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46 PCB007 MAGAZINE I NOVEMBER 2022 uct of this reaction, your water consumption will be reduced. What is also useful about this option is that you can use a simple pump system to feed it into your etcher. is pump system would connect to the chemical drums and tie it in with a few controls (i.e., metering pumps, ORP monitors, and/or panel counters). ese controls will be used to cue the pump system to provide your etcher with an adequate sup- ply of regenerating reagents (Figure 2). e drawback of this option is that H 2 O 2 is a thermodynamically unstable molecule, and over time it will decompose and become water. is means the longer it is sitting idly in a drum aer opening, the less effective your regenera- tion controls will be because you will no longer have an accurate understanding of your H 2 O 2 concentration. ere are typically some addi- tives to ensure the H 2 O 2 does not break down too quickly, but it is still a possibility. With H 2 O 2 there may also be additional safety mea- sures required since it is a highly reactive oxi- dizer. Sodium Chlorate and HCl Utilizing NaClO 3 and HCl for regeneration will look similar to how regeneration is done with H 2 O 2 and HCl, since it can also be set up with a simple pump system. Utilizing these reagents provides the same benefit of reducing water consumption in maintaining SG. NaClO 3 will give the same benefits as H 2 O 2 without the worry of your chemicals decomposing over time. Both NaClO 3 and H 2 O 2 are strong oxidiz- ers, but NaClO 3 is easier and safer to handle. Perhaps these are the reasons why regenera- tion through NaClO 3 is the most popular of the three options. Although it has some great benefits, it has the drawback where water is no longer the only byproduct. For this reaction, NaCl is also a byproduct and over time, as you are etch- ing and performing regeneration, you will accumulate salt inside your etcher. At a cer- tain point, the salt content will be so high that the salt will take the form of a solid inside your etcher, which can be difficult to remove. is can be problematic from a few standpoints. From a production standpoint, it can inter- fere with how effective your etching process is by plugging up your nozzles and it can cause abrasions on your PCBs or damage the pho- toresist. From another standpoint, it can also impact the longevity of your equipment. If it goes untreated long enough, you may see more mechanical issues with your machine. Although salt build-up could be severely prob- lematic, it can easily be prevented with routine maintenance and cleaning. Chlorine Gas Chlorine gas for regeneration may be the most efficient option available. is is because the Cl 2 regeneration reaction produces no byproducts that can accumulate or mess with the balance of the etchant. It is also highly eco- nomical because the cost of the gas is signifi- cantly lower than the other reagents. Although it is generally considered the best option, it is a method that is not highly used due to the number of regulations that are imposed on the use of Cl 2 . Even with the reagent cost being significantly low, in some cases, the amount of Figure 2: A metered pumping system for regeneration made by Chemcut.