An Investigation into Thermomigration Failure of Flip Chip Solder Joint Interconnects used in High Reliability Applications

The experimental study described herein investigates thermomigration of both eutectic Sn/Pb and lead free Sn/Ag/Cu solder joints, with the additional focus on the development of an Arrhenius failure model of time-to- failure as a function of temperature. Flip chip test vehicles were assembled with daisy chain die, with and without underfill, attached to ceramic and organic package substrates, using standard reflow processes. Three different under bump metallurgy technologies were investigated: sputtered thin film Al/NiV/Cu, thick electroplated nickel, and thick electroplated copper (i.e., copper pillars). The test vehicles were subjected to unbiased high temperature storage (HTS) testing with temperatures ranging from 125°C to 200°C. Failure was determined from continuity testing at regular intervals until an open circuit or high resistivity was detected. The results demonstrate the robustness of Al/NiV/Cu UBM at temperatures less than 130°C, and of the thick electroplated UBM at temperatures of 150°C. Based on the HTS test results, and corresponding analyses, a thermomigration failure model was generated for eutectic Sn/Pb and lead free Sn/Ag/Cu solder alloys using an Arrhenius-like fit to the failure data.