Which, of course, was just a cover story.

I should have read the preceding message closer.  If the problem is in the 
bake out oven, I don't know that I would use the same methods as for a 
humidity chamber.  In a humidity chamber, you are usually looking at 
accumulated scale and mineral deposits, potentially addressing rust issues 
in stainless steel (fuming red nitric acid, nasty nasty process).

If you are talking about cleaning out a standard forced air oven, you may 
be better ahead buying a new oven, depending on how old and abused the old 
oven is.  Such ovens are usually highly abused and preventative 
maintenance almost never involves cleaning out accumulated crud.  You 
often have baked on materials that are very hard to get off. 

What I have done on occasion is to take apart most of the oven and fit a 
random orbital sander with Scotchbrite pads and go over most of the 
surface.  Follow that with a wipe down of the chamber interior with 
naphtha and then acetone, then a final wipe down with isopropanol.  If you 
don't wear a vapor respirator when you do this then you will justly appear 
in next years Darwin Awards e-mail.  This should get most of the 
accumulated material off the walls.  You should also take the opportunity 
to replace the heating elements as they may also be coated.  A final wipe 
down with deionized or distilled water is also a good idea.  Generally to 
wash off the accumulated blood smears from all the sharp edges you come up 
against.

Is it a lot of work?  Yup.  Is it a pain in the butt to do?  Yup.   Will 
your maintenance people gripe and moan?  Yup.  Is it worth it to stop 
scrapping boards?  Yup. 

Doug Pauls




"Whittaker, Dewey (EHCOE)" <[log in to unmask]> 
12/04/2007 08:19 AM

To
"TechNet E-Mail Forum" <[log in to unmask]>, <[log in to unmask]>
cc

Subject
RE: [TN] SILVER IMMERSION BOARDS ISSUE






Doug's attempts at getting a cleaning contract for SMT reflow ovens were
foiled.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls
Sent: Tuesday, December 04, 2007 7:06 AM
To: [log in to unmask]
Subject: Re: [TN] SILVER IMMERSION BOARDS ISSUE

Guy,
I have been involved with the SIR Handbook for quite some time and can't

recall any sections on cleaning SMT reflow ovens.  Humidity chambers,
yes. 
 Reflow ovens, no.

Doug Pauls




Guy Ramsey <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
12/04/2007 07:57 AM
Please respond to
[log in to unmask]


To
[log in to unmask]
cc

Subject
Re: [TN] SILVER IMMERSION BOARDS ISSUE






Yes, I think our problem was oven contamination. We started wrapping
immersion silver boards in aluminum foil (loosely) during the bake. We 
have
not had any problems with delaminating or solder performance using this 
bake
out process. 

We have not tried to clean the oven yet, as we rarely see immersion 
silver.
I understand it is rather difficult. I think there are instructions in
the
IPC SIR Handbook. 

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