Die-attach bonding at 230 °C using micron Sn-coated Zn particles for high-temperature applications

Abstract

The advancement of wide bandgap semiconductors has posed higher requirements for power chip packaging technology. Nanoparticles (Ag, Cu, and Cu@Ag) sintering was regarded as an innovative low-temperature bonding method that can be serviced at a high temperature. Considering the expensive cost of silver nanoparticles, Zn particles have been considered as an alternative. Herein, a novel type of submicron Sn-coated Zn particles was proposed to overcome the easy oxidation and high sintering temperature problem of Zn. The structure of Zn70Sn30 (wt.%) core/shell was determined by Scheil model calculation to meet the requirements of low-temperature bonding and high-temperature applications. Multiple reducing agents and reduction times were tentatively investigated to prepare Zn70Sn30 (wt.%) particles. The solder joints prepared based on Zn@Sn preform achieved bonding at 230 °C and exhibited an average shear strength of 28.13 MPa at 250 °C. Unlike the Zn–30Sn solder alloy, the lower reflow temperature produced only a single layer of Cu5Zn8 at the interface of the solder joint, which ensured that all fractures occurred primarily in the Zn@Sn preforms. The electrical resistivity and thermal expansion coefficients of Zn@Sn preform were 8.1 μΩ cm and 12.7 × 10−6/K, respectively. Therefore, the Zn@Sn particles were a potential die-attach material for high-temperature power device packaging.