Conductive epoxy for very small contact area

You can add thinner to nail polish. AFAIK even a few drops the remover might work.

MG-Chemicals makes a thinner for their stuff, I just don't know what happens when you go past 50% thinning:

The other issue is I need all this end of next week and much is banned from air shipment.

I had a conductive ink dispenser that was way too runny. Dried up on me though and I threw it out. That was really like ink, holds ok on paper but on any slick surface such as Kapton it went all over the place.

The words "small enough" are exactly the reason for my post. Bare Paint is almost there. But only almost.

but mostly keeping

Yes, we can make just about everything necessary. Mostly you only need to tape it down and gently bend it with a dentist's pick until it hovers right where you need it. No coffee before and no sneezing during that process.

Am 12.09.2015 um 23:07 schrieb Joerg:

Liquid indium? Does indium solve gold wires like tin does?

cheers, Gerhard

I have no clue but given the fact that one can't easily buy liquid indium as a product there might be something amiss :-)

You might try Achesons Silver DAG - DAG just stands for Deflocculated Acheson Graphite.

The web is full of variations on the name but none of them loaded all that quickly. We got ours from electron microscope service suppliers.

Acheson has half a gazillion DAGs. Do you remember which one it was and how runny it was?

But isn't solder used to mount BGA's. So I would think it would not be " w ay too thick " And using focused light with a timer ought to let you apply just enough heat to melt the solder , but not enough to affect the polyimi de.

From Wiki

Polyimide (sometimes abbreviated PI) is a polymer of imide monomers. Polyim ides have been in mass production since 1955. With their high heat-resistan ce, polyimides enjoy diverse applications in applications demanding rugged organic materials, e.g. high temperature fuel cells, displays, and various military roles.

Dan

I have no idea why you keep talking about applying this stuff to a surface. The way to do this would be to dip the end of the wire in it to pick up a small amount. Then put the wire in contact with the surface. Surely that small amount won't run.

Hover? Don't you want the wire in contact with the pad with as little interference from the glue as possible? The glue is put on the end of the wire before placement and held in place while drying.

I think trying to put the glue on a 1 mil wire end while it is in place on the pad is a fool's errand. Literally anything will reposition the wire end off the pad.

Isn't polyimide used in PCBs? How do they solder those?

Another thought. Maybe you can make a glue mask of kapton tape. Make a small hole in the tape and use it to hold the wire in place on the pad. Now a small amount of glue can be applied with a lot less finesse and without all the worry about it running 5 mil. When dry lift the tape and hopefully it won't pull the whole thing off.

Maybe the hole can be made with a mechanical pencil end... or something. That seems to be the sticky wicket with this idea. How do you make a clean 5 mil hole? Laser?

Polyimide is used for high temperature PCBs, usually specified as for 'continuous operation at 200C'. The PCB making processes are identical as is the soldering.

It's more expensive, and fewer places stock it so it's a bit niche.

Kapton tape is polyimide too.

Cheers

Good point. Take some solder paste and dilute it with a little extra flux and IPA. You can push the balls around under a microscope with a sharp point - the IPA evaporates slowly and you can build piles of balls on your 5 thou pads.

Cheers

Good point. Take some solder paste and dilute it with a little extra flux and IPA. You can push the balls around under a microscope with a sharp point - the IPA evaporates slowly and you can build piles of balls on your 5 thou pads.

Cheers

Because it needs to be applied to a surface.

The previous stuff I had did run. So little wicking to the wire above the conductive surface that they kept coming off. Other stuff was way to pasty and just clumped around. Ideal would be something that can be dialed in with a thinner that allows more than the 50% range of the MG versions.

Sure. First you make it hover and then give it a wee ding at the root so it pushes against the surface.

Done it many times successfully with plain old RadioShack Bare Paint. Probably 100 times by now. But this time the available area is much smaller and I can't have it clump or run off.

An added problem is the demise of RadioShack which makes procuring the stuff in the squeeze tube a slow process. It'll be there Friday. Maybe. Or maybe not. Amazon and others generally sell the pens which aren't as practical and dry out faster.

Laser would be easiest because the facility has one. But masking is tough because you can't easily apply the tape. There is no space, nothing to stick it to. Three sides are just air and the fourth is a wall and a sensor surface on the other side onto which nothing shall wick.

Then you *haven't* done this 100 times.

... and causing lots of issues there :-)

That goes for thick stuff like flex circuits. However, above 300C it can quickly go to hell. we have very thin stuff. Way less than the usual Kapton tape and that deforms fast. The other issue is to dispense such a miniscule amount of solder. Regular solder on a spool from Kester and others is out because the diameter is way too large.

That's a good idea, thanks. Maybe we can tolerate a little deformation in the Kapton.

Oh yeah, I did. Probably more than 100 times. I had sort of a conveyor-style system going on my lab bench. Regular bond wires.

If necessary I'll keep doing it but I was looking for some kind of conductive paint that makes this job easier and ideally something that isn't from RadioShack (because hard to get these days). Hence my post here.

You just said you haven't done anything this small before. Make up your mind.