Sustained High Temperature Fracture Toughness Evolution of Chip-UF and Substrate-UF Interfaces in FCBGAs for Automotive Applications

Automotive advanced driver-assistance systems (ADAS) require the use of high I/O ball-grid array architectures including flip-chip ball-grid arrays (FCBGAs) in underhood environments. Drive-critical functions enabled by electronics include lane-departure warning systems, collision-avoidance systems, driver-alertness monitoring, park and drive assist systems, adaptive cruise-control, and semi-autonomous navigation. Electronics in underhood applications may be mounted on-engine, on-transmission, on firewall or on wheel-well where the temperature may be in the neighborhood of 150-200 °C. FCBGAs require the use of underfills to provide supplemental restraints for the flip-chip bumps to achieve the needed thermo-mechanical reliability. Current modeling methods lack foundational interface material-data for assessment of fracture at the substrate-UF and chip-UF in thermal cycling, monotonic loading, or mechanical fatigue. In this paper, the effect of sustained high temperature operation on the interfacial fracture toughness of the chip-underfill and substrate-underfill interface has been examined under both monotonic loads and fatigue loads. Bi-material specimen have been fabricated to study the interfacial fracture toughness of the interfaces after sustained high-temperature exposure. The measurements have been used to extract the fracture toughness values as a function of duration of sustained operation at high temperature. Paris’s Power Law parameters have been extracted for both the substrate-UF interface and the chip-UF interface.