Etch Factor
For different copper base thicknesses ( what is to etched, we need to etch an etch factor, we need basically increase the width of tracks, however this has an adverse effect in that we also decrease the spacing, which is fine if the customer has designed the board with say 0.004” tacks ( 0.10mm) and 0.006” gaps, we cant hen etch compensate the 0.004” tracks to 0.005” tracks.
When doing layers with 0.004” tracks/gaps, or even 0.005” tracks/gaps, as the customer is we could use 17um copper, this makes a big difference in the sidewall effect, spends less time in etcher and less undercut.
Etch factors are basically, add the copper thickness you are etching down.