Direct heat sink printing on metallized ceramic substrate for power electronics applications: heat treatment identification and its impacts

Abstract:
The aim of this paper is to evaluate a new packaging technology developed for high power density and harsh environment power module applications. The assembly was achieved using Selective Laser Melting (SLM) technique in order to directly print AlSi7Mg0.6 alloy heat sinks on the back side of direct bonded aluminum metallized substrate. Thermal simulations were conducted in order to evaluate the potential benefit of this technology. Results show a reduction of more than 22% of the junction to ambient thermal resistance compared to conventional structure. Experiments were conducted on both aluminum and nickel finish metallization of the Direct Bonded Aluminum (DBA) substrates. The assemblies were studied under several scales from the metallurgical and mechanical study of the interfaces to the measurement of the macroscopic strains of the substrates. The heat treatment temperature of 250deg C has been identified based on the hardness versus temperature curve of the AlSi7Mg0.6 alloy. After a stress relieve thermal treatment of 2 hours at 250deg C, the warpage of highly deformed substrates with printed heat sink is reduced significantly (more than 30% in some cases) without altering the metallurgy and the mechanical properties of the interfaces for both Ni and Al finish layers. The thermal conductivity of the printed alloy is improved by about 20% at temperatures below 100deg C after the heat treatment.