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Potting a breadboard circuit? Reliable?
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Potting a breadboard circuit? Reliable?

by SeattleDavid on Wed May 12, 2021 7:56 pm

I would like opinions about whether potting a push-in breadboard circuit with an electronics epoxy is likely to be a reliable solution for 5~10 years of use.

After making a breadboard circuit work, it would be nice to place it in a tray and fill the tray with electronics-grade thermally conductive potting compound. Then, this block would be mechanically and hermetically sealed.

Adafruit makes a lot of nifty i2c and other mini-boards, and they are fun to make one-time show-off circuits. But they aren't really easy to make into a system that will stand up to 5~10 years of service. But if I then wanted to put a circuit into real-world use and not have it fall apart or fail I don't know where to go or what to do. It would be nice if I could just pot it and know it would likely work for 5~10 years.

Or, does everything inside just corrode or otherwise fail?

I assume that placing the breadboard in a dry-cabinet (like used for 3d printer filament to bring the humidity down to 25% would be a good idea, if this concept is viable at all.

Does anybody have experience with this type of implementation?

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Re: Potting a breadboard circuit? Reliable?

by adafruit_support_mike on Wed May 12, 2021 9:41 pm

SeattleDavid wrote:I would like opinions about whether potting a push-in breadboard circuit with an electronics epoxy is likely to be a reliable solution for 5~10 years of use.

That should certainly be possible. Potted/encapsulated circuits are a whole sub-category of freeform electronics.

SeattleDavid wrote:Or, does everything inside just corrode or otherwise fail?

That would only happen if you have something corrosive on the board, like the flux from plumbing solder.

Washing the board thoroughly before potting it will get rid of anything that could cause problems. I use a mix of 1 part ethanol, 1 part acetone, and 2 parts toluene which is effective at removing flux residue and oils. If you want, you can follow that with a good wash in a lab detergent like Alconox (pricey, but an excellent cleaner), then a rinse in distilled water.

SeattleDavid wrote:I assume that placing the breadboard in a dry-cabinet (like used for 3d printer filament to bring the humidity down to 25% would be a good idea, if this concept is viable at all.

That is a good idea. Getting the hardware good and dry will help the epoxy bond to the surfaces.

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Re: Potting a breadboard circuit? Reliable?

by SeattleDavid on Wed May 12, 2021 9:46 pm

Again, I am NOT talking about potting a PC Board.

I'm talking about potting a push-in breadboard:
Image

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Re: Potting a breadboard circuit? Reliable?

by adafruit_support_mike on Wed May 12, 2021 11:24 pm

Ah.. that's another story.

I'd rate successfully potting a breadboard as 'not provably impossible'. Even if you could make it work, there would be a *lot* of technical problems. You'd have to deal with the chemical bond between the epoxy and the nylon breadboard, trying to fill the voids inside the breadboard, the effects of thermal expansion on the connection between the clips and the component leads, whether the epoxy will melt the foam backing that holds the clips in, and so on.

It would be much easier to move the circuit from the breadboard to one of our Perma-Proto boards:

https://www.adafruit.com/?q=Perma-Proto&sort=BestMatch

then pot that.

The Perma-Proto has the same connections as a breadboard, so you can move the assembly across without needing to rework the layout or connections, and then you can solder the components in.

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Re: Potting a breadboard circuit? Reliable?

by SeattleDavid on Thu May 13, 2021 12:16 am

I'd rate successfully potting a breadboard as 'not provably impossible'. Even if you could make it work, there would be a *lot* of technical problems. You'd have to deal with the chemical bond between the epoxy and the nylon breadboard, trying to fill the voids inside the breadboard, the effects of thermal expansion on the connection between the clips and the component leads, whether the epoxy will melt the foam backing that holds the clips in, and so on.


The last time I heard somebody speak like that they worked for Boeing.

I have several of the Adafruit perma-proto boards but have never figured out how to actually make them work. Or, yes, they are a way to solder things together but they lack all of the flexibility to rearrange things to get the circuit working. I looked at the Adafruit Perma-Proto boards and asked why I would use them rather than just go to a Chinese website and have them make me a fully custom PC board in three days for $5. (Maybe I am missing something fundamental.)

The benefit of using a push-in breadboard is that I can fiddle the circuit easily until I get it to do what I want.

And, you discuss thermal expansion and filling the voids, etc. Is there any necessity to fill the voids at all? Isn't potting the circuit just to hold everything fixed in place the goal? Electronics epoxy is pretty good at thermal conductivity.Is there even any need for a bond to form between the epoxy any anything? Isn't the point of potting to just mechanically lock everything in place and seal it from external elements?

So I think I am back to the original question...as a practical matter is it highly likely to work, or improbably at working and rife with problems, or is this actually done by people, or has it been tried?

In short, moving from theory to experience, anybody have any experience with this?

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Re: Potting a breadboard circuit? Reliable?

by adafruit_support_mike on Thu May 13, 2021 9:38 pm

SeattleDavid wrote:And, you discuss thermal expansion and filling the voids, etc. Is there any necessity to fill the voids at all? Isn't potting the circuit just to hold everything fixed in place the goal? Electronics epoxy is pretty good at thermal conductivity.Is there even any need for a bond to form between the epoxy any anything? Isn't the point of potting to just mechanically lock everything in place and seal it from external elements?

