SnAgCu Lead-Free Electronics Reliability Under Combined Temperature and Vibration Environments
Authors: Pradeep Lall and Geeta Limaye Company: Auburn University Date Published: 10/14/2012
Abstract: Electronics installed in automotive systems are subjected simultaneously to mechanical vibrations and thermal loads in underhood applications. Typical failure modes include solder joint failure, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. The solder interconnects accrue damage much faster when vibrated at elevated temperatures. Industry migration to leadfree solders has resulted in a proliferation of a wide variety of solder alloy compositions. Presently, the literature on mechanical behavior of leadfree alloys under simultaneous harsh environment of high-temperature vibration is sparse. In this paper, a test vehicle with a variety of lead-free SAC305 daisy chain components including BGA, QFP, SOP, TSOP has been tested to failure by subjecting it to two elevated temperatures and harmonic vibrations at its first natural frequency. The test matrix includes variation in the amplitude of vibration from 10G to 14G as well as variation in temperature. Full field strain on the PCB has been extracted using high speed cameras operating at 100,000 fps in conjunction with digital image correlation. The vibration simulation using global-local finite element models is correlated with the system characteristics such as modal shapes and natural frequencies. The vibration simulation provides a fatigue life prediction that has been validated with the experimentally obtained cycles to failure. In addition, the packages have been cross-sectioned to study the failure modes. A comparison of failure modes for different surface mount packages at elevated test temperatures and vibration has been presented in this study.