Modeling of Effect of Underfill Properties on Flip Chip Bumps and Solder Balls of FCBGA Package in Automotive Underhood Applications

Thermo-mechanical reliability of Flip Chip Ball Grid Arrays in automotive underhood environments has received a lot of attention owing the emergence of new application in advanced driver assist systems including guidance, navigation and control. The reliability and the extended time survivability of the materials and interfaces in the advanced package architectures is not well understood. In this paper, the effect of four different developmental underfill encapsulant properties on flip chip bumps and solder balls were investigated using lidded FCBGA model. The material properties of the developmental underfills which have been measured in a prior study by the authors, have been used for the purpose of modeling. The effect of the underfill properties on the plastic work in the package-level solder joints and chip-level solder joints has been modeled under the automotive thermal cycle of -40 to +125 degrees C. Each cycle is of 2 hours and consist of 40 and 20 minutes of ramp and dwell times, respectively. Interaction of the material properties on the plastic work on the flip-chip solder joints and the package-level joints has been examined. The results have been computed for packages with and without a compressive heat sink. Non-linear interconnect material models have been used for both chip-level and package-level interconnects. Anand viscoplasticity has been used for modeling the interconnects and the hysteresis loops studied as a function of the underfill properties.