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Here I will explain how to make your own PCB or Printed Circuit Board without the need of expensive equipment. Of course there are several ways to make PCBs at home, but I am just explaining the way I am making mine. First we have to transfer our design from the computer onto paper. To do this I use Calque paper. This paper is half transparent and absorbs ink, which is perfect for the job. The Calque paper is just inserted into the inkjet printer and with the PCB program (EAGLE in my case) we can print the circuit board onto the paper. Use the best printing settings on your printer as the black ink needs to be as black as possible to prevent the UV light to pass though the paper. Using special transparent sheets won't work, just trust me. I had no luck with them.
The next step is to transfer the pattern on the paper to a photo sensitive PCB. For this job we need an UV source. Like for example a sunbed. The paper is put on the "sunbed" and on top of that we put the photo sensitive PCB. How long the PCB need to be exposed to the light depends. But it is roughly between 30 seconds and 10 minutes. First make a few test strips to find out which timing is best.
Developing of the UV exposed PCB is easy. Make a bath of water (at room temperature) and caustic soda (lye). About 10 grams of caustic soda per liter of water is enough. Dump the PCB in the bath and stir it around. The exposed parts should start to disolve. Keep shaking the bath until you see a clear difference between the exposed and non-exposed parts. After developing wash the PCB with water to stop the developing process. A warning is in place here, caustic soda or sink cleaner is very reactive so use gloves, or if you don't, wash your hands with lots of water. My advice is not to touch the bath with your bare hands!
The next step is to remove the copper on the parts which are exposed with UV light and where the protective layer is gone in the developing process. Etching can be done with many different chemicals. Before etching would be done with iron trichloride (FeCl3) but this chemical is completely banned in the Netherlands. The alternative is to use ammonium persulfate (NH4)2S2O8. But don't be fooled, this substance is as bad as the other one and may cause an allergic skin reaction so definitely use glooves with this stuff. Etching works faster and better if you heat up the etching solution to around 45° Celsius. At that temperature the etching should take about 6 minutes. Although the etching can be done by putting the PCB into a bowl and shake it around, this will take a long time, it is better to buy a system with pump and heater which will work much faster and is a lot less messy.
After etching, we need to remove the remaining photosensitive layer. Soldering though this layer is very hard, so it is best to removed it before soldering. This can be done by putting the PCB on the "sunbed" again for a few more minutes and wash it in the bowl with the castic soda.
Drill the holes and solder all the parts onto the board and test its functionality. When soldering try to prevent the touching of the blank copper. Where the copper is touched it will corrode faster. We can spray the copper layer with plastic spray to protect the board from further oxidising.
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