Effect of Mean Temperature on the Evolution of Strain-Amplitude in SAC Ball-Grid Arrays during Operation under Thermal Aging and Temperature Excursions

Abstract

Electronics in automotive applications may be used for a number of safety critical systems including lane-departure warning, collision avoidance, drive assist systems, and adaptive cruise control. Furthermore, electronics in fully-electric vehicles may be used for power generation and management. Automotive electronics may be mounted on engine or on transmission or in the base of the automobile and may be subjected to operational temperature excursions in addition to environmental temperature extremes. Further, automotive electronics systems may be subjected to prolonged periods of storage at ambient environmental low or high temperatures. There is need for tools and techniques for proactive assessment of consumed life, remaining useful-life, and spot assessment of thermo-mechanical reliability of electronics to assure reliable operation for the automotive benchmark of 10-years, 100,000 miles. In this study, the effect of thermal aging on thermal cycling reliability and the evolution of strain has been studied using digital image correlation. Leadfree assemblies which have been subjected to prolonged periods of aging have been subsequently subjected to thermal cycling and the strain amplitude experienced in the solder joints has been measured using digital image correlation. These strain state results then were correlated with microstructural damage rate (obtained from a separate study) to develop a damage mapping model. Finally, a new approach of life model along with Remaining Useful Life (RUL) estimation technique has been presented based upon microstructural damage rate.