Highly Reliable Silver Sintering Joints for Power Module Application

Abstract

The increased popularity and large-scale production of electric vehicles in the automotive industry have led to the urgent need for highly reliable power modules. Bonding materials have to endure high temperatures and should have extremely high thermal and electrical conductivities for rapid heat dissipation and low electric loss. To address this need, a pressure silver sintering assembly material that is highly reliable as tested by a liquid-to-liquid thermal shock test from - 65°C to 150°C has been developed. The reliability has been demonstrated for sinter bonding between various mating materials aiming at different locations in the power module, including die-attach (Si/AMB), clip-attach (Si/Cu), clip and baseplate to substrate-attach (Cu/AMB), and baseplate to heat-sink-attach (Cu/Cu). The initial shear strength of the joints is in the range of 50 to 65MPa, and it remains strong at similar values even after 2,000 cycles of TST for all the configurations mentioned above, implying that it is possible to use this silver sintering material for total sinter joint assembly of power modules. The sintered joints have a thermal conductivity of 285W/mK, and have an electrical resistivity of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$34\mathfrak{n}\Omega\cdot \mathrm{m}$</tex> . The Young's modulus of the sintered joints is 47Gpa. The porosity of the joints is 7% and does not change even after 3,000 cycles of thermal shock testing. High-Pb solders are also tested under similar conditions for die- and clip-attach. For the high CTE mismatch configuration of clip-attach (Si/Cu), the shear strength of the joint loses at least half of its initial value even after 1,000 cycles due to the solder fatigue observed by the generation of a large number of cracks in the bulk solder phase.