Creep-Fatigue Behavior of Micro-electronic Solder Joints

Even at room temperature, solder joints exhibit both creep and fatigue behavior that is strongly dependent on solder joint configuration, the thermal environment, and the solder alloy properties. The microstructures of solder joints with up to 25 years of aging have been studied using SEM/EDS and metallographic techniques. Data are presented on grain growth and metallurgical composition versus aging time. A special nonlinear finite element creep-fatigue simulation model has been developed, based on measured strain-rate hardness relationships, and used to analytically predict the effects of observed metallurgical changes and the effects of lead stiffness in solder joint creep-fatigue interaction. To cor-roborate the analytical results, a special bimetallic test fixture has been developed to accelerate the thermo-mechanical loading of solder joints in thermal cycling environments. Measured time-to-failure data for various electronic-package lead configurations/stiffnesses, including gullwing and J-lead, are presented and shown to be in reasonable agreement with the analytical results