- Production throughput requirements: The prep work needed, the speed of the coating process, and how quickly the boards can to be handled after the coating process.
- Board design requirements: Connector laden designs, solvent sensitive components, and other issues impact your decision.
- Equipment requirements: If a coating is only sporadically required, tying up capital and floor space with additional equipment may not make sense.
- Pre-coating processing: Some processes require masking or taping before coating.
- Quality requirements: Mission critical electronics that require a high degree of repeatability and reliability will generally move you to more automated application methods.
The following are the application methods for traditional conformal coatings:
- Manual spraying
Conformal coating can be applied by an aerosol can or handheld spray gun. It is generally used for low volume production when capital equipment is not available. This method can be time-consuming because areas not requiring coating need to be masked. It is also operator dependent, so variations are common from board to board.
- Automated spraying
Programmed spray system that moves the board on a conveyor under a reciprocating spray head that applies a conformal coating.
- Selective coating
An automated conformal coating process that uses programmable robotic spray nozzles to apply the conformal coating to very specific areas on the circuit board. This process is used in high volume processes and can eliminate the need for masking. An applicator may have a built-in UV lamp to cure coating immediately after it is applied.
The circuit board is immersed then withdrawn from the conformal coating solution. Immersion speed, withdrawal speed, immersion time and viscosity determine the resulting film formation. It is a common conformal coating technique for high volume processing. A great deal of masking is generally required before the coating process. Dipping is only practical when coating on both sides of the board is acceptable.
Brushing is a simple application technique used mainly in repair and rework applications. The conformal coating is applied with a brush to specific areas on the board. It is a low cost but labor intensive and highly variable method, best suited for small production runs.