PC Board Construction -
1. The 'Low Tech' Method
I have used this method for single or double sided boards for years with very few problems but it does require a fairly steady hand and some practice -
You will need graph paper, 2H drawing pencil, soft pencil rubber, two pots of different coloured cellulose paint, cellulose thinners, modellers small and medium size paint brushes, modellers scalpel, rubber gloves, electical modellers drill and stand, assorted small high speed drills to match the component hole sizes, single or double sided printed circuit board as required, hacksaw, flat file, Ferric Chloride etching solution and some cleaning tissue. Typical PCB material is usually 1/16 inch thick G10 (fibreglass) material with 1 ounce copper on one or both sides.
Draw the electronic circuit for your board making sure that it is tidy, signal flows are clear, inputs and outputs are not next to each other and with the minimum of cross-
Using a piece of graph paper (I prefer 0.1 inch squared paper but metric is fine), roughly lay out the components of your circuit as viewed from the solder (non component) side and decide on an initial mechanical arrangement. At this stage you may need to consider any physical limitations that will affect the size of layout of your board -
Here is the trick -
Now draw in the mounting pads and centres of all drilled holes at a 1:1 scale -
When you are satisfied, outline the edges of the layout, dot the drilling points with an ink pen and then photocopy the layout without too much contrast -
Lay the photocopy onto the piece of PCB and line up the edges by looking through the paper towards a good light source. When in line, fold and fix the paper in place with Cellotape or similar. Now drill through all holes with a pilot drill -
Remove and discard the paper, copper/PCB swarf and gently rub down the copper surface(s) with fine emery cloth or a flexible rubbing down block -
Now paint each pad using a small model paintbrush and one of your colours and then paint in the interconnecting, non 0v track in the same colour. If you make a mistake, leave it to dry, scrape away the incorrect paint with a small model makers scalpel and make the necessary corrections. Now paint in all of the 0v track using your other colour paint and leave to dry. If you are making a double sided board paint in the track on the component side -
Examine the finished article to make sure that all tracks are correct and do not have any hairline cracks or overlaps onto other tracks -
When you are satisfied, etch the PCB using a warm ferric chloride solution (about 20 minutes at 40 degrees C solution temperature), rinse and examine to check that no unwanted copper remains -
Practice each of the steps until you are proficient. You should note that Fibreglass is very abrasive and wears out drills and files quite quickly.
Keep your layout, circuit and design notes for the future.
2. I have recently been experimenting with the One4All acrylic pens instead of cellulose paint with some success. The non-
These pens are easier to use than small paint brushes and can produce thinner tracks but the acrylic material when dry is not as rugged as the cellulose paint so more care is required.
If in doubt, conduct an experiment on a piece of scrap PC board -