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24 PCB007 MAGAZINE I MARCH 2022 Christopher Bonsell, a chemical process engi- neer at Chemcut, is a new columnist for I-Con- nect007. His columns will appear monthly in PCB007 Magazine and will focus on topics con- cerning wet processes, wet processing equipment, and how changes in these areas can improve PCB manufacturing. Printed circuit board manufacturers who uti- lize wet processes have always strived to obtain a uniform etch across their panels. Although it is one of the most common matters these man- ufacturers tackle, it is perhaps the least under- stood. ere are a few reasons for this, one of them being that there doesn't seem to be an agreed-upon terminology within PCB manu- facturing. e term that I have been using to describe the consistency of etch across a single panel is "etch uniformity." Sometimes this term can be Etch Uniformity and the Puddle Problem equated to the consistency of etch across sev- eral panels, but perhaps a more suitable term is batch uniformity, which is directly related to how you maintain the chemical properties of your etchant. When it comes to etch uni- formity, however, the factors that affect it can become complicated. What are the obstacles to etch uniformity? ere are two primary things that limit your ability to get a uniform etch: conveyor den- sity and the "puddle effect." Overall, the issues of etch uniformity stem from the idea that the etching reaction is drastically affected by diffu- sion and how quickly fresh etchant can contact the surface. Conveyor Density Conveyor density, in relation to wet process- ing equipment, can refer to how much space the wheels inside the processing chambers The Chemical Connection NEW COLUMN by Christopher Bonsell, CHEMCUT

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