Reliability Research On Package On Package (PoP)

PoP(Package on Package) is a new form of three-dimensional packaging. PoP allows its devices to be tested before assembly, which can ensure the higher yield rate and greatly reduce the total stacking assembly cost. PoP has been widely used in mobile phones, digital cameras, and other electronic products. But the structure of PoP is relatively complex. Its heat dissipation problem, thermal mismatch problem caused by thermal expansion coefficient mismatch between packaging materials, and the problem of reliability under drop impact load restrict the further development of PoP package. Therefore, it is very important to study the reliability of PoP packaging devices.In this study, the board level drop test simulation of package on package was performed by finite element analysis. Study results showed that the repeated bending of PCB may be one of the main reasons for the failure of Ball Grid Array. The results showed that with the increasing of pulse amplitude and pulse time, the maximum displacement of PCB increased,possibly would cause the solder joint failure rate increased.In this paper, the 1/4 finite element model was built by using the finite element analysis software ABAQUS to inspect the reliability of the solder according to the JESD22-A104 C standard.The results showed that the maximum equivalent stress value of the solder balls concentrated at the corner of the PoP package. The accumulated equivalent creep strain maximum point was located in the inner layer solder ball array, and was near the edge of the chip. The cumulative equivalent creep of the top module was larger than the bottom module.Increase the thickness of the chip, the max equivalent stress and thermal fatigue life was increased. Increae the thickness of the substrate can make the package thermal stress decreased, but the fatigue life of solder joints would be reduced. Among the four kinds of substrate materials, AlN,SiC, BeO, and Al2O3, BeO substrate had the highest thermal fatigue life.With the increase of thermal expansion coefficient of plastic material, the maximum solder joint stress decreased, the fatigue life increased.