Ag and Si particles sintering technology for SiC power device

Ag sintering technology is one of the best candidates for SiC die attach because of good mechanical and thermal properties at high temperature. However cracks propagates into SiC dies or DBC substrates at thermal fatigue test at more than 200 °C because Ag is too hard for die attach materials and 10ppm/ °C of CTE mismatch between SiC dies and Ag layers is too big. Therefore a development of low CTE sinterng materials is dispensable for SiC power device operated at high temperature. In this study, a method to coat Si particles with Ag layer at room and its sintering properties are researched. Si particles with $\varphi 30\mu m$ and Ag flakes with $\varphi 5\mu m$ are prepared and Si-20,40 and 60 vol%Ag particles are produced by utilizing high-speed 3D motion of a patented 3D Ball Millproducted by Nagao System Inc.. It is revealed that their Si particles after the ball milling are almost covered by Ag layer except for Si-20vol.%Ag particles and furthermore the coated particles are crushed to 5pm by SEM observation. Their Si-Ag particles are mixed with a solvent to formulate into pastes. These Si-Ag pastes are printed onto Ag electroplated Cu plats, and then the bonding experiments are carried out at temperatures of250°C for 60 min without pressure at air atmosphere. It is revealed that some Ag layers are jointed on the surface of Si particles and others are delaminated by FE-SEM observation. Si particles are connected via Ag layers on their surface. The strength between Ag layer and Si particles must be improved in order to adopt Ag-Si sintering paste to die-attach technology..