Circuit Board Construction

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Etching Circuit Boards



This is a quick primer on how to make printed circuit boards. If you have had no experience in making electronic boards before then you will find the following information simple and useful for a range of projects.

The first thing you will need is blank circuit board. You can get this from any Jaycar or Dick Smith store. There are basically two types; single sided and double sided.
Next you will need some sort of chemical to etch the board. Various acids can be used to etch the board, but these are often dangerous or at least messy. By far the best etchant to use is called Ammonium Persulphate, which you will also find at Jaycar or DSE. It is a relatively harmless chemical to use and with a little bit of practise you can etch boards as quick as the more dangerous acids.
Ferric Chloride is slightly better than Ammonium Persulphate, but it will stain just about anything it touches and it will slowly burn your skin if you get any on you. The powered form can also explode if you don't follow the instructions carefully.
You can also use Hydrochloric acid. This is a dangerous chemical so you should handle it with care. Hydrochloric acid will NOT react with copper, but it will react with copper oxide. So you need to mix in an oxidiser into the acid to make it work. Hydrogen Peroxide is just such an oxidiser, the stuff from your local chemist is perfect. This mixture works well but you should avoid using it because the bi-product of the reaction is a small amount of chlorine gas (green) which is very toxic and will burn your lungs and eyes if it comes in contact with them. Nitric Acid is very good at eating copper, but it is a very dangerous chemical. Many times have I printed up a circuit board, put it in nitric acid just to find it was a fraction too strong and the whole board disappeared in a cloud of brown toxic smoke. If it gets on your skin it will burn it in an instant and turn it permanently yellow. The acid also reaks poisonous vapours, and if this isn't enough to discourage you, if the acid comes in contact with the wrong materials at the wrong time, the very large explosion that results will scatter pieces of you and your circuit board across the suburb.

Enough of the chemistry and on with process at hand

Ok, now that you have your circuit board you will need to etch it. This involves using the Ammonium Persulphate as an acid to eat away the parts of the board that you do not want to use. It's a lot like developing film, only your working with copper. In order to keep the parts of the board that we want, we need to protect it from the acid. There are a number of ways of doing this. By far the simplest is using a thing called a "Dalo Pen". You draw your pattern onto the board with the pen, and the dry ink protects the copper from the acid while unmarked areas are eaten away. I have found that a permanent marker also works, though it sometimes dissolves in the acid too, and this can ruin your final result. Dalo pens are also sold at Jaycar and DSE.
You can also buy some rub on or stick on transfers. Like a lettera-set. Just take a pencil and rub them onto the location you require. This gives your project a more professional look when it is finished, though you do have to be careful when you etch the board as sometimes the transfers peel off and you get open circuits in your tracks. You can correct this with a dalo pen if the board is still dry and the acid hasn't already eaten the copper, or you can buy some silver paint Jaycar and touch up the board if the damage has already been done. In minor cases you may just care to add a little extra solder to the tracks.
You may also use things like strips of electrical tape or clear plastic contact etc. These work very well for making straight tracks or covering large areas. I've even used a whole piece of it on a board and cut pieces out and peeled them away where I want the copper to be removed. This is made even easier if you draw or print your design onto the contact before you start slicing it off. You can use combinations of these. I use contact for the easy parts of the design and a dalo pen or oil paint for the bends. Just about anything works.

Now your board is ready to be etched.
Prepare your Ammonium Persulphate as per the instructions on the bottle label. It's rather safe stuff so not much can go wrong. Using hot water will speed things up. I don't have any fancy bubble etching tanks etc. They will make things work quicker too, but for us common people, standing there for 30 minutes or so soaking the board while gently rocking the acid bath will do fine. If you keep the acid flowing over the board it will help it etch quicker. The bigger the board, the longer it will take to etch.
After a short time you should start to notice parts of the exposed copper on the board start to fade and then dissolve away until you can see no more copper, just your artwork and the fibreglass board.
Remove the board from the acid and wash it clean with fresh cold water and remove the resist / artwork. If you used electrical tape or contact, peel it off. If you used a dalo pen or transfers, methylated spirits, steel wool or scouring pads will remove the resist very quickly.
Now you will see nice shiney copper tracks where you artwork was, it's now ready for use.
The blue stuff left in the etching tank is copper sulphate. You could simply wash it down the sink without fear of it eating away your plumbing. Throwing it on your garden will kill the plants. I just save mine and let it evaporate in the sun and make big copper sulphate crystals. The white crystals I sometimes recycle and re-use.

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