Hi PICListers..

There was a little interest recently about using a laser printer to make
PCBs. I decided to play around some more (I did it a while ago for some
boards, but nothing recently.)

I needed to make a prototype of a small 30mm square PCB, so I though, lets
give it a go. This PCB was Double sided and had SMT components on it (0805
resistors & caps and SOT-23 Transistors). The track size I used was 0.3mm
(about 12mil).

The process I used worked surprisingly well, and so I thought I'd share it
with the list and see if other people have any other ideas.

I'll just explain a single sided board, to do a double sided you have to
line everything up, tape it together (Masking tape, not plastic!) and evenly
heat both sides.. Takes a bit of practice.

Don't expect to get it right first time. Transferring the toner is tricky.
If you mess it up, just scrub it off and try again with a new print out.

You will need:
        - Scouring Pad (preferably the "plastic" types)
        - Kitchen "Cream Cleaner" like Ajax
        - A Clothes Iron
        - Small bucket of hot water and detergent
        - Old tooth brush
        - Flat and solid block of wood that the PCB fit on (10mm thick at least)
        - A book or magazine
        - Stanley Knife (Box Cutter or Craft Knife for non-Aussies)
        - Sheet of ordinary paper
        - Sheet of Tracing Paper.
        - Laser Printer

Method:

The trick that makes this work well seems to be using tracing paper. It has
very small fibres so when you come to remove it, they are bridging across
tracks (try it with normal laser printer paper, it works ok, but you'll see
what I mean).

Cut and clean the PCB, I like to cut the PCB a few millimetres larger so
that it makes placing the pattern less critical. Clean with the scouring pad
and cream cleaner and dry. I find that if I scour the PCB in two directions
I get a light crosshatch effect on the surface that helps the toner stick.

Print your PCB onto a sheet of tracing paper. I got a "book" of "Utoplex"
60-65gsm from Officeworks. Remember that you may need to "Mirror" the print
so that the toner goes against the copper. I used a HP Laserjet 4L and set
the "print density" to medium (3). I tried with a higher density, but the
toner bleeds to easily.

Trim the tracing paper so it is about 1cm bigger then the pattern, careful
not to touch the area where the toner is and make sure the toner surface is
"up" so that it doesn't get damaged on the cutting board.

Set you Clothes Iron to "Silk" (lower temperature). Once the iron is up to
temp, preheat the PCB by placing it copper side up on the wooden block and
cover with the sheet of normal paper. Apply the iron and move it around for
about 10 seconds. Try to workout at this stage how you will hold the iron
and move it to cover the entire PCB evenly.

Take the paper off the PCB and position the tracing paper, toner side down
over the PCB. Carefully "roll" the paper on then quickly cover with the
normal paper and apply the iron. Note that the toner may "grab" when you do
this. I gently curve the tracing paper in the middle, allow it to touch and
"roll" the ends down to avoid creases.

With a light pressure (basically the weight of the iron) move the iron
around the PCB ensuring it is flat. It should only take 5 seconds or so for
the toner to stick. Check the tracing paper often. You have to stop ironing
it just before the toner starts to "bleed". You may be able to get away with
it on a tracks with larger width and spacings..

The tracing paper has a tendency to curl up when you iron it, the sheet of
plain paper will help prevent this, but you have to be careful when you
check it. When your happy, cover the tracing paper again with the plain
paper and place a book or magazine on it to hold it down while it cools a
little so you can pick it up.

Once it has cooled, be VERY careful not to lift the tracing paper, this will
damage the track pattern. Hold the PCB so that your fingers are lightly
holding down the tracing paper and place it in the hot water and detergent.
Once the paper starts to wet, you can let go and leave it sit in the water
for a few minutes.

Patience is important! Carefully and gently rub the paper with the tooth
brush or your thumb, rinsing often to wear it away. Be careful not to drag
large chunks off as this can pull up the pattern. It isn't too difficult,
take it very slowly. Once the majority of the paper is off, you can scrub it
surprisingly hard without much damage, but do it lightly just in case :)

It should clean up nicely, there shouldn't be any visible fibres at the
edges of tracks, there may be some imbedded in the middle of larger areas,
but that's fine.

Dry the PCB and if necessary you can do some touch-up with a permanent
marker ("Sharpie" brand seems to work well) and etch. You can remove the
toner with the scouring pad and cream cleanser.

You should carefully examine the tracks with a magnifying glass because
there can be hairline cracks in them which you will have to fix with solder.

Hope this helps people.
Ash

---
Ashley Roll
Digital Nemesis Pty Ltd
www.digitalnemesis.com
Mobile: +61 (0)417 705 718

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