Easily measure the hydrogen peroxide concentration in acidic etching baths for PCB manufacture
18 June 2003
Manufacturing / Production Technology, Hardware & Services
The PCB manufacturing industry uses etching baths based on sulphuric acid for various production processes, such as the manufacture of through-hole plating for multiplayer PCBs (black-hole method) the 'microcleaning' stage and for pre-treatment (pre-etching) during track formation. In most cases, the etching baths consist of an approximately 8,5% sulphuric acid (H2SO4) solution, with a hydrogen peroxide (H2O2) component of about 25 g/litre.
The concentration of hydrogen peroxide, in particular, is decisive for the quality of the product, and should be kept as nearly constant as possible. Depending on the number of boards being processed, this concentration diminishes as a result of dispersal and decomposition.
It is usual practice that several times a day, depending on the throughput and the operational life of the plant, technical staff carry out laboratory tests (titration of a sample with a potassium permanganate solution) to determine the hydrogen peroxide concentration. The disadvantage of this method is that isolated manual dosing causes overdosing of hydrogen peroxide at some times, and insufficient dosing at other times. In order to achieve a consistent rate of etching, and with it a consistent PCB quality, the hydrogen peroxide concentration should be kept constant by continuous automatic dosing.
ASSTech Process Electronics & Instrumentation says that the new Jumo Corrotode, can fulfil this task of measuring the hydrogen peroxide concentration. The Corrotode is a potentiometric sensor (CPPS = corrosion potential-based potentiometric sensor) with an output signal covering a voltage range of several hundred mV. Evaluation and control are performed by a transmitter with integrated control contacts. An attached dosing pump supplies hydrogen peroxide from a reservoir.
For more information contact Anastas Schnippenkotter, ASSTech Process Electronics & Instrumentation, 011 794 7057.
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