Conductive pen technique and substrate

You'll be happier with copper tape and scissors, I think.

Cheers

Phil Hobbs

Limited experience with those things tells me their resistance is high, and reliabliity and longevity low. Colloidal carbon makes a far more reliable conductive ink, but has much more R.

NT

What Phil said. "conductive" ink is often a poor conductor, and very expensive compared to either copper tape or attacking a bare copper board with an Xacto knife (or paint and ferric chloride - if you can paint the pattern you want, you can paint it on copper with a paint marker or a brush and etch the copper you don't want off, and have a real conductor.)

I do have firsthand experience, and I hate the stuff.

Jeez, just use tin or copper alarm foil. It comes with the adhesive already on it.

Well,if he were to go that route, the silver filled conductive epoxy would be the choice. Mill tiny groves in G-10 plates (milling is cheap) and fill them with it. Makes for precise uniformity of trace dimensions.

You can get grooves down to 0.035 easy. Some will do 0.015 for you. Those are mils.

Pueblo Dancer wrote: : Well,if he were to go that route, the silver filled conductive epoxy : would be the choice. Mill tiny groves in G-10 plates (milling is cheap) : and fill them with it. Makes for precise uniformity of trace dimensions.

: You can get grooves down to 0.035 easy. Some will do 0.015 for you. : Those are mils.

Do you really mean 0.9um and 0.4um (metric)? We do have a milling machine (FEI Helios) that can do it, but I would not call this easy, or a subtitute for an xacto knife. Filling the grooves with epoxy would be even more difficult. A typo maybe?

One would need a squeegee of some sort to remove the extra epoxy even if you meant 35 mils i.e. 0.035 inch grooves - sounds a bit messy.

Regards, Mikko

Yes, it might be fine for straight lines, but we are wanting to do tight curves, zig zags, crosses, etc. That could be tricky with tape.

Won't bend uniformly. Have to solder cross-overs, etc.

If anyone ever came up with a laser printer cartridge that deposited (real) conductive ink on flexible plastic sheet, they would make a fortune.

Ken

That would make each trace uniform, Hell, you could pull solder paste into the grooves. And no, it would not be difficult to apply.

It makes uniform traces. Hand cut foil does not. Foil requires attachment. Epoxy would get "laid up" in the cracks with a single, easy swipe.

You can buy printers that use food coloring for printing images on cakes. I am quite sure you could make an epoxy mix that it would print just fine.

Don't piece the tape, use wide stuff and cut it to shape. (I'm assuming this is a microwave antenna.) I have 3-inch wide Cu tape in my drawer, as well as a roll of 12-inch-wide copper-plated Kapton.

If you need something really complicated, if your time's worth anything you'd be much better off making Gerber files and having it made on flex. A good board house can do big flexes with 4-mil lines and spaces.

Cheers

Phil Hobbs

But there are already a number of good ways to do fast prototyping of circuit boards. Unless there's a good reason why FR-4 doesn't work as a substrate for you, your best bets, IMHO, all revolve around leveraging everything that has been learned about circuit board fabrication in the last 60 years, instead of messing around with reinventing the wheel.

Paint then etch, or direct etch with an X-Acto knife and peel the rest off (heating with a soldering iron does wonders for making the copper debond from the substrate), drawing up what you want in a PCB program and sending it off to a quick-turn PCB house, and getting one of those PCB prototyping milling machines are all viable answers to your problem. Furthermore, all of them give you an antenna with a known and controllable conductivity, and some of them give you an easy way to duplicate antennas and/or carefully control what gets laid down.

That having been said, I think that your best bet for doing this according to your preconceptions is to use silver-filled epoxy, thinned with 99% isopropyl alcohol until it flows nicely, and painted on with a brush. But -- check your conductivity, because you might not like the result.

Conductive particles have a problem with working in an electrostatic process - the fact that the toner is non-conductive plastic is not irrelevant to the process working. Some fairly crude efforts in inkjet have been made, as I recall. Perhaps they have even got a bit less crude - here's one.

But any of these are likely to provide a result that is not going to behave the same way that copper on FR4 (or flex if that's what you are prototyping for) will. So they may be of limited value as prototypes, anyway.

Tim left out (though I find it horribly crude - it's quick) Print out the pattern you want in reverse, and iron it onto a board, then etch (soaking the paper off first.) Laser printer toner is actually decent resist (though pinholes are an issue.)

You could also probably have your local screen-printing place zap out a quick screen of your design and print that onto boards for etching.

In the "old tech you'd be lucky to find working" line, one of our labs used to plot resist pen directly on copper-clad with a flatbed pen plotter. The rise of the pesky roll and inkjet plotters makes that harder to manage now. Optimists would then think that a conductive ink pen in such a plotter would solve all your issues - good luck with that if you head there.

Or the old way - printout a laserprinter transparency and expose a photo-resist board, develop, then etch - but that's work, and more importantly in many places these days, a bunch of moderately nasty chemicals. One reason quick-turn board houses get so much business - in any regulated work environment, setting up to be compliant for handling and disposing of and having all the chemistry on hand costs the company more than letting the quickturn house deal with all that. The good ones really are quick, too.

You're not going to get terribly precise geometry hand-painting the things, that's for sure. And the "conductivity" needs the quotation marks, and costs the earth with all that silver that's mostly not touching all that other silver, so it mostly doesn't conduct much.

snip

I think even easier would be to stick some copper foil on a bare piece of fr4 or what ever backing that has the right properties, then cut and peel digikey has adhesive copperfoil up to several feet wide

-Lasse

Press-n-peel blue. Stick it in a laser printer, print, then iron onto copperclad board. Etch.

Cheers