Bare conductive paint

[John-Del]

So I had this membrane keyboard assy from a Swiss machining center in for repair as a couple of the switches had failed, and intended to replace the two with mechanical NO switches as the membrane is NLA from TESA. I couldn't trace one of the printed switch conductors back to the main circuit, so I had to peel the membrane apart to see what happened. One of the printed traces had opened, so I picked up some Bare conductive paint from Radio Shack to repair the trace.

http://www.amazon.com/Bare-Conductive-10mL-Pen/dp/B00B888LQ8/ref=sr_1_1/188-6989773-8983665?ie=UTF8&qid=1400163421&sr=8-1&keywords=bare+conductive+paint

This product sold on the premise that it could be used to replace or fabricate circuit traces or use to attach components without solder. On the back of the package, they show a painted circuit connecting an LED to a battery.

Since this is just low voltage/low current key matrix, I figured that this would work fine. Before painting it on, I drew a two inch trace (maybe an eighth wide, about the width of the printed traces) on a piece of plastic and measured the resistance the next morning. The two inch trace read over 1K. That's right, 500 ohms per inch on a fairly wide circuit trace. The small blob I would need would read between 50 and 75 ohms. Maybe it would work, maybe not, but I'm not taking a chance.

I can't imagine any use for this stuff whatsoever.

Has anyone used this stuff and measured the resistance of it? :

http://www.amazon.com/CircuitWriterTM-Precision-Pen-silver-based-grams/dp/B0002BBVQO/ref=sr_1_7?ie=UTF8&qid=1400163782&sr=8-7&keywords=conductive+paint

[N_Cook]

It was "designed" by design students, say no more.

[John Robertson]

I've used it once - seemed to work, no call-back.

Once opened it has a short shelf life of a few months...however as a
conductive paint it is better than the brown stuff.

John :-#)#

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[Gareth Magennis]

"N_Cook" wrote in message news:ll2qtd$cvd$1...@dont-email.me...

This may or may not be relevant, but useful to know:

I recently bought some of this stuff to repair an unobtainable fader on a
vintage synthesiser:
http://www.ebay.co.uk/itm/Conductive-Wire-Glue-Paint-NO-Soldering-Iron-Gun-Solder-/320599571856?pt=UK_Home_Garden_PowerTools_SM&hash=item4aa5393d90

It turned out to have rather a higher resistance than I anticipated, but I
got it to work in the end.
I tried a line of it on a piece of paper, maybe 5mm wide, and it had
hundreds of ohms per millimetre when dry, which sounds similar to the OP's
experience.

However, it does work well as a glue, and it is a damn sight cheaper than
any of the other silver loaded conductive epoxy's I came across.


My problem was the fader's earth tag was not connected to the start of the
track, so I had to glue a very fine wire onto the metallised section of the
track end that connects the carbon track to the pin, and feed the wire
through a tiny drilled hole to the outside world. The contact wipers sit on
this metallised section at zero, so it had to be connected right on the edge
so as not to foul the wiper.
Simply dropping a blob of this glue onto the wire and track produced 300 to
400 ohms of connection resistance, meaning the fader would not zero.

I had to bend and hold the wire in such a way that the end couple of
millimetres were actually sitting flush on the track. Not easy. Dropping the
glue onto this arrangement eventually produced a solid join of around 20
ohms resistance, which was enough for the synthesiser to read the zero as a
zero. (faders used as potentiometers feeding a DAC)



Cheers,


Gareth.

[Maynard A. Philbrook Jr.]

In article <a7e30b00-3093-4d10...@googlegroups.com>,
ohg...@aol.com says...

>
> I can't imagine any use for this stuff whatsoever.
>
> Has anyone used this stuff and measured the resistance of it? :
>
> http://www.amazon.com/CircuitWriterTM-Precision-Pen-silver-based-grams/dp/B0002BBVQO/ref=sr_1_7?ie=UTF8&qid=1400163782&sr=8-7&keywords=conductive+paint
>
>
>

get the window defroster heating element repair cement.

it's ground up copper and is conductive on the surface.

Jamie

[Jeff Wisnia]

I've used conductive epoxy with excellent results over the years,
repairing things where soldering was not readily possible.

I just looked around a bit at conductive paints and this one:

http://tinyurl.com/mdv7a7x

Seems to have pretty low resistance. Unless I've forgotten my math the
listed resistivity of Less than .015 ohm/square per 1.0 mill
(25 microns) dry film. That would mean to me that a 50 mil wide trace
made from this paint would have a resistance of only 0.3 ohm per inch.

Someone please correct me if I'm wrong on that.

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

[John-Del]

I don't know that product, but since this thread popped back up and I was the OP, I'll update it.

I ended up throwing out the Bare crap and bought a Circuit Works silver paint pen. The traces I made to replace the missing traces on the plastic membrane keyboard were about an ohm for an inch IIRC. What I do remember is that I made several samples traces on a plastic sheet before committing to the repair, and a couple of them were *much* higher in resistance than they should be. Circuit Works recommended shaking the pen for a short time, but if you get one, shake the beejeesus out of it for 10 minutes or more. Short shake times result in high resistance.

[isw]

In article <d26d452f-085b-4bc7...@googlegroups.com>,

Since the signaling currents in a keyboard scan matrix might very well
be in the microamp range, a few k -- or a few dozen k -- simply won't
make any difference at all. Except maybe for response time. Maybe.

Isaac

[N_Cook]

I hope you were aware that:
You paint a patch of the paint, let it dry , and then score lines in it
with a scalpel to make the "insulators"

[John-Del]

> >
> > I ended up throwing out the Bare crap and bought a Circuit Works silver paint pen. The traces I made to replace the missing traces on the plastic membrane keyboard were about an ohm for an inch IIRC. What I do remember is that I made several samples traces on a plastic sheet before committing to the repair, and a couple of them were *much* higher in resistance than they should be. Circuit Works recommended shaking the pen for a short time, but if you get one, shake the beejeesus out of it for 10 minutes or more. Short shake times result in high resistance.
> >
On Tuesday, November 11, 2014 3:48:29 AM UTC-5, N_Cook wrote:
> I hope you were aware that:
> You paint a patch of the paint, let it dry , and then score lines in it
> with a scalpel to make the "insulators"

The original keypad was made using several layers of plastic sheets, with the original traces painted on with no solder resist applied on top. I put some adhesive tape down along the path of the original traces, painted between, and removed the tape. It looked and ohmed out (yes, ouch) the same as the original, so no insulator was needed.

But will you explain the score lines making insulators?