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pcb board moisture coating specification

anovickis , 05-14-2019, 06:57 PM
I'm applying a moisture coating to a PCB, however it can't cover the connectors and some other components on the board
The coating is applied by spray nozzle that travels about the board

A new layer would work, but I'm looking for an example of such a layer and best way to specify a "keepout" area

robertferanec , 05-16-2019, 12:57 AM
I have never used coating, so I am also curious to see some answers here.

But I would probably ask the company what would be doing the coating for some examples of the documentation or I would ask them to describe the format of document, what they would need or what they prefer.
Derek , 05-17-2019, 07:34 PM
Hello anovickis,

When you say moisture coating I'm assuming your talking about conformal coating of which there are a number of different types. The 17 years I spent in the aircraft industry we coated every flight board, and I never had to deal with a keep-out area. Primarily that was due to us having manufacturing engineers in house, and to be honest if this is anything more than a hobby type product I really recommend a manufacturing engineer get involved with this. There are many variables and you can run in to problems depending on the type and thickness of coatings. Those MFG engineers can be worth they're weight in gold on this topic because they will know the environment the assembly is in and which coating products will be suitable.

I'm relatively new to Altium but maybe something a little similar I have done in PADS in dealing with keep-outs was to create a separate layer that could be individually printed, or included in ODB (or DXF) files detailing the keep-out areas. This was dealing with selective soldering of mixed thru hole and SMD boards, but I think something similar would work and of course it would be on the assembly drawing. How about coming up with something and we'll take look at it?

Almost forgot...though I never had to put a keep-out on a PCB database, assembly drawings would have details of coatings along with notes.
anovickis , 05-31-2019, 12:44 PM
There's the dip method for applying conformal coating, and the spray nozzle on an x/y table, or there is also the spray can

there's also a variety of materials to choose from that have varying thickness, cost, and resistance to various elements in the environment (solvents, moisture, water, salt, temperature, etc)
some materials set in a few minutes, and some take 24 hours to harden

For some boards you can dip, others that have connectors it's not desirable to coat the connectors.

From what I see there is a DXF file that's supplied with data for
1) areas that must be coated
2) areas that must not be coated (electrical or optical connectors, certain sensors, etc)
3) areas where it does not matter if coated or not

IPC-830 covers coating types and guidelines
IPC-850 covers potting

(sorry I can not post those here)

Some coatings lend themselves to rework, and some are harder to rework.

Additionally some coatings are used to understand if a board was tampered with after assembly (usually this is the thick black stuff, whereas the environment barriers are clear)

My question is more of - this specification could be done on a "mechanical" layer in altium/etc, but everyone seems to do this as a separate (DXF) drawing
And, I'm not sure why that is exactly

I suspect it's a an "80x24" thing that hasn't advanced to current tools

robertferanec , 06-03-2019, 01:26 AM
@anovickis, fantastic answer. Thank you!
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