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40 PCB007 MAGAZINE I JUNE 2018 across the working panel. Electroplating and etching are prime examples. For several years, people have been using re- verse-pulse rectification to enhance the plating effect and to enable them to achieve higher as- pect ratios of panel thickness to hole size with less variation of plating-hole thickness. Reverse pulse uses a high-current, short-period reversal of polarity to unplate material from the prod- uct surface. The high current means that the effect is greatest where the material is deposit- ing most thickly during the forward current cy- cle. This gives a smoothing effect and a more even thickness both on the surface and in the holes. Right now, the effect can be further en- hanced by using continuous plating methods that move the panel though the plating cell on a conveyor system so the whole panel has the same view of the anodes. This enhances the distribution on the surface and in the holes, which can allow you to go much further with the products you are able to run. Downsides to the process include a larger footprint in the factory than the equivalent conventional plat- ing process, but clever layout can often gain some of this space back. For etching, the vacuum process has really started to move things on. It has always been tough to achieve exactly the same effect on the top and bottom sides of the working panel as it passes though the etch machine. A lot of the reason for this is simply gravity. The bottom- side spray hits the panel and the drops back off assisted by gravity, which leaves a space for the next spray to hit the panel. On the top side the spray hits the panel and stays there. This means solution turnover is much less effective on the top side because of the puddle which remains. To make matters worse the puddle runs off the edges of the panel but the closer to the centre you get the harder it becomes to move the solution. Vacuum etch uses a vacuum head following every spray bar. This removes the puddle of solution, which allows the subsequent spray to be much more effective. Solution turnover at the surface is much improved and results in the top and bottom sides being more even- ly etched than with the traditional process. As process requirements become more extreme, with thicker metal layers being etched, the vacuum gives more and more of an advantage. A further enhancement to the etched result is possible by having an atomising etch cham- ber after the main etch chamber. This allows you to target the foot of the etched metal fea- ture to achieve a squarer cross-sectional pro- file. This approach is not widely used but it certainly offers a further improvement for the most testing of product designs. We are always trying to find ways to offer a more efficient, faster, smaller, more accurate process. To be able to best apply that to a par- ticular factory it is important to understand what needs to be achieved. Wet process equip- ment is usually expected to last at least 10 years, so getting a handle on the roadmap for process development is imperative to ensure a new machine is fully up to the task. Ideally, suppliers work together with their customers to discuss the pros and cons of the types of fea- tures detailed in the examples above. Currently, the company I work for is busy, which means the industry we supply is busy and process development along with invest- ment in new equipment is strong. This is a good sign for the future of electronic manufac- turing; long may we continue to find new ways to enhance the effect of spraying and dipping your panels. PCB007 Marc Ladle is director at Viking. To contact Ladle or to read past columns, click here. The high current means that the effect is greatest where the ma- terial is depositing most thickly during the forward current cycle.