Session: 10-01 Interactive Presentations

Paper Number: 99225

99225 - Interfacial Damage Mechanics at Fcbga Chip-Underfill Interfaces Under Thermo-Mechanical Loading for Automotive Underhood Applications 

Automotive underhood applications are becoming more dependent on electronic components for the safety and critical functions of the automotive. In flip-chip ball grid array (FCBGA) packages, underfill (UF) forms the integral mechanical support between the substrate and die. In addition, underfills protect the chip against shock, vibration, moisture, and radiation. Underfills provide great mechanical support to the solder interconnects and limit the amount of plastic work during temperature excursions. FCBGA used in underhood electronics are subjected to very high thermo-mechanical loads over a sustained period. Interfacial fracture toughness at the chip/UF interface under thermo-mechanical loading is an important factor in determining the reliability of the electronic components in these applications. Chip/UF interfacial delamination has been one of the important failure modes in FCBGA packages under very high thermo-mechanical loads. The interfacial fracture toughness of the chip/UF interface evolves with sustained thermal exposure and mechanical loading. The interfacial crack at the chip/UF interface could easily penetrate further to the solder joints culminating in system failure. This further changes the reliability of the electronic systems in underhood applications. Chip/UF interfaces have not been studied widely under cyclic fatigue loading with sustained high-temperature exposure. Most of the studies on chip/UF interfacial reliability are focused on the temperature loading without taking into account the mechanical loading at the interface. This study focuses on understanding the evolution in interfacial fracture toughness in chip/UF interface with respect to sustained high-temperature exposure. Chip/UF bi-material samples are prepared and subjected to long-term high-temperature aging at 100^oC and then tested under four-point bend fatigue loading. The specimens have been exposed to isothermal aging for 30 days, 60 days, 90 days, 120 days, and 180 days. The interfacial crack growth rate with respect to the number of fatigue cycles has been determined from the experiment. The steady-state energy release rate and range of mode-I stress intensity values (ΔK_I) have been computed for each of the test conditions. Paris power law has been used to establish the relationship between the crack growth rate and the range of stress intensity factors. Paris exponents (A,n) are determined from the relationship to understand the evolution in interfacial fracture toughness with respect number of days of aging under fatigue loading.

Presenting Author: Aathi Raja Ram Pandurangan Department of Mechanical Engineering