Today, several methods for spray application of conformal coatings exist including conformal coating aerosols conformal coating spray booths and automated selective conformal coating spray robots. However, they fall into one of two process categories being complete and selective coverage processing.

Why choose the conformal coating selective spraying process?

A typical conformal coating selective robotic spray process consists of a programmable XYZ coordinate platform with a valve or valves attached to a controllable arm, depositing coating onto a printed circuit board (PCB) in areas specified by the programmers of the system. Extra angles including rotation of the valve head can increase the flexibility of the system.

Technology varies between the platforms and the valves but essentially they achieve the same result. The principle is to deposit coating where you want it, removing the issue of masking which is required in batch processing with dip or spray booths. This “selective” application genuinely offers in most cases a more cost-effective solution to batch spray coating.

Advantages to be gained with selective robotic conformal coating:

Masking and subsequent de-masking stages can often be minimised or completely eliminated. Consequently masking mistakes, which can cause expensive stripping and rework, are also largely eliminated.

The process is infinitely repeatable. A far more controlled coating thickness can be achieved from board to board and from batch to batch.

The process no longer requires a skilled operator to operate the machinery during application of the coating.

Finishing is minimized after coating, as there is little or no masking to be removed, tears or lifting in the coating can be minimized.

Less material is used, since the system only sprays sufficient coating to cover the relevant areas of the board, offering another reduction in cost.

Brushing

Brushing is the least efficient application method because of difficulty in achieving uniform coverage (hence, uniform coating thickness) and controlling bubbling.
While this operator dependent method is not practical for high volume production, it is suited to short run, prototype and touch up after repair/rework. This method also works well for high topography assemblies (power supplies)
Particular attention should be paid to the
underside of components and lead wires. Care must be exercised to avoid deposit of brush fibers in the coating.

Dipping

This method, in which the masked assembly is immersed in a tank of liquid coating material and withdrawn, ensures uniform coverage and predictable, repeatable film thickness. Variables include rates of immersion and withdrawal and viscosity of the liquid material. The assembly should be immersed slowly to allow the coating material to displace the air surrounding components, remain immersed until bubbling has ceased, and then withdrawn.
Typical immersion and withdrawal speeds are 2 to 12 inches per minute for the first dip, with subsequent dips made at higher speeds. Immersion and withdrawal speeds depend on the size and complexity of the assembly. Timing may be manual or automated.

Curtain coating

This is a way to apply material to board. The material will continuous fall like material curtain. Then the conveyer will move the board pass though that curtain. Material can reuse in this case. But the viscosity need to be close monitored. The contamination of material reuse is critical to create the defect.

Manual Spray

Spraying manual is the most popular and the fastest method for applying conformal coatings. With the proper combination of solvent dilution, nozzle pressure, and pattern, reliable and consistent results are obtainable. For high – volume production, spray coating is readily automated.

Automated (Spray) Dispensing

Automated or selective coating is well suited for high volume applications where repeatability, speed and efficiency are essential for success.
Selective coating use programmable robotic X – Y – Z positioning system to accurately manipulate the applicator in and around the product being
coated. By using an automated system, repeatability is introduced and speed is greatly enhanced. With proper programming, material waste
can be greatly reduced and in many cases masking can be completely eliminated.

Automated (Selective) Dispensing (What we Use)

Nozzle/Film coating nozzle Select coating can be used for moderate to high – volume applications and often eliminates the need for masking because the material is dispensed only on selected areas of the circuit. Coating thickness is affected by material viscosity, fluid temperature, pressures used, nozzle speed and dispense head configuration.