Conductive Ink

What do you mean SMT? SOIC-8? Or some sort of QFN? CSP? Specify. I've done some work with just a one-sided copper clad board, I sliced it up with a grinding wheel for ground/power areas, and just tied the signals together with 30 gauge wire. This was for a 32MHz VCXO.

Oh, I used Surfboards from Digikey too.

Of course, they're a whole 2 dollars. :)

For more RF-style stuff, I just engrave strips into copper clad boards.

You could also use silver conductive epoxy. It's quite good, we've pushed 3GBps signals in a test splice with the stuff.

I don't know yet. To me, SMT == Surface Mount Technology. I guess I've got some reading to do.

Well, I've answered my own question - here's the first hit on "conductive ink pen" at google:

Thanks! Rich

While you can go with conductive paint, silver paint, etc (your search terms)...

For a paying project, unless you are a masochist and in a terrific hurry (hi D), have a prototype board house crank you out a few boards for cheap, in a few days, with top and bottom copper, soldermask, plated through holes, the whole nine yards. Looks better to the client who's paying - "more professional". You can mount parts on both sides if it makes it work better, or is easier to layout that way (but keep track of which way is what or you'll be bending leads to flip packages).

Also: I'd be leery of trying to draw/paint to connect to typical small-lead-spacing packages of most SMT ICs. The are pretty easy to solder with a good layout and soldermask (you want the pads a bit beyond where the leads stop for best manual soldering), but that same spacing would be a real challenge with lumpy silver paint and a toothpick or tiny brush.

expresspcb (I've worked with their boards, but they were ordered by a guy I was doing assembly and test work for, so no direct connection) seems to do nice work, and will spit out 3 for $51 plus shipping if you keep it at their specific size limits for that deal. They and many others have many other options...

Pardon - that's the "no soldermask, no screenprint" version.

OK here's a real question - teh chem-tronics one is anywhere from $18 to $23; RS has one for $5.98:

But the chemtronics one says "150 feet of traces" ; the RS one is so cheap, should I expect more like 60 feet of traces? And the RS one isn't stocked, so either one would have to be ordered.

Thanks, Rich

I was just trying to get an idea of which technology you were thinking of, and what frequency range/edge rates you want to tool around in. How many chips? Surfboards are good for a few chips. More complex stuff I would look into Olimex or a local proto PCB shop.

Can they work from a schematic, or do I have to get software? The thing is, this client seems to be in a hurry, so I was thinking of the quickest way to get something running, that can be refined on the spot, "today".

I was thinking: Get something working in ink, characterize it, modify as needed on the spot, and when it passes spec, _then_ get the board(s) made.

And really, the only reason I'd want to use SMT is because that seems to be about all that's available today, plus the small size and all of that. I should probably check with him - I'd be much more comfortable with through-hole - I can do that on perfboard or VectorBord(R).

Thanks, Rich

One tradeoff with surface mount is that it's harder to work without a pcb, but on the plus side it's easier to make homemade pcbs because there's no drilling. Assembly goes quicker because the parts and the circuit are on the same side.

If I were you I'd get a resist pen and the single sided board and draw + etch. Even if you don't want to use a layout program and do toner transfer for everything, consider printing some footprints on clay coated paper that you can iron on as needed before drawing the rest of your circuit.

Rich Grise hath wroth:

I've used those and had some problems.

The pen has a fairly fine tip, but not fine enough to lay an very thin trace. It's great for laying large blobs, but not fine lines.

It comes out as a thick liquid, which like all good liquids, runs downhill. If he board you're working on is anything but perfectly horizontal, the ink will run.

Once used, the tip drys out and clogs after a few days. The tips come in two sizes, but are not replaceable. I can clean it perhaps twice, but no more. To solve this problem, I cracked open the pen, and poured the contents into a medical glass syringe. Now, I have an easily cleanable tip (stiff wire or cigarette lighter) and much better control over the amount deposited.

