Experimental Damage Mechanics of Microelectronics Solder Joints under Concurrent Vibration and Thermal Loading

Abstract

Concurrent vibration and thermal loading is commonly encountered in the service life of electronic packaging, such as in automotive, airplane, military and mobile electronic devices. Solder joint reliability has been a critical issue of the overall design of microelectronic devices. However, the contribution of vibration to thermal fatigue life of solder joints has rarely been investigated. Presently, vibration is taken as a loading case that only causes elastic material response. Literature is scarce on vibration plasticity and vibration caused fatigue for micron scale structures. 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 for micron scale solder joints. There are a number of constitutive models to simulate thermomechanical behavior of solder joints, yet few of these, if any, models are verified by test data obtained from actual microelectronics solder joints. The authors see the need of such tests for the purpose of better understanding of material behavior of micron scale 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. Moiré 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 are assembled together to perform the concurrent cycling. The cyclic plasticity of solder joints and microstructure evolution are discussed and related to fatigue life prediction. The results obtained in this study agree with findings reported in the literature from micron scale material testing where it has been shown that “smaller is stronger.”