Dear Larry, density of ferric chloride is a common cause for undercut - in our experience. We have used the following solution of ferric chloride with quite some success on the SS-alloys you mentioned: 300 kg ferric chloride and 16 l hydrochloric to 400 l final solution to Baume 35 deg. It is also very important that the surface is clean and free of any oxides etc. to ensure resist adhesion. Sometimes the rolling mill uses some very greasy stuff when rolling SS. This can be very difficult to remove. Lack of resist adhesion is probably the most common cause for undercut on this type of material. But you would have to evaluate the reasons for the problem. Maybe have a look at the sidewalls of the resist after etching. Consider if the problem is locally or general. Hope this helps _________________________________________________________ Jan Thuesen Process Engineer Chemitalic A/S Egebjergvej 128 DK-8700 Horsens Tlf.: ++45 76 28 70 00 Fax:++45 76 28 70 95 mailto:[log in to unmask] <mailto:[log in to unmask]> http://www.chemitalic.dk/ <http://www.chemitalic.dk/> -----Oprindelig meddelelse----- Fra: Larry J. Fisher [mailto:[log in to unmask]] Sendt: 4. marts 2001 13:58 Til: [log in to unmask] Emne: [TN] Optimum Baume Ferric Chloride For Stainless Steel I have a customer who is using standard aqueous dry film on #301, #302 & #316L stainless steel and then etching with ferric chloride (this is actually a chemical milling process, not really printed circuits). He is having slight undercut under the dry film which dulls the surface (unacceptable to his customer). He is using 45 Baume strength ferric chloride and has asked if either lower or higher strength would work better and not cause the undercut. Any ideas out there? Regards, Larry Fisher