Suppression of Ag dewetting in submicron Cu@Ag particles in paste for improving sinter bondability through surface modification

Abstract

Operating temperature of a wide-bandgap semiconductor-based power device can reach 300 °C, which requires a next-generation die-attach sinter material. Ag-coated Cu (Cu@Ag) particles have been considered as a low-cost filler material in pastes for sinter bonding, replacing pure Ag particles. However, there are two main problems: out-diffusion of core Cu and Ag dewetting. Although the Ag shell is sufficiently thick, Ag dewetting induces accelerated out-diffusion of the core Cu and the resultant Cu oxidation through the formation of thin Ag coating parts. Accordingly, a surface-modification method using stearic acid was developed to suppress Ag dewetting and improve the sinterability of Cu@Ag particles. Sinter-bonding characteristics were examined using pastes containing surface-modified submicron Cu@Ag particles. Sinter bonding was conducted at 250 °C under 10 MPa for 1–10 min with N2 blowing using eight types of initial and surface-modified submicron Cu@Ag particles with Ag contents of 10, 20, 30, and 40 wt% (A10, A20, A30, and A40). The shear strength of the bondline containing surface-modified A10 exhibited 17.56 MPa when bonded for 3 min, compared with 11.67 MPa of the initial A10. After a bonding time of 10 min, the shear strength increased to 20.41 MPa. Surface-modified A10 (low Ag content), with the highest efficiency in Ag dewetting suppression, exhibited sinter-bonding characteristics similar to those of Cu@Ag particles with higher Ag contents without surface treatment. Surface-modified A20 provided a sufficient strength of 20.83 MPa after 3 min of bonding.