Superglue conductive?
September 15, 2006 3:50 PM   Subscribe

Is super glue (cyano acrylate) electrically conductive when dry? or wet? I just finished soldering something, and the joints are very close together. I'm trying to figure out if it's a good idea to coat everything in super glue to better insulate it.
posted by fvox13 to Science & Nature (23 answers total) 1 user marked this as a favorite
I don't normally find superglue to be a good gap filler. Perhaps a rubber cement, epoxy or even a hot melt glue would suit you better.
posted by tomble at 4:06 PM on September 15, 2006

hot glue sounds like a better idea. hot glue is quite elastic, super glue significantly less so.

how close is "very close"? Would other glues flow into the gap?
posted by misterbrandt at 4:08 PM on September 15, 2006

air is a good enough isulator. don't put anything between the solder joints.
posted by b1tr0t at 4:12 PM on September 15, 2006

All I have at my disposal (that is, all that I have in my dorm room) is super glue. The joints are probably 1mm apart, and it wasn't very easy to get the wires "stuck" because there weren't really any holes or anything to stick the wires onto. I'm thinking super glue because it'll make up for a poor mechanical connection, but I want to make sure it's non-conductive first.
posted by fvox13 at 4:14 PM on September 15, 2006

Conductivity is not addressed in Krazy Glue's MSDS sheet.

do you have a circuit tester? Could you make a blob and check for a circuit across it?
posted by misterbrandt at 4:22 PM on September 15, 2006

I wouldn't think it would be a good choice for a physical insulator. It forms too thin a layer to really do any good, and any kind of abrasion will take it off. Hot glue, or silicone, or epoxy, or even rubber cement would all be better choices if you feel you need a physical insulator beyond a simple air gap.
posted by Steven C. Den Beste at 4:23 PM on September 15, 2006

I wish I had a multimeter, but I didn't think to bring one to school with me. Any MeFi-ites have a meter and some super glue and would be willing to try it for me?
posted by fvox13 at 4:24 PM on September 15, 2006

Do not use epoxy.

I once "filled in" a circuit with a silicone epoxy and it sorted it. I can't begin to tell you what a bitch it was removing the shit to get to the components again.

I'd recommend air and a proper enclosure. Better heat dissapation properties, to boot.
posted by Civil_Disobedient at 5:08 PM on September 15, 2006

I can't tell you if it's a good idea for your particular situation, but I can tell you that cyanoacrylate glue is used in the creation of glass-coated tungsten microelectrodes used in recording of neurons, for exactly that purpose (insulation).
posted by Eldritch at 5:12 PM on September 15, 2006

I wouldn't depend on using anything to make the mechanical connection more robust. Double check your soldering and if you feel the need for strain-relief you can use the cyanocrylate glue to take the strain off the joints. I used to use silicone RTV to tack down wires but given the way it cures, I'd go for hot melt glue now.
posted by tommasz at 5:28 PM on September 15, 2006

It's not conductive (it's essentially acrilyc, a plastic), but as mentioned above, I might want to get a little more distance before depending on it. However, if your application isn't that critical, go for it.
posted by tellumo at 6:02 PM on September 15, 2006

Hubby just did the experiment you requested. On a glass sheet he laid a 2 cm x ~4 mm wide bead of Smith's brand thin CA. Using a Fluke multimeter model 179 he measured the resistance in ohms when the CA was still wet and after curing with an accelerator.

Across the 2 cm length:
off scale when wet
still off scale when dry

Placing the probes about 0.5 mm apart immersed in the wet sample:
resistance = 16 megaOhms.
Placing the probes about 0.5 mm apart across a small flake of dry sample, off scale.

Conclusion: CA is a good electrical insulator.

The low viscosity type would get into your gap pretty well, and you could add multiple coats for extra buildup.

Hubby hopes this helps!
posted by Quietgal at 6:03 PM on September 15, 2006

A common answer is potting epoxy, or as they call it in the trade, "pour in the reliablity" -- it keeps everything from moving, which makes even the most bodged ugly bug constructed devices running.

If you just need to insulate a wire you've soldered, the answer is heat shrink tubing.
posted by eriko at 6:16 PM on September 15, 2006

Listen, if you're afraid of your wires popping off, you've done a poor job soldering, or you've used wires that are too large. Trust me on this. I've ruined a number of modchip installations by not learning this quickly enough.

