Potting to protect printed circuits ?

Just google it.

Avoid potting if you possibly can. It's expensive and messy and makes repair/failure analysis pretty much impossible.

John

Why expensive?

True

Fine if disposable.

I am building a PCB with double decking components. Namely, hand- wired components on top of SMT components. So, I am thinking about potting to fix and protect them. There is no room to put all components on the PCB.

Lots of labor: mixing, degassing maybe, potting, waiting, cleanup.

Use both sides?

John

Jeez, you are stupid! There are MANY applications where such a treatment is specifically needed, and many where it is specifically REQUIRED.

You are thick! Your pot life has been surpassed. WAY too many brain cells got burnt up in your youth, John boy.

And many more are driven by paranoia and ignorance. And it's messy and expensive whether it's required or not.

You can't even remember your name.

John

We did this in systems where vibration level is very high, (the components popped themselves from the circuit board) and flooding by water and/or liquid chemicals could occur, and I can tell it was the best way to avoid all these things.

Not only that, but one can trap water vapor which then can proceed to accelerate all kinds of chemicl reactions...and failures.

:On Apr 26, 11:44 pm, John Larkin : wrote: : :> Avoid potting if you possibly can. It's expensive and messy and makes :> repair/failure analysis pretty much impossible. : :We did this in systems where vibration level is very high, :(the components popped themselves from the circuit board) :and flooding by water and/or liquid chemicals could occur, :and I can tell it was the best way to avoid all these things.

If you absolutely have to encapsulate then I would suggest Dow Corning 3110 RTV for general purpose potting. You can at least cut the rubber away if you need to get down to component level without too much trouble.

The materials aren't free as well.

Switch to 0402 parts?

And hard epoxies can exotherm - cook parts - and shrink - crush parts.

John

I've used "conformal coating" in the past, but as has been mentioned, the board needs to be bone-dry; possibly baked.

Cheers! Rich

Have you tried standing them up? I.e., rather than horizontally, hold the part vertically and bend the upper lead 180 degrees so the two leads are separated by, say, 0.1". I used to do this all of the time. If the thing is subjected to high G forces or much vibration, you might still need to pot it, but at least you wouldn't have flying joints. And it _does_ save substantial board real estate.

Good Luck! Rich

Yes, already doing so.

Not really a problem with component sizes, but routing from one section to another of the PCB. Unless we go with more than 2 layers, one area of a the board is just filled with traces.

We just need to double deck two SOT-23 and several small resistors. The lower deck will be leveled and insulated with potting compounds. There will not be any repair attempts. If it does not work the first time, the PCB will be trashed after removing a couple of expensive items.

you would rather hand wire smd components on top of each other and add potting than make the PCB more than two layers??

-Lasse

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d-

out

They might go into a small PCB on top or bonded directly on lead- frames. It just seems too expensive to go multi-layer for this.

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It of course depends on how many he needs to build, but hand wiring and potting could quickly become expensive and messy ...

-Lasse

Yeah, no kidding. Working in a production shop, I'm the sucker that gets to build the stuff that the pencil pushers design. Unless this is in the sub 10 unit range, the OP is hereby advised to redesign the board. If putting a component on the board costs a nickel, putting it in mid-air and adding epoxy costs at least $1, more likely $2.

Put DIP parts over the SMT parts on both sides on the PCB. Don't ask me to solder it.

Sure I can. I just do not go 'round handing it out to deranged retards like you.