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] ______________________________________________________________________