Negative impact of certain adhesive configurations on solder joint reliability of package on package architecture: A comprehensive experimental and numerical study

In this study we assessed the impact of adhesive configurations on package-on-package (POP) interface solder joint reliability (SJR). This problem has not been previously well understood and we applied both experimental evaluation and computational mechanics modeling to develop insights into the underlying physics. We found that certain adhesive configurations can degrade POP shock performance very significantly - so significantly that the overall package shock performance with adhesive is lower than one without. This is contrary to prevalent expectation of impact of adhesives on shock capability. These shock degrading underfill and corner glue configurations are where the overall height of the adhesive is low, such that adhesive does not contact POP interface. The reason for this loss in POP shock capability is due to overall stiffening of board-package interface and higher transfer of shock stresses to the POP interface. Further, it was found that, POP shock risk can be reduced with appropriate adhesive configuration, in particular by using a high glue height such that the glue covers the POP interface. The impact of low coefficient of thermal expansion adhesive configuration on POP temperature cycling (TC) was also studied; similar impact of glue height was found.