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86 PCB007 MAGAZINE I MARCH 2023 ple system to restore the chemical contents of your etchant. ere are some exceptions to this because, in some cases, the link between mon- itoring and adjusting is not so direct. With fac- tors such as chloride and free HCl content, it is harder to simply monitor them; therefore, the adjusting of those factors will have to be done differently. If one of these factors were found to be out of range aer performing a titration, you would likely have to manually add the chlorides or HCl into the machine. Along with that, if your process technicians do not perform the titrations regularly, then ing process? In etch chemistry control, there will be multiple feedback loops involved. is is because each parameter of the etchant has its own method of control. Every etchant available has its own set of parameters. Before you get started with an approach to process control, you will need to first evaluate all the parameters that contribute to etch quality. e most common parameters you will see in an etchant are shown in Table 1, along with their monitoring methods and ways to control them. It should be noted that temperature and spray pressure are major contributing factors to etch quality, but these parameters are auto- matically controlled in all etching equipment; therefore, they will not be covered. From the table, you will notice most of the parameters in etching have a specific measure- ment tool that makes the monitoring stage sim- ple. Since each factor monitored describes a contributing chemical in your etchant, most cases just require adjustments through adding the lacking chemical. is makes it simple because, with a proper monitoring system, you can link it to a pump that will trigger when it is out of range. is will provide a sim- Before you get started with an approach to process control, you will need to first evaluate all the parameters that contribute to etch quality. Table 1: Common etchant chemical parameters and their respective monitoring and adjusting methods. Associated etchants only show cupric chloride, alkaline cupric chloride (alkaline), and ferric chloride. Other etchants that are not mentioned may have similar or the same contributing parameters