SEVERAL WAYS TO MAKE PCBS
ALTERNATE HOME METHODS
WARNING! - When using firbeglass PCB, always wear a respirator while cutting, grinding, filing or sanding. It has been reported the small glass fibres floating in the air can cause the same problems as asbestos. For the cost of a respirator, its just not worth the risk.
PROPER METHOD
PCBs are made commercially by photolithography, that is, etching copper away from a board after parts have been protected by a photographically hardened pattern. The PCB is coated with a photographically sensitive emulsion. Both positive and negative emulsions are available but negative is by far the best. In this process, a photographic negative of the copper pattern is placed over this emulsion or the image is projected onto the board using a process camera. The whole thing is exposed to ultraviolet light and those pieces where copper is required (the light areas of the negative image) become hard(er). The emulsion coated PCB is developed in a weak alkaline solution. Those parts not exposed wash away while those exposed, remain. The exposed copper can then be etched away using Ferric Chloride, Ammonium persulphate or some other oxidiser string enough to etch copper. Once the unwanted copper is etched away, the remaining emulsion is dissolved away using a stronger alkaline solution. Calcium carbonate is often used as the first developer and it can also be used to clean the board after etching, just stronger and longer. It is quite a delicate process.
It is possible to purchase just the emulsion but cheaper, easier and more reliable to purchase already coated boards. Even printed circuit board manufacturers usually leave the coating process to companies expert in that field. If you really want to make a lot of circuit boards, this is the way to do it.
If you decide to go down this path, setup costs can be expensive. You need developing baths, a UV light and etcher isn't cheap. It is best also to use a process camera to expose the boards rather then directly laying the pattern over the board. It isn't particularly difficult to make such a camera and if you needs details, contact me. I have made my own before although I no longer use it.
ANOTHER METHOD FOR PROTOTYPES OR ONE OFS
CLEAN PC BOARD PROPERLY FIRST WITH VERY LIGHT SANDPAPER OR STEEL WOOL.
The important thing is to properly protect the copper you want to keep on the PCB. One method I use is bitumastic paint. Hardware stores sell roof sealing paint which is nothing more than bitumen. Read the label before buying and if it says bitumen or hydrocarbons, it is probably the stuff. It is always BLACK. If this is all you want to use it for, buy the smallest tin available. A few millilitres will last years. If allowed to dry properly on a surface it usually remains fairly soft and can be washed away with a petroleum product like kerosene. It works with normal gasoline as well but this is NOT recommended. A litre of kerosene is a lot safer, not all that expensive and will last a long time.
The paint first needs to be thinned. In this case, a few drops of gasoline is best. Kerosene is safer but takes a long time to dry. Once gasoline is mixed with the bitumen it becomes a little safer. Keep it away from naked flame and don't work near open flame or heaters. It needs to be thin enough to be easily applied with a normal, small paint brush. If you make a mistake, allow it to dry in the sun for a while and clean it up with a sharp knife.
If you want to have holes in the board, it is best to drill them first. The pad around the holes can be made by dipping a piece of wire into the thinned paint then poked through the hole until a sufficiently wide and quite neat circle appears around the hole. Practice makes perfect. If you don't get it right, it is easy to clean the board in kerosene and start again. If it takes a day to do the first one, it will probably only take a couple of hours the second time.
YET ANOTHER METHOD FOR ONE OFS - THE ONE I USED FOR THE SWR meter
CLEAN PC BOARD PROPERLY FIRST WITH VERY LIGHT SANDPAPER OR STEEL WOOL.
To make the SWR meter board, I simply marked the strip widths on the PCB then covered both sides with thin, transparent packing tape. I used a utility knife to score the tape then pealed off the strips I wanted etched away. Quite complicated boards can be made in this fashion although holes don't go too well with this method. An alternate method for making the pad for diode, capacitor and connection is shown at right. This method also facilitates a protected path for the wire through from the back of the board. Using this method means only cuts need to be made in one direction. This is a lot easier to do with the knife than running cross ways and possibly lifting the tape from the board. Once unstuck, this type of tape often doesn't restick properly. Remember to completely cover the back of the board with tape or paint as described above. |
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ETCHING
Use plastic containers only. Things need to be kept warm but not too hot so microwave safe dishes and the like are best. Remember, you will get them dirty and will not be able to use them for other things afterwards. A flat type tray is best for the actual etching.
The best chemical to etch the board is Ferric Chloride. This isn't cheap but 100g will last a long time. DON'T MIX IT TOO STRONG. It may work faster but this can be a disadvantage. After the board has been in the etch for a couple of minutes, lift it out with plastic tongs and check to make sure the copper you want removed has gone slightly pink, tarnished and no longer shiny. If there are shiny bits left, wash it off under a tap outside. (not the kitchen sink because it will stain it.) Ferric Chloride is a strong oxidiser and will kill plants it comes in contact with but, once diluted, is quite harmless to the environment. In some iron deficient areas, it might even be an advantage.
It is best to warm the etch solution before using. DON'T MAKE IT TOO HOT. This is best done by placing the etch in a plastic bowl and placing that in another larger container of hot or boiling water. Once the etching solution is warm, place the board in the tray and pour in the solution. The etching bath needs to be agitated. It also should take about 15 to 20 minutes to complete and this can be quite boring to do by hand. It can be left and checked every now and then without the agitation but it might take an hour. The etch can be agitated by blowing bubbles with a fish tank compressor but be careful not to splash any around.
Another method of agitating the etch bath is shown below. The lever needs to be long enough to rock the bath back and forth gently. I made the base and support out of old wood lying around the place and the lever from a piece of scrap steel. I made mine so that the lever comes apart so it can be stored more conveniently.
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I think that's pretty fair, don't you?
