A Simplified Approach of Pressure Assisted Die and Substrate Attach Made Accessible in a Single-Step: A Silver Sintering Technology to Face Harsh Conditions

ABSTRACT With increased demands for power electronics, silicon devices are progressively substituted by Wide Bandgap semiconductors (WBG) like SiC or GaN. WBG imposes even harsher conditions to actual power modules working environment due to higher electric breakdown field, therefore high thermal expansion exposes microelectronic packages to high mechanical stress and jeopardize their lifetime. Providing interconnection material with low electric and thermal resistance could remove one of WBG bottlenecks by replacing Sn-solders and thermal interface materials. Numerous industries including automotive, downhole drilling, aeronautics, space exploration, nuclear environment, radars, could benefit from increased bonding performance. This paper presents novel silver sinter-bonding for harsh electronic conditions improving joint mechanical strength through a new pressure-assisted packaging process. By combining sintering of both die-level and substrate-level in a single step, this process made affordable a twofold productivity increase while holding high-quality uniformed silver layers. The attach process takes advantage of great sintering homogeneity to be able within the same flow to sinter dies just as well as large surface substrates (3000 mm 2 ) to attach DBC or AMB to copper heat-spreader. Focusing on the atmosphere control, temperature, pressure and cooling rate was key to ensure consistent quality. Successful sustainability versus thermal expansion is confirmed by C-SAM with no visible voiding and just slightly delamination under 5 percent occurring after 1000 cycles of thermal shock cycles at the die-DBC and DBC-copper heat-spreader interconnects. This paper demonstrated easy transposable solution to tackle harsh environment's challenge. In parallel thanks to the versatility of this silver sintering technology, a pressureless version has been developed to ensure high performance die-attach where processes avoid pressure assistance. To investigate sintered silver joints with advanced characterization techniques, die-shear test, microscopy and spectroscopy are carried out. Sintered silver interconnect for copper-to-copper showed strength above 30 MPa with mixed adhesive bond fracture offering high performance material able to sustain harsh conditions.