Chapter 33
Performance of Stable Brominated Epoxies in Encapsulants for Microelectronic Devices
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D. B. Fritz and C. S. Wang Dow Chemical Company, Freeport, TX 77541
Epoxy molding compounds, used to encapsulate microelec tronic devices, contain bromine to provide flame retardancy to the package. This bromine, typically added as tetrabromo bisphenol-A or its epoxy derivative, has been found to contain many hydrolyzable bromides. These bromides, along with the presence of chloride impurities, are detrimental to the life of the elec tronic component. Bromine especially has been suspected (proven) to cause wire bond failure when subjected to moisture and/or high temperatures. With the addition of a more thermally and hydrolytic stable bromine compound, flame retardancy does not have to be compromised to increase the device reliability. Stable brominated cresol epoxy novolac, when formulated into a microelectronic encapsulant, increases the reliability of the device without sacrificing any of the beneficial properties of present-day molding compounds. Cresol Epoxy Novolac (CEN) and t h e epoxy d e r i v a t i v e o f tetrabromobisphenol-A (TBBA) a r e t h e r e s i n s t y p i c a l l y employed t o encapsulate m i c r o e l e c t r o n i c d e v i c e s i n molding compounds. The brominated r e s i n , which i s u t i l i z e d as a f l a m e - r e t a r d a n t a d d i t i v e t o impart a degree o f i g n i t i o n r e s i s t a n c e t o t h e encapsulant, c o n t a i n s many u n s t a b l e h y d r o l y z a b l e bromides. These bromides, along with t h e presence o f chloride impurities, are detrimental to the l i f e o f the e l e c t r o n i c component. S p e c i f i c a l l y , bromine has been suspected and proven t o cause wire bond f a i l u r e (1-3). Brominated compounds, where t h e bromine i s i n t h e meta p o s i t i o n to the p h e n o l i c h y d r o x y l , have been shown t o be more h y d r o l y t i c a l l y and t h e r m a l l y s t a b l e than ortho-brominated compounds such as TBBA (4). These s t a b l e bromine compounds can be i n c o r p o r a t e d i n t h e CEN molecule and formulated i n t o a molding compound. These molding compounds p r o v i d e i n c r e a s e d d e v i c e r e l i a b i l i t y without s a c r i f i c i n g any o f the b e n e f i c i a l p r o p e r t i e s o f present molding compounds. 0097-6156/89/0407-0405$06.00/0 β 1989 American Chemical Society
Lupinski and Moore; Polymeric Materials for Electronics Packaging and Interconnection ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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406
POLYMERS FOR ELECTRONICS PACKAGING AND INTERCONNECTION
T a b l e I shows t h e t y p i c a l a n a l y t i c a l p r o p e r t i e s o f s t a b l e b r o m i n a t e d CEN and t h e s t a n d a r d h i g h p u r i t y r e s i n b l e n d o f CEN (QUATREX* 3430) and t h e e p o x y o f TBBA (QUATREX 6 4 1 0 ) . T h i s r e s i n b l e n d o f CEN and t h e e p o x y o f TBBA was m i x e d i n a r a t i o t h a t c o r r e sponds w i t h what i s t y p i c a l l y u s e d i n m i c r o e l e c t r o n i c e n c a p s u l a n t s . The s t a b l e b r o m i n e CEN was s y n t h e s i z e d t o match t h e b r o m i n e c o n t e n t o f t h e r e s i n b l e n d . The t o t a l b r o m i n e c o n t e n t o f t h e r e s i n b l e n d and t h e s t a b l e b r o m i n e CEN i s 7%; however, t h e h y d r o l y z a b l e b r o m i d e i m p u r i t i e s o f t h e s t a b l e b r o m i n e CEN i s much l o w e r t h a n t h a t o f t h e s t a n d a r d r e s i n b l e n d . T h i s low c o n t e n t o f h y d r o l y z a b l e b r o m i d e , a l o n g w i t h t h e low c h l o r i d e c o n t e n t , c o n t r i b u t e s t o a n i n c r e a s e i n device r e l i a b i l i t y TABLE I.
T y p i c a l A n a l y t i c a l P r o p e r t i e s Based o n R e s i n ( s ) at 7% Bromine
QUATREX 3430 + S t a b l e Bromine C r e s o l EDOXV N o v o l a c OUATREX 6410 Property 7.0% Bromine, wt. % 7.0% V i s c o s i t y @ 150°C, c k s 300-600 300-600 E p o x i d e , wt. % 20.5% 20.3% E p o x i d e E q u i v a l e n t W e i g h t (EEW) 210 212 H y d r o l y z a b l e C h l o r i d e , ppm
