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.