Impact of uneven solder thickness on IGBT substrate reliability

Computer simulation method have been used to investigate the effects of uneven thickness of substrate solder interconnect on the reliability of an IGBT power electronics module under cyclic temperature loading conditions. The solder material that has been used in the simulation is Sn3.5Ag and the Garofalo equation has been used to describe the solder´s nonlinear mechanical behavior. The equivalent plastic strain per temperature cycle of the solder joint has been used as a damage indicator and its values for a few solder joints with various degrees of solder joint unevenness have been compared. The uneven thickness of a model is created by tilting the substrate about an edge of the substrate while the solder volume is kept constant. The results showed that the impact of the substrate tilt on crack initiation time is very similar to that of the solder joint thickness for solder joints with even thickness. A solder joint thickness control method of using ceramic spacers has also been analyzed in order to evaluate the effects of the spacers on the reliability of substrate solder joint.