Chip-Underfill Interface Damage Model Under Fatigue Loading after Sustained High-Temperature Exposure

FCBGAs enable advanced safety and control functions on the automotive platform. The substrate and die interfaces in FCBGA packages are reinforced by underfill material. Underfills may be used to protect the chip from shock, vibration, and moisture. Underfills significantly reduce the amount of plastic work during temperature excursions and offer great mechanical support to the solder connections. Additionally, underfills offer FCBGA that are subjected to extremely high thermo-mechanical loads over an extended period of time when employed in underhood electronics. One of the dominant failure modes at chip/UF interfaces has been delamination. In this paper, the Chip-UF interface has been studied under repetitive loads. Bimaterial specimens of Chip/UF interfaces have been fabricated and exposed to high temperatures of 100°C and 150°C for 30, 60, 90, 120, 180, 240, 300, and 360 days. After iso-thermal aging, the samples undergo four-point bend fatigue. The interfacial fracture toughness values have been determined for each of the loading conditions. In fatigue loading, the crack growth rate with respect to the number of fatigue cycles is computed. The interfacial crack growth rate and the stress intensity factor for the interface are related to each other using Paris law. The Paris constants (A, n) are computed from fatigue loading interfaces, which directly represent the evolution of interfacial properties with respect to sustained high-temperature exposure.