Heat Spreading in Uncovered Copper Sintered Die-Attach Layers Examined with Lock-In Thermography

For the attach of dies to a substrate in power electronic assemblies, sintering is one of the common technologies. Sintered die-attach layers always contain pores due to diffusion processes and uncompacted gaps between metal particles in the sinter paste. In copper sinter paste with flake-shaped particles, the sintered structure exhibits regions with varying contents of gap-shaped pores. To meet heat transfer requirements, it is important to investigate whether these pores have a large effect on heat diffusion within the layer. Four different sintering materials were evaluated in generic test assemblies, where half of the samples had the die removed to reveal the uncovered sintered interconnection layer. These layers have been analyzed and lock-in thermography was conducted to identify their heat transferring capabilities. While optically visible structures, that correlate with pore clusters, are found in all samples, the heat transfer was not significantly reduced. Only one sample type with a very strong inhomogeneous structure showed significant influence on the heat dissipation. That infers, that even some stochastic pore cluster structures in the sintered layer of a copper sintered die-attach only have a negligible effect on heat dissipation.