Making the PCBs
The process of making your own printed circuit boards can be divided into the following steps:
- Design the PCB layout
- Print the PCB negative
- Transfer the negative to a light sensitive board
- Develop the board
- Etch the board with ferric chloride
- Clean up
Depending on your temperament, some of these stages are more enjoyable than the others.
To design the layout of the board it is best to use an object based drawing
package. There are of course specialist pcb design programs, but they tend to be
expensive and complicated to learn. For simple jobs any drawing or art
program than can place circles and lines onto a 0.1 inch grid will do
the job. I use a program called Draw on a computer system few people
have ever heard of and it does the job admirably well.
The next step is to transfer your hopefully faultless design onto a
clear acetate sheet. For this the simplest way is to use either a laser
printer or an ink-jet printer. Both methods have one serious flaw
though. When both types of printer print black areas, they leave hundreds
of tiny pinholes where the the ink or the toner have failed to cling onto the
surface. When this is transferred to the photosensitive board the
resultant pcb looks terrible and is often unusable.
I have found a simple solution to the problem. I use a Canon
IP4000 printer and I simply set the print-run to highest paper quality
and print the thing twice - one run on top of the previous run. The line-up is usually very good and the
printed tracks end up as black and solid as the Duke of Wellington's
In the past, when I was poorer, I used to print the design onto
ordinary paper which I then rubbed with olive oil. This made the paper
semi-transparent and with 10 to 20 minute exposure time, produced quite
good boards. In this day and age this method is of course only good for
Once you have your negative it is time to cut a suitable size of
pre-sensitized photosensitive board. These are
covered with a black protective plastic layer, which you should avoid
scratching or damaging in any way. I store my boards wrapped in black
plastic at the back of a dark cupboard. As they are sensitive to ultra
violet light - and daylight consists partly of this frequency - any
unnecessary exposure should be avoided. On the right is a group portrait
of the cut board and the negative.
After sawing the board make sure to remove any rough edges with a file.
This makes sure that contact between the two is as close as possible
during the exposure stage.
A word about pre-sensitized boards. Using a
good quality board is vital. I've had total disasters after using the
same years-old techniques on a different board and no matter what I did, with
certain type of boards I could never get a decent result.
next step is to transfer the track pattern to the board. I use an ultra
violet exposure unit. Peel the black protective film from the board and
place the negative onto the board. This is where mistakes can easily be
made. If you place the negative the wrong side around, you end up with a
mirror image of the intended. circuit which is only fit for the bin.
I always make sure that there is some writing on my pcbs, because that makes it easy to determine correct positioning.
With my set-up, a 2 minute exposure gives perfect results. With
other boards I had to use as much as 5 or 10 minutes. A few experiments
will quickly determine the correct timing.
Above can be seen the negative in contact with the board and on the right is the board after exposure.
Notice the very faint greenish lines. If you can see those, all is well.