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44 PCB007 MAGAZINE I NOVEMBER 2022 Cupric chloride (CuCl 2 ), if you recall my June 2022 column "Etchants of the Indus- try: Cupric vs. Alkaline," is the second-most used etchant in PCB etching next to alkaline etchant. It holds many benefits such as sim- ple maintenance, easy wastewater treatment, reduced cost of etching, and efficient regener- ation. Many times, I have discussed how criti- cal it is to implement regeneration because it allows you to maintain a consistent etch quality and reduces the cost of etching. What makes cupric's etch regeneration simple is that it is a matter of what you choose to use. ankfully, utilizing any regeneration option for cupric chloride is as simple as feeding your regener- ation chemicals into the etch bath and letting the chemistry take place. Although all are rela- tively simple to implement, some have certain benefits over others. When it comes to regeneration for CuCl 2 , you have three options: hydrogen peroxide (H 2 O 2 ) Cupric Chloride Regeneration Options and hydrochloric acid (HCl), sodium chlorate (NaClO 3 ) and HCl, or chlorine gas (Cl 2 ). e regeneration reactions for the listed reagents are shown in Table 1, and how these reactions all tie in together is shown in Figure 1. Hydrogen Peroxide and HCl e first regeneration option is H 2 O 2 and HCl. One great benefit of this option is it only has one byprod- uct to the reaction: water. As a byproduct, this water is not problematic because it can be used for maintaining the spe- cific gravity (SG) of your etch- ing solution. As you etch more copper, the SG of your etching solution will increase because of the metal content rising. With water being the byprod- The Chemical Connection by Christopher Bonsell, CHEMCUT Table 1: Etch and regeneration reactions for cupric chloride 1 Figure 1: Diagram of how each regeneration reaction provides a chloride ion to convert CuCl (the spent form of the etchant) back to CuCl 2 .