Following on from a previous tech note, we mentioned the non-corrosive silicone rubber we use. Dowsil 3140. If you are used to builders and DIY silicones, then this is a very different product to work with!
Firstly, it is flowable. If you apply it over electrical components or wire to board PCB joints, it is thin enough to flow down and fully cover everything but with just enough viscosity to leave a typical 3mm thick layer. It is a clear rubber surface potting compound. Very useful!
Secondly, it is non-corrosive. When most single-part silicone sealants cure, a by-product of the cross-linking catalyst is acetic acid, whilst it is not in great amounts, this residue is enough to attack metals like copper, zinc, brass, tin, and galvanised steel. Critically it goes to town on the copper and tin found on PCBs. If after application an item a cured in free air it can reduce issues but in general electronics and PCB should only have non-corrosive silicones applied.
The best we have found is Dowsil 3140, the price has risen in recent years but the most economical way to buy it is in the 310ml tubes and then dispense small amounts into disposable syringes. But, be careful as this stuff does flow – leave the nozzle unplugged and this expensive stuff is all over your desk, don’t ask how I know!
Even if you only use small amounts, the shelf life seems good, we have had a 310ml tube opened for well over a year and the whole tube is still usable. Even in small syringes last if you keep the air out.
Lastly, once applied it will skin over in 6 hours, touchable after 8-12, and fully cured within 24.
After the first application, just watch your sleeves it can get everywhere!