Making High Quality PCB's Fast And Cheap.

[The_Doctor]

Some PCB makers in China do an awesome job cheaply, but if you want one board that might not be the cheapest way, and you'll have to wait for them too.

If you're making diode drivers, you're dealing in RF circuits because the speeds of pulses and possible overshoots can depend on the board as well as the components, so you can't simulate or do it on a pin deck, the closer you can get to the final design the better, even at early testing stages.

I won't write a book, this thread won't just be for my indulgence, so for now I'll just add the stuff I learned that is most likely to work, and passes the initial tests for suitability for speed, cheapness, and real effective work.

First, there is an ink tested by people looking into drawing direct to PCB copper. There are posts in old web archives from Usenet about this. Staedtler's Lumocolor permanent ink was found by several people to be by far the best. It comes in pens with various tip thicknesses ranging from 0.4mm through 1 mm to large chisel tips 2x5mm for bulk fills of large areas. It's fast drying, can redraw over itself without disturbing the earlier layers if motion is even and brisk. This quick drying ink forms a film that resists further drying, so pens can be left uncapped for hours or days with no harm done. Its solvent is isopropanol, so it's fairly safe, nice to use. Best of all, Staedtler do 'refill stations' that hold 15 ml of the ink in a way that makes it easy to fill a pen by putting its tip into the refiller and waiting a hour or three.

There are two ways this ink is extremely useful, one is manual drawing, including scraffito, which is great when you want ground planes or heatsink traces. Direct drawing is obvious so I won't explain that. Scraffito is nice, you take a large marker and blot out a large bit of copper area, then a few minutes later it's tough enough to stand gentle placing of a steel ruler on the surface. (And VERY easy to retouch if you do scratch it a bit). Then take a large jewellers screwdriver and run the edge of the blade tip along the ruler to scribe through to the copper, run two or three gentle scores and you get a very clean flakefree fine line for etching narrow gaps with a very small amount of etchant used.

Where this ink really scores is in plotters. You can clean out the plotter pens to remove old ink, and with water/isopropanol or other solvent, wash the tip and the ink reservoir wadding and rebuild, possibly after redrilling the tip channel to take tips removed from the original Lumocolor pens to increase your range of track sizes. Then you can refill the plotter pens from the refill station.

Plotters are what really makes this cool. People don't want them much now, because inkjet and laserjet printers are common and can print arbitrary graphics more easily, but you can't run an FR4 board through the paper intake mechanism, not even if it's only 0.2 mm thick, nor can you control the ink types as widely as you can with plotter pens. A plotter worth several hundred several years ago will go cheap now. I just bought a 22 year old HP Agilent plotter for £6! No power supply, but it was bought by the MOD for the British Navy, and was never used. All the materials it was built of seem to look as good as new. I've yet to look inside for signs of aging, but I suspect it will be in better shape than a lot of modern stuff would be if left on a shelf for just 5 years. This plotter can work to resolution of 0.025 mm, (0.001 inch), and a moderately sized copper clad board can be stuck to a transparency film for accurate handling.

That's as far as I got so far but I think it's good stuff, I don't expect any dead ends based on what I've seen so far.

PS. One possible extension of the use of a plotter is to attach the far end of a fibre-coupled 3W laser to use as a marking/cutting tool. That might take some careful work but it's an awesome thought.

[chimo]

First post.... Hello everybody.

For small quantity of boards I have used the Toner Transfer System. You can use an iron for the transfer, but a good, high-pressure laminator works well.

There are ways of economizing the sheets (print a sample), cut out a piece of transfer paper to cover the area and stick it on with a laser-safe label.

I have used it on smd boards successfully. The rapid-etch method on their site works too!

Paul

[The_Doctor]

That looks good. I've heard of similar, but this is better than the variants I heard of, I think. Still wants a laser printer though, and those (or at least the toner once you've used up the limited supply that comes with the printer) are not cheap.

A plotter might even manage THREE tracks between standard 0.1" pitch IC pads. I'm not convinced it can do it accurately, but an HP Agilent 7440A is specified with accuracy that implies it can, but we might have to be careful with steady ambient temperature during a draw.

Alignment with a plotter might be easier for double sided boards. The big score with the plotter is being able to chose inks for specific tasks, something no other method allows unless you go to the expense of setting yourself up as a PCB fab industry. And I can't beat the idea of using a program like GerbTool to render via HPGL direct to a plotter to the PCB with no intermediate stage. One moment it's digital, a few minutes later after a single button push, it is ready for etching. With so few stages from digital image to hardware, I suspect the accuracy won't be in doubt, because there is so much less to go wrong.

And as a plotter can be had for the price of a decent electric flat iron, I'm in.

[dave]

I have used press and peel blue in the past, with good results.

For low runs, i use custom pcb in Malaysia, however the Chinese board makers do a great job...

[dave]

BTW, laser printers are getting very cheap these days Doc

[The_Doctor]

BTW, laser printers are getting very cheap these days Doc

Is the toner and other vital replaceables also cheap? If so, then I'll have some. But as far as I know, the printer sellers sell cheap printers then having hooked us like crack whores they pimp out their consumable at extortionate rates. I welcome exceptions to that rule.

Press and Peel nearly tempted me. Thing is, I never saw it go cheap. 15 sheets of that stuff cost more than I paid for a plotter, including postage over 800 miles.

I'm definitely keen on this toner transfer thing, I just think that for me, the plotter idea is more exciting right now.

[dave]

Hehe, I myself don't have a laser - i just do all the printing i need in at work, where the toner is free.

Its been years since i have bothered making boards. I would rather get a pro job done, rather than drilling all those little holes. And Plated thru holes? I know there are ways, but someone else will do a better job, professionally.

BTW, a great etchant i have found is hydrochloric acid, with a dash of hydrogen peroxide.

Perhaps for you European ppl, Olimex would be the go. I have used them in the past, and they do good work. Seriously, $25USD for a single sided board is good competition to wasting time drilling holes

http://www.olimex.com/pcb/index.html

[The_Doctor]

Yeah, drilling holes is a pain. I decided that SMT was what I want to do now for small scale stuff, and the traces for that are so exacting that plotting or printing is mandatory. What I really need to plot for is test boards, so I can quickly do a board that is near enough as good as a final. It's easily beats having to try SPICE modelling then try to guess the RF behaviour of sharp edged pulses on FR4 when I built the test circuit on a pin deck. Even a first test needs stable layouts and good connections, and if it's good enough I can always sell it on eBay as a used prototype if I have no further use for it.

The proof of the pudding is in the eating. So long as it's not half baked.

[pixpop]

If you're talking about using a plotter...

you can get presensitized boards that are positive acting.. you need to expose the parts that will remain as copper.

The photoresist has some response at 405 nm.

So, if you could mount a 405nm laser in your plotter pen holder, maybe you could write directly onto the resist. You could probably write very fine lines this way. Writing fat lines.. well, that's left as an exercise for the student.

[ajohnson30]

I tried the toner transfer method & it was fine for basic single-sided circuits, however I found that the DAC0832's I was trying to build were too much of a pain. I could get both sides to line up but the plate-through (or lack thereof) and drilling was killing me.

I eventually gave up when I found ExpressPCB. I found their free software fairly easy to use, and thought $51 for 3 2.5"x3.8" boards with plate throughs was worth it.

You don't get silkscreens with that, but I cheated and put text down as copper layer where I wanted it