This demonstration takes the opto-sensor circuit
used elsewhere on old-sock pages and creates a small circuit-board.
The method is derived from information found
on the WWW and modified for local conditions - items either
being unavailable, or out-of-stock, or certain points just not working
as described.
The method has been used here a dozen times and
works quite well. Better methods do exist on the WWW. Try searching using
'laser pcb' or 'press-n-peel' as key-terms.
1. Design circuit with fleXYcad. Print PCB layout to laser-printer from the Newton. 170-g/m2 matte inkjet paper was OK. |
2. Keep the PCB board from moving. Ensure the copper is flat. Iron the image onto clean copper until it sticks. *Don't* peel it back! |
3. Soak paper in water for 20 minutes *before* peeling it off. Image transfer can be perfect. |
4. Etch the PCB in Ferric Chloride. This board took 20 minutes. Clean off laser-toner with acetone. |
5. Drill out holes with 0.8mm bit. De-burr holes with an oversize bit. |
6. Insert components ... |
7. Solder components ... |
8. My first PCB !! |
Observe all Health and Safety requirements when
using dangerous chemicals.
Use rubber gloves & glasses; keep acetone
away from flame; don't breathe or touch Ferric Chloride.
Further points, to match the pictures:
1.
Different printer-paper may work. My heavy-weight
matte inkjet paper just happened to be on the shelf. It is branded Kodak
Premium Matte Greeting Cards. (Stock No: CAT 194 4495). It is probably
the same as Kodak Picture Paper which is also 170-g/m2. Others use
transparency film. The laser-printer needs to have an 8-pin LocalTalk port,
with PostScript. Good-quality toner might make a difference.
2.
Check the copper board for flatness, and bend
it flat with light flexing. Acetone cleaner (Nail Polish Remover) is flammable
and seems to be sold in plastic bottles designed to topple over. Clean
the copper board thoroughly. A plastic pan-scourer helps, but it does disintegrate
eventually. If the copper board has a light-sensitive layer then the acetone
will dissolve this easily - it isn't needed here.
The paper is prevented from moving by taping
it along two edges. With a hot 'Linen' setting, apply firm static pressure
for 30 seconds, then move the iron around. The paper and ink will stick
to the copper. In my jig for holding the copper board the 4 screws are
too close to the PCB and stop the iron from making a good pass.
3.
*Don't* peel back the paper. Trim off excess
paper and drop the hot board into a bowl of water. Have a rest. After 20
minutes the paper is practically dissolved, leaving the laser-toner stuck
to the copper. Remaining paper rubs off easily, but a very thin annoying
layer does stick to the toner. Spend time removing this, or it will create
jagged edges on the final layout.
4.
Etching with Ferric Chloride is messy and dangerous
and causes stains. Use gloves. I didn't check the water temperature, but
it seemed warm enough. It took 15 minutes to see any change, then the copper
dissolved quickly. The board was suspended on cotton thread. When ready,
the board was washed in water, and the laser-toner removed with more acetone.
An old toothbrush was useful. After making a dozen boards, the etching
takes an hour and the solution has changed colour.
5.
For drilling I used a Minicraft MB0160 at 30,000
revs/minute. Rather too fast, but there was nothing else. It needed a steady
hand. Four of the solder-pads were too close together so I widened them
using the drill.
6, 7.
FleXYcad's D9 component shape will allow
a choice of serial connector. The two larger mounting holes will require
a 2.5 mm drill bit. During the ironing stage, I must have missed pressing-and-heating
the title text area. Some letters are missing. 30 seconds total ironing
time was an experiment and probably should have been longer.
8.
The DC power connector could be positioned better.
Date: 29 November 2007. Making a Small PCB Text and Images: www.old-sock.co.uk/pcb.htm