Etch effects exposed: discover where your copper really goes

Etching inner layers involves cleaning the copper on both sides of the piece of laminate, applying a photoresist, exposing the photoresist to create the inner layer pattern, developing the resist, etching away the unwanted copper, and removing the etch resist. This process is automated in most shops and the chemistry is automatically monitored. As a result, the accuracy and repeatability is quite good. It is possible to etch inner layer traces using this process to an accuracy of ±0.5 mils. This accuracy control helps keep impedance within the tolerances required for transmission lines.