Drop test reliability of the 20 mm x 20 mm RDL-first FOWLP on bottom and 8 mm x 8 mm WLCSP on top
for Package on Package (PoP) test vehicle was validated by the experimental testing in this paper. The results show that the built up PoP test vehicle can pass 30 times of drop impact test and some samples can pass 200 times drop impact test with the loading of 1500 G/0.5 ms. The failure mechanisms of Cu pad peeling off, cracking of dielectrics and Cu trace on the bottom RDL-first FOWLP and crack on package corner solder joints of top WLCSP were identified by cross section observation. The peeling stress level on the solder joint and dielectrics layer were investigated by the dynamic explicit nonlinear drop impact simulation.
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