Investigation on Inelastic Strain Energy of IGBT Solder Layers During Aging by the Clech Algorithm

The Clech algorithm provides a promising solution for simulating the mechanical properties of solder joints under cyclic load. It can be utilized to represent loading history and calculate the inelastic strain energy density ∆W of solder layer. In previous energy-based lifetime models using the Clech algorithm, the inelastic strain energy density ∆W per cycle of the soldering critical region is treated as constant. However, ∆W will actually change with aging. In this paper, by finite element analysis (FEA) the assembly stiffness K and imposed strain D in the Clech algorithm are shown to change with solder aging, which would greatly change ∆W calculated. The birth and death technology of ANSYS is used to emulate crack propagation, the corresponding K and D values are yielded. Finally, the results of crack initiation and propagation are compared to verify the idea that ∆W obtained by the Clech algorithm needs to be constantly updated as the solder layer ages, which would shed light on the improvement of energy-based lifetime prediction by the Clech algorithm.