Moisture-curing silicone conformal coating sets fast

Paul Boughton

Moisture-curing silicone conformal coatings are useful as protective coatings for sensitive board components in demanding environments.

However, electronic manufacturers have previously avoided using silicone coatings due to their long cure time that did not allow rapid assembly. Master Bond has now developed a rapid, tack-free, ready-to-use silicone conformal coating called Master Sil 773, which is formulated to provide excellent protection for electronic circuitry in high-humidity environments as well as under exposure to shock and vibration. It cures quickly at ambient temperatures to a highly flexible, transparent, low-hardness silicone coating.

Adhesion to critical board components is said to be outstanding. A useful characteristic of this product is that it maintains its low modulus over the wide temperature range of -65 to in excess of +200 degrees C. This one-part, ultra-low-viscosity silicone adhesive is suitable for application as a low-stress coating, affording protection to sensitive board components in demanding environments. Master Sil 773 is 100 per cent reactive and cures by the moisture mechanism. If needed, a UV tracer dye is also available with this system.
Master Sil 773 can be applied by dipping, spraying or brushing. It is suitable for either manual or highly automatic coating techniques, as its tack-free time is less than five minutes. The cured silicone conformal coating is also easy to repair; no solvents are required for either application or repair procedures. Electrical performance is exceptional, with volume resistivity of 1x10^14ohm-cm, dielectric strength of 25kV/mm, dielectric constant of 3.3, 60Hz and a dissipation factor of 1x10^-4.
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