This paper discusses a through hole copper filling process for application to high density interconnects constructions and IC substrates. The process consists two acid copper plating cycles. The first cycle uses periodic pulse reverse electroplating to form a bridge in the middle of the hole, followed by direct current electroplating to fill the resultant vias formed during the bridge cycle. This process can provide defect-free filled holes with total plated copper on the surface below 25 μm, with dimple less than 5 μm for boards with core thickness of 0.2 mm and 0.25 mm. This process was designed to be deployed in specially constructed vertical continuous platers (VCP), thus reducing capital equipment compared to horizontal conveyorized electroplaters. The chemical components, copper, acid and additive, for periodic pulse reverse plating cycle, are optimized via experimental conditions selected from DOE (design of experiments) software. Critical parameters are identified and the impact on cavity formation during the bridging step is quantified. The additive and copper concentrations play key roles in reducing defects during bridge formation and on the resultant via formation.
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