Constitutive behaviour and life evaluation of solder joint under the multi-field loadings

The mechanical behaviour and service life of the 63Sn-37Pb solder joint under coupled thermal-electrical loadings have been investigated. The mechanical properties of solder material are calibrated by uniaxial tensile experiments at different strain rates and working temperatures. In order to describe the mechanical responses of solder alloy, a constitutive model is proposed based on a thermo-visco-plastic flow rule. Furthermore, the fatigue life of solder joints is predicted by establishing a 3D finite element model under the coupled electrical-thermal-mechanical loadings. Temperature distribution, current density and thermal stress are numerically obtained in the solder joint. Based on the distribution of stress and plastic strain, the vulnerable location in the solder joint is determined, which is critical for predicting the service life based on the Coffin-Manson model. By varying the loading conditions, a parametric study is performed to develop an empirical formula of fatigue life, and the dominant factor under complicated working conditions is assessed. It is found that the current density and heat sink temperature pronouncedly influence the fatigue life of solder joint. The empirical predictions show reasonable accuracy compared with the Coffin-Manson model and finite element simulations.