Active elements (B, Cr, Al, Ti and Zr) are added in Cu matrix to improve the wettability, leading to the establishment of chemical interaction between diamond and Cu. In a narrow range of Cr content about 0.05% (molar fraction) or a B content about 2.5% (molar fraction), the TC increases and the CTE decreases due to the transition from weak bonding to strong bonding by the formation of carbides [21]. If the content of active element exceeds this level, the TC decreases due to the reduction of matrix conductivity. Therefore, the amount of active element must be optimized in order to maintain high TC.