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RickNel
October 30th, 2012, 03:01 PM
This from the latest Jameco newsletter:


A team of chemists at the Massachusetts Institute of Technology created a carbon nanotube "lead" that can be used to draw freehand electronic circuits using a standard, mechanical pencil.

MIT chemist, Katherine Mirica and her colleagues pulled off the amazing trick by using a special material called carbon nanotubes to replace the normal graphite pencil lead. Best of all, the special pencil lead is fairly cheap and easy to use, according to the MIT researchers.

I've recently used a silver polymer circuit pen to repair some corroded traces. It works, but has a number of limitations. It draws a line about 1mm thick, but this remains liquid (and non-conductive) for some hours, tends to spread a little on a lacquered PCB surface, and is difficult to keep straight and narrow. A pumping action is needed to feed the fluid to the felt tip, which also makes precise drawing difficult. The thick line would make it difficult to use for any typical TTL DIL socket pin spacing, let alone anything smaller.

Surely a conductive ink using carbon and metal powder should be feasible? I'd like a little pot of conductive ink that I could draw with a calligraphic pen nib - easy to clean, variety of trace widths.

I'll be watching for the retail version of MIT's circuit pencil - then we will see what "fairly cheap" means. Also whether it is erasable, which would be handy for design and prototype use.

Any other experience with conductive inks for drawing or printing?

Rick

RJBJR
November 5th, 2012, 05:19 PM
I've got a circuit writer pen that works the same way yours does and it has the same drawbacks.

A variation on just pumping it out of the pen onto a trace is to work with a drop of the liquid using a needle to apply while wearing magnifying eyeglasses(my eagle eyes are no longer).

Chuck(G)
November 5th, 2012, 06:04 PM
There are also repair pens that use a suspension of silver or copper to do the job.

Those pens are also great for repairing auto rear window defoggers:

http://ecx.images-amazon.com/images/I/515SS17QYVL._SS500_.jpg

RickNel
November 5th, 2012, 08:48 PM
There are also repair pens... for repairing auto rear window defoggers:



Window defoggers are heating resistors - does the repaired trace section have a significant resistance factor? Or just a low-res link between resistor sections?

Chuck(G)
November 5th, 2012, 08:51 PM
Low-res link--I don't think the repaired link generates significant heat.

RickNel
November 5th, 2012, 08:51 PM
A variation on just pumping it out of the pen onto a trace is to work with a drop of the liquid using a needle to apply while wearing magnifying eyeglasses.

Good idea - I hadn't thought of using the felt-tip just as a dispenser. I suppose using a calligraphy pen with the fluid would still give a better grip and control than a needle, where space would allow. I'll give it a try when next needed.

Chuck(G)
November 5th, 2012, 09:07 PM
Masking the trace to be repaired also helps. That way, you can be sloppy and still do a neat repair.

nige the hippy
November 9th, 2012, 07:38 AM
I wonder if a Rotring pen would do a good job? they have a needle in the tip to control the ink flow. The silver ink might be a bit thick though.

RickNel
November 9th, 2012, 01:08 PM
I wonder if a Rotring pen would do a good job? they have a needle in the tip to control the ink flow. The silver ink might be a bit thick though.

Yes, even with standard inks the Rotring pens are hard to keep clean. I used them for years, as they work well for left-handers on most papers. The silver polymer solutions are very viscous and set solid and adhesive. I think an open nib would be easier to keep clean.

Rick