Reliability of package on package (PoP) subjected to thermal and power loadings

Traditional thermal loading test neglects the influence of power applied to PoP. To address this challenge, board level reliability of PoP subjected coupled thermal and power loadings were investigated in this study. In order to provide the coupled thermal and power loadings, high temperature storage (HTS) and constant current source were chosen for the accelerated test. Five test conditions (0A, 0.5A, 0.75A, 1.0A, 1.5A at 120°C) were adopted to evaluate the board level reliability of PoP. Experiment results revealed that the thermal and especially the power loadings had critical impact on the resistance of solder joints of PoP. The larger the current applied, the more the voids produced. Most of the voids were located on the inner ring of the bottom package. Besides, when solder joints suffered a large current, the generated Joule heat could melt down the solder balls in a short time. Current applied to PoP should be carefully considered and the critical spots located on the inner ring of the bottom package need to be specially tackled to improve the reliability of PoP.