To guarantee a safe work environment for high-end chips, electronic packaging materials should have high thermal conductivity, matched coefficient of thermal expansion to semiconductor, low density, good impact toughness, and tensile strength. Diamond/graphite flakes-reinforced composites are considered as the new generation of heat sink material, however, the poor chemical affinity between copper and diamond and between copper and graphite flakes hinder the composites from achieving high thermal conductivity. The interface between copper matrix and diamond reinforcement or graphite flakes reinforcement is the key factor for improving heat transfer of the composites. This study aims to investigate the mechanisms of how the interface improves the thermal conductivity of the diamond/graphite flakes-reinforced composites. The primary research includes: (1) study the effect of vacuum sintering process on the formation of carbide layer; (2) investigate the effect of the volume fraction of diamond particles on relative density and thermal conductivity of the copper/diamond composites, and (3) explore the feasibility to fabricate graphite flakes reinforced copper composites by powder forging and investigate the effect of graphite flakes’ volume fraction on the thermal conductivity of the fabricated composites. Tungsten carbide (WC) can be formed during the vacuum sintering process, however, the formed WC were broken during the subsequent 1050 ℃ hot forging process. The WC can be formed during the vacuum sintering process above 550 ℃ for 30mins, on both diamond -{100}facet and -{111}facet. Cu-55WDia-1050HF has a thermal conductivity of 230.5W/(mK) which is higher than Cu-55WDia-VS800C2h-1050 of 195.1W/(mK). With the volume fraction of diamond from 45vol% to 65vol%, the thermal conductivity reduced from 250.8 to 65.1W/(mK). For copper/graphite flakes composites, the addition of carbide forming element Ti helped to improve the thermal conductivity. Because of the excessive copper fluidity in Cu-Ti-50GFs-1050HF, Cu-Ti-50GFs-1050HF has the lower thermal conductivity of 202.7 W/(mK) than thermal conductivity of Cu-Ti-50GFs-950HF which is 375.0 W/(mK). With the volume fraction of the graphite flakes from 30% to 70%, the relative density changed from 100% to 83.3%.