The core problem is that hardware doesn't do what we want. It does what it can. Design is a process of imposing limits to prevent everything except the behavior we want.

We can only prevent things we know about though.

Formal evidence theory provides a useful framework for such issues by assigning 'belief functions' T() and F() to any statement that can be true or false. (T=1,F=0) is certainty that a statement is true, and (T=0,F=1) is certainty that the statement is false. 'Not provably false' is (T=0,F=0), which can be equally well interpreted "no reason to think it will work" and "no reason to think it will fail". It supports both the question, "what can go wrong" and the answer "anything".

In practical terms (T=0,F=0) means "need to collect more evidence".

You're welcome to try potting a breadboard circuit and see what happens.. it's not like I have any power to stop you. Be aware that you're collecting information instead of implementing a known-good solution though.

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Re: Potting a breadboard circuit? Reliable?

by SeattleDavid on Thu May 13, 2021 11:55 pm

This is probably a topic that could form the basis for numerous PhD thesis or seven or eight committees of Boeing engineers. As they studied it, the problem would undoubtedly get increasingly more complex, as these sorts of things tend to do. This is one big reason why the US (NASA) can no longer land men on the moon...instead of calculated risks by experienced and smart people using prudence and judgment we make everything complicated.

What I really am looking for is whether people have practical experience with potting a push-in breadboard, and what we know (if anything) about this method. It seems like an obvious enough way of "preserving" a circuit that some folks must have tried it and may have experience to share. That experience would be 3.14159 * 10^Gazillionth more useful than pontificating the improbabilities of coefficients of unknown possibilities.

In short, has anybody potted a push-in breadboard and had a success or failure, and what type?

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Re: Potting a breadboard circuit? Reliable?

by jps2000 on Fri May 14, 2021 1:06 am

The problem may be the unknown contact materials. I case wires and the push in board is gold plated then it may work longer.
It is also a matter of current drawn over a contact and if resistance fluctuation hurts or not.

There is an effect called fretting corrosion. Vibrations are deadly. Even thermal movements can cause problems.

Think also about that potting material is sucked between the springs of the board. if it expands thermally it may push the contacts away.
frequently you find connectors protected /secured with silicone. But it should never come between contacts.

There is good reason that a soldering is considered best.

I would not do what you suggest although it may work. But it is a planned time bomb / russian roulette.

So there is likely no practical experience available and if so it tells only about that particular case.
It is like Covid does not exist because I have not got it / can not see it

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Re: Potting a breadboard circuit? Reliable?

by SeattleDavid on Fri May 14, 2021 1:15 am

Well, actually, studies have proven that soldering is not best. Wire wrap is far more reliable than soldered by any metric.

Again, I’m not so much interested in academic speculation of the multitude of theoretical possible problems.

I’m interested in whether somebody has experience—good or bad—and has some pragmatic history to share on this.

That is, yes, but, does it actually work well or poorly?

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Re: Potting a breadboard circuit? Reliable?

by jps2000 on Sat May 15, 2021 12:34 am

Then I whish you happy wrapping.

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Re: Potting a breadboard circuit? Reliable?

by SeattleDavid on Sat May 15, 2021 1:56 am

I used to do a lot of wrapping, and then soldering, but now its either a custom PCB or push-in breadboarding. In the phone company we originally soldered connections until that was replaced with IDC/Punch connections (even faster and more reliable) and then with integration things went into chips and SMT and then COB. Much of the gear for the space program was wrapped, because it was so much more reliable than soldered.

But for little prototypes I was hoping people has experience with using a push-in breadboard that was potted. Sounds like this is not a common practice. But I also somewhat get that there isn't a lot of "prototype it and then put it into actual use" going on either. That is, not a lot of one-off builds with the idea that it will have a five or ten year service life. Appears to mostly be lego-land "gee, look what I built" environment.

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Re: Potting a breadboard circuit? Reliable?

by SeattleDavid on Sat May 15, 2021 2:10 am


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Re: Potting a breadboard circuit? Reliable?

by jps2000 on Sat May 15, 2021 4:33 am

I have no objectives against wrapping.
It is huge work though. And it is reliable also because there is no move between wire and ( mostly gold plated) pins. It needs dedicated (matched) wires and pins.
This technology was popular in the sixties as there were no reliable multi layer boards available. Circuits also took more power and higher current/ voltages keep contacts alive.

The rise of smd components make soldering mandatory and is considered reliable technology. Due to small pitch and low power design moisture needs to be avoided anyhow. So no corrosion issues.

Push in boards are quite simple. The spring inside clamp the wire on just two points with poorely defined contact force. The contact area is round to enable multiple and fast in / out for experiments.
This is completely different to IDC/Punch connections where a sharp edge contacts the wire with high force. Mostly single use. In mains switches or connectors you need to push the spring back to get the wire loose.

Details make the difference

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Re: Potting a breadboard circuit? Reliable?

by adafruit_support_mike on Sat May 15, 2021 5:27 pm

Wire wrapping also introduces a lot of parasitic inductance. It’s good up to about 1MHz, but then you have to start compensating for it.

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