Surface Preparation
Chemical roughening of copper foil or electroplated copper is a standard wet-process step used to improve the adhesion of subsequent organic coatings or plating layers. This treatment, known as chemical micro etch, uses mild acid or oxidizer mixtures to remove a tiny fraction of the surface metal, creating a microscopic topology. The reaction removes oxides and exposes a clean, high-surface-area copper grain structure.
Process Control
Controlling the etch rate depends on managing acid concentration, copper loading, and temperature within tight operating windows. Industrial applications usually deploy sodium persulfate or sulfuric acid with hydrogen peroxide to achieve a uniform bite depth of around one micrometer. Spray pressures in the conveyorized module must remain consistent to avoid uneven surface roughness or over-etching fine features.
Frequent laboratory analysis tracks copper concentration to prevent depletion of the active chemistry. Automatic dosing systems inject fresh oxidizer based on the processed area or real-time chemical titration. Regular maintenance prevents nozzle clogging that causes striping patterns across the panel surface.
Quality Assessment
Verify the effectiveness of the treatment by measuring the water contact angle or using scanning electron microscopy to observe the micro-roughened surface profile. Inadequate surface roughness leads to delamination during solder mask application or dry film lamination. Conversely, excessive etching thin down trace thicknesses below allowable limits, which degrades impedance control on outer-layer signal traces.
Testing usually involves cross-sectioning or optical inspection to ensure that the trace width retains its nominal dimensions.
