Reliability enhancement of electrically conductive adhesives in thermal shock environment [electronics packaging]

The elimination of lead containing interconnect materials from electronics has gradually become a critical issue in recent years, and electrically conductive adhesives (ECA) have been considered as promising alternative interconnect materials for lead containing solders. However, ECAs are, among others, usually poor in impact capability. This leads to lower reliability performance of ECA/component joints in thermal cycling/shock conditions. The approach of using flexible polymer binders for ECA materials was devised to enhance the thermal cycling/shock reliability while maintaining an acceptable bulk conductivity. The curing behavior, modulus, coefficient of thermal expansion and moisture absorption were measured in the designed ECA formulations. Adhesion to Cu/OSP and tin surfaces was studied through substrate shear tests. Electrical bulk resistivity and contact resistances were monitored on specially prepared test coupons that were exposed to 85°C/85%RH atmosphere. Experimental results showed that the rubbery ECA samples could typically give very similar bulk conductivity to that of conventional ECA materials. Some of the formulations exhibited acceptable contact resistance stability under thermal cycling conditions, while the ECA/component joint interfaces kept intact through the thermal cycling tests.