Silver sinter paste optimized for pressure sintering under air atmos-phere on precious and non-precious metal surfaces with high reliable sintered joints

摘要

In recent years, silver sinter materials have drawn increasing attention as an interconnect material in power electronics for its unique properties such as high thermal and electrical properties and also as lead replacement solution. Our previous studies have demonstrated the feasibility of semiconductor devices attachment on silver and gold surfaces by either non-pressure or pressure sintering. In this paper, we extended our study to die attachment on bare Cu surfaces by pressure sintering process. We attached Ag metallized Si dies to bare Cu, Ag, and Au metallized substrates by pressure sintering at 230°C with a pressure of 10 MPa for 3 min. An average initial die shear strength of > 10 N/mm~2 was obtained for all sintered samples. The die shear strength increased to > 40 N/mm~2 for all samples after temperature cycling test (-40°C/+150°C) and high temperature storage at 250°C. Our hypothesis is that Ag, Au and Cu continued to diffuse during temperature cycling test and high temperature storage resulting in higher bonding strength. Bending test results further confirm the increase of bonding strength by thermal cycling. After 1000 hours storage at 250°C, cohesive break in the Cu layer was observed for Ag metallized and bare Cu substrates. Our hypothesis is that Cu in the substrate diffuse into silver sintered layer and concurrently Ag diffused into Cu layer of substrate during high temperature storage. Further investigation is required to verify this hypothesis. In contrast, cohesive break in the sinter layer was observed for Au metallized substrate after 1000 hours storage at 250°C indicating that Au metallized layer acts as a barrier to prevent Cu from the substrate from diffusion into silver sintered layer.