[sdiy] PCB making

[Batz Goodfortune]

Y-ellow Bill 'n' all.

At 04:52 PM 1/1/07 -0800, bill bigrig wrote:
>Howdy,
>
>  I usually just make circuits on pre-made
>projectboards, but would like to start making PCBs
>again(after 20 years). I read about using the printer
>as a pattern maker. Does this have to be a laser
>printer

Yup.

Not only that, it has to be an older laser printer or photo-copier that 
doesn't have toner-saving on it. It can be done with or without toner 
transfer film but the principal is the same.

The toner is basically a powdered plastic gunk. When printed on a piece of 
acetate film, this can be re-heated with a clothes iron and melted back 
onto a blank bit of PCB. The toner thus becomes the etch resist. The blue 
transfer film simply aids the transfer of the gunk because it tears away 
from the backing readily. Making sure that all the toner sticks to the board.

THAT IS, IN THEORY.

In practice your mileage may vary. And if you were thinking of using SMD 
parts, forget it. The resultant resolution is just about good enough for 
thru-hole. All this heating and pressing tends to make the toner smudge out 
a little. Great for overcoming under-cut but that's about all. More often 
than not there will be patches where the toner won't stick to the board 
surface no matter how much you cleaned it. Or think you cleaned it. I some 
times use to think it stuck better to a dirty board because at least it had 
something to grip to.

Process number 2:
Print your PCB pattern to an acetate as before with your lazy printer. Then 
attempt to use that as a photo mask. Using either pre-sensitized board or a 
spray on photo-resist such as "Postiv 20"

Problems:
There are usually pin-holes in the printed lines which transfer to the 
final board and are exacerbated by undercutting in the etching process. 
This usually results in tiny breaks in the tracks and if you're really 
lucky you might spot them before you actually start populating your board. 
I had once thought that maybe you could print 2 copies of the board layout 
and stick them together some how. The theory here being that at least it's 
unlikely that the pin-holes would strike in the same places on 2 different 
print runs.

Doing boards is messy enough but positiv20 has got to be the bastard 
product of the last century. You need almost clean-room conditions to spray 
it on. And then don't get it on anything other than the board. This stuff 
sticks to glass. I kid you not. The glass-doored cupboard in my kitchen 
still has a gloop of it stuck on from boards I made 15 years ago. Can't 
even scrape the shit off. But then what do you expect from some gunk that 
develops with caustic soda?

I use to have better luck with the paint-on stuff but I haven't seen that 
for years. I have no idea if you can still get it? I was once planning to 
use an old 14" disk drive and platter as a centrifuge to get an even 
coating of the crap. Similar to the way they put the etch resist onto 
silicon wafers. But a friend though my disk drive would make a better 
potting wheel.

Next up we have a slightly more professional method.
You still have to use pre-sensitized or other photo-resisted boards but you 
get the photo mask made professionally. That's if anyone still does process 
photographic work out there anywhere anymore? I use to take mine to my man 
Doug but he probably traded his process camera for a 1-hour photo booth. 
But if you do know someone who still knows how to use a process camera then 
this method has a better than 50% chance of working first time.

Ideally you need a printer with a 15" carriage but you could do it with a 
lazy printer or trouble-jet. The reason for the bigger format printer is 
that then you can print the layout at 2:1 resolution. IE: exactly double 
the size. When this is run through the process camera it is reduced to 
exactly the right size and together with the normal process of doing the 
transparency, you end up with a perfect PCB layout of super high resolution 
and zero pin-holes.

NOTE: Pinholes are a photographic problem as well.

I use to print on fan-fold paper and Doug use to remove any signs of 
perforations and other imperfections. I don't know how he did this exactly 
but since you first produce a negative, I assume he could paint out the 
pin-holes and marks. At least, that's how I use to do it when I was doing 
photographic processing but this was 30 years ago.

THE GALLERY OF THE UNTRIED:
Many years ago we use to do a real sleaze-bag method. Get some tracing 
paper, trace out a circuit from a book in pencil, then go over the pencil 
with a black texta colour a few times. The tracing paper passes at least a 
bit of UV and even better when it was soaked in cooking oil. So you could 
press the tracing paper against the board and take it outside for a few 
minutes. For some reason I could never get this to work at night. No idea 
why. :)

What I'm thinking is that perhaps you could cut some tracing paper to size 
and ram it through your stink-jet. Then use a similar method of exposure.

Oh did I mention that all these sensitized boards are only sensitive to UV 
light? And lots of it. You'll need a good UV source. And I'm not talking 
about a black-light bulb.

Possible methods number 2:
The ink in a dalo pen, -etch resist felt tipped pen- is basically 
engineer's marking blue. A kind of thick ink that's trying to be a paint. 
But almost any damn thing will resist etching. Even a sharpie will do a 
half assed job. I've often used a permanent marker to fix problems with 
etch resist and it's worked just fine.

So here's some possible workable solutions. Find yourself a flat bed 
plotter. They're getting rare these days but when they do come up, they're 
usually cheap-as. Replace the ink in one of the specially little plotting 
pens with some marking blue or perhaps even the original ink will work. 
Stick a piece of blank board onto the plotter and plot away. Remembering of 
course to tell your  computer to plot it inside out.

Get one of those ink jet printers that can print directly onto blank CDs. 
Butcher it to take a piece of laminate instead and print your pattern 
directly onto the board. Worth a shot if you can afford to butcher an ink 
jet printer.

By now you'll have realized I have very little respect for printers.

There is of course one relatively shure-fire way of doing PCBs. That is, 
send your digital artwork to some guys in Bulgaria who just happen to own a 
PCB fab and have a lot of time on their hands. Once you get over the 
language barrier I'm sure you'll get a nice PCB in the post. All sliced 
into bits and everything. And it might even work.

Note to the chemists on the list: I'm still waiting for a solution that 
will allow me to draw conductors directly onto a substrate. Any suggestions?

Hope this helps.

Be absolutely Icebox.

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