Hi Steve,
You might try looking at the panels under UV light or a water break test.
Hans
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hans M. Hinners
Electronics Engineer
Warner Robins - Air Logistics Center (WR-ALC/LUGE)
226 Cochran Street
Robins AFB GA 31098-1622
mailto:[log in to unmask] <mailto:[log in to unmask]>
Com: (478) 926 - 5224
Fax: (478) 926 - 4911
DSN Prefix: 468
-----Original Message-----
From: Ted Stern [mailto:[log in to unmask]]
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
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