Reliability modeling of Sn-Ag transient liquid phase die-bonds for high-power SiC devices

In this work, a novel foil-based transient liquid phase bonding process has been used to mount the SiC Schottky diodes. The Sn-Ag TLP interlayer material was produced in the form of preforms of multilayer foils, using electrochemical deposition. The foils were designed to keep the overall composition of Ag and Sn about 80% and 20% respectively. The optimized TLP bonding process parameters were used during the assembly process. The die attachment characterizations revealed that resulting intermetallic compounds (Ag3Sn and zeta) have melting point beyond 480 degrees C. The die-attachment produced low bending stresses, while heated from 30 degrees C to 400 degrees C. The reliability of Sn-Ag TLP bonded samples was studied during passive temperature cycling and during active power cycling. During power cycling, the crack rates were determined by measuring the crack lengths of the TLP bonded joints after failure. The failure criteria were set to be an increase of diode's forward voltage by 10% since the start of the power cycling tests. The thermo-mechanical simulations were performed to determine the damage parameter i.e. strain range amplitude Asp. Based on mechanical characterization of the TLP bonded layers, a plastic material model was used. The crack propagation rates were modeled using Paris' Law. Based on comparisons with state-of-the-art silver sintering technique, it can be stated that the TLP bonding is a promising die-attachment technique and Its power cycling reliability is similar to silver sintering. (C) 2016 Elsevier Ltd. All rights reserved.