Conformal Coating Requirements

Obviously, clean enough :-) I don't think I've ever seen a specification, although some companies obviously have in-house ones. It would depend on the process used. For ex., if you used Parylene, where the coating is done in a vacuum chamber, you would not have the same requirements as an ambient-curing sprayed product that remained sticky for 12 hours.

If a 20 x binocular examination showed no inclusions ascribable to air-borne muck, then I'd say you are OK.

More important is the cleanliness of the PCBs before coating, meaning both ionic contamination (the defunct MIL-P-28809 was specifically pre-coating, as was MIL-P-55110 pre-solder-masking) and particulate matter. A dust fibre in contact with two conductors, trapped in the coating, can become a short-circuit.

Hope this helps

Brian

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Jeff,

Depends on what you are doing and where you are located.

What? As Brian rightly said, you need to have a reasonable clean environment that is dust free - class 10,000 is usually MORE han enough. However, if you are coating CSP's or other miniature devices, medical or other precision STUFF, then you may have to go to Class 10,000 or even down to Class 1,000 - I have seen that for conformal coating in the space industry.

Where? In the UK, we have to satisfy HM Health & Safety Exec. (No doubt this applies elsewhere but I dont have the data) They ROUGHLY mandate that the area MUST be fitted with fume extraction and be exhausted > 20 times per hour. Lights should be behind "Georgian wired" glass rather than Ex'd' and all electrics should be hard-wired. Zone the room 1 = safest = around the coating machine and drying cupboards 1 meter from material. Zone 2 = > 1 meter away = OK for prep and handling, Zone 3 = > 3 meters away = OK for cleaning, masking, de-masking and inspection.

Hope this helps, Graham

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