Nanoscale Silver Paste and its Sintering for Attaching Semiconductor Devices

Summary form only given. Nanoscale silver paste is a promising material for device interconnection. It can be sintered at 300 degC or lower, has superior thermal, electrical and mechanical properties over silver and can withstand higher service temperatures. The paste, consisting of silver nanopowder and an organic binder system, was used to attach SiC devices on silver and gold-metallized Ni-coated alumina and aluminum nitride direct-bond-copper substrates. The silver paste sintered at 280 degC had a density greater than 80%, a thermal conductivity around 55% that of bulk silver (2.38 W/K-cm), and an electrical resistivity that is 2.4 times that of bulk silver. SiC devices attached to the silver-metallized DBC at 300 degC developed a die-shear strength of 40 MPa after 40 minutes. Devices attached on gold-metallized DBC only had half the strength because of the longer sintering time required for the gold-silver bond to develop full strength. Thermal cycling from room temperature to 250degC caused the joints on the AlN BDC to lose half of their strength after 6000 cycles. Joints on the Ag-metallized alumina DBC lost half of their strength earlier at around 4000 to 5000 cycles