Fabrication of Cu@Sn TLPS joint for high temperature power electronics application

In this study, a novel Cu@Sn TLPS joint was fabricated for high-temperature power electronics application. Cu@Sn core-shell composite powder was firstly prepared by a methylate electroplating method, and then pressed into a preformed sheet. The Cu@Sn preform was reflowed at 250 ∼ 280 °C for 40 min under the pressure of 0.1 × 10^-3 MPa, and the resulting bondline can withstand high temperatures up to 600 °C. During the process, the Sn layer was transformed to Cu₃Sn, and the Cu₃Sn surrounded the outside of the residual Cu particles. The joint characteristics were controlled by size gradation of Cu particles, the ratio of Cu/Sn, preform forming pressure and TLPS process. The joint shear strength was no less than 48 MPa after aging at 400 °C for 1000 h. Young's modulus and hardness were 98.35 GPa and 2.62 GPa, respectively, which are much lower than the pure Cu₃Sn joint. The electrical resistivity and thermal conductivity of the joint were 5.1 μΩ cm and 148 W m^-1 K^-1, respectively. It is superior to pure Cu₃Sn joints and the other Cu/Sn system TLPS joints. The high shear strength, high thermal conductivity and high melting temperature demonstrate that Cu@Sn TLPS joint is a promising interconnect technology for high power density modules.