Effect of solder ball pad design on cavity down BGA solder joint reliability

Solder joint reliability is a critical requirement for successful application of BGA packages in electronic industry. Cavity down BGA package is drawing more and more attention because of its high performance, superior electrical and thermal characteristics. Solder ball pad design is one of the most important parameters to affect BGA package solder joint reliability. In this study, both temperature cycle test and finite element analysis were used to analyze the effect of pad design on solder joint reliability of a fine pitch Cu-based cavity down BGA. Three dimensional (3D) finite element (FEM) slice model based on volume weighted average viscoplastic strain energy accumulated per temperature cycle for the interface elements has shown consistent results with temperature cycle test experiments. Based on this model, parametric finite element analysis was carried out to determine the effect of solder ball pad size on cavity down BGA package solder joint reliability. Normally solder mask defined (SMD) pad is used for package land and none solder mask defined (NSMD) pad is used for printed circuit board (PCB) land. All of the test and FEM models for this study consider the same conditions. The results reveal that when PCB board land pad size is closer to and smaller than package land pad size, the package shows better solder joint reliability. This result will help end users to design PCB board properly.