Making a small PCB

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:

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.

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.

*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.

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.

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.

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