Low Temperature Silver Sinter Processes on (EN)EPEAg Surfaces for High Temperature SiC Power Modules

Low Temperature Silver Sintering is a suitable process to attach SiC dies used in high temperature power modules. Typically, these modules are operated above 200 °C. This paper investigates the properties of newly proposed electroless Ni/Pd/Ag layers (ENEPEAg) and electroless Pd/Ag layers (EPEAg) as surface finish on copper DCBs for power modules. The suitability of the (EN)EPEAg layers for power devices with sintered dies was validated by means of silicon chips sintered at 260 deg C and 15 MPa. After thermal storage of 96 hours at 300 deg C under air, the mean shear values exceeded 40 MPa. Shear strength for the ENEPEAg samples after 512 hours at 300 °C still exceed 20 MPA. XPS and FIB-SEM inspections performed after the thermal storage reveal copper and silicon diffusion as well as palladium and silver diffusion in EPEAg layers with a 300 nm Pd layer. Nickel, however, effectively blocks the copper diffusion. Hence, both EPEAg and ENEPEAg seem to be promising surface finishes for high temperature power modules.