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68 The PCB Magazine • August 2015 filters on the copper tank, run it for a few hours and say, "Voila, it's treated." Sorry, but not even close. Look at your copper tank. If it's not a clear, very light blue, then it's not treated properly; if it's greenish and cloudy, then you have a lot of dry film and other contaminants in the solution that will hurt your plating quality. The proper way to treat a copper tank is first by heating it and/or adding hydrogen peroxide, which removes the brighteners and levelers. Then run the solution through large bags of acti - vated carbon until the solution is clear and blue, typically overnight. Add a full load of brighteners and levelers and then use a Hull cell. The magic Hull cell is an old-time way of knowing what your plating tank is doing. It tells you if the throwing pow - er is good, if your levelers are proper, and if the brighteners are correct. But not many plat- ing areas use them anymore, let alone even know how to do a Hull cell and what to look for. I have used the automatic titration machines the vendors have sold for many years and they work as they should, tell - ing you the brighter and lev- eler percentages, but they can never tell you how the tank is plating. Only a Hull cell can do that. The percentages of sulfuric acid and hydrochloric acid affect the plating speed and quality, as does the cop - per content of the bath. One of the worst ways to run a copper tank is to put 10-inch carbon- polishing filters on the tank pump and run 24/7. This creates a few problems; most significantly it reduces the levelers and brighteners, which you do not want to do unless you like paying your chemical supplier more money. Meanwhile, the little activated carbon in the filters really does not remove much of the dry film contaminants. Along with proper carbon treating, another important maintenance item is the proper re - moval of metals other than copper. The copper tank will have a small percentage of lead, tin and other metals present in the shop, mostly from rack carry-over and accidental cleaning of a tin- lead board in a rinse right before the copper tank. To remove these metals is an easy job, yet lately I have seen few plating staff performing this task or having the special plates to remove these vari - ous metals. This is something that we regularly did to keep copper ductility at the proper speci- fication. A special stainless steel plate is made with sharp, 2-inch zig-zag bends, so as to look like an accordion; the various angles and dis- tances from the anodes facilitate removal of the different metals because they plate out at dif- ferent current densities. Metal contamination of the copper tank can result in a grainy and bumpy copper surface. It is im- portant to work at fixing the problem by controlling the process/dripping time of the rinse tanks and performing a metal plating clean cycle every few months. The type and number of anodes can have a significant effect on the quality of the copper. With too large an an - ode area and a higher sulfu- ric percentage, you can easily build up too much copper in the bath from the etching ef- fect of the sulfuric acid. I have used both straight copper/phos- phor anodes and titanium baskets with copper/phosphor nuggets or balls. Both work well, with the edge going to 1-inch copper balls and rectangular titanium baskets, as you can keep the copper surface area in control and add new copper balls as needed to maintain area. Both require constant maintenance with sched - uled anode removal, cleaning, re-bagging, and smut removal with a proper reactivation plating cycle. During the '90s, my PCB shop made special heavy copper circuits; we had to learn how to plate up to 40 ounces of copper in three-dimen- sional layers. Believe me, when a single panel is in the copper plating tank for 40 hours, if you the magic Hull cell is an old-time way of knowing what your plating tank is doing. it tells you if the throwing power is good, if your levelers are proper, and if the brighteners are correct. But not many plating areas use them anymore, let alone even know how to do a Hull cell and what to look for. " " FeAture PLATING AND QUALITY ARE CLoSE PARTNERS continues