In this paper, we describe our accomplishments in infiltrating a carbon/carbon composite material with polycrystalline diamond. This development results in an ultra high thermal conductivity electronics baseplate featuring an electrically insulating coating with high thermal conductivity. This novel composite material exhibits thermal conductivity higher than all existing coldplate materials. We have prepared diamond-infiltrated composites, and characterized the resulting material including the thermal conductivity measurement of the base carbon/carbon, SEM and Raman spectroscopy, and DC electrical resistivity measurements of the integrated diamond/carbon/carbon composites. We have achieved metallization of the diamond surface, demonstrating in part the feasibility of surface mount technology applied to the dielectric heat sink composite. We discuss our technical accomplishments to date, our objectives for the ongoing technical program and future applications of this material.