Design rules for batch spraying

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Spraying conformal coating under UV light makes the process a lot easier

Spraying conformal coating with a spray gun is a technical process without doubt.

However, for the design of the circuit board it is probably the least challenging and simplifies the guidelines and design rules.

Here are a list of rules and guidelines that could be considered.

  1. Match the conformal coating to the spray process
  2. Fill the via’s to avoid capillary flow
  3. Avoid 3D Problems with components
  4. Include space for masking
  5. Press fit connectors
  6. Use the correct components
  7. Apply silicone RTV after conformal coating 

Match the conformal coating to the spray process

Avoid using masking materials and UV cure coatings in the batch process. This is due to the UV cure coating potential to dry hard and not allow the masking material to be removed.
 

Fill the via’s to avoid capillary flow 

Avoid open via’s beneath connectors since capillary of coating can allow penetration through to the other side.

Fill via's on a circuit board to stop conformal coating leaking through to the other side of the PCB. This can cause problems due to coating in the wrong areas.
Via’s on a circuit board can allow conformal coating to leak through to the other side of the PCB. This can cause problems due to coating in the wrong areas.

 

Avoid 3D Problems with components

Don’t specify coating 3D components unless you really must. If so, ensure you apply several thin layers to avoid coating running or building up.
 

Include space for masking

Allow 2-3mm around components that must be masked that it doesnt matter if it is coated or not.

Ensure adequate spacing between a component that needs to be coated next to a component that needs to masked.

Ensuring space around components allows a fast masking process that is reliable
Allow space around components to be masked with tapes or boots. This ensures a good seal.

For example, do not place small resistors adjacent to a connector that will be masked down to the board surface or the resistor may not be coated.
 

Press fit connectors

Press fit connectors can be installed after liquid coating the board and the barrels if completed quickly. The pins will have sufficient contact when inserted.
 

Use the correct components

Use the male header pin type connectors that can be masked easily with boots rather than the female sockets which cannot be easily.

Male pin connectors makes conformal coating much easier due to the ease of masking with a masking boot
Male pin connectors makes conformal coating masking much easier due to the ease of masking with a masking boot

Apply silicone RTV after conformal coating

Apply RTV after conformal coating to avoid de-wetting issues.

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