Conformal Coating PCB – Choosing The Correct Type
Conformal Coating PCB Advantages & Issues
Conformal coating is used primarily to protect PCBs from environmental contamination and damage, but it can also have other beneficial effects. However it is a tricky process to automate and control. Especially if the boards are awkwardly shaped and volumes are low and there are also several different types of coating available. This article discusses the merits of some of the different coatings available and highlights the advantages that a specialist coatings company can offer.
Conformal Coating PCB – why coat at all?
The answer is that with electronic systems being used in very many environments where there is a chance of chemical contamination such as fuels, coolants, cleaning fluids etc. Complex and costly PCBs need to be protected. Moisture, too, can be a killer for sensitive electronic systems, so products that are used in high-humidity atmospheres, or which might be exposed to salt spray will need to be coated. In humid and tropic conditions, corrosion and mould growth can also be prevented by the correct choice of conformal coating. There are other benefits, too. A conformal coating, literally, ‘conforms to the shape of the populated PCB’, forming, if you like, a kind of shrink-wrapped protective envelope. This can dampen the effects of vibration and also help reduce current leakage.
In general, there are five types of Conformal Coating PCB products available:
- Acrylic – solvent or water-based
- (Poly) Urethanes
Conformal Coating PCB Rework
Re-work is, perhaps, worth more consideration here. Ideally, there should be no reason to re-work a board, but in reality, quite often boards require re-work for a number of different reasons. Components may fail, the board may become damaged, or the design may need up rating or require an FPGA to be reprogrammed for example. Acrylic coatings can be spot removed, the component in question de-soldered and removed. With silicone products, the process involves either de-soldering through the coating (depending on the type of silicone coating) or spot removing before any re-work is possible. The complete removal of a silicone coating is extremely laborious (especially heat cured versions). Some Urethane materials contain isocyanates which may produce carcinogenic fumes if you attempt to desolder through the coating; because of this and the difficulty of removing the coating, great care must be taken when re-working PCBs that have been coated using these types of Urethane material.