Etching dissolves exposed copper with sprayed etchant: alkaline ammoniacal etchant on outer layers protected by a tin etch resist, or acid cupric chloride on inner layers protected by photoresist. Etchant attacks sideways as well as down, so traces finish narrower at the top than drawn; this undercut is why fabricators compensate artwork and why heavy copper needs wider spacing. Etch control decides how closely finished widths hit their impedance targets.
Inner layers are over-etching by half a mil, the 4 mil traces are coming out at 3.5, check the conveyor speed.
Also heard as
- etch
- copper etching
Related terms
Artwork
Image of each board layer used to make the phototools for fabrication, and by extension the layer data itself.
Acid trap
Acute inside angle in copper artwork where etchant can pool and over-etch, a classic DFM flag.
Copper weight
Thickness of copper on a board layer, expressed as ounces of copper per square foot.
Plating
Electrochemical deposition of copper or other metals on a board, building hole walls and surface conductors.