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72 The PCB Magazine • August 2015 time and can potentially etch some thin copper base laminates. The micro-etch test coupon is a 3-inch by 3-inch single-sided copper laminate that has been dried and weighed. The test sample is placed in the tank and timed at 30 seconds. After it is washed and re-dried and weighed, the differ - ence in grams multiplied by 365 is the number of millionths removed, or 9.7 times weight loss in microns removed in the 30 seconds. Copper plating adhesion can be tested quickly by heat- ing a sample etched pad with a soldering iron; if the copper peels off leaving the original copper you have a problem. Severe cases of peeling will cause the tracks to fall off before final processing, and it is solely from not monitoring and control- ling your micro-etch tank closely enough. The micro-etch is followed by a second set of cascad- ing rinses; these are important because the per- sulfate or hydrogen peroxide is a poison to the copper tank. The last tank is a 10% sulfuric acid tank that helps remove any last oxides and sets the acid pH of the panel going into the acid-based copper tank. After plating, a set of cascading rinse tanks is used prior to going into the tin tank. Many shops have a dead rinse tank after copper plating to further limit the copper drag-over into waste processing. One of the biggest improvements you can make to the copper plating line is to slow down the operation after removal and let the panels drip after each tank, before you move the racks. A "slam dunk" only causes excessive contamination carryover and further pollutes and reduces the life of your copper tank. other Points to Consider Oils in the plating area from a hot-air unit or hot-oil reflow tanks in the plating area will cover any panels waiting for processing with a very thin coating of oil (it's in the air and is at - tracted to the panels' negatively charged surfac- es). The oil film is very difficult to remove and causes open spots of non-plating. I have seen this enough times to warrant mentioning it. Run a water break test to see if your plating surface is clean. The plating current you run is not constant. It should change based on the panels your plat - ing, line widths and copper balance between sides; it will also change during the plating pro- cess. In order to have an even amount of plat- ing on each side of the panel, it is important to Figure 3: copper surface before (a) and after (b) micro-etch. a B Figure 4: chart showing etch rate in micro-etch bath. FeAture PLATING AND QUALITY ARE CLoSE PARTNERS continues