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88 PCB007 MAGAZINE I MARCH 2023 you can be out of range without knowing it. To avoid this, there is another option where instead of queuing chemical additions man- ually aer titrations, you could simply add a certain amount of those reagents aer a spe- cific number of panels are run. is would need some fine-tuning for your process and thus require some testing and trial-and-error. Once you have nailed it, that factor of the process becomes much easier to control. Despite the fine-tuning, you will need to con- tinue monitoring the contents to account for any variations that can occur during the etch process. To Regenerate or Not to Regenerate e next major contributing factor is ORP. As discussed before, ORP is the measurement of your ready-to-etch etchant and your spent etchant. As the spent etchant dilutes your etchant bath, etching becomes less efficient. erefore, it is important to keep a steady ORP factor for a consistent etch process. To do this, you will have to consider whether you are able to regenerate your etchant. e PCB etching process primarily consists of cupric chloride or alkaline cupric chloride; you have the option to regenerate your etchant and therefore have an easier time keeping your ORP consistent. If you are utilizing an uncom- mon PCB etchant, such as ferric chloride, you will not be able to effectively regenerate your etchant. is is because of an unwritten rule that is in etching chemistry. e rule is that it is ideal to use etchants that are more "alike" to the metal you are trying to etch. is means the metals you etch should have the same metals in the etchant, if that is possible. is is because the larger the number of different components dissolved in the etchant, the more difficult it becomes to mon- itor the etchant effectively and to perform regeneration. For example, if you etch copper with cupric chloride, the copper can be directly used to make more cupric chloride. However, if you etch with ferric chloride instead, the iron con- tent of the etchant would become less con- centrated because you are adding copper into the solution—this gets in the way of regener- ation and develops complications. If you are using an etchant that is not copper based, you will likely have to settle for what is referred to as the "feed and bleed" process to control your ORP. is is simply a method where aer so many panels are etched, some of the used etchant will be pumped out of the machine as fresh etchant is pumped in. Once fine-tuned, this process allows you to main- tain a steady state for your process to remain consistent. Conclusion From this brief introduction to etchant chemical control, you should have a fair under- standing of how you would implement con- trols in your etching process. With tools such as normal monitoring methods, control based on panel count, and "feed and bleed," you should be capable of mapping out a chemical control method that works for nearly any etch process. PCB007 Christopher Bonsell is a chemical process engineer at Chemcut. To contact Bonsell, click here. If you are utilizing an uncommon PCB etchant, such as ferric chloride, you will not be able to effectively regenerate your etchant.