Void-free and high-speed filling of through ceramic holes by copper electroplating

In order to achieve void-free and high-speed filling for through ceramic holes (TCHs) to prepare direct plated copper (DPC) ceramic substrates, copper electroplating technology combined with nano-carbon coating process was used in this work. The nano-carbon coating process was adopted to form a nano-carbon film as a conductive layer on the hole wall. For the TCH electroplating, an ameliorative plating additive mixture was proposed, which consists of accelerator thiazolyl dithio-propane sodium sulfonate (SH110), leveler nitrotetrazolium blue chloride (NTBC) and inhibitor polyethylene glycol (PEG, MW = 8000). Experimental results indicate that the optimized formula of the additives is 6 ppm SH110, 5 ppm NTBC, and 200 ppm PEG. By this optimized formula, the filling speed was further improved by duly increasing current densities. Consequently, TCHs with high aspect ratios (ARs) of 6.25 (500 μm depth and 80 μm diameter) were completely and void-free filled at the high current density of 1.5 ASD for 2 h, which promotes the development of vertical interconnection for DPC ceramic substrates and enhances their reliability for high power packages.