Thermo-mechanical reliability analysis of package-on-package assembly

Package on Package (PoP) is a packaging technology that one package is placed on top of another package to integrate different functionalities while still maintain same foot print size. The advantages of PoP are evident, but there are also some challenges with respect to packaging and Surface Mounting Technology (SMT). Due to the complex architecture of PoP, some reliability issues have been raised, reliability related to thermo mechanical issues are major challenges in the design of PoP. In this paper, package warpage and solder joint reliability during lead free reflow temperature, high temperature storage test and steady state temperature humidity test were investigated. After test, all components were electrically measured for continuity. The samples and their cross-sections were examined by scanning electron microscope (SEM). The intermetallic compound (IMC) thickness of solder/PCB interface and two interfaces of solder/substrate of top solder joints were measured. The results showed steady state temperature humidity test have no significant impact on mechanical reliability of PoP package. After high temperature storage test, the package emerge larger warpage and the thickness of IMC was grow comparatively large. It can be found that the thermal stress play an important role on the mechanical reliability of PoP Package. Finally, 3D finite element analysis (FEA) was performed, and the stress distribution under reflow process reflow temperature warpage was investigated. The results of this study can be used as a reference by original equipment manufacturers (OEMs) to estimate mechanical reliability of PoP Package.