Reliability of Ag Sinter-Joining Die Attach Under Harsh Thermal Cycling and Power Cycling Tests

Silver (Ag) sinter-joining is an ideal connection technique for wide bandgap (WBG) power electronics packaging due to its excellent high-temperature stability and excellent thermal conductivity. In this work, we applied Ag sinter-joining to die attach for a WBG power module and focused reliability of Ag sinter-joining under harsh thermal and power cycling conditions. The die attach structure using a Ag flake paste had an initial shear strength of over 45 MPa due to the excellent sinter-joining ability of the paste. Variation of die attach shear strength and failure mode under a harsh cycling condition (-50 similar to 250 degrees C) have also been systematically discussed. Thermal diffusivity of sintered Ag and thermal resistance of the die attach structure were also measured, showing a superior thermal performance to solder materials. Meanwhile, a simple SiC diode module was assembled via Ag sinter-joining and aluminum (Al) ribbon-bonding for evaluation of Ag sinter-joining reliability during a severe power cycling condition. A power cycling test with a high junction temperature of 200 degrees C was conducted to evaluate the reliability of Ag sinter-joining. It is found that the main failure of the SiC diode module was located at ribbon-bonding rather than the Ag sinter-joining layer degradation, based on the variation of forward voltage and junction to case thermal resistance. This investigation indicates that the Ag sinter-joining has a long lifetime under a severe operating condition of power electronics.