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84 DESIGN007 MAGAZINE I NOVEMBER 2021 ere are several ways to catch this pH end- point. Indicators can change color at a given endpoint. You can track pH with a meter during titration. Some reactions will provide answers by creating a precipitate (a solid) at the desired pH. If you know precisely how much chemical has been added, a simple calculation will tell you the concentration of the component in the bath. Colorimetric Tests Another common testing method uses ultra- violet-visible (UV-Vis) spectrophotometry. We use a UV-Vis spectrophotometer to ana- lyze a sample of a bath at a given wavelength of light. As we do, the absorption or trans- mittance of the light as it passes through the sample will give a reading. When this reading is applied to a calibrated curve of known con- centrations, it can provide the bath concentra- tion. Elemental Analysis Elemental analysis is a sound method for finding concentrations of various types of met- als in a chemical sample. Common elements found in PCB manufacturing include copper, gold, nickel, silver, tin, and lead. One of the most accurate ways to detect metal is through flame atomic absorption analysis (FAAS). Using this method, a sample of the chemical bath is burned in an atomic absorption flame, and it measures the absorption of light at spe- cific wavelengths to detect gas phase elements. is absorption value is compared to a stan- dard curve of known concentrations to deter- mine the composition of the solution. Functional Tests Functional testing is a type of black box test- ing that bases its test cases on the specifica- tions of the component being tested. ese tests are especially useful in electroplating because they can help you understand how some components are functioning. One exam- ple of a functional test is a grain refiner in a copper bath tested using a special bench top unit called a Hull cell. A sample of the plat- ing bath is added to a Hull cell, along with an anode and a brass plating coupon. Next, cur- rent is applied. is causes an electroplating reaction to occur, and a metallic deposit will accumulate on the brass Hull cell coupon. Allowing the Hull cell to sit for a period will ensure that there is adequate metallic deposit to analyze. is type of test can cover a variety of plat- ing current densities. You can also add stan- dard additions of grain refiner to the plating cell and compare it to the plating bath. is will help you to understand appropriate addi- tives that will achieve the desired copper deposit. All these tests and the results they produce will help you to maintain the chemical pro- cesses within their given operating ranges. You will also be better able to quickly identify prob- lems with equipment or chemistry to ensure that an expected outcome is the result of every chemical process. DESIGN007 Matt Stevenson is the VP of sales and marketing at Sunstone Circuits. To read past columns or contact Stevenson, click here. Common elements found in PCB manufacturing include copper, gold, nickel, silver, tin, and lead.

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