Dear users

I am a university student and my thesis relates to microcircuit (Hybrid thin
film) fabrication.  I use Alumina/Nichrome/Nickel/Gold sandwich structure and I
wanna make traces with 1 mil (25 micron) width.I use FeCl3 solution for nickel
etching and unfortunately I faced heavy undercut during nickel etching. Could
anyone please instruct me?

Best regards