Achieving quality electrolytic copper metallization during the production of high aspect ratio PCBs, such as back panels, isn't easy. These panels can be from 3 mm to 10 mm thick, with typical aspect ratios of 10:1, and the current trend is for thicker panels with aspect ratio up to 15:1. One of the limiting factors in copper deposition is the mass transport of ions into high aspect ratio holes. Achieving the required copper thickness in the hole with out overplating the surface (causing resist overplating with pattern plate or poor line definition with panel plate) is the biggest problem in the production of high aspect ratio pan els. Also, component mounting with the press-fit technique is difficult when copper deposit distribution is poor. To overcome throwing power problems, low electroplating current densities have been used, but this has a negative impact on productivity. As a solution to these problems, reverse pulse plating can allow the use of higher current densities with improved surface distribution and throwing power in the through holes.
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