Microstructures and properties of alumina/copper joints fabricated by ultrasonic-assisted brazing for replacing DBC in power electronics packaging

Direct Bonded Copper (DBC) is now commonly applied as heat transfer substrates for high power electronics. The metallizaed surfaces are designed for improving the heat conduction and joining with copper heat sink. However, due to the mismatch of coefficient of thermal expansion, the joining area is usually the failure regions. In the present work, the alumina ceramic substrate and the copper substrate were directly brazed by using an Zn-Al filler with an ultrasonic-assisted method. A high quality of joints without obvious drawbacks at the both interfaces was obtained under optimized brazing parameters. With the increase of ultrasonic power, the amount of intermetallic compounds (IMCs) increased evidently. At a constant brazing time, the shear strength of joints increased firstly then decreased. When the ultrasonic power was 200W at a brazing temperature of 480 °C and a brazing time of 30s, the average shear strength reached 80MPa. With such a rapid and lower temperature brazing by the ultrasonic-assisted, we can acquire high-performance joints than traditional methods.