Implementing a Conformal Coat Machine for PCBs

[desertjay]

I have been tasked by my company to automate the conformal coat process. Right now we spray in a spray booth with a spray gun and cover any connectors needed to be covered. I think this is optimal but safety from fumes is the biggest concern. The enclosed machine will make it safer. It has been a nightmare trying to get this thing ready for production. I mean we are trying to spray a material that tacks in 10/15 minutes through tiny nozzles and connection points. The maintenance and cleaning has been crazy and will continue to be. The PCB I am programming for takes about 15 minutes to run (very large board) This causes conformal coat to start tacking on the tip of the nozzle. It’s been a year since we started this project. The quality is also much lower compared to the current method (a lot of process indicators like small bubbles and wet lines). The higher ups think this machine fell from heaven when it feels so inefficient to me and like a terrible purchase.

I am curious if anyone has any experience with conformal coat machines and any tips or tricks??

[moffy]

I would suggest a low pressure degassing stage before it gets tacky to remove bubbles from the conformal coating.

[Harry-CYSMT]

1. There should be a small cup in the machine for dipping the nozzles, In the program, set it so that after the nozzle finishes one area and before moving to the next, it first moves above the solvent cup and briefly dips the nozzle into the solvent for 1–2 seconds. This "wet cap" action effectively prevents the paint from drying in the air, making it especially suitable for long-cycle operations.
2. Changing the material is the most direct and fundamental approach to solving the problem. There are various fast-curing materials on the market designed specifically for high-speed automated spraying, which can fundamentally eliminate the trouble of nozzle drying and clogging.
Example: UV/Moisture Dual-Cure Conformal Coating – the "perfect partner" for automated spraying. It cures within seconds under UV light, eliminating the issue of nozzle drying and clogging. At the same time, its moisture-curing capability ensures complete curing in shadow areas, such as beneath components.
3.Adjustments for "Bubble" Defects:

Reduce atomizing air pressure: The most common cause of bubbles is excessive atomizing air pressure, which forces air into the coating. Lowering the air pressure appropriately is usually the first step.

Apply thin multiple coats: Avoid applying too thick a coat in one pass. Using several thin coats allows each layer to flow and release trapped air, effectively preventing bubbles and orange peel.

Adjust the curing profile: Do not place the coated part directly into a high-temperature oven after spraying. Add a "solvent evaporation zone" or extend the room-temperature flash-off time to allow solvents to evaporate fully before raising the temperature. This prevents the surface from skinning over too quickly while trapped solvent vapors create bubbles beneath.