There are quite a variety of ways of building an electronic circuit. A good source of information can be found in publications such as the ARRL Handbook.This page will concentrate on the most common printed circuit board (pcb) method. It will be assumed that you already have the desired artwork available from a magazine or designed on a computer so that it can be printed actual size. Actual size is important for accurate placement or registration.
PCB - A printed circuit board consists of a non-conductive base with copper conductive tracks on one (single-sided) or both (double-sided) sides providing connections between components. This leads to a neat, repeatable layout and general ease of construction. Once designed, a PC board is easily duplicated.
To make a PC board, you need to have a circuit pattern to be applied to the pcb. A resist material (the artwork) is applied to a copper-clad bare PC board, which is then immersed in an etching bath to remove unwanted areas of copper. The remaining conductive copper tracks and pads are what electrically connect the components. The biggest stumbling block or hurdle for amateur constructors is the method of placing the desired artwork on the bare pcb stock ready for etching.
Resist - Resist is a material that is applied to a pcb to prevent the etchant from eating away the copper from areas of the board that are required for conductors. The resist should be an accurate reproduction of the artwork or the finished board. The pcb stock must be clean before any resist is applied and it can be applied by hand drawing the image on the blank board. This can be quite painstaking and does not readily lend itself to easy repeatability for complex boards. There is an easier way - or two.
1. UV Exposure - This method requires that the artwork be printed on clear film such as an overhead transparency. The artwork is reusable. The method also requires the use of photo-sensitised board blank and chemical developer. Such board stock is available under a number of brands. Bear in mind that brands will require either a negative or a positive image. My choice now is the Kinsten brand which requires a positive image and an Internet search will soon find a source.
Having ascertained whether you need a negative or a positive image, print the image onto the film. I have not used an inkjet printer, only a laser. I would suggest that you print the image in reverse so that the printed side can be placed against the board. Once the image is printed and proved to be accurately sized, follow the board manufacturer's instructions for board exposure and development. Etching should be virtually the same for all boards at this point.
2. Heat Transfer - This method requires that the artwork be printed on clay-based, glossy paper and a means of heat transfer to be described. The artwork with this method is not reusable and must be reprinted each time. A degree of experimentation is required here. Influencing factors will include the amount of toner deposited on the print, the speed at which the laminator passes the board, the temperature of the laminator and its ability to heat the board, the paper used, etc. Once perfected, this method is cheaper and quicker than the clear film process. You don't need photo-sensitised board, developer or a source of UV light for exposure. The results are identical to the previous method.
Glossy brochures are usually printed on clay-based paper. It doesn't matter that the paper already has print on it. The image at the left shows a number of artwork prints over the top of a colour brochure. These were actually uses in a board making demonstration and produced perfect results. Photocopy the required artwork
in reverse on to the paper with the copier set on high contrast. Check for clarity and contrast. Once this checks out OK, we need to be able to fuse the toner from the print onto the blank board which must be very clean.
We now need a means of heat transfer.You can use an electric iron but this is relatively imprecise due to heat variation, period of application and applied pressure. There is another, more reliable, method. The following method was demonstrated at the PIC-A-STAR lecture held in the clubrooms on June 9th, 2007.
This image shows the essential parts of a laminator - including the power supply mounted in a plastic box. The case has been removed to make it more accessible and usable. There could potentially be some exposed wiring that must be protected. Laminators can be purchased quite cheaply these days and represent a good investment for circuit board production.
Make sure the laminator is fully warmed up and place the artwork face down on the cleaned pcb blank and feed it into the laminator. The only thing that will be ruined if you're careless is the artwork print so don't despair if it doesn't work. You may need to pass the board through a number of times to ensure proper fusing. Laminators are designed for melting plastic, not toner. Be careful handling the boards as they can be quite hot. Once you think the process has worked, it's time to prepare the board for etching.
You'll need a small dish for this process. Place the board, with the paper attached, in the dish with some warm water and leave it soak. After a few minutes you will find that the paper can be easily freed from the board and, hopefully, the toner will be left on the board. You now have a board that can be etched in your favourite manner.
Etching - There are two common forms of etchant and appropriate safety handling procedures should be used with both as they are corrosive. Ferric Chloride is a rather nasty smelling etchant but works well. If you spill or splash it, it can be difficult to remove. Ammonium Persulphate is a much cleaner, friendlier etchant and is what I normally use. Follow the manufacturers' instructions in each case - and be careful.
The etchants are generally warmed for use. A fancy etching tank is not essential. I have a cheap one and have used it once. One would imagine that a proper tank has got to be an advantage but not necessarily so. Try an old frying pan (maybe even buy a new one), place about two centimetres of water in it and turn the thermostat to low and warm the water up. Place a plastic tray large enough to hold the board in the pan and pour in about a centimetre of etchant. Place the board flat in the bottom of the tray with the copper side up and place the tray in the pan. Agitate the tray a little and there you have your own thermostically controlled etching equipment plant.
The advantage of the frying pan method? You don't use anywhere near as much etchant, is easier to manage and you don't need an additional heater to keep the etchant warm.
Now, if you don't have either, a suitable, non-metallic, tray is required. The board is placed face up in the tray and covered with sufficient etchant. The tray is agitated slightly to keep the etchant disturbed. You may only notice a change in the copper colour initially but, after some minutes, you will see that copper will have disappeared in some places. The etching is finished when all the unwanted copper has disappeared, leaving just the toner with copper underneath it.
Carefully remove the board, rinse in water, and use steel wool or something similar to remove the toner - exposing the required tracks. Some purists like to spray the new board with circuit board lacquer to prevent tarnishing. It's up to you.
Now, if you printed the artwork image the right way round, you now have your new circuit board ready for drilling and fitting the components. If you don't, you should know what you have to fix up.
Trials and Tribulations - Having seen the above heat transfer image making process in action, with gauranteed results, I went and purchased a laminator from Office Works, printed off a couple of sheets with a Brother 7420 laser Multi-function centre and eagerly commenced making a board. The first attempt failed and required around 10 passes through the laminator before the toner stuck to the board to any real degree.
The second attempt was from a copied print on the same machine at full contrast. Once again, failure. The toner was not taking to the board. Large patches were not too bad but, overall, nowhere good enough for serious board making.
The next attempt was with the laser printed image photopied on a Ricoh-engined photocopier. The image looked more like the one that I saw demonstrated. Once again, failure. The toner had not stuck to the board at all after four passes through the laminator. I am beginning to think that the laminator is either not hot enough or the passes are simply too quick. A hot iron may be better.
The next attempt was with the Multi-function centre copy on laser film and an electric iron. I applied that much heat that I thought the board might burn. It didn't - neither did the toner properly adhere to the board.
An inspection of the laminator showed a programmable timer (for warm up) and a synchronous, 240V drive motor. I had thought it must have been a stepper motor and I might be able to slow the pass down. No go. Maybe I could change the heat switch for something hotter.
Maybe I didn't find the right toner for the board stock I had. Maybe the laminator isn't hot enough. Maybe the paper is wrong. Maybe ...
In disgust, I parked the whole thing. I will use the UV exposure method that I know works. If you get the laminator method sorted, please let me know. I've given up and I have boards to make.
Created 2007 by
Kevin Crockett. Comments and suggestions may be e-mailed to
