Study of Interface Monotonic and Fatigue Fracture Measurements at the Substrate Potting Compound Interfaces Under Flexure Loading

Abstract

Electronics in harsh environments are often subjected to extreme shock loading up to 50,000Gs, moisture, and high temperature. Potting of PCBs is often used to provide protection from extreme mechanical shock loads, vibration loads, and thermo-mechanical loads. The cured potting materials are prone to interfacial delamination under dynamic shock loading, which in turn may potentially cause failures in the package interconnects. The literature on potting compounds primarily focuses on the reliability in end application or the study of bulk material properties. This paper uses a four-point bend specimen to study the Substrate/Epoxy system and measure the fracture parameters of the bi-material strips to determine the interface delamination mechanisms. The bi-material strips of Substrate/Epoxy was kept at elevated temperatures of 100°C for aging. Then the sample specimens were subjected to quasi-static monotonic and cyclic loading to observe the critical stress intensity factors, fatigue slope parameters, and degradation interfaces bond adhesion of bi-material strips. Epoxy-A is a stiff material with 12,260 psi of tensile strength. The monotonic critical stress intensity factors and fatigue crack growth of the interfacial delamination for the two epoxy systems were characterized using strain energy release rate. A prediction of a number of cycles to failure and the performance of different epoxy system resistance was evaluated during cyclic bending loading using Paris Power Law.