Investigations on advanced soldering mechanisms for transient liquid phase soldering (TLPS) in power electronics

This paper gives an overview of the optimization of the present state-of-the-art soldering technologies for diffusion soldering in power electronics, in particular for Transient liquid phase soldering (TLPS) with enhancements in process conditions to reduce the void percentage in the interconnections and at the same time accelerate the rate of intermetallic phase (IMP) formation. Addressing the difficulties in realizing a void-free TLPS joint in large-area die-attach in power electronics, the variations in soldering process parameters like temperature, pressure and time are discussed. The complete transformation of thin Sn-Cu solder interlayers (15-20μm) into Cu6Sn5 and Cu3Sn IMPs and related void information for varying solder profile variants have been explained. To evaluate the potential for TLPS process, the advanced reflow soldering mechanisms like vacuum vapor-phase soldering and over-pressure convection soldering have been investigated. Depending on the void percentages and IMP formation rate, an optimized interconnection process has been introduced which is capable of realizing TLPS joints with convectional electronic production equipment.