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NOVEMBER 2020 I PCB007 MAGAZINE 65 processes, like HDI via fill and SAP metalliza- tion. As shown in Figure 2, there are five very important characteristics of copper plating: 1. Throwing power 2. Leveling 3. Crack resistance 4. Maximum current density 5. Appearance Those five characteristics are controlled by six parameters, and five of them are chemical concentrations: 1. Brightener 2. Leveler 3. Copper concentration 4. Sulfuric acid 5. Chloride concentration 6. Temperature Although many parameters affect plating distribution, chemical concentrations are some of the most important and most influential. These need to be controlled as they change faster than any of the other parameters. Oth- er justifications for better chemical control in- clude to: • Identify process problems • Reduce human error • Enhance product reliability • Tighten operating windows • Reduce chemical operating costs Most Common Chemical Sensors The most common sensors for chemical use in PWB fabrication are: 1. Electrochemical 2. Specific gravity 3. Colorimetric (spectrometers) 4. Electronic colorimetric 5. Electroanalytical techniques (voltammetric) 1. Electrochemical Sensors Electrochemical sensors, like pH, are some of the most used for analysis, but equally impor- tant are oxidation-reduction potential (ORP), Figure 2: The influence of plating parameters and what happens if the concentration goes up. The first five parameters can be automatically analyzed and controlled.