Inelastic behavior of microelectronics solder joints under concurrent vibration and thermal cycling

Concurrent vibration and thermal environment is commonly encountered in the service life of electronic packaging, such as automotive, airplane, military and mobile electronic devices. Solder joint reliability has been a critical issue of the overall design of microelectronic device. However, the contribution of vibration to thermal fatigue life of solder joints has rarely been investigated. Vibration is taken as a loading case that only causes elastic material response. Literature is scarce on vibration plasticity and vibration caused fatigue. The standard practice in the industry is to use Miner's rule to calculate combined environment fatigue life. This study shows that using Miner's rule for fatigue life under combined loading is inaccurate. There are a number of models on thermomechanical behavior of solder joints, yet few models are verified by test data obtained from actual package size solder joints under realistic thermomechanical loading. The authors see the need of such tests for the purpose of better understanding of material behavior of solder joints under thermal and vibration loading and providing a solid basis for more accurate material modeling and fatigue life prediction. This paper reports observations from a series of concurrent thermal cycling and vibration tests on 63Sn/37Pb solder joints of an actual ball grid array (BGA) package. Moire interferometry (MI) is used to measure the inelastic deformation field of solder joints with submicron resolution. A large capacity Super AGREE thermal chamber and a high acceleration electrodynamic shaker is assembled together to perform the concurrent cycling. The cyclic plasticity of solder joints and microstructure evolution are discussed and related to fatigue life prediction.