Modeling thermo-mechanical reliability of bumpless flip chip package

FEA of the thermo-mechanical reliability of a bumpless flip chip package (BFCP) was investigated. Both package-level and board-level assemblies are modeled using 2D plane strain models. The package-level temperature cycling profile used was -65°C to +150°C, with 2 cycles/hour, upper and lower soak time of 10 minutes. The package survived 2000 cycles without any failures. The board level assembly test is planned and modeling is conducted for a temperature cycling profile of -40°C to +125°C, with 1 cycle/hour, upper and lower soak time of 15 minutes. For the package level analysis, the copper interconnection material properties were modeled using different properties from bulk Cu and electroplated Cu data. The mechanical properties of both the bulk and electroplated copper were used in the FEA simulation and the results compared. A fatigue life prediction study, using the appropriate thin-film properties of Cu and the fatigue properties of thin-film Cu gave reasonable predicted life. For the second level solder joint analysis, the deformation behavior of the compliant terminals with the solder joints were investigated. Visco-elastic properties were used for the epoxy resin, viscoplastic properties were used for the eutectic Sn-Pb solder joints. The elastic energy density method was used for solder joint fatigue life prediction.