Etching baths with sulphuric acid are used in PCB processes, such as the through-hole plating of multilayers (black-hole method), the microclean stage and pre-treatment (pre-etching) during track formation. The bath consists of an approximately 8.5% sulfuric acid (H2SO4) solution, with a hydrogen peroxide (H2O2) component of about 25gm/liter. The concentration of hydrogen peroxide is decisive for the quality of the product, and should be kept constant. Several times a day, depending on the throughput, technical staff carries out tests (titration of a sample with 0a potassium permanganate solution) to determine the hydrogen peroxide concentration. In order to achieve a consistent rate of etching and with it a consistent PCB quality, the concentration should be kept constant by continuous automatic dosing. The patented Jumo Corrotrode fulfills the task of measuring the concentration. A transmitter performs evaluation and control, and a pump doses hydrogen peroxide from a reservoir.
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