Compound cast heat sinks have various advantages over conventionally manufactured ones, but oxides present on the metals and formation of a brittle intermetallic layer (IMC) make casting difficult. In the present study, a novel approach was used that employs a silane-doped argon environment to overcome these issues. Oxidation could be fully suppressed and thermal heat conductivities around 67 W/(m·K) were obtained for the compound zone. The microstructural analysis revealed that the thickness of the IMC layer could be kept below the critical value of 3 µm. Yet, the process window was found to be extremely tight. The modelling revealed that the critical time period for formation of the IMC layer is only on the order of a few 10 s.