Printed circuit boards (PCBs) were immersed in a 35℃mixed solution of hydrogen peroxide and sulfuric acid to investigate the micro-etching on the copper substrate in this work. The degree of micro-etching on the copper surface was estimated by measuring the flatness and roughness. The average roughness (Ra) was of the most interest and it would depend on the concentration of hydrogen peroxide and sulfuric acid. The satisfactory micro-etching on the copper substrate revealed Ra in the range from 0.2 to 0.3μm. In the micro-etching process, the concentration of hydrogen peroxide and sulfuric acid was varied to explore its effect on the etching rate by virtue of monitoring the open circuit potential (OCP) of the system. An attempt was made to construct a diagram which correlates the OCP with concentration of the components in the mixed solution. This diagram is useful in design a monitoring and control system for this process. In the system of 35℃mixed solution containing hydrogen peroxide and sulfuric acid, OCP predominately depend upon the concentration of hydrogen peroxide. The OCP increases with increasing the concentration of hydrogen peroxide. The etching rate on copper is enhanced with increasing the OCP. The measurement of OCP and its adjustment by controlling the concentration of hydrogen peroxide provide a key to control the etching rate in the micro-etching.
Key words: mixed solution, micro-etching, average roughness, copper, hydrogen peroxide, sulfuric acid.
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