Reliability issues for high temperature interconnections based on transient liquid phase soldering

Abstract

New high temperature interconnection technologies emerge because of the need for electronics use at temperatures beyond 150°C. Transient liquid phase (TLP) soldering is one option with the advantage of processing conditions being close to those for conventional soldering. In the Cu-Sn system addressed in the paper, a high post-processed melting point of the solder interconnects is achieved due to the formation of Cu6Sn5 and Cu3Sn intermetallic compounds (IMC). A specific low melting solder paste under development can be used if applications for both power and logic electronics are addressed. To accelerate the development of IMCs in thicker solder layers, metallic particles are embedded in the solder paste. New challenges concerning the thermo-mechanical reliability of these devices arise as the material properties of the IMC interconnect differ substantially from those known for soft solders. Based on material characterization of pure IMC effective material characteristics of the TLP joint, consisting of a mixture of different constituents, have been derived based on a micromechanical model. Due to the change in material stiffness and strongly decreasing ductility of the joining material, the potential failure modes of an assembly made by TLP soldering change. The new thermo- mechanical failure risks are evaluated for a power module, an IGBT on DCB substrate, by both conventional FEA and cohesive zone modelling.