When my career started (1973) I was a chem miller.  We used 36 degree Baume
ferric
for stainless and when the edges got ragged we used it for mild steels and
when
even that didn't give smooth lines we diluted it to 32 Baume and etched
coppers.

The first project I was given was to evaluate dry films as a replacement for
dip
coated liquid resists.  I took each metal from stock, tried about six
variations
of pre-clean processes and etched them all together.  The choice of best
pre-clean
was based on how much resist lifting we saw before the resist was stripped
and
how much burning was evident after stripping.  The trick seemed to be not in
the Baume
of the etchant but rather in the pre-clean.  Higher Baume typically gives
less undercut
and better sidewalls at a slower etch rate.

The dulling you mention sounds like the early stage of typical resist
adhesion failure.
The most successful pre-clean we used for stainless involved some form of
passivation.
I suggest you dig out your metal finishing handbook and make sure your cycle
is
in line with industry standards and then contact the cleaner rep for
recommendations.
  -----Original Message-----
  From: TechNet [mailto:[log in to unmask]]On Behalf Of Larry J. Fisher
  Sent: March 04, 2001 7:58 AM
  To: [log in to unmask]
  Subject: [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