Thermal cycling lifetime estimation of sintered metal die attachment

Sintered metals are considered to be high temperature die bonding materials for SiC power devices. Thermal cycling tests have shown that sintered copper is expected to achieve excellent lifetime properties, especially as compared to sintered silver. However, the mechanism behind this has not yet been confirmed. To clarify the mechanism, it is necessary to know the basic strengths of sintered metals, such as their stress-strain relations and fatigue properties. In this study, we measured the stress-strain relations and fatigue properties of sintered metals and estimated thermal cycling lifetime using these data and finite element analysis (FEA) to clarify the mechanism. The stress-strain relations were determined using three-point bending tests and FEA. The fatigue properties were measured using micro-fatigue testing equipment. Strain of the sintered layer was calculated by FEA and compared with the fatigue testing data. The estimated thermal cycling lifetime of sintered copper was longer than that of sintered silver, which is consistent with experimental trends. We analyzed the results and found that the long thermal cycling lifetime of sintered copper stems from the lower plastic strain of sintered copper layers due to the higher yield stress of sintered copper.