A lead free joining technology for high temperature interconnects using Transient Liquid Phase Soldering (TLPS)

This Paper reports an emerging lead-free joining technology for high temperature application, which can be used for operating temperatures above 200 °C. It is called: ""Transient Liquid Phase Soldering (TLPS)"". The TLPS paste used contains a tin-copper powder mixture and is almost completely transformed into Cu6Sn5 and Cu3Sn intermetallic phases after soldering. Due to the reaction between the liquid tin and the copper powder a skeleton of intermetallic phases are formed immediately during soldering and prevents the paste from collapsing so that a lot of voids remain in the solder line. The challenge for this investigation was to understand the mechanism of the skeleton formation, describe them in detail and find possibilities to avoid the skeleton formation. In this paper a new TLPS paste and two processes are described as a means to manufacture an almost void-less joint. Furthermore, a model was developed that describes the TLPS process in detail. The activation of the TLPS joint is crucial and will be described. Temperature cycling results, failure mechanisms and conclusions to increase the lifetime as well as reliability of such TLPS interconnects will be presented in this paper.