Inner Layer Process
(III): Etching and Stripping

Once the circuit pattern is clearly defined through exposure and development, the process proceeds to etching.

The purpose of etching is to remove the exposed (unprotected) copper, leaving only the intended conductive traces.
The most common etchant is an acidic cupric chloride solution, and precise control of concentration, temperature, and flow rate is crucial for maintaining accurate line width. Improper control may lead to over-etching (resulting in thinner lines) or residual copper (causing potential short circuits).

After etching, the photoresist stripping process removes the hardened photoresist, exposing the final copper circuitry.
Although this step may appear straightforward, incomplete stripping can leave residues that affect subsequent lamination or impedance stability.
Therefore, the etching and stripping stages are often followed by Automated Optical Inspection (AOI) to verify that circuit edges are clear and that there are no open or short circuits.
This step essentially determines the final shape of the circuitry and plays a vital role in defining the PCB’s electrical characteristics.