Making printed circuit boards using a computer

A detailed story about the popular "laser-ironing" technology for manufacturing printed circuit boards, its features and nuances.

Printed circuit boards have been used in radio engineering for a very long time. In the production environment, there are various equipment that allows the production of boards on a mass scale. Such boards were previously produced by offset printing methods, which is why they were called "printed" ones.

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At home or in factory electrical laboratories that repair electrical equipment, such boards had to be painted by hand with various varnishes. A wide variety of drawing tools were used, from a simply sharpened match to needles from a syringe and glass ruling pens.

The productivity of such work was low, and the quality left much to be desired. If it was required to make several identical boards, then the second one was drawn without much inspiration, and the following ones did not add optimism.

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Now computer technologies have penetrated into all spheres of human activity, including amateur radio. You no longer have to draw printed circuit boards by hand, only very simple ones, which can even be cut with a knife. But first things first.

First of all, the printed circuit board must be designed according to the circuit diagram. This work is done on a computer using special programs. The simplest and most accessible programs are Sprint-Layout. They are free and can be downloaded online. Their interface is intuitive and easy to use.

Circuit DiagramSource

In versions of programs, starting with the third, it is possible to insert a picture and simply outline it with lines of printed tracks. This feature allows the production of boards published on magazine pages. A picture from a magazine, if you just print it, usually does not give the required quality.

After the PCB is designed and tested, it should be transferred to the blank of the future PCB. And it is at this stage that care and accuracy should be shown.

First of all, you should tell how to print and on what. These are the two main questions on which the final result depends.

The board drawing is printed on a laser printer when all economy modes are turned off, which allows you to apply the thickest possible layer of toner to the paper. This helps to improve the transfer of toner to the PCB blank. Now this technology is called "laser-ironing".

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Its general meaning is quite simple: the drawing is placed on a workpiece (foil-clad fiberglass), of course, with a pattern to the foil, and then ironed with an ordinary iron. The toner is melted and transferred to the foil, leaving a board pattern on it. After that, the paper is soaked in water, and the board is etched as usual in a solution of ferric chloride.

First of all, what to print on? When this technology was known only by rumor, it was believed that the drawing should be printed on paper of the lowest quality. This paper, thin and brown, was intended for typewriters. It was simply impossible to soak this paper, so it was suggested first to dissolve it, it seems, with hydrochloric acid. The paper did not dissolve well, and with it part of the drawing.

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Then most of the researchers, apparently, printed such pictures on state printers, so there were proposals to make printouts even on household aluminum foil, some kind of films and I don't remember on what yet.

In fact, everything turned out to be much simpler: coated paper from glossy magazines is best suited. At the same time, pictures and photos on the pages do not affect the quality. The only thing that should be empirically selected the magazine that gives the best quality. Some magazines are coated to the point that they will smooth to the foil even without toner.

It is better to indicate the boundaries of the board on the printout using "crosses" (this option is present in the program), rather than in the frame. The frame can pull on the paper during the smoothing process and distort the pattern.

It happens that a drawing is not smoothed out well the first time, so several copies of it must be printed on one sheet of paper. The number of figures per sheet is set in the program.

The blank for the board should not be cut exactly to size, but so that a margin of 6 ... 10 mm remains at the edges. It is cut off after the board is ready. This is necessary in order for the outer paths of the drawing to turn out well. It is not clear why, it is these paths that are smoothed out badly. Therefore, the sharp edges of the foil should be dulled by removing small chamfers.

Before smoothing the drawing with an iron, the workpiece should be cleaned with sandpaper so that the surface of the foil acquires a matte shade. After that, degrease the surface with acetone or gasoline.

Then put the paper with the pattern up on a flat surface, and already on it with the foil down, orienting the board blank along the crosses. To fix the blank, fold the edges of the paper inside the resulting bag. When ironing, put the bag, of course, with the paper side up.

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A regular iron for ironing linen should be warmed up to 200 degrees. The temperature can be monitored using a thermocouple avometer, or selected empirically.

Smoothing should be done first with the entire plane of the iron to warm up the board, and towards the end of the process, smooth the paper with the edge of the iron. To prevent the coated paper from sticking to the iron, at the beginning of ironing, you can put plain, clean paper under the iron. It is better to put a cardboard folder for papers or a magazine under the workpiece to be ironed. This will allow the board to bend slightly, which will eliminate the influence of unevenness, both the board itself and the desktop.

After ironing, the entire bag should be cooled by applying another iron, only cold, so that the pattern is better fixed on the board.

After these procedures, the smoothed paper should be soaked in warm water of 50 ... 60 degrees. When the paper is sufficiently wet, it should be carefully removed. Remove the remaining paper adhering to the board by rubbing it with your finger, like decals.

After a good quality impression is obtained, the workpiece should be etched as usual in ferric chloride solution. After etching, the pattern is removed with acetone or gasoline.

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Sprint-Layