Conductive epoxy for very small contact area

Hello Folks,

Need to contact wires to pads that are tiny. The wires are in the 0.001" or 25um category, the contact areas around 0.005" or 125um. Which kind of conductive epoxy would be suitable for this?

Too "blobby" and we'll get shorts, too runny and it'll be all over the place, barely wick the wire and not hold on too well. If the resulting resistance is in the tens of ohms that would be ok as long as the connection is reliable, at least for a few weeks of testing time. Pad metallization can be all sorts but mostly will be a very thin gold plating.

I've done similar jobs with black "Bare Paint" from RadioShack which Amazon also seems to sell but it is tough to sponge off droplets that are tiny enough.

Any suggestions?

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg
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Weld or wirebond (same difference). ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

It's not possible in this case since the base material is a polyimide or similar. Can't be mounted easily in a wire bonder anyhow.

The problem with most silver-epoxy is that it's more a paste than a liquid. I need something that's liquid but clings easily instead of running away.

If all else fails maybe we can add some stuff into the RadioShack bare paint to lower its viscosity. Conductivity isn't stellar and the stuff becomes ratehr brittle after curing but for experiments that is acceptable. But what? Paint thinner?

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

1"

ting.

I wonder how conductive something like this is?

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-Lasse

Reply to
Lasse Langwadt Christensen

Silver conductive paint? Widely available, but I guess you'd need something else on top for mechanical strength.

Cheers

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Syd
Reply to
Syd Rumpo

Should be quite good but almost anything that comes out of a can usually dries fast and can't be used to pick and dab.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

It doesn't have to be super strong. Do you have anything particular in mind, maybe from Ladd or Acheson? There is such a myiad of products.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

What are the wires made of? What are the pads made of? Why can't you use solder? Maybe use heat from a halogen lamp and lense. And timer to turn lamp on and off.

Dan

Reply to
dcaster

On Sat, 12 Sep 2015 11:58:59 -0700, Joerg Gave us:

Conductive epoxy usually requires thermal cure, so there would be no "too runny".

search up Epotek H20E-FC

That is what all the chip makers use to bond a chip substrate to a can lid, etc. use.

Reply to
DecadentLinuxUserNumeroUno

I've used Electrolube stuff before, this could be it...

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Cheers

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Syd
Reply to
Syd Rumpo

Mostly all gold but not all the time. Solder is way too thick and most of all heat cannot be tolerated.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Is that runny, similar to nail polish?

Unfortunately they only list two European distributors, one of them being Farnell but Newark does not carry it :-(

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

You think nail polish is runny? If you are trying to wet a 5 mil pad, I think you are going to find nail polish is far too viscous to apply to such a small area and would need to be thinned.

How much clearance do you have around the pads? If that is large enough maybe you will be ok.

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Rick
Reply to
rickman

My experience with silver conductive epoxy is it is great for grounding somthing to prevent it from charging up, but you'll NEVER get down to tens of Ohms. More like MEG-Ohms! We use it to ground metal foils on particle detectors to prevent electrons from charging the foils until they spark. Works great for that, but using an Ohmmeter later, you often get Meg-Ohm readings.

Jon

Reply to
Jon Elson

Too runny during application, before cure.

Thanks, it's two-component but I'll check that out.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Well, I never wore nail polish so far so I don't know for sure :-)

But I remember snatching my mom's nail polish on occasion as a kid to secure very thin enameled wire when winding high inductance coils. Some of it was very runny and it was super-easy to apply a tiny droplet. That also must have been the more expensive stuff because I was almost read the riot act when she found out that it had ended up in my tool chest.

There is no clearance. Three sides are in free air and the fourth is against the sensor body and not much should wick onto the sensor, at least not farther than 0.002" or so. That's the problem with one silver epoxy I have tried which is almost like spilling a drop of gasoline, goes everywhere.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I routinely got

Reply to
Joerg

Well, yeah, gasoline is some orders of magnitude more fluid than nail polish. I also worked with airplane dope and I found it similar to nail polish. I can't say I know of a conductive version though. I just can't picture an epoxy that runs at all. Every one I've seen is very viscous like molasses.

I would think the trick to gluing a 1 mil wire to a 5 mil pad wouldn't be the glue, it would be the alignment. I'd want a 3 or 4 mil L at the end of the wire, dip it in the conductive glue and the touch it to the pad. I can't picture a glue of any sort that would run very far at all, more likely at that size it would be hard to get it to run. Harder will be to get a small enough glob on the end of the wire, but mostly keeping the wire in good contact with the pad while it drys. Do you have some sort of fixture to apply and hold the wire?

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Rick
Reply to
rickman

Hmm, "Exceptional" isn't a number.

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Reply to
Jasen Betts

We had this silver stuff, and it did NOT give really low resistance. Maybe the carbon dust is a lot finer than silver particles, and makes a better continuous path.

Jon

Reply to
Jon Elson

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