Stress–strain behavior of Cu on the AMB‐Si 3 N 4 substrate undergoing thermal cycles via in situ strain measurement

Abstract The active metal brazing of a Si 3 N 4 substrate with Cu has been evaluated for excellent reliability, demonstrating durability up to 1000 cycles in a cycling test ranging from −40°C to 250°C. While the finite element method (FEM) is commonly used for predicting thermal stress–strain in cyclic tests, experimental data on the measurement of thermal stress–strain on metallized substrates have remained limited. In this study, a digital image correlation (DIC) method was employed for the in situ measurement of thermal strain on a fully Cu‐coated Si 3 N 4 substrate (AMB‐SN substrate) in various consecutive thermal cycles, ranging from 1–2 to 199–200. The thermal strains exhibited hysteresis curves that expanded slightly with cycles. By incorporating the coefficients of thermal expansion (CTE) of plain Cu and Si 3 N 4 , both the thermal stress and strain of Si 3 N 4 and Cu on the AMB‐SN substrate were computed. The stress–strain curves of Cu revealed that the yield stress of Cu increased with the number of cycles, attributed to the cyclic hardening of the Cu layer. The Cu stress–strain curve calculated in this work showed a good agreement with the previous results obtained from compression/tension test of Cu at room temperature, which indicates the stress–strain curve of Cu on the composite was not sensitive to the temperature during the thermal cycle.