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30 PCB007 MAGAZINE I JUNE 2023 improve the etch uniformity of your PCBs from the leading-to-trailing edges. is refers to the edge perpendicular to the direction of travel. e leading edge enters the horizon- tal etching machine first, while the trailing edge enters last. Variation on this part of the panel is the most difficult to control because of how the panel gets pulled through the etch- ing machine. When you adjust for side-to-side variations, the solution mostly likely is having higher spray pressures in the middle than on the edges. ese can continuously spray and target the areas you want to change. With leading-to-trailing uniformity, you cannot simply have a continuous spray and improve uniformity (at least not with today's technology). To achieve leading-to-trailing uniformity, etching must start and stop only in the middle; this is effectively what intermit- tent spray does. To improve leading-to-trail- ing uniformity, intermittent spray uses a sen- sor to indicate where the first edge of a panel is located in an etching machine. Once the panel is partially through the module, intermittent spray initiates and targets a spray of etchant only in the middle of the panel, shutting off before reaching the trailing edge. By doing this, you gain greater control over the middle sections that tend to be under-etched. Conclusion ere are many different tools available to approach etch uniformity. e few that were shared in this column only touch on a handful of options that are available to you. With this information, you should now be aware of some of the etch uniformity technology that exists today and what exactly each option does. PCB007 This is the final column for Christopher Bonsell, who has left Chemcut for a new posi- tion with Tecomet. This column will continue under a different writer from Chemcut. To read past columns, click here. Optimized Spray Optimized spray is not necessarily an anti- puddling measure on its own, however it is still a technology implemented inside etching machines to provide better uniformity. Opti- mized spray describes an attribute inside the main etch chamber. Functionally, it means that the spray tube pressures are calibrated and adjusted with the expectation that etch- ing will vary across the panel. In practice, this means that spray tubes located over the edges of your panels must be adjusted to provide a less aggressive etch in comparison to the mid- dle spray tubes. Optimized spray is highly important for all matters of etch uniformity. Without good baseline spraying, using any additional counter-puddling technology will just make the process more complicated and may even exacerbate variations. Etch Adjust Etch adjust is a process that can be used to counteract the puddle effect. is process focuses on side-to-side uniformity of panels. Side-to-side uniformity refers to the edges of a panel that are parallel to the conveyor side rails. Etch adjust functions in a similar way to optimized spray in that it allows you to make spray zones and provide them with a spray pressure that would reduce any variation caused by the puddle effect. e etch adjust module differs because it's a unit of operation separate from the main etching chamber. It can target more refined spray zones and thus give you greater control over the side-to-side variations. is type of process can be useful if you copper plate your own panels. Depend- ing on how your plating process operates, the stock material for your PCBs can have thicker copper on one end. With etch adjust, you can more easily compensate for this variation than you could with optimized spray alone. Intermittent Spray Intermittent spray is a counter-puddling measure that you can take if you want to