Optimization of external and internal conditions for high thermal conductive Cu-diamond composites produced by electroplating

Aiming to realize the potential application of Cu-diamond composites with high thermal conductivity (TC) in microelectronic industry, we recently utilized electroplating technology to synthesize void-free Cu-diamond composites (TC above 600 W/m K). In this work, the detailed external conditions (current density, temperature and forced convection) and internal condition (diamond content) for improving TC of the composites were investigated. It was found that the nucleation energy along crystal orientation varied with the current density, and copper nodules tended to appear at high current density. Microstructures of the composites were severely affected by the temperature, since the additives were deactivated at high temperature. Additionally, the adsorption of additives changed oppositely at strong forced convection, leading to the decrease of electroplating efficiency. Bulk Cu-diamond composites were synthesized with different plating time to verify the electroplating condition for void-free microstructure and compactly combined diamond/copper interface. Using the optimal conditions, the composites with bimodal diamond particles were produced by electroplating for the first time, reaching a higher diamond volume fraction than that with single particles and a high TC of 651 W/m K. The improved TC mechanism of bimodal diamond composites was explained by double EMT model. This work revealed the detailed effect of current density, temperature and forced convection on void-free copper matrix composites, which were helpful for improving the diamond content and the TC value of the bimodal diamond composites.