The "silicone contamination" question has been raised in my plant
again.  An end user has requested that we certify that we don't use ANY
silicones in our electronic assembly facility (they have paint lines).

        In various locations we use silicone RTVs and the like to seal face
plates, in addition to using RTVs in the maintenance areas for gasketing.

      Are these "silicones" a threat to our customer regarding carrying
contamination into their plant?

*In a word, yes.  I know that in our facility, silicones are a major
contributor to conformal coating adhesion problems, which rapidly become MY
problem.  Paint would likely be similar.  Coatings do not like to adhere to
silicone RTVs, or to any outgassing or exuded oils or cure byproducts, or
"re-distributed" silicones.

        And, knowing that various silicone oils and mold releases are a
definite no-no, are there other classes of silicones that are
dangerous/safe?

*The two most common here are silicone RTV adhesives and silicone thermal
grease (silicone gel filled with zinc oxide particles).  Our manufacturing
procedures make sure these are very closely watched items, and life in
manufacturing would be easier if we could get certain concepts through to
certain design engineers (e.g. with a baseball bat).  RTVs are mildly
cleaned before coating to get the exuded alcohol cure byproducts and the
silicone thermal grease does not go on until the automated wash processes
are over.  This prevents our saponifier chemicals from washing the stuff
out.  We also maintain a very aggressive preventative maintenance schedule
to make sure that even if there is silicone contamination, it does not
build to problem proportions.  We are currently looking at non-silicone
alternatives to both materials.

*As far as mold release agents go, PTFE agents are more common, but
represent the same threat of adhesion loss that silicone does.  If you are
using circuit boards, be advised that the use of silicones sometimes occurs
in PWB manufacturing, so you may have silicone surface residues coming in
from the boards shop and not know it.  While not a common occurrance, it is
something to think about.


        Where does one find references to such?

*Well, you just asked the best source for technical advise (TechNet, not
me).  I don't know if you will find published articles on the topic.  The
best experience in manufacturing problems comes from bad experiences in
manufacturing.  Because of the "L" word (liability), most manufacturers do
not publish articles admitting they EVER had a manufacturing problem.  You
might look for technical bulletins on Dow Corning's web site.

Doug Pauls
Rockwell Collins

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