Rapid sintering of copper nanopaste by pulse current for power electronics packaging

Sintering of metal nanopaste (NP) has been proposed as an alternative in die-attach bonding for the soldering to overcome such high operation temperature in wide-gap semiconductor power devices. Silver (Ag) NP as one of the candidates has some obstacles for mass production due to the high cost of Ag and vulnerability to the electrochemical migration. In the present study, the authors developed a simple solution method to synthesize copper (Cu) nanoparticles with the mean diameter of 57.5 nm. Cu NP was prepared by dispensing as-prepared Cu nanoparticles into deionized water with the assistance of ultrasonic. Pulsed Electric Current Sintering (PECS) was used to join two pieces of bare copper with Cu NP to achieve strong joints in a short time less than 200 ms. Die-shear testing was used to evaluate the bonding strength. The bonding strength increased with the increasing current and reached the highest value of 58.5 MPa at the current of 1.0 kA. Microstructural analysis of the sintered joints showed that the sintered Cu NP layer had a uniform microstructure with micrometer-sized porosity with the potential for high reliability under high-temperature applications. The PECS was recommended to bond two pieces of bare copper with Cu NP in power electronic applications without any protective atmosphere.