Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Conformal Coat and RTV

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Conformal Coat and RTV | 3 January, 2007

Is it acceptable to apply an acrylic conformal coat, cure and then apply a silicone RTV on top (for staking tall components)? Should there be a concern with the bond between the acrylic and the RTV?

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Conformal Coat and RTV | 3 January, 2007

Comments are: * General purpose RTV (RTV-108) releases an acetic acid (vinegar) during cure and corrodes copper, brass and sensitive metals. It is therefore NOT for use in delicate electrical or electronic applications. However, there is an electrical grade RTV (RTV-162) made by GE Silicones, General Electric Co; Waterford NY, 12188; 518-237-3330. * We see problems with acrylic and urethane coatings not wanting to stick to RTV. Some acrylics seem to be worse than urethane. * We appreciate the need to fix the components, but why RTV? If you use a correctly mixed and cured epoxy, you will have no problems. We admit that we avoid using silicones of any nature being used for anything in electronics. They are never a good protection and generally are quite fragile. * Although RTV is water repellent, it is the most humidity-porous of all coatings, some 20 times worse than epoxy coatings. So, if you have any hydroscopic contaminant under the RTV, it will get nicely damp and stay damp, just ideal for creating corrosion.

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