Development of brazing interconnection to low thermal expansion glass-ceramics for high performance multichip packaging

The development of brazing interconnection technology to low thermal expansion glass-ceramics is discussed in detail. A two-paste thick-film metallization system which acts not only as a chemical barrier to the braze alloy, but also as a high-ductility stress cushion to reduce joining stresses on the glass-ceramic was developed along with a braze alloy paste with enhanced ductility and wettability. Results of studies on joining Kovar, Invar, and Platinite-2 (with temperature coefficient of expansion (TCE) ranging from 1.5 to 5.5 ppm/°C) to low TCE glass-ceramics are presented. Attention is given to the development of process and design guidelines which were driven by the stringent demand on limiting the total stress so that the combined stresses generated from thick-film metallization, braze joint, and adhesion strength do not exceed the fracture strength of the glass-ceramic. Process conditions that allow the post thin-film multilayer metallization of the cofired glass-ceramic, thus combining the capabilities of both MCM-C´s and MCM-D´s for high-performance multichip packaging, was developed. Thermal cycling reliability data for two multichip modules (MCMs) with brazed pins, leads, and large windowframe are also discussed