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Subject:
From:
John Maxwell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Maxwell <[log in to unmask]>
Date:
Mon, 12 Aug 2013 20:33:14 -0700
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Everyone,
It is silicone and not silicon:-)

John
On Aug 12, 2013, at 3:45 PM, Inge Hernefjord <[log in to unmask]> wrote:

> The fear of silicon in electronics has its roots in a Swedish Defence
> report 50-60 years ago. At that time a military component test lab
> performed tests of small signal relays. Thousands of relays were tested
> with numbers of conditions.  A few relays had increasing contact resistance
> after thousands of operational elapsing time. Analysis gave that the
> contact had small spots of some silicon product, which was never decided in
> detail. The team made an anticipation, that the silicon somehow had
> 'migrated' from a silicon grease that was used for some reason. The grease
> was not on the PWBs, but had been creeping all over the equipment, and had
> finally found its way on inside of the relays. It was called 'silicon
> migration'. Relay failures were the most feared in the military boxes at
> that time. Note that the relays were low contact force constructions, so
> called 'tongue' relays. Power relays were not involved in the risk group.
> Personally, I have analyzed hundreds of reported relays during decades, and
> have never seen contact issues caused by silicon. We use silicon products
> of all sorts since the 60's and have no silicon issues. I talk about
> millions of boards. The academic high priests reported horrible facts
> ,that  increased the fear even more, e.g. a paper that concluded, that just
> a few drops of silicon oil could spread over an area of a football arena in
> short time! I have demonstrated my scepticism lots of times, and assured
> them that the risks are pretty exaggerated.
> 
> Inge
> 
> 
> 
> The use of silicones for electric and electronics protection is as old as
> some military application from the late 1940's. Since then the silicones
> have become one of the most relevant alternatives for electronics
> protection for reliable applications, and its share continues to growth due
> the increase demand of current applications and the limits of organic
> alternatives.
> 
> The term "Silicone Migration" is also rather old, the first articles
> talking on the subject date on early 1950's. Why then, if this phenomenon
> is known and recognized for over half a century the use of silicones is
> well accepted, recognized and in some cases proven indispensable?
> 
> The "Silicone Migration" term is one almost every electrical engineer has
> heard, yet very few actually know its true meaning. Often this term is used
> to simply restrict or discourage the use of silicones without further
> explanation and most of the times also unjustified/unnecessarily.
> 
> One of the reasons is that this term is equally used to describe any of the
> three contamination mechanism for silicones (which by the way are the same
> for epoxy, acrylics and urethanes yet then is simply called
> "contamination").
> 
> The three contamination mechanisms are: Transfer by contact (something
> touching a wet silicone and then touching any other surface), Transfer by
> atomization (by fine spraying silicone that can be then move airborne and
> collect in any surface) and Transfer by Low Molecular weight species than
> can volatilize and condensate at normal operation conditions.
> 
> The first two account for most of the surface contamination experiences,
> being the last one the least observed and the most difficult to generate
> since it requires strictly several conditions to be present to occur.
> 
> One of the easiest way to prevent the volatile silicone migration is simple
> to select a Controlled Volatiles product. Since one of the elements that
> must be present is the SVCC (Silicone Volatile Condensable Compounds)
> selecting a CV product eliminates the problem.
> 
> Krayden offers CV products of the Dow Corning product line that include
> Adhesives, Conformal Coatings, Encapsulants and Thermally Conductive
> products. These CV products don't have the hefty price tag of space grade
> materials and are the right answer against this potential "Silicone
> migration."
> 
> The Volatile Migration is relevant only if all the conditions are present.
> Not all the volatiles are relevant, only the ones that can condensate at
> operational conditions. Also it is required to have the electronics in a
> hermetically confined volume for this to be relevant; if the volatiles can
> escape their high diffusivity will prevent them to condensate again in
> relevant amounts.
> 
> Also an intermittent electrical contact is required for the migration to be
> relevant like a switch, relay or a motor; an already plugged connector is
> not an issue if it is not in and out constantly.
> 
> Finally the volatiles will show it's presence in a certain range of voltage
> and current intensity. The SVCC are fairly inert and will not dissolve,
> oxidize or react with any other element on the board.
> 
> There are means to calculate the amount of volatiles present in an
> application if all the data is available. Krayden can help via Dow Corning
> to get this information if required.
> 
> One important thing to clarify that the risk of the silicone volatile
> migration has to be estimated on its proper terms, one average a person
> carry far more silicones volatiles due the use of antiperspirants, hair
> products, clothes, make up that an average coated PCB!
> 
> Silicone migration is a far misunderstood and feared topic, yet if you
> allow us we can help you take the right approach in your material selection
> for your electronics applications.
> [image: image] *Wayne Wagner*<http://www.circuitnet.com/experts/panel_331.shtml>
> *President*
> *Krayden Inc.* <http://www.ipcoutlook.org/directory/49103.shtml>
> Wayne Wagner has over 25 years in the conformal coating industry and is the
> president of Krayden Inc., a leading distributor of engineered materials.
> 
> 
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