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The Effect of Layer Thickness Variation on the Thermo-Mechanical Properties of Direct Aluminum Bonded Substrates on AlSiC
Keywords: Direct aluminum bonding, Power packaging, AlSiC
Automotive and telecommunications are two major industries pushing for power electronics with higher power densities and reliability in less than ideal thermal environments. The modules are subject to internal thermal stressing. To meet the growing power demands, increased reliability through improved thermal management has become a central issue. Direct aluminum bonded (DAB) substrates have the potential to provide the higher reliability. DAB substrates have a thermal conductivity that is comparable to direct bonded copper (DBC) and a tolerance to thermal cycling that is shown to be substantially better. DAB is able to withstand thermal cycling better than most substrates because of the malleability of aluminum and the strong bonding mechanism between layers, particularly to AlN. A substitution of aluminum silicon carbide (AlSiC) for the traditional aluminum baseplate is made to significantly reduce thickness and weight, and slightly reduce thermal impedance. The effects of thermal cycling on a DAB substrate have been studied using finite element modeling. The modeling varies the thicknesses of the aluminum, ceramic and AlSiC layers as well as varying ceramic types (Al2O3, AlN, BeO). The investigation used 288 combinations simulating thermally induced stress profiles in a typical IGBT/ceramic structure. The results provide a better understanding and insight into substrate optimization for power modules and produce a guide to optimization of layer thicknesses and ceramic type for different electrical and thermal environments. Nearly identical work was presented in an IMAPS Journal paper that showed thermal stress variations due to changes in layer thickness and ceramic type for direct bonded copper (DBC) structures. This work repeats the DBC work for model verification and then contrasts the application of DAB structures. This is a comprehensive work and presents new information in the industry.
Troy R. McKay,
SUNY at Buffalo
Caledonia, NY

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