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. > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > For more information please contact helpdesk at x2960 or [log in to unmask] > ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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