Transient Liquid Phase Bonding Process Using Sn-coated Cu Dendritic Particles

Abstract

To reduce bonding time in the die bonding process of power devices, we propose a novel technique based on the melting and reactions of Sn shells in Sn-coated Cu dendritic particles during heating. In this study, transient liquid phase (TLP) die bonding was performed at 250 °C in air under 10 MPa of pressure. Sn coating content was considered as a main process parameter. During the immersion Sn plating (coating) of Cu dendritic particles, excessive Cu6Sn5 and Sn were formed in situ. Coating the Cu dendritic particles significantly reduced the oxidation of core Cu during heating in air. When the average Sn coating content was 18 wt%, abundant Cu remained based on Sn shortages, even after 10 min of reaction. However, pure Cu was virtually eliminated in the bondlines following an identical reaction when the Sn content was 45 wt%. A paste containing 45 wt% Sn-coated Cu dendritic particles provides more effective TLP bondability, resulting in average shear strengths of bondlines of 19.6 and 21.4 MPa following die bonding for 3 and 5 min, respectively.