Catalog #: 64-4339

Is that what you are looking for?

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

I have an idea, might be good might be bad. Is aluminum paint, the stuff sometimes people use to paint radiators, conductive enough for traces?

Rich Grise snipped-for-privacy@example.net posted to sci.electronics.design:

Chemtronics is slightly more reputable.

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Hello Rich,

having just done the whole board fabrication stuff i can offer this.

If you are near a fry's ? they sell a similar pen (CircuitWriter by CAIG labs, silver/acetone/acrylic resin) can be soldered to but it is difficult to control as one compresses the tip to release the liquid. it seems to dry quickly and the pen gunks up if you go backwards or over another not so dry trace.

The copper etching method is quite easy, alot easier than i imagined. Since you are doing SMC (surface mount components) then all the easier as the through hole drilling is the worst part

if you want a ground plane then Radio Shaft sells double sided copper boards (probably super cheapo but it worked for me). just spray paint the ground side completely with some ? acrylic/laquer paint ? before etching

draw and print the PCB with a **laser printer** on magazine paper, iron onto the cleaned copper board , wash paper off, check for thin etch resist (fix with sharpie), etch with (muriatic + %3 peroxide - 1:2), approx 4 minutes later PCB is etched , remove and wash with water, remove etch resist with acetone

PCB is ready.

my first attempt i was able to get nice looking traces as small as .015" with .015" spacing and i think i could easily get .010" or less.

hope you did not already know this , robb

ewwwww...conductive ink prototyping.. :P I've considered it, but won't try it...

My favorite is to do fast thinking layout and connections in CAD. Autoroute..and human clean up. I like the software error checking when I'm in a rush.

I still like homebrew photoresist boards and etch for fast prototypes.

(Small boards can be done in a rice cooker.) D from BC

Rich, count me with robb and Jeff--the silver ink pens' traces are unsuitable: too wide and too delicate for surface mount stuff. I've tried it.

For very simple boards you can use a resist pen; with this and a needle you can make very fine features. Plan the layout on paper, then place the parts on the copperclad. Draw in the traces, lifting parts as needed to draw pads. You can easily define a fine wire going through a small gap by painting crudely with the resist pen, then scratching the fine details with the needle. Etch.

Or you can lay out the board as above, then route out isolation channels with a Dremel and a broken [sic] remnant of a carbie pcb drill bit.

Another choice is dead-bug. Splaying alternate smd pins in opposite directions gives you plenty of access and space to access and solder each pin.

Or, for a more professional job, use the toner transfer method.

HTH, James Arthur

Rich,

I had to read this twice before I stopped assuming that you'd have a problem with soldering to the newly-drawn traces.

You're not, though, are you? You're thinking about letting the conductive ink flow onto the component's leads as if it _were_ solder... but without the usual concerns about "cold solder joints".

Wonder how one would go about laying down a non-conductive drawing pattern on a phenlolic-like surface for those of us () who have trouble drawing straight lines?

Oh. You could use this approach to lay out a (working) circuit on plastic... or glass... or lots of other things.

Thanks for the concept, Rich. I don't have an immediate application for it, but if I ponder what you're pondering for a few months, I'm sure I'll come up with one or two.

Maybe a glass firefly jar whose inner surface is coated with SMT LEDs? Maybe... (Sorry. Gotta get back to RealWork(tm). )

Frank

-- "Whatever you can do, or dream you can, begin it. Boldness has genius, power and magic in it" -- Goethe

-- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)

Don't print on paper, print on the glossy backing used for stickers. Toner just peels right off.

Isn't that a problem--the toner falling off too easily? What brand of backing did/have you used?

Cheers, James Arthur

stickers.

i have same issue as James.

you must be using something different as the stuff i used the toner was knocked off coming out of the printer and i experimented with lots of diff paper... label backing, gift wrap, diff weights copy paper etc

even tried parchment which you can blow the fused toner off of :o

robb