Issue link: https://iconnect007.uberflip.com/i/1525368
50 PCB007 MAGAZINE I AUGUST 2024 specific gravity of the solution." Next month, I will provide the design graphs to make this SG sensor with the specs to use for UHDI final etch control for less than $50. Plating Additives (Ampere-hour Measurement) Measuring the current load in electroplat- ing has been around for a long time. It is use- ful because many additives to a plating bath are consumed by the electroplating process, and that depends on its current usage over time. Figure 3 shows a high power-very low resistance (50 mΩ) shunt. e current shunt is attached in series between the power sup- ply and the plating tank. e amp-hour total- izer can be set for alarm or to activate additives to the plating tank. Color Indicators Color change in a process solution can indi- cate chemical concentration changes in that process. Many experienced operators learn this aer years of working with the same pro- cess. Unfortunately, our eyes are not that cali- brated and cannot distinguish the subtle color changes that a sensor can, especially if you happen to be color blind. Fortunately, the solution can be very affordable. If you have ever encountered a backyard pool and need to control the chlorine content (to prevent algae or other growths), you may assign that sim- ple task to your kids. Pool test kits (and test kits for most PCB processes) cost less than 60 cents per test (Figure 4). If data (control) or visibility is required, moving to an electronic colorimeter is quite easy. I found a portable colorimeter for $668 from Hach, and a Chi- nese-made lab colorimeter for $279 on Ama- zon. e alternative is to make your own, just as middle and high school students around the world have been doing 2 for years. Examples of three DIY colorimeters are shown in Figure 5. e most famous is the LEGO Student Color- Figure 3: Amp-hour totalizers can be purchased, or the simple voltage-to-frequency circuit can be designed and built for less than $20 and attached to a purchased 50- or 100-milli-ohm power shunt.