Redo your joints. Clean them very well, and apply flux paste. If you don't have flux paste, go get some. Heat the joint with the soldering iron, and apply the solder directly to the joint - not to the iron. If it doesn't melt without applying it to the soldering iron, your joint is not hot enough, and the solder will not flow into a proper joint.
posted by odinsdream at 6:57 PM on September 15, 2006

If you're worried about the wires actually pulling loose under physical strain later, then find a spot nearby on the PCB where you can gather the wires, and use hot glue to stick these ends down - thus creating a little stop on the way to the modchip.
posted by odinsdream at 6:59 PM on September 15, 2006

Don't put cyanoacrylate anywhere near anything that gets heated. When it turns gaseous from being hit with hot solder or a soldering iron, the vapors burn the living crap out of your eyes. So says the voice of experience.
posted by plinth at 7:43 PM on September 15, 2006

Thanks for all the help!
posted by fvox13 at 7:52 PM on September 15, 2006

Professional circuit board assemblers use CA glue all the time to secure 30 gauge (wirewrap) wires used to make rework corrections on circuit boards. They even have an accelerant that they spray over on it to make it cure in seconds. It sounds like what you are doing is similar what they would do. The glue is for securing the wire. Solder is used for the electrical connection.
posted by JackFlash at 8:15 PM on September 15, 2006

It may be a good insulator but its flammability properties could be desasterous. If the pins are already too close and you get electric arcing between them, that progress to a fire with a really good fuel source (the super glue).

I think hot glue would be a better option.
posted by nickerbocker at 8:21 PM on September 15, 2006

To answer this question, you simply must know what conductive means to you. Depending on the application, 10k might look like a good insulator, or a hard short. That doesn't even begin to address the reactive issues (are you increasing the capacitance).

If you can't answer what a large impedance means to you, go with the very most conservative suggestions (eriko's or b1tr0t's, with some elaboration later by others). If you want help determining what a large impedance is for your "something", we may or may not be able to help, depending on what it turns out to be..

It is my understanding that hot-melt is slightly conductive. However, it is sometimes used in manufacturing environments to secure components which need mechanical support. The label, hot-melt glue, is bound to refer to a large variety of chemical compositions anyway, so it is almost pointless discussing the matter..

You need the data for the glue you actually have! :P

do you have a circuit tester? Could you make a blob and check for a circuit across it?

It would be exceedingly difficult to get a reliable result this way, especially on a dry sample - the contact impedance where probe meets material is just way too unpredictable - I wouldn't trust any such number without a proven test methodology.

or as they call it in the trade, "pour in the reliablity"

I love it!
And that spelling error - which I noticed only after an external spell check because of my own terrible spelling/grammar - awesome!
posted by Chuckles at 11:28 PM on September 15, 2006

JackFlash, I'd like to hear more about your experience. Based on the description, the glue doesn't necissarily get anywhere close to a conductor.. Or, it might be all over a conductor, but nowhere close to any other conductor, such that it's own conductivity is a non-issue.
posted by Chuckles at 11:32 PM on September 15, 2006

I'm going to bold out something that Chuckles said.

Depending on the application, 10k might look like a good insulator, or a hard short.


Dramatic example. Go to basement, make a tweak to my Van de Graaff generator, and the voltage drops. Oh well, I undo the tweak. Voltage doesn't drop. Other tweaks drop it further, and I can get it back to this one level, but nothing puts the voltage back where it was.

So, I'm thinking I've got a corona problem, turn off all the lights, and turn on the generator. What I see is an faint arc travelling two feet -- to the end of a broom handle. Despite the many gigaohm resistance of the (very dry -- dehumidifers running) six foot long broom handle, to the 200KV voltage of the VdG, it was a conductor. I move the broom handle, and the voltage jumps.

So, yes, you do need to use a very different insulator if you're insulating the output of a flyback transformer, as opposed to the output of a 7805 voltage regulator.

They even have an accelerant that they spray over on it to make it cure in seconds.

Make your own! Dissolve a little baking soda into boiled water, then filter. Better are the alcohol/cellulous versions. But the big rule with accelerants is you always cap the superglue before you uncap the accelerant. Also, have acetone handy, which cleans up superglue messes nicely.

fvox13, if you could post a picture of what you're trying to insulate, we could probably give you a much better answer, or at least point out a soldering problem, if you have one.
posted by eriko at 6:09 AM on September 16, 2006

Chuckles, I should have clarified that I was speaking of low voltage circuits (no more than 12V). Assemblers will put blobs of glue that cover multiple exposed traces and vias with no problem.

fvox13 needs to provide two critical pieces of information -- the voltages he is working with and the dimensions of the separation. In most cases air would be the best insulator. Glue should be used just to prevent the wires from coming loose and shorting. I wouldn't use glue explicitly as an insulator.

Safety regulations apply to voltages above 42VAC and 60VDC. The two critical factors are clearance (air gap between conductors) and creepage (distance between the conductors on the insulating substrate). Below those voltages I wouldn't worry about separation at all, as long as there wasn't a short.
posted by JackFlash at 11:36 AM on September 16, 2006

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