Reliability of a flip-chip package thermally loaded between-55°C and 125°C

Low-temperature reliability of flip-chip plastic ball-grid array packages is a concern for manufacturers. Packages that perform well when thermally cycled from 20 to 120 degrees C fail at an unacceptable rate when the temperature is extended down to -55 degrees C. Electron-beam moire was used to study local deformations in a flip-chip package and the interactions among the various materials found within the package. The specimen was subjected to a total often complete thermal cycles from -55 to 125 degrees C over several nonconsecutive days. Debonding initiated between the solderball and the solder mask where that interface meets the printed circuit board. Deformation was also induced within the solderball, becoming more pronounced with more thermal cycles. Out-of-plane strains appear to be the dominant mechanism for deformation at this location.