Etching factor
In printed circuit board production, the etching factor is the quotient of the etching depth d and the lateral undercutting a under the cover mask.
In circuit board production, the circuit board has a complete copper layer before it is etched. The copper structures that must be present on the base material after etching are protected with a masking varnish during etching. The masking lacquer itself and the copper underneath remain largely unchanged during etching. During etching, the etchant not only attacks the copper in the direction of the base material, but also infiltrates the copper structures covered by the cover mask in a lateral direction.
During the etching process, the cover mask is partially infiltrated, so that the remaining copper conductor track becomes narrower than the mask in some areas.
With increasing etching time, the infiltration of the resist increases. As a result, the width of the remaining copper track decreases due to the undercut on both sides. This in turn reduces the copper cross-section of the connection. In the case of conductor tracks for larger currents that are severely undercut, the current density can increase impermissibly.
In the case of immersion etching, the undercut factor can drop to 1. For other processes such as spray etching , it is 2-4. The use of side protection agents can increase the etching factor up to 10.
Anisotropic etching can largely avoid undercutting.
Individual evidence
- ^ Norbert Schwesinger: Textbook microsystem technology. Oldenbourg Verlag, 2009, ISBN 978-3-486-59411-9 , p. 432 ( limited preview in Google book search).