How to make Printed Circuit Boards (PCBs)

There are several methods of assembling electronic circuits - point-to-point soldering for simple projects, breadboard, perfboard, and so on. But they all have disadvantages: they're often not very stable (mechanically speaking), look very ugly and are not suitable for complex projects like digital electronics. So that's why all industrial products are assembled on boards with holes for the components and traces to provide the connections (the recent SMD boards don't even have holes).

 

Here I'll show you how to make them by yourself - it's not that difficult, and you won't regret it, believe me. Besides, once you've got some experience, they save a lot of time and hassle.

First you buy a board of the size you need. If it's not the proper size, you can cut it: just carve it several times with a cutter, then break it over an edge of a table. The board you buy is copper-clad on one side; usually 35 µm thick. Now the question is how to make traces into the copper. You could try with a scalpel, but that's very difficult.

It's easier to do it chemically: you use a suitable etchant which etches the copper away where you don't want it. But before I tell you about etchants: somehow the etchant must know where to eat the copper away and where not. And that's the most difficult part of the whole story.

You can buy special pens with etch-resistant ink and draw the traces directly onto the copper. However that's almost impossible for boards with ICs. It would be better if you could design the pattern with a special program on the PC and then transfer it to the board. That's the way it's done. The pattern is then printed on transparencies (those for overhead projector use will do).

You can buy special copper-clad boards that carry a photo-positive coat on the copper. You first expose this to UV light (of course with the transparency pattern on it). Then when you put it in the developer that's made for it, the coat will be dissolved where the light got on the board. What remains is etch-resistant.

As I said, you need a UV light source to expose the board - UV-A is required, UV-C as emitted by germicidal lamps for erasing EPROMs will take hours to expose. I use a solarium, and it takes only 2 minutes to expose. A bright (> 500 W) light bulb will do, too, but it will take up to half an hour or even more. There are also special UV light bulbs. The sun will work, too. First you remove the protective black foil on the board (do that in a dim place), put the transparency on the board, fix everything with a heavy glass plate (although not too thick; plexiglass is best because it lets UV through much better) and expose it. Then put the board into the developer (of course make that first). A very dilute solution of sodium hydroxide in water will work, but the special developers for this purpose are better.

After about 3 minutes, the image should be visible on the board, and on the exposed parts you should see the blank copper. If everything's OK, you can etch the board.

There are two common etchants: ferric chloride (FeCl3) or sodium persulfate (also ammonium persulfate). Ferric chloride is cheaper, doesn't need heating and is easier to dispose of. However it makes stains that are almost impossible to remove. The other two are more expensive, work best at 40° C and are not so dirty and produce slightly sharper traces. I always use ferric chloride.

Ferric chloride is not aggressive to skin, as long as you don't put it in your eyes. Without heating, ferric chloride takes about 30 minutes to dissolve all the copper. If you move the board on the etchant, it's faster.

Now if everything's hopefully perfect, it's time to remove the photo-resist. Do that with acetone.

Now the holes can be drilled. Tape it on a wooden board, fix it in place with sticky tape and drill.

After all, a bit of soldering lacquer helps when soldering later, but it's not absolutely necessary.

© 1999 by Manuel Kasper. All rights reserved.

 

  Electronics-lab.com (C) 2002-2008
Any logo, trademark and project represented here are property of their respective owner - [Privacy Policy]