Reliability analysis and case studies on FCBGA packaged devices

Failure modes and failure mechanisms under external stress generated by high temperature, electricity and moisture were studied with 0.13-µm/6-level copper-based FPGA with FC-PBGA package. Case Studies and the results indicate that FC-PBGA devices have three main kinds of failure modes: Vcc electrically short to GND, Vcc+ electrically short to Vcc- and I/O pins electrically open to GND. The thermal stress induced by the internal and external reflowing temperature difference and high temperature reflowing process when assembled is the root cause of these failures. It brings different degrees of damage to solder bump on the flip chip, underfill between the die and substrate gap, die and its internal structure, resulting in the device failure. The thermal stress made the solder bump on the flip chip melt again and bridge the adjacent solder bumps to lead to device short-circuit failure. It also induced crack or delamination in the underfill, crack in solder bump or solder bump fallen off to lead to device open-circuit failure. The residual stress on Cu/low-k interconnect structures affects the structure integrity and reliability. The result of this study can serve as guidance for reducing or preventing the occurrence of failure and improve the application reliability of FC-PBGA packages.