Issue link: https://iconnect007.uberflip.com/i/1534385
APRIL 2025 I PCB007 MAGAZINE 37 Is Alkaline Etchant Better? While not a misconception, the idea that alka- line etchant will automatically improve your etch factor is not always true. You must run at the lowest pH possible, the highest specific gravity possible within the suggested range, and use a minimum ammonium chloride-to-copper ratio: 2 moles NH4Cl/mole Cu (typical chlo- ride-to-copper ratio is 2.4 to 2.5: 1). is pro- vides the best etch factor but also the slowest etch rate. As you raise the pH and lower the spe- cific gravity to increase etch rate, you lower the etch factor until it is possible to have an etch factor as low as 1:1 (etching as fast sideways as downward). So, you do get a better etch factor with alkaline etch, but it's not automatic. is lack of understanding occurred when we replaced an ancient alkaline etcher from a competitor at a company. We immediately received complaints that low etch factors on the new etcher were causing problems. We visited the company and discovered they had two major customers: one with boards with PTFE substrates, the other with normal fiber- glass substrates that needed straighter etched sidewalls for whatever frequency those boards were controlling. When the etchant was configured for the best etch factor (pH 8.0), the other customer's boards had a grayish coating le on the PTFE substrates. When they adjusted the etchant so as not to leave a coating on the PTFE aer etching (pH 8.3), the etch factors were too low to pass specifications for the other cus- tomer's boards. When I tried to explain this, I was told, "We never had this problem on the old etcher." e process engineer for the etchant supplier was called in and agreed with my analysis (a pleas- ant surprise). Again, we were told, "We never had this problem on the old etcher." We were both familiar with the old etcher and neither of us could see why it would get better etch factors than the new etcher. e problem was eventually solved by adding a mild acid rinse to the line to take care of the gray residue on the PTFE substrates. I later learned the rea- son they had never had a problem with the old etcher was because they never checked etch factors until they received the new etcher. ere are many more misconceptions about etching and other wet processing steps, but these are the ones I hear about repeatedly. PCB007 Don Ball is a proces engineer at Chemcut. To read past columns or contact Ball, click here.