Design Center
PCB FABRICATION:
One of the main constrains faced by the electronic students and hobbyists, who are really interested in prototyping their circuit designs, is in making their own PCBs. PCB manufactures are available in the electronic markets for surplus, but at high costs. Making their own PCBs is also tedious job as the circuit pattern transferring onto the copper clad board is a difficult task. This circuit pattern transferring process is the most costly among the procedures for PCB fabrication. This article shows a cheaper and easier solution for it!
After we design a circuit, we are supposed to fabricate it using a printed circuit board because a board offers a lot of advantages. For one, the solder connections are more stable, and for another, the project will get a professional touch. There are several ways to make boards including etching, direct plating and copper removal. For the hobbyist, etching is probably the easiest and most cost effective. Etching is the process of chemically removing the unwanted copper from a plated board. You must put a mask or resist on the portions of the copper that you want to remain after the etching. These portions that remain on the board are the traces that carry electrical current between devices.
One way to put a pattern on the board is the direct draw approach using a resist pen. This is the quickest way to get a circuit pattern on the board, but it is difficult to position the traces accurately, especially if you are using any IC packages in your design. Plus, since the ink doesn't apply uniformly, there is a risk that the traces will be etched away since the etchant can get to the copper through an extremely thin layer of resist.
Another approach is to use a photo sensitive resist. The advantage to this approach is accurate and neat traces, and once you make the photo negative, it can be used over and over to make additional boards. However, you need a photo lab to do this, and the entire process takes quite a lot of time.
THE EASY WAY OUT:
Now that laser printers are affordable to the common folk, creative people have developed methods of using them to produce the resist pattern. One method uses a specially coated paper and is sold through electronics outlets. The circuit pattern is printed onto this paper and the paper is ironed onto the copper clad board. The board and paper are placed into water, and after a while, the resist pattern lifts off the paper. But these papers are not easily available in the electronic markets of Chennai.
I have experimented with other types of paper in search of a replacement for this specially coated paper. In doing so, I have found another, fairly consistent paper that I now use to make all of my printed circuit boards. This paper is similar to what is used in magazines. It is a white, glossy paper that prints well and costs about 15 rupees per sheet. What makes the paper glossy is also what makes it work in this process. The reason the paper is glossy is because it is covered with clay. You can find this paper at office supply stores - just ask for '80 pound coated paper'. You can also experiment with 'master paper' or 'photo glossy paper', if the above mentioned paper is not available.
After the pattern is printed onto the paper (I use AutoCAD or ExpressPCB to draw the circuit, by the way), it is ironed onto the copper clad board using a hand iron set to maximum temperature with no steam. This process melts the toner and allows it to stick to the copper. Note that the copper board needs to be very clean in order to make the toner stick. The ironing process only takes a few minutes, and it helps to keep heavy pressure on the iron to keep the toner in contact with the board.
When the board is cool, it is placed into hot water. Little by little, the paper saturates with the water, and starts to disintegrate. With a little work, you can gently rub the paper off, and what's left is the toner resist, with a little of the clay also attached to the toner. It is the separation of the clay from the paper that allows the toner to remain on the board. In the picture, you can see the white clay that is still attached to the toner. At this point you can examine the board and fix any holes or cracks using a resist pen. Then the board is etched with Ferric Chloride or Ammonium Persulphate as usual.
This is just another approach to making PC boards that will find the easiest and most cost effective.
After we design a circuit, we are supposed to fabricate it using a printed circuit board because a board offers a lot of advantages. For one, the solder connections are more stable, and for another, the project will get a professional touch. There are several ways to make boards including etching, direct plating and copper removal. For the hobbyist, etching is probably the easiest and most cost effective. Etching is the process of chemically removing the unwanted copper from a plated board. You must put a mask or resist on the portions of the copper that you want to remain after the etching. These portions that remain on the board are the traces that carry electrical current between devices.
One way to put a pattern on the board is the direct draw approach using a resist pen. This is the quickest way to get a circuit pattern on the board, but it is difficult to position the traces accurately, especially if you are using any IC packages in your design. Plus, since the ink doesn't apply uniformly, there is a risk that the traces will be etched away since the etchant can get to the copper through an extremely thin layer of resist.
Another approach is to use a photo sensitive resist. The advantage to this approach is accurate and neat traces, and once you make the photo negative, it can be used over and over to make additional boards. However, you need a photo lab to do this, and the entire process takes quite a lot of time.
THE EASY WAY OUT:
Now that laser printers are affordable to the common folk, creative people have developed methods of using them to produce the resist pattern. One method uses a specially coated paper and is sold through electronics outlets. The circuit pattern is printed onto this paper and the paper is ironed onto the copper clad board. The board and paper are placed into water, and after a while, the resist pattern lifts off the paper. But these papers are not easily available in the electronic markets of Chennai.
I have experimented with other types of paper in search of a replacement for this specially coated paper. In doing so, I have found another, fairly consistent paper that I now use to make all of my printed circuit boards. This paper is similar to what is used in magazines. It is a white, glossy paper that prints well and costs about 15 rupees per sheet. What makes the paper glossy is also what makes it work in this process. The reason the paper is glossy is because it is covered with clay. You can find this paper at office supply stores - just ask for '80 pound coated paper'. You can also experiment with 'master paper' or 'photo glossy paper', if the above mentioned paper is not available.
After the pattern is printed onto the paper (I use AutoCAD or ExpressPCB to draw the circuit, by the way), it is ironed onto the copper clad board using a hand iron set to maximum temperature with no steam. This process melts the toner and allows it to stick to the copper. Note that the copper board needs to be very clean in order to make the toner stick. The ironing process only takes a few minutes, and it helps to keep heavy pressure on the iron to keep the toner in contact with the board.
When the board is cool, it is placed into hot water. Little by little, the paper saturates with the water, and starts to disintegrate. With a little work, you can gently rub the paper off, and what's left is the toner resist, with a little of the clay also attached to the toner. It is the separation of the clay from the paper that allows the toner to remain on the board. In the picture, you can see the white clay that is still attached to the toner. At this point you can examine the board and fix any holes or cracks using a resist pen. Then the board is etched with Ferric Chloride or Ammonium Persulphate as usual.
This is just another approach to making PC boards that will find the easiest and most cost effective.
Etch the PCB in the Iron Chloride (ferric chloride) solution. The Iron Chloride should have a temperature of about 40 degrees centigrade for optimal performance. Use about 1kg with 1 L water. If the temperature is too high you may spoil your PCB in one of two ways: strong under etching of the tracks. If the temperature is too low you may spoil your PCB because the traces become under etched as well. If you start with fresh etchant of about 45 degrees centigrade you will be able to etch a PCB in about half an hour without reheating. The end temperature of the solution is something like 30 degrees centigrade then, depending amongst others on room temperature, volume and rate of agitation. If the temperature becomes lower than about 25 degrees centigrade etching will become slow, and you will have to reheat the solution. During etching the tray should be agitated constantly, and the PCB should be turned every few minutes. Some people have used aquarium air-pumps to generate bubbles to agitate the solution. If you plan to use this I recommend you do not use a low development tray, but something which is at least 15 cms higher than the etchant level as small droplets may spoil your (stainless steel) kitchen sink. After etching is complete rinse and scrub the PCB in warm running water for at least two minutes to remove all traces of etchant.
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