Addition of SiC Particles to Ag Die-Attach Paste to Improve High-Temperature Stability; Grain Growth Kinetics of Sintered Porous Ag

Abstract

To improve the high-temperature reliability of sintered Ag joints, three types of silicon carbide particle (SiC_p) of different size and morphology were added to Ag micron-flake paste. Quality sintered joints between Cu dummy chips and Cu substrate were obtained at a relatively low temperature (250°C), in air, under low load (0.4 MPa), and 35 MPa die-shear strength was achieved. High-temperature stability was investigated by means of aging tests at 150, 200, and 250°C for 500 h, and by thermal cycling between −50°C and 250°C for up to 170 cycles. The best distribution and compatibility with porous sintered Ag structures was observed for sub-micron SiC particles with an average diameter of 600 nm. After high-temperature storage for 500 h at 250°C, mean Ag grain size of the SiC-containing joints was unchanged whereas that for pure sintered Ag increased from 1.1 to 2.5 μm. Ag joints containing the optimum amount (2 wt.%) of SiC_p retained their original strength (20 MPa) after storage at 250°C for 500 h. The shear strength of Ag joints without added SiC_p decreased from 27 to 7 MPa after 500 h because of grain growth, which obeyed the classical parabolic law. Grain growth in pure Ag joints is discussed in terms of a temperature-dependent exponent n and activation energy Q. Our SiC_p-containing joints resisted the grain growth that induces interfacial cracks during thermal cycling.