Abstract
Power semiconductors for automobiles were joined by high Pb soldering to joint properties at high temperatures during operations. However, this process is being replaced by low-temperature sintering. In the low-temperature sintering bonding method, Cu powder is low-cost and exhibits high-performance material and excellent bonding properties. In this study, the effect of high-temperature aging on Cu paste sintered joints and the failure mechanism of the shear test were investigated. Cu monomodal and bimodal pastes were manufactured, and electroless nickel immersion gold (ENIG) surface treatment was applied on the Cu chip side. In the ENIG-treated joints, a significant number of Kirkendall voids were observed at the interface under Au after 2,000 h at 200 °C, and Cu2O was also formed. This is attributed to the difference between the interdiffusion coefficients of Au and Cu, which decreases the shear strength of the junction and rapidly increases the electrical resistance. After the shear strength tests, the crack propagation pattern at the interface of the ENIG-treated joint was confirmed via cross-section scanning electron microscopy. Future studies on surface treatment are required to clarify the long-term stability of the joints.
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