Reliability evaluations of flip chip package under thermal shock test

The microstructural investigation and thermo-mechanical reliability evaluation of the Sn-37Pb solder bumped flip chip package were carried out during the thermal shock test of the package. In the initial reaction, the reaction product between the solder and Cu mini bump of the chip side was Cu₆Sn₅ IMC layer, while a layer of Ni₃Sn ₄ was formed between the solder and electroless Ni-P layer of the package side. The primary failure mechanism of the solder joints in this type of test method and package was confirmed to be thermally activated solder fatigue failure. The brittle interfacial failure mode was sometimes detected from the cross-sectional studies, but nearly whole of the failed packages showed the occurrence of the typical fatigue cracks. The finite element analyses were conducted to interpret the failure mechanisms of the packages. The finite element analyses revealed that the cracks were induced by the accumulation of the plastic work.