Non-interfacial growth of Cu3Sn in Cu/Sn/Cu joints during ultrasonic-assisted transient liquid phase soldering process

The non-interfacial growth of Cu3Sn intermetallic compounds (IMCs) in a Cu/Sn/Cu interconnection structure during the ultrasonic-assisted transient liquid phase (TLP) soldering process was investigated. In the traditional TLP soldering process, the Cu3Sn phase always nucleated at Cu6Sn5/Cu interfaces and grew at the expense of the Cu6Sn5 phase and towards the joint centre, eventually forming a full intermetallic joint consisting of a single Cu3Sn phase with columnar grains. While in the ultrasonic-assisted TLP soldering process, the Cu3Sn phase nucleated and grew randomly within the whole joint, the resulting intermetallic joint consisted of a single Cu3Sn phase with equiaxed grains. This anomalous behaviour can be wholly ascribed to the effects ultrasonic on the nucleation and growth mechanisms of Cu3Sn.