A paste based on Cu@Sn@Ag particles for die attachment under ambient atmosphere in power device packaging

Abstract

This paper presents a novel die attach material based on Cu@Sn@Ag particles, in which the outermost Ag layer prevents the oxidation of the Sn layer and expedites the consumption of the low-melting point Sn phase. The die attach material can be reflowed at 250 °C for 15 min under a pressure of 3 MPa in the atmosphere, subsequently, the bondline can sustain a much higher temperature up to 480 °C. The results show that the Sn phase was totally transformed into Cu3Sn and Ag3Sn intermetallic compounds (IMCs) after reflow. Moreover, the Cu particles were evenly distributed in the Cu3Sn and Ag3Sn IMCs. After Cu@Sn@Ag particles were heated at 250 °C for 6 h, the average mass increased only by 2.8%, which indicates that the oxidation resistance property of Cu@Sn@Ag particles is excellent. The average electrical resistivity of the bondline was 4.6 µΩ cm, and the thermal conductivities were 159.97 W m−1 K−1, 142.71 W m−1 K−1, 137.28 W m−1 K−1 at 30 °C, 150 °C, 300 °C, respectively. The average shear strengths of the bondline were 25.8 MPa and 19.7 MPa at 30 °C and 400 °C, respectively. The coefficient of thermal expansion of the bondline was measured to be 15.77 × 10–6/°C. This novel paste shows great potential in die attachment in power device packaging.