PCB007 Magazine

PCB007-Aug2019

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12 PCB007 MAGAZINE I AUGUST 2019 usually, it is the work at the extremes of capa- bility that suffer. For example, very thick heavy panels are hard to transport using commonly used top-clamping methods (they can drop out of the clamps unexpectedly). Very thin panels need extra support to stop them folding when they are dipped into the tanks and also to keep them in a stable position in the centre of the tank between the anodes (the plating will be too heavy on the side closer to the anodes and too thin on the side which is further from the anodes). For both problems, simple solutions are available, but the same fix does not suit both extremes at the same time. The plating chemistry has also advanced when compared to the simple solutions and re- plenishment additives of years ago. Again, the major problem for smaller manufacturers is the sheer amount of variation in the work they have to put down the line and the fast turn arounds required by customers that prevent them from batching similar work together. The chemistry in a bath can definitely be tuned to provide even plating of a large area, such as panel plating where the whole surface of the panel is plated as well as the through-holes, but the same tuning is likely to make it very difficult to plate isolated details or very small plating areas. In the worst case, the additives have to be stripped out of the solution using a carbon filter and then added again to suit the next requirement. Solutions and Developments All of the previous cases are real examples I have come across during the last year, and they are very big problems for the companies involved. In some cases, the only practical so- lution is a larger factory and a second special- purpose plating line. Development of hardware to meet the needs of the large range of chal- lenges facing the plating operation has recent- ly been quite strong. There are a number of features becoming more commonplace on new equipment and some that could also be retro- fitted to existing equipment. Zoned anodes are an interesting approach to help overcome distribution issues. Tradi- tional soluble anodes using titanium baskets filled with copper balls do not lend themselves to being able to control different areas of the plating window. They are typically hung on a single anode bar, and the plating current is ap- plied evenly to the whole anode area. Using insoluble iridium mesh anodes allows zoning of the anode area, and you can control the cur- rent by depth by splitting the anode into sec- tions and only applying the current to the sec- tion of the anode with a panel in front of it. This allows more accurate plating of different panel lengths without having to revert to float- ing shields. Multiple rectifiers give the capability to split the plating window into sections across its width. This could be used to allow flight bars to run partly loaded with much more pre- dictable results. This approach could be used alongside zoned anodes to provide an almost endless combination of ways to be able to split the plating window to achieve more ac- curate copper plating. Like the zoned anodes, this approach has many possible applications Figure 1: Zoned anode section.

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