High temperature thermal cycling reliability of silver sintered and electroplated tin based transient liquid phase joints

Abstract:
The long-term reliability of a large range of candidate die attach materials for use in thermal cycled applications in SiC-based high temperature power modules up to a peak temperature of 350deg C have been evaluated and tested. These include various types of silver sinter materials in film and paste forms, and transient liquid phase (TLP) joints using tin preforms and electroplated tin, bonded with and without pressure. The silver sinter joint lifetimes have ranged from 104 to 504 x 0-350 °C passive thermal cycles to date and all TLP joints have reached 504 cycles to date without shear test failures. Our silver sinter failure analysis have indicated a time and initial densification-dependent coarsening of the microstructure and aggregation of pores at the die attach interface during thermal cycling, eventually leading to a weak die attachment. Although initial TLP bonds using tin preforms gave good thermal cycling results, process issues led to unsatisfactory voiding of the TLP joints and significant fracturing between these voids after cycling. A new process also using electroplated tin instead of pre-forms has been used to produce much improved joints and work is now underway to determine their relative thermal cycling lifetimes.