Thermo-mechanical behaviour of DBC substrate assemblies subject to soldering fabrication processes

Camilleri, Duncan (2012) Thermo-mechanical behaviour of DBC substrate assemblies subject to soldering fabrication processes. Soldering and Surface Mount Technology, 24 (2). pp. 100-111. ISSN 0954-0911

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Abstract

Purpose – Power electronics are usually soldered to Al2-O3 direct-bond-copper (DBC) substrates to increase thermal diffusivity, while at the same time increasing electrical isolation. However, soldering gives rise to inherent residual stresses and out-of-plane deformation. The purpose of this paper is to look at the effect of soldering processes of Al2-O3 DBC substrates to copper plates and power electronics, on their thermal fatigue life and warpage. Design/methodology/approach – A numerical thermo-mechanical finite element model, using the Chaboche material model, was developed to identify the thermal plastic strains evolved during soldering of DBC substrates to copper plates and power electronics. The plastic strains in conjunction with established extremely low cycle fatigue life prediction model for ductile material were used to predict the number of soldering cycles to failure. The predicted out-of-plane deformation and number of soldering cycles to failures was compared to realistic tests. Findings – Soldering processes drastically reduce the thermal fatigue life of DBC substrates, giving rise to thermal cracking and premature failure. In this study the soldering process considered gave rise to out-of-plane deformations, consequently reducing heat dispersion in soldered DBC substrate assemblies. Furthermore, soldering gave rise to interface cracking and failed after three soldering cycles. Numerical finite element models were developed and are in good agreement with the experimental tests results. Research limitations/implications – The influence of soldering processes of DBC substrates to copper plates and electronics on the thermal fatigue life should be taken into consideration when establishing the design life of DBC substrates. Finite element models can be utilised to optimize soldering processes and optimize the design of DBC substrates.