We etch in Ferric chloride so do not use any tin chemistry - however Rudy's
comments are interesting - we do have an immersion tin line so we can easily
do this test. Thanks Steve Kelly
  -----Original Message-----
  From: TechNet [mailto:[log in to unmask]]On Behalf Of Ted Stern
  Sent: Friday, April 26, 2002 11:47 AM
  To: [log in to unmask]
  Subject: Re: [TN] test for film residue


  Steve:
  Another potential source of "residue"  on copper surfaces during dry film
stripping is absorption of oils - often attributable to antifoam and/or
excess use of antifoam.
  Because copper  is very oleophilic, minimal contamination may be
problematic (including fingerprints) and can contribute to a variety of post
strip processing problems; incomplete final etching ("copper spots") being
one of the more common defects.  The methods suggested by Rudy would detect
this problem.

  As a severe (and unusual) example of oil contamination, we once
encountered a customer employing compressed air agitation to dislodge
accumulated dry film particulate in the corners of the dry film stripper
spray sump.  The air was introduced when the line was idle  to improve
continuous dry film particulate filtration.   The customer had been
employing the process for quite some time when random copper spots began to
be observed.  If the stripper was replaced, the problem disappeared; only to
reoccur in 1-2 days.  To make a long story short, it was determined (after
eliminating anti-foam, checking for tin in the bath and on panels,
addressing copper oxidation, examining rinse water quality, dry film
leaching in the alkaline etch, etc.) a leaking seal in the air compressor
was contaminating the stripper sump with minute volumes of oil, but enough
to contaminate the copper surface and inhibit alkaline etching.

  Regards,
  Ted

  Rudy Sedlak wrote:

    In a message dated 4.25.02 12:23:23 PM Pacific Daylight Time,
[log in to unmask] writes:


      Does anyone know of a test to look for film/stripper residue after
copper
      stripping.
    Assume you mean after stripping film from Copper?

    Stripper residue is a tough one, and not real likely to be an issue.

    Tarnish could be another issue that is very difficult to test for except
by sight.   Depending on stripper, this could be significant....the clue is,
if the problem gets worse as the stripper chemistry gets older, it is quite
possibly tarnish...

    Film residue is the most likely residue.  One way to test that is a good
test, but, can make your test board need rework is to drop on an immersion
plating solution.  Two different ones are common.  Some people use immersion
Tin to test if the surface is clean.  A drop should plate uniformly, and
adherently.  Another test is to drop on Silver Nitrate solution...usually
use the stuff that is used for titration in the lab.  The surface should
essentially immediately turn black, and it should be adherent.

    Another residue problem that can occur, and especially in old stripper
chemistry, is immersion Tin residues....this does not relate to the test
above.  Rather, your stripper chemistry can pickup Tin from the oxide on the
plating on outerlayers, and redeposit this on the Copper next to it.   The
potential for this problem is magnified tremendously if you strip in a tank,
rather than exclusively in sprays, and can be strongly affected by the
condition of the Tin plating solution.  If your Tin electroplating solution
looks very milky, this is disperse Tin oxide, which co-deposits with the Tin
metal, then easily dissolves in certain kinds of stripper chemistry,  and
redeposits, sometimes even is sprays, on the adjacent Copper.

    The film residues have become an especial problem in recent years, as
the new generation of photoresists, which stick VERY well, require specially
formulated types of stripper chemistry.

    I probably have told you more than you want to know, but, in case I
haven't, you can call me to discuss it.

    Rudy Sedlak
    RD Chemical Company 650-962-8004