I asked our ex-resist salesman engineer what he would recommend to remove
scale. Below is his reply.
Dave Sullivan
PWB Applications Engineer
Rockwell Collins, Inc.
[log in to unmask]
---------------------- Forwarded by David D
Sullivan/CedarRapids/Collins/Rockwell on 11/25/97 09:37 AM
---------------------------
Peter M Carter
11/25/97 09:27 AM
To: David D Sullivan/CedarRapids/Collins/Rockwell@Rockwell
cc:
Subject: Re: [TN] FAB: Procedure to remove tin-scale in a resiststripper
(Document link not converted)
Possible alternatives (need to be bench-checked):
1)Remove all nozzles, and clean separately on the bench.
2)THOROUGH plain water leach out :elevate the water level above normal
levels by putting extensions on overflows, etc. Elevate the
operating temperature above normal if possible. Try to rig some sort of
filter basket in the overflow sump to protect the spray pumps and catch
loose flakes. You may want to look at some kind of resist flake
filter/cyclone/screening system anyway to extend the life of your
proprietary strip solution, so maybe this is the time to put it in. The
water solution may present a disposal issue if your local discharge permit
specifies tin.
3) While the level is still elevated, and the nozzles are still out,
try circulating a solution of sulfamic acid (dry powder, often used in
boiler clean-outs, etc). This is the part I'd play with on the bench in the
lab first to get the temperature and concentration right. Sulfamic
won't bother MOST stainless alloys, but you should spot check this. This
solution will almost certainly require some treatment before
disposal, both from a pH and a metal content basis.
4) Another THOROUGH plain water leach out. Higher than normal
temperature and water level. Maybe twice; if so second time with DI
if you can.
5) Ideally, before going into service, I'd sacrifice one make-up with
the new chemistry to repeat the leach-out, at the
higher-than-normal liquid level. You might be able to substitute this for
the second water leachout mentioned in (4), above.
No warranty, expressed or implied, your mileage may vary, user
assumes all risk, etc.
Marc Carter
ex-resist-tech-service-guy
David D Sullivan
11/25/97 08:50 AM
To: Peter M Carter/CedarRapids/Collins/Rockwell@Rockwell
cc:
Subject: [TN] FAB: Procedure to remove tin-scale in a resiststripper
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image moved (Embedded image moved to file: PIC18387.PCX)
to file:
PIC31661.PCX)
Aren't you glad you have these types of problems behind you??
Dave S.
---------------------- Forwarded by David D
Sullivan/CedarRapids/Collins/Rockwell on 11/25/97 08:49 AM
---------------------------
[log in to unmask] on 11/25/97 04:44:45 AM
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Subject: [TN] FAB: Procedure to remove tin-scale in a resiststripper
For resiststripping after plating we have a machine in stainless steel. Due
to several years of using KOH as stripping solution it has built up a thick
layer of scale, primarily of tin-hydroxide Sn(OH)2. The scale deposits
inside the spraybars, pumps, sumps, nozzles etc. The scale always
loosens/breaks up into small pieces (only to a certain degree) when we set
up a fresh stripping-solution. It eventually stops when there has been
processed panels enough to saturate the solution with tin, so that the
deposition of tin-hydroxide stables the scale.
Now we want to remove so much of the scale as possible before we shift to a
proprietary resiststripper. The proprietary stripper will not dissolve tin
from the panels, hence the scale will break into pieces and block the
nozzles almost continuously and instantly. This could make production
almost impossible for a period of time, testruns of the chemistry has
indicated this.
For Christmas the machine is taken out of production for a week and we hope
at that time to have an effective procedure to remove the scale in the
stripper.
Experiments on the LAB has shown that only a solution of nitric acid and
hydrochloric acid will dissolve the scale effectively, but this will also
dissolve the machine.
Other suggestions have been to use flouroboric-acid, but a acid-based
solution will precipitate residues of photoresist, causing new problems.
I would think that round-pumping of the machine every day for a week with a
strong alkaline solution at high temperature added with a chelating agent
like EDTA or ethanolamine, could remove some of the layer. Even though the
solubility product for tin in alkaline solution is very low, the chelating
agent should dissolve some. The solution then has to be made up fresh every
morning, after a thoroughly high-pressure rinse with water of the inside of
the machine. But will a week be enough to dissolve considerably amount of
scale?
Any suggestion to a procedure would be very welcome !
With best regards
CHEMITALIC A/S
Jan Thuesen
Process Engineer
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