Intro: Chemical and Drilling Free, Card PCBs
Most of us who are into electronics feel the need to produce a PCB for our new project. However, if like me you cant etch at home you're limited to using strip-board. The obvious alternative, getting a prototype PCB made is both expensive and fraught with difficulties. What if you pay your money but find that your layout oscillates or the component(s) you've been using go obsolete, or you've miscalculated the mechanical parts and you cant get it to fit into your case aghhhh!
These are all too common problems that I have encountered several times over the years. The only inexpensive part of the design process is the use of the computer. Recently I decided to buy some strip-board only to find it had been discontinued by my usual supplier. This set me thinking, if I can't roll my own boards or obtain strip-board then I'd have to find another hobby, or find a better way of producing boards. In a previous life I used to design electronic kits for a well known supplier. Unfortunately he didn't like spending money on PCBs . On one kit he insisted that he couldn't afford to sell it unless I did away with the PCB. So in a fit of pique I mounted the parts on a sheet of white card. I got my commission and my client was happy. Since the 1980's, computers have become widely available and PCB design programs are freely available on the net. Eagle springs to mind for example and there are some others. So the question is can you match using a nice cheap material like card and computer graphics to produce a board? The answer is yes!
Step 1: Wiring
Reverse side of early prototype showing point to point wiring. Please go to next step.
Step 2: Materials Required
Card , overlay and track prints, glue stick, scissors hammer, Paper Mache box (from 'Hobbycraft ) and or normal card, see text, push pin and large self tapping screw (not shown)
Step 3: Tools Required
Shown above the blue object is the head of a suitable push pin (rabbit headed ones should be avoided!) Also the hammer that I used. If it looks a little like overkill it is. I inherited it from my late father and I'm kind of attached to it.
Lastly but not least a piece of corrugated cardboard (not shown). It's function is to go underneath the board to allow easy hole making.
Step 4: Making a Board
Actually making a board is quite straightforward. First though a word about suitable card. Cardboard is an ubiquitous material but most of it is unsuitable for board manufacture. The thin corrugated card, used for most packing cases is definitely unsuitable. It folds easily and is incapable of standing rough handling. The best material that I have found comes from dismantling paper Mache boxes. These can be found at modeling shops for a reasonable price. This material is quite thick and is best suited to discrete devices like the transistor amp module shown. If you’re going to use IC's then normal card, as obtained in good stationers is suitable. The reason is simply that the IC pins get lost with the thicker Mache material.
Whichever material you are using the first task is to cut out your layout drawings with a pair of scissors. Glue the overlay to the card. Carefully trim the card to match the board edge. If you have printed out the trackside as a mirrored 1:1 image you can glue this to reverse side of your card. if you aligned these properly then you will have a guide to making the connections once the components have been added.
Next comes mounting the components. Put your card, overlay face up on a piece of scrap corrugated cardboard. Almost any old piece of box will fulfill this function. Take the large self tapping screw and use it like a centre punch to make an indent with the sharp end where you want your holes to be. Take care with IC pins as these are rather unforgiving of errors. Now using the push pin as a punch we can make the component mounting holes through the indents. The hammer is optional but pushing the pin through with your hand makes your thumb ache! If you've mounted the track layout correctly you should find your pinholes coincide with the component holes.
Using a pin has the extra benefit of a hole which reduces in diameter on the track side due to its point. As a result components are held firmly in place by the board when inserted. Drill a conventional hole and the parts become unsteady and easily wiggle about, even after soldering.
Insert the components one by one and solder their leads directly together to make the appropriate connections. Follow the track diagram. Connecting components together directly substantially cuts down on the number of connections required compared to a conventional PCB. Audio buffs like myself would say this is a distinct quality advantage. Its also necessary to use a little single core hookup wire to make longer connections. If you have board with a few top sided connections these can also be made with single core wire using the cable’s sleeving as insulation
What you should end up with is a functioning analog of the board that you designed. Any problems you find can be tackled at this stage before ordering a professionally made board. Of course for people like me, one design a week merchants this idea is a Godsend. Not only do I get a better functioning prototype but I also get to design a board for possible future use.