l o w e r f o r t h e s i l i c o n e - e p o x y s a m p l e s . Semiconductor

Grade

Epoxy

Results

TGA. U n l i k e t h e p r e v i o u s two s e t s o f m o l d i n g compounds, the semiconductor grade n o v o l a c s i n v e s t i g a t e d i n t h i s s e c t i o n do n o t d i f f e r s o l e l y i n t h e p r e s e n c e o r a b s e n c e o f a f l a m e retardant. However, t h e y a r e c o n s i d e r e d t o be r e l a t i v e l y equivalent. W e i g h t l o s s m e a s u r e m e n t s f o r t h e FR f o r m u l a t i o n , sample F, and t h e non-FR compound, sample G, a r e p r e s e n t e d i n F i g u r e 7 f o r b o t h n i t r o g e n and a i r . S e v e r a l d i f f e r e n c e s a r e observed i n t h e weight l o s s c u r v e s f o r t h e s e samples. F i r s t , b e l o w 3 0 0 ° C t h e w e i g h t l o s s i n a i r f o r b o t h compounds i s l e s s than the l o s s i n n i t r o g e n . In f a c t , f o r t h e samples heated i n a i r a s l i g h t weight i n c r e a s e i s r e c o r d e d near 250°C. T h i s l a t t e r b e h a v i o r i n d i c a t e s t h a t o x i d a t i o n o f t h e epoxy samples o c c u r s w i t h a r a t e t h a t , a t l e a s t i n i t i a l l y , i s f a s t e r t h a n w e i g h t l o s s t h r o u g h d e g r a d a t i o n and v o l a t i l i z a t i o n . However, t h i s behavior i s only t r a n s i e n t s i n c e weight l o s s e s g r e a t e r t h a n 20% a r e o b s e r v e d a f t e r i s o t h e r m a l l y h e a t i n g t h e s e samples i n a i r a t 220°C f o r 12-days. F u r t h e r m o r e , t h e non-FR sample e x h i b i t s a l o w e r t h e r m a l s t a b i l i t y i n b o t h a i r and n i t r o g e n t h a n t h e FR compound. This was c o n f i r m e d by t h e i s o t h e r m a l w e i g h t l o s s d a t a , p r e s e n t e d i n F i g u r e 8, w h i c h i n d i c a t e a s i g n i f i c a n t l y l a r g e r w e i g h t l o s s f o r t h e n o n - F R epoxy compound. A f t e r 1 2 - d a y s t h i s sample h a s l o s t 70% more w e i g h t t h a n t h e FR-epoxy ( s a m p l e F ) . The i s o t h e r m a l d a t a f o r t h e FR-epoxy i s v e r y s i m i l a r t o t h a t c h a r a c t e r i s t i c o f t h e e l e c t r i c a l g r a d e n o v o l a c e p o x y and t h e s i l i c one-epoxy. EGA. The o v e r a l l i o n p r o f i l e s f o r t h e s e m i c o n d u c t o r g r a d e e p o x y compounds a r e p r e s e n t e d i n F i g u r e s 9 and 10 f o r s a m p l e s F ( F R ) and G ( n o - F R ) , r e s p e c t i v e l y . Very l i t t l e outgassing i s o b s e r v e d f r o m t h e s e s a m p l e s b e l o w 2 0 0 ° C , i n marked c o n t r a s t t o t h e r e s u l t s o b t a i n e d f o r t h e e l e c t r i c a l g r a d e epoxy s a m p l e s ^ . T h e s e d a t a c l e a r l y r e f l e c t t h e e f f e c t s o f t h e more s t r i n g e n t p r o c e s s i n g c o n t r o l s employed i n t h e p r o d u c t i o n o f t h e s e m i conductor grade m a t e r i a l s . A l s o , because of t h e lower o u t -


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TEMPERATURE ( ° C ) Figure 10.

Isometric plots of mass spectral ion profiles from novolac epoxy Sample G(no FR).


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gassing, less interferences a r epresent i n t h e ion signals c h a r a c t e r i s t i c of the v o l a t i l e flame retardant s p e c i e s . Form a t i o n o f HBr f r o m t h e FR-epoxy ( s a m p l e F) s t a r t i n g a t 3 5 0 ° C i s c l e a r l y e v i d e n t i n t h e i o n p r o f i l e d a t a o f F i g u r e 9. No d e t e c t a b l e products a t t r i b u t a b l e t o t h e flame retardant are observed below 300°C. DSC. Exotherms c h a r a c t e r i s t i c o f t h e semiconductor grade epoxy s a m p l e s a r e p r e s e n t e d i n F i g u r e 1 1 . T h e l o w t e m p e r a t u r e e x o t h e r m a t 3 3 0 ° C i s u n i q u e t o t h e FR compound. However, s i n c e t h e s e two epoxy compounds a r e n o t s t r i c t l y e q u i v a l e n t , a s mentioned e a r l i e r , t h e appearance o f t h i s exotherm cannot be u n e q u i v o c a l l y a t t r i b u t e d t o t h e p r e s e n c e o f t h e f l a m e retardant. T h e h i g h t e m p e r a t u r e e x o t h e r m a b o v e 3 5 0 ° C , on t h e o t h e r h a n d , i s o b s e r v e d i n b o t h s a m p l e s , w i t h t h e FR-compound e x h i b i t i n g a l a r g e r peak. This behavior i s i d e n t i c a l t o that o b s e r v e d f o r t h e e l e c t r i c a l g r a d e n o v o l a c epoxy ( F i g u r e 2) and t h e s i l o c o n e - e p o x y ( F i g u r e 6 ) , a n d , i n t h i s c a s e , i s a t t r i b u t e d t o r e a c t i o n s i n v o l v i n g t h e flame r e t a r d a n t . Again, no s i g n i f i c a n t d i f f e r e n c e s a r e o b s e r v e d i n t h e DSC p l o t s below 300°C. Elemental Analyses. The X-ray f l u o r e s c e n c e measurements o f T a b l e I I i n d i c a t e a somewhat h i g h e r t o t a l B r c o n t e n t f o r t h e s e m i c o n d u c t o r g r a d e n o v o l a c ( s a m p l e F) t h a n f o r t h e e l e c t r i c a l grade (sample A ) . However, t h e d a t a o f T a b l e I I I i n d i c a t e h a l i d e c o n c e n t r a t i o n s i n t h e e x t r a c t t h a t a r e an order o f m a g n i t u d e l o w e r f o r t h e s e m i c o n d u c t o r g r a d e n o v o l a c ( s a m p l e G) i s a f a c t o r o f t h r e e m a t e r i a l (sample F ) . Discussion E l e c t r i c a l / E l e c t r o n i c Grade Epoxy. TGA and DSC a n a l y s e s r e v e a l e d no d i f f e r e n c e i n t h e r m a l d e g r a d a t i o n below 200°C due t o t h e p r e s e n c e o f FR. DSC and EGA m e a s u r e m e n t s showed t h a t t h e FR b r e a k s down a b o v e 3 5 0 ° C , i n t h e r a n g e where i t c a n p e r form i t s d e s i g n a t e d f u n c t i o n . However, t h e EGA a n a l y s i s d i d d e t e c t a s m a l l q u a n t i t y o f b r o m i n e - c o n t a i n i n g f r a c t i o n s below 200°C, and aqueous e x t r a c t i o n r e v e a l e d a f a i r l y h i g h B r " c o n c e n t r a t i o n o f 160 ppm. S i n c e n o d i f f e r e n c e was f o u n d b e t w e e n FR a n d n o n - F R f o r m u l a t i o n s i n d e v i c e a g i n g s t u d i e s ^ , some o t h e r c a u s e must account f o r t h e r e l a t i v e l y e a r l y f a i l u r e s observed^>^ f o r d e v i c e s m o l d e d i n t h e e l e c t r i c a l g r a d e e p o x y m a t e r i a l and aged u n d e r b i a s a t 2 0 0 ° C . These f a i l u r e s a r e a t t r i b u t e d t o c h l o r i d e contamination present i n t h enon-semiconductor grade epoxy r e s i n . T h e e x t r a c t a b l e CI"" c o n c e n t r a t i o n i s a f a c t o r o f f o u r h i g h e r t h a n B r " , a n d t h i s i s c o r r e l a t e d w i t h a much h i g h e r c o n c e n t r a t i o n o f C H ^ C l t h a n CH~Br i n t h e EGA d a t a b e l o w 200°C . The h i g h B r " c o n c e n t r a t i o n i s a l s o a t t r i b u t e d t o t h e 1


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to t h epoorer "housekeeping" i n p r e p a r a t i o n o f a non-semicond u c t o r g r a d e compound, r a t h e r t h a n t o a n i n h e r e n t p r o p e r t y o f a FR e p o x y . I t s h o u l d be n o t e d t h a t even t h i s n o n - s e m i c o n d u c t o r g r a d e n o v o l a c was f o u n d t o h a v e a d e q u a t e r e l i a b i l i t y f o r molded d e v i c e s o p e r a t e d below 100°C^. Semiconductor Grade S i l i c o n e - E p o x y . TGA, DSC, a n d EGA a n a l y s e s r e v e a l e d no d i f f e r e n c e b e t w e e n t h e FR a n d non-FR compounds b e l o w 2 0 0 ° C . T h e FR m o i e t i e s a g a i n decomposed o n l y i n t h e temperature range above 350°C. T h e r e was v e r y l i t t l e C l ~ o r B r " i n t h e a q u e o u s e x t r a c t , and n o CH3CI o r CH^Br was d e t e c t e d i n t h e EGA p r o d u c t p r o f i l e s . T h i s shows t h e c a p a b i l i t y o f m a t e r i a l formulators t o supply very c l e a n semicond u c t o r g r a d e m o l d i n g compounds. N o n e t h e l e s s , t h e FR s i l i c o n e - e p o x y h a s y i e l d e d s i g n i f i c a n t l y l o w e r r e l i a b i l i t y t h a n t h e e q u i v a l e n t compound w i t h o u t FR i n b i a s aging o f d e v i c e s a t 200°C^. I n those experiments, both t h e a c t i v a t i o n e n e r g y a n d t h e e l e c t r i c a l f a i l u r e mode w e r e i n d i c a t i v e o f f a i l u r e s due t o c a t i o n m i g r a t i o n . This i s i n marked c o n t r a s t t o t h e a c t i v a t i o n e n e r g y a n d f a i l u r e a n l a y s i s r e s u l t s r e p o r t e d f o r t h e e l e c t r i c a l g r a d e e p o x y ^ , w h i c h showed d e v i c e f a i l u r e s due t o c o r r o s i o n o f m e t a l l i z a t i o n , presumably due t o CI"". T h e r e f o r e , d e v i c e f a i l u r e f o r t h e FR s i l i c o n e epoxy i s , a g a i n , n o t d i r e c t l y r e l a t e d t o t h e p r e s e n c e o f B r . However, i t a p p e a r s t h a t t h e f l a m e r e t a r d a n t s y s t e m may b e r e s p o n s i b l e f o r c a t i o n g e n e r a t i o n v i a some m e c h a n i s m a s y e t unexplained. Semiconductor Grade E p o x i e s . A s was t h e c a s e f o r t h e s e m i c o n d u c t o r g r a d e s i l i c o n e - e p o x y , t h e r e was n o d i f f e r e n c e between FR a n d non-FR e p o x i e s r e c o r d e d b y e i t h e r DSC o r EGA below 200°C. However, t h e n o m i n a l l y e q u i v a l e n t non-FR e p o x y e x h i b i t e d s i g n i f i c a n t l y lower thermal s t a b i l i t y as i n d i c a t e d by t h e i s o t h e r m a l TGA d a t a . F u r t h e r m o r e , t h e aqueous e x t r a c t o f t h e n o n - F R compound c o n t a i n e d more t h a n t w i c e a s much C l ~ a s t h e c o m b i n e d c o n c e n t r a t i o n s o f C I " a n d B r " i n t h e FR e p o x y . A l t h o u g h t h e r e h a v e been n o d i r e c t c o m p a r i s o n s o n d e v i c e a g i n g w i t h t h e s e two e p o x i e s , t h e a b o v e f i n d i n g s i n d i c a t e t h a t t h e FR compound, b e i n g c l e a n e r a n d more t h e r m a l l y s t a b l e , c o u l d a c t u a l l y be t h e b e t t e r m a t e r i a l f o r e n c a p s u l a t i o n a p p l i c a t i o n s . A c k n o w l e d gmen ts The a u t h o r s t h a n k A. Z a b o t t i f o r t h e r m a l a n a l y s i s d a t a , R. J . Holmes f o r X - r a y f l u o r e s c e n c e m e a s u r e m e n t s , a n d T. W. Z u b e r f o r m o l d i n g .


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Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

Lum, R. M.; Feinstein, L. G. Microelectronics and Reliability, 1981, 21, 15. Feinstein, L. G. Microelectronics and Reliability 1981, 21, 00. Masessa, A. J.; Feinstein, L. G. To be published. Sherman, S.; Gannon, T.; Buchi, G.; Howell, W. R. in "Kirk-Othmer: Encyclopedia of Chemical Technology", Vol. 9, 3rd. edit., John Wiley and Sons, 1980, pp. 267-290. Helfand, D.; Villani, T. Proc. 14th. Elec./Electr. Conf., 1979, pp. 290-297. Melliar-Smith, C. M.; Matsuoka S; Hubbauer, P. private communication. Lum, R. M. J. Polym. Sci. Chem. Ed. 1979, 17, 203. Davidson, T. E . ; Roberts, C., W. J. Appl. Polym. Sci. 1980, 25, 1491.

RECEIVED November 3, 1981.


Thermal Degradation of Polymers for Molded Integrated Circuit (IC

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