Conformal coating batch spraying

Co-authors and contributors

Batch spraying is one of the widest used techniques used in low and medium volume conformal coating processing.

Using a compressed air spray gun, the conformal coating is sprayed across the whole of the circuit board.

It can produce a high quality coating finish that gives the best protection due to good edge coverage.

It is not a selective process. All parts are coated on the circuit board.

Therefore, masking may be required to protect components that must not be coated.

The key areas for batch spraying

conformal coating spraying 2 reduced size
Batch spraying is one of the widest used techniques used in low and medium volume conformal coating processing. Photo courtesy of SCH Technologies

Which conformal coatings can be used in batch spraying?

Nearly all conformal coatings can normally be applied by batch spraying.

However, the coating viscosity may need to be adjusted with thinners to allow the coating to be sprayed correctly.

Other considerations are the pot life of the material and whether they change their properties whilst in the process of application.

This is significant when using moisture cure and two part coatings.

What equipment do you need for batch conformal coating spraying?

For conformal coating spraying a typical set up are:

  • Spray gun
  • Air Compressor for the Air Supply
  • Spray booth

This is a low cost set up that can handle a fairly high volume of product.

However, the quality of the finish is dependent on the quality of the spray equipment itself.

A dedicated conformal coating spray booth can help with the correct application
A dedicated conformal coating spray booth can help with the correct application. Photo courtesy of SCH Technologies

Is batch spraying of conformal coating a complex process?

Spraying coatings is a skilled process.

This is no different for conformal coatings. It requires training and knowledge to achieve good quality coating finish.

Blending the conformal coating to the right viscosity is crucial.

The wrong viscosity can produce many conformal coating defects such as bubbles, runs, ripples, and capillary effects.

Also, setting up the spray gun with the right amount of atomisation pressure and material feed is critical to ensure a good coating finish.

Conformal coating defects such as orange peel can be dominant if this is not set up correctly.

How cost effective is the conformal coating batch process?

Spraying conformal coating within a spray booth is a very cost effective process for low and medium volume coating.

However, if masking is required, then the cost of processing must be considered with this in mind.

The masking does not need to be as good as for dip coating.

This is because the conformal coating masking is only providing shielding from the spray process.

However, there is still skill required in the masking process.

Is batch spraying a low, medium or high-volume technique?

Normally, conformal coating batch spraying is a low and medium volume batch process.

It can be a high volume process but it will depend on the level of masking required and the cost of labour.

What variables control the quality of the conformal coating finish in batch spraying?

Variables that influence the quality of the coating process in spraying are:

The operator skill

Spraying in general of coatings is a skilled process.

Conformal coating application is no different.

Quality of the spray equipment

A low cost spray gun will produce an adequate coating finish for a short period of time. It will wear with time.

A high quality spray gun will produce a high quality finish and continue to do this over a much longer period of time.

Viscosity of the conformal coating

Blending the conformal coating to the right viscosity is critical.

The wrong conformal coating viscosity can produce many conformal coating defects and also give process problems.

The level of masking required

If the masking is complex then there are more likely to be problems due to the application of the coating due to leakage of the masking.

What are five advantages of the batch spray conformal coating process?

  1. Low cost set up of spray process
  2. Fast start up to begin the process
  3. Best coverage for protecting the circuit board
  4. Flexible process suitable for multiple coatings
  5. Masking requirements not as difficult as dipping

What are five disadvantages of the batch spray conformal coating process?

  1. Highly skilled process for the spray gun operator
  2. Quality Control issues due to operator dependence
  3. Cost of process is dependent on the masking required for the circuit board.
  4. Viscosity Control required to achieve a good quality finish
  5. The equipment quality can influence the quality of the finish

Links