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72 PCB007 MAGAZINE I DECEMBER 2022 Basics of Cupric Chloride Etchant vious columns that as you etch more panels, the metal content of your etchant increases. is increase in metal content makes your etching solution have a higher SG, and SG and etch rate tend to have an inverse relationship; thus, the higher your specific gravity gets, the slower your etch rate will be. e maximum etch rate for cupric comes in between the range of 28 to 36 °Bé (SG: 1.2393 to 1.3303) 1 . ankfully, the normal CuCl 2 etching solution you will receive comes in the range of 32 to 36 °Bé. Although specific gravity is one of the key factors, unlike alkaline etchant, there are no critical risks to falling out of this range. If the SG gets too high, you can simply add more water to your etching solution; if it is too low, just simply add more cupric crystals or etch more panels. Cupric chloride (CuCl 2 ) is an etchant that has capabilities that make it a great applica- tion in PCB manufacturing. Although it is not the most used etchant in the industry, it proves to be beneficial by being simple to maintain. Maintaining CuCl 2 is relatively forgiving in comparison to alkaline etchant because there are only a handful of parameters you need to monitor. If CuCl 2 seems like it would be an appealing etchant to use for your PCB etch process, here are some basic parameters that are key to understanding how to maintain it. Specific Gravity Specific gravity (SG) is a main factor that must be watched and controlled to maintain a consistent etch quality. I've mentioned in pre- The Chemical Connection by Christopher Bonsell, CHEMCUT

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