Issue link: https://iconnect007.uberflip.com/i/1524164
72 PCB007 MAGAZINE I JULY 2024 oxidized back to Cu +2 to maintain a steady etch rate. e alternatives were all batch etchants that required frequent make-up of new baths and, especially in the case of chrome/sulfuric acid etchant, were environmentally unfriendly. Alkaline etch has three etchant parameters that must be controlled to keep everything in a delicate balance: • Specific gravity: is is the main control point. Copper is etched and dissolves into the etchant, raising the specific gravity. When the specific gravity increases to the specified control point, replenisher fluid is added to the system until the specific gravity falls below the set point. e replenisher fluid is basically etchant with is month, I continue my discussion on how much process control is actually needed for high-density circuit production. However, in the last month, I have been called on to help with a specific process control problem: how to control an alkaline etch bath when you're not etching much copper. is problem has been cropping up more frequently as smaller shops (and a few larger ones) concentrate on low-volume, high-value plated through-hole panels such as prototypes, resistor cores, etc. Alkaline etchants were introduced in the early 1970s as production of double-sided and multilayer boards requiring plated through- holes began to increase. e advantage of alka- line etchant over the alternative etchants was that the Cu +1 etching byproduct could be re- Controlling an Alkaline Etch Bath With Low Copper Loading The Chemical Connection by Don Ball, CHEMCUT