Substrate Copper Trace Crack Characterization and Simulation

Substrate copper trace crack issue was detected during Temperature Cycling Test (TCT). This study investigates supplier dependent performance using concurrent approach of material characterization and Finite Element (FE) simulation analysis. Substrate with thinner trace width and thickness is found to be more susceptible to trace crack in post failure analysis. Series of material characterization are preformed to understand relationship between mechanical properties and micro-structure of copper foil. Stress-strain curves of copper foils were successfully obtained using DMA at TCT temperature range from -65°C to 150°C, which serves as an important input to simulation models. EBSD compares grain size and its correlation to modulus and ultimate tensile strength (UTS) in DMA stress-strain test. Nanoindentation test discussed fracture toughness comparison by using E/H ratio. FE simulation is performed to validate effect of dimension of copper trace, where thinner trace profile shows significantly higher plastic strain at failure location. By varying copper stress-strain input to simulation model, significant difference in plastic strain response is predicted between suppliers. Mechanism of crack initiation and propagation is elaborated with both material characterization and simulation results. Trace dimension, micro-structure and mechanical properties of copper foil are successfully related to supplier dependent reliability performance.