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14 I-CONNECT007 MAGAZINE I MAY 2026 T H E C H E M I CA L C O N N ECT I O N panels to be over-plated, trapping resist under the over-plated areas that interfere with the etching of the base copper. The first thought is to increase spray pressures in both the stripper module and rinses, but it turns out that this is not as simple as it seems. One customer was using a power wash at 400 psi after stripping and requested a 400-psi rinse after the strip chamber for their proposed new stripper. This would involve special high-pressure pumps with a very high flow rate, stainless steel plumbing, very good filtration (it would have to have a recirculat- ing sump to keep water consumption at a reason- able level), etc. When all is said and done, it is very expensive. We decided to put together a 400-psi test stand to get an idea of what would be involved in actually putting one of these things together, which turned out to be a good idea. We got some test panels from the customer, and to my surprise, the 400-psi rinse seemed to have no effect whatsoever. Somewhat apprehensively, I stuck my hand under the spray and felt hardly any impact even though the pressure gauges were reading 400 psi. To achieve 400 psi with the pump they had available, our engineers kept reducing the nozzle openings until they reached 400 psi. Unfortunately, the opening size was so small that spray droplets were broken up into such tiny drop- lets that they had hardly any impact force at all, even at 400 psi. We had invented a "velvet touch" high pressure spray system. A bigger pump was obtained, add- ing nozzles with a more reasonable opening size, and found that the customers' objectives could be reached with a 150-psi rinse—a much more rea- sonable proposition, but still requiring more effort than expected. Another unanticipated consequence occurred when people started flash etching to remove very thin base copper from their boards. It should have been a simple proposition, a quick spray of etchant to remove two or three microns of base copper and on to the next process. However, we started getting reports of residues of base copper left on the panel in long strips, like tiger stripes. This did not occur on their normal copper weight panels (1- ounce, half-ounce, etc.), just their flash etch panels run at high conveyor speeds, so it was not due to clogged nozzles or misaligned conveyor wheels. Measurements showed that the distance between the stripes was about the same as the distance between the spray tubes, so we speculated that the conveyor speed needed for the flash etch might result in a harmonic being reached with the spray tube oscillation rate. Most etchers and developers use some type of spray tube oscillation to sweep etch solution back and forth across the board sur- face as it travels through the etch chamber. At the end of each oscillation stroke, even though it doesn't look like it, the tube must decel- erate to a stop, then accelerate in the opposite direction. There is a brief time when the tube is stopped and, at this moment, the area directly under the spray gets a little more etch time. At the oscillation rates and conveyor speeds used for normal copper weight boards, these areas tend to even out as the panel goes through the etcher, as a different part of the panel is below the spray tube at the end of each oscillation stroke. It is conceivable, however, that at the high con- veyor speed needed for flash etching, a harmonic could be reached where the same part of the panel could be under the spray tube at the end of each oscillation stroke and that little bit of extra etching could accumulate and cause striping. This proved to be the case when altering the oscillation speed by 25% in either direction caused the tiger stripes to go away. I doubt there is anyone who could have antici- pated a harmonic relationship between conveyor speed and etcher oscillation rate when flash etch- ing was first thought of (anyone who could have thought of it would probably not be working in the PCB business anyway). So, when taking another look at additive manufacturing, keep in mind that there will be consequences further down the pro- cess line. I-CONNECT007 Don Ball is a process engineer at Chemcut. To read past columns or contact Ball, click here.