Chapter 37
Ordered Polymers for Interconnection Substrates
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Richard Lusignea, Joseph Piche, and Richard Mathisen Foster-Miller, Inc., 350 Second Avenue, Waltham, MA 02254
Ordered polymer films made from poly benzthiazole (PBZT) and poly benzoxazole (PBO) can be used as substrates for multilayer printed circuit boards and advanced interconnects to fill the current need for high speed, high density packaging. Foster-Miller, Inc. has made thin substrates (0.002 in.) using biaxially oriented liquid crystal polymer films processed from nematic solutions. PBZT films were processed and laminated to make a substrate with dielectric constant of 2.8 at 1 MHz, and a controllable CTE of 3 to 7 ppm/°C. The films were evaluated for use in multilayer boards (MLBs) which require thin interconnect substrates with uniform controllable coefficient of thermal expansion (CTE), excellent dielectric properties, low moisture absorption, high temperature capability, and simple reliable processing methods. We found that ordered polymer films surpass the limitations of fiber reinforced resins and meet the requirements of future chip-to-chip interconnection. The r e q u i r e m e n t s f o r advanced m i l i t a r y MLBs a r e shown i n T a b l e I . One o f t h e major problems o f u s i n g l e a d l e s s c e r a m i c c h i p c a r r i e r s i n advanced a v i o n i c s (VHSIC and VLSI) a p p l i c a t i o n s i s t h e mismatch between t h e CTE o f a l u m i n a c h i p c a r r i e r s (6.4 ppm/°C) o r s i l i c o n (3 ppm/°C) and c o n v e n t i o n a l g l a s s / e p o x y s u b s t r a t e s (12 t o 17 p p m / ° C ) . T h i s mismatch r e s u l t s i n w o r k - h a r d e n i n g and c r a c k i n g o f s o l d e r j o i n t s which a t t a c h t h e d e v i c e s t o t h e s u b s t r a t e . Thermal c y c l e s as extreme as -65 t o +125°C may be e n c o u n t e r e d , and a r e known t o cause s o l d e r f a i l u r e and o t h e r damage. O r d e r e d polymer f i l m s c a n s o l v e t h i s problem because t h e y c a n be matched t o the c e r a m i c CTE. Moreover, o r d e r e d polymers have e x c e l l e n t
0097-6156/89/0407-0446$06.00/0 c 1989 American Chemical Society
Lupinski and Moore; Polymeric Materials for Electronics Packaging and Interconnection ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
447 Ordered Polymers for Interconnection Substrates
37. LUSIGNEA ET AL. Table I. CTE ( x - y ) CTE ( z ) Dielectric
Requirements f o r S u r f a c e Mount MLBs
constant
Moisture absorption Single layer thickness Flexural strength Resin-reinforcement adhesion Tg Processing
3 t o 7 ppm/°C t a i l o r a b l e ~17 t o 18 ppm/°C
