Re: Silicon oil leakage on PCB - how to remove?

Aubrey McIntosh, Ph.D. wrote: 


John Woodgate wrote:


You can't wipe the stuff off because of its surface tension and viscosity. You may be able to get a 'removing fluid' from the oil suppliers. It may be costly. 

I am assuming that the problem oil is something like a polydimethylsiloxane
( http://www.chemexper.com/chemicals/supplier/cas/63148-62-9.html )

I would worry that the KOH / Methanol will "clean" the polymers off of the pcb silkscreen, chips, and even the PCB substrate. I have seen 250 mL beakers that I used as a KOH/Methanol bath display significant etching. It dissolves skin. Use gloves. It dissolves corneas faster. Use goggles. Spatter is invisible on clothing, and transfers to unprotected skin. Change clothes and shower after handling. NaOH/Methanol forms insoluable crud, so KOH is preferred.

The KOH/MeOH, NaOH, HClO4 and related mentions were more for fun than considered to be applicable to the problem at hand, as they are certainly NOT. That was spelled out in my post. The diethyl ether was the serious recommendation.

A couple of web sites mention benzene. You can't (or shouldn't) get that now, but toluene or xylene may substitute. I'm a little surprised that they work, and don't remember trying them directly. I suspect that you can get mixed xylenes at an art supply house as some or other paint thinner or brush cleaner. They burn easily -- act as if you are handling gasoline.

Someone else mentioned diethyl ether. The flammability of (this) ether makes gasoline look safe. More problematic is that you will be tempted to keep the left over material. On exposure to oxygen, even in a "closed" container, it forms explosive material with LEGENDARY sensitivity.

It's not a big deal if dealt with using normal precautions for volatile flammables. An explosion proof fume hood typical of chem labs is the best idea, otherwise a garage or outside patio with a check for potential ignition sources nearby should be appropriate levels of precaution.

Most diethyl ether is stabilized with some addatives, so the peroxide problem isn't that big of a deal. I think we generally disposed of ether older than 6 months or something like that. Not too difficult to do a little research to determine prudent practices for this time. Bill Sloman might have something to say. Or go on over to sci.chem and ask about how to keep oneself safe with ether.


Another web site did not offer any information specifically relevant to this newsgroup at all: http://www.indecentblogging.com/blog.php?id=5906

Despite the general acceptance of opinion over lab work in most newsgroups, I do mention the entry from the paper mill. Use your browser to search for "Table 1" about a third of the way down the article. My gut sense was ethyl acetate would be a good solvent, and their finding of methyl ethyl ketone fits in nicely with that. Their finding of hexane surprises me some, but hey, they went to the lab and I didn't.

http://tappsa.co.za/archive2/APPW_2004/Title2004/Determination_of_silicone_defo/determination_of_silicone_defo.html

Ether really was the only thing that worked for silicone vacuum grease. Oils might be a little easier to solvate.


good day!



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Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
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