Investigation of PoP package structure with copper pillar replace the solder ball

Package on Package (PoP) is a widely used high density package solution for package stacking technology in various device applications. Normally, the top package will connect to the bottom package by solder ball with several hundred micrometer diameter. The I/O number will be limited due to the solder ball will collapse during the reflow. In this study, a copper pillar with diameter of 200µm and height of 150-180µm will be used to replace the solder ball. With the structure of copper pillar, only a very small volume of solder will be used for the joint to connect the top and bottom package. In this paper, the finite element Modeling (FEM) simulation will be used to calculate the temperature distribution in the new PoP package with copper pillar. Also, the Cu pillar/solder joint microstructure evolution will be studied in several reliability tests, including 500 cycles temperature cycling test (TCT) and high temperature storage test (HTST) at 150°C with 500h.