Artwork Scaling
Width additions applied to photolithographic circuit patterns compensate for the lateral removal of copper during wet chemical processing. In raw board fabrication, etch compensation modifies the starting trace widths on the phototools to account for the chemical action of the acid bath. This adjustment ensures that the finished copper features match the nominal dimensions specified in the gerber files.
Conductor Width
Acid sprays dissolve unwanted copper vertically, but they also attack the sidewalls of the traces, creating a trapezoidal trace profile. The amount of lateral loss depends directly on the starting copper foil weight, with thicker foils requiring larger trace additions than thin foils. Fabricators increase the trace width on the phototool by a fixed multiplier of the copper thickness to ensure that the trace retains its target cross-section.
Without this modification, traces would emerge too narrow, which increases electrical resistance and alters the controlled impedance of high-speed transmission lines.
Process Adjustment
Alkaline and acidic chemistry systems generate different etching profiles and require separate compensation tables. Production staff must calibrate the scaling factor for every copper weight and chemistries option used in the wet process line. Consistent spray pressure and conveyor speed are necessary to keep the actual trace widths within acceptable quality margins.
