Low Temperature Sintered Silver Nanoflake Paste for Power Device Packaging and Its Anisotropic Sintering Mechanism

Sintered silver pastes have emerged as a kind of packaging material for wide-bandgap (WBG) power devices because of their superior electrical and thermal conductivity. Herein, silver pastes containing monodisperse triangular silver nanoflakes with a size distribution of 40–260 nm were prepared. The sintered silver joints exhibited a significant high shear strength of 49.8 MPa, larger than that of traditional silver paste, and with a relatively low porosity of 5.1%. These remarkable properties were attributed to the special anisotropic sintering process and bridging effect of the silver nanoflakes. Anisotropic sintering of the silver nanoflakes refers to the successive deformation of the corners, edges, and surfaces during sintering. Especially, the deformation of surfaces provides large diffusion paths for the silver atoms, resulting in a denser sintered silver joint. The bridging effect results from two separate silver nanoflakes that are linked by a single silver nanoflake, which increases the connection between the silver nanoflakes and thus improves the mechanical property of the sintered silver joints. This anisotropic sintering mechanism and bridging effect should inspire other researchers to investigate the sintering mechanism of other materials and optimize the performance of the corresponding pastes of these materials.