Moisture Rich Environment

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Hi,

This is more of a mechanical question...

Just wondering what other products are out there to protect my PCB and uC (Mega128L-is the processor of choice 8) ) against humid and/or dripping wet environments.

In the past I’ve used clear epoxy. The epoxy works well but the board becomes a throw away item. This new project, the boards have to be serviceable as they are too expensive to be throw away items.

I’ve also used the spray silicon based conformal coating but was wondering if there are any other options out there.

Ideas?

Thanks,

Oc.

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Hello,

The first thing that comes to mind is a Ma' Bell splice. There housings are pressurized with nitrogen to prevent moisture from entering and decaying the connections...Just an insight..Good luck!

John

Just some guy

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johnrk wrote:
Hello,

The first thing that comes to mind is a Ma' Bell splice. There housings are pressurized with nitrogen to prevent moisture from entering and decaying the connections...Just an insight..Good luck!

John

I agree. But there is a simpler, less expensive approach. As you must repair the deffective boards, an IP67 enclosure is a must.

To be fully IP67 compliant, all signal conductors must exit the IP67 enclosure using IP67 connectors.

Is IP67 expensive? Yes! But much less expensive then an enclosure pressurized with Nitrogen, But, one or the other is a must, if you want to maintain water integrity!

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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IP67 or (from theatrical experience) if you don't have too many external connections and/or heat generated on the board, heat seal/vacuum pack in a thick polythene bag. The wires go through the seal. You then have to cut the bag to service them and re-do the connections - but it's cheaper than water-tight boxes/cable glands. The vacuum packing is to reduce the possibility of condensation if you don't pack them in a dry atmosphere - I haven't tried silica-gel in them but it could(?) work.
C.H.

C. H.
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It's only waste if you don't use it!

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Thanks for the ideas ;)

I'm looking for more of a coating than a box or condom hehehe.

Oc.

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OK then...

As long as your design does not generate a great deal of heat...I use liquid latex for other designs and prototyping and you may be able to "dip" the entire board into a container filled with a batch and keep adding layers until you get the desired thickness. For servicing you could peel back the latex. My current board would have no problem at 200ma max.

John

Just some guy

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How about a solderable protective lacquer?
Here's one: ELFA
Click "Show in table of contents" for more.

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Wow cool Thomas...never knew that even existed!!!

John

Just some guy

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I was also going to suggest PCB lacquer, as I've heard TV repairmen bitch about it in the past when they couldn't get a reading off a component, only to realise their multimeter probe was being insulated by a layer of invisible lacquer!! :)

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Yeah, I know the lacquer provides insulation. But I like that, the whole circuit is totally insulated from its surrounding environment! Good for humid/dripping wet environments!

Geoff's point is valid, when performing measurements one should apply a little force to ensure the probe penetrates the lacquer.

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MY circuit (AVR + LED display and AA batteries) is housed in just a normal IP67 box like Carl suggested earlier.
All holes are plugged with normal sanitary silicone (you know that transparent sticky thing used in bathrooms). Nothing gets in, and nothing gets out. It works 100% underwater (It was cool to test it. the LED's shine quite nice underwater :P)

Where am I using it? in sauna. 80-90 degrees Celsius and 100% humidity. Also showers water splashes onto it. Harsh environment IMHO ;)

Rain

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Isn't there a danger of having condensation inside your box?
Might not be a problem in a sauna, but in a car with temperatures from -30 to +40 deg C...

Guess the safest option is to use some potting compound, at the expense of serviceability. That's how ignition modules for cars used to be (still are?) made.

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Just shove a silicone gel pack in the box ;) it "eats" the moisture away and as nothing gets in anymore, the place stays dry.