PCBs are sometimes coated with conformal coating to protect them in harsh operating conditions where humidity and contaminants, such as dust and metallic particles, can cause shorts in electronic components. Also, some conformal coatings are intended to provide thermal insulation, shock-vibration dampening, and electrical insulation for high-voltage parts operating at high altitudes.
Conformal coatings are sometimes used on pure tin surface finishes to lower the risk of tin whiskers. These characteristics make conformal coatings particularly appealing for high-reliability applications.
Types of Conformal Coating
| Type | Advantages | Disadvantages | Application Environment |
|---|---|---|---|
| Epoxy Resin | – Very hard – High chemical resistance – High abrasion resistance – High dielectric strength – Good moisture resistance – Good solvent resistance – Good adhesion – Prevents high-voltage arcing, short circuits, and static discharges |
– Shrinks during curing – Can cause stress on components during thermal extremes – Very difficult to repair |
– Aerospace – Automotive – Industrial |
| Silicone Resin | – Superior moisture resistance – Solvent free – High adhesion to difficult-to-bond substrates – Wide operating temperature |
– Some types have poor adhesion – Low chemical resistance – High cost – Difficult to repair |
– Aerospace – Automotive – Marine environments – RC circuits and drones – Outdoor signs and displays – Vibration dampening |
| Parylene | – Excellent adhesion – Excellent chemical resistance – Excellent moisture resistance – Tin whisker suppressant – Very thin application profile |
– Very difficult to repair – Expensive |
– Aerospace – Automotive – Marine – Medical – Military |
| Urethane Resin | – Good moisture resistance – High chemical resistance – High abrasion resistance – Excellent solvent resistance – Good adhesion |
– Lengthy cure cycles for optimum curing – Difficult to repair |
– Aerospace – Automotive |
| Acrylic | – High moisture resistance – Easy to repair – Good abrasion resistance – Good temperature range – Easy to apply – Dry quickly – Long pot life – Low cost – Low glass transition temperatures – Fungus resistant |
– Poor solvent resistance | – Gas meters – LED assemblies – Computer motherboards – Power supplies • Defibrillators • Game cameras • Other printed circuit boards |