Conformal coating material is applied to electronic circuitry to act as protection against moisture, dust, chemicals, temperature extremes that if uncoated (non-protected) could result in a complete failure of the electronic system. Furthermore coating material has proved to actually reduce the effects of mechanical stress and vibrations on the circuit.
The coating material can be applied by various methods, from brushing, spraying and dipping but due to the increasing complexities of the populated boards being designed and with the ‘process window’ becoming smaller and smaller the necessity for accurate coating via robot selective coating is growing in demand.
Coating material when dry (after curing) should generally have a thickness of between 50-100 microns.
Material selection is one of the Process Engineers most critical decisions. (Please see Amtest section: “Materials” for guidance)
The complexity of the populated board; primarily the location of the ‘Must Coat zones’ and the ‘No Coat Zones’, will allow selection of the correct method of coating.
After applying; the material needs drying to allow the chemical properties to react and cure
and dependent on type, secondary cure. Drying is governed by two factors, the demands of
the material; example natural air or Ultra Violet and secondly production demands for quick handling and/or packaging of the coated PCB which will necessitate a faster cure need, via explosion proof IR/ convection ovens.
 |
|
 |
Material - Coating |
|
|
Test – Measurement gauge |
|
|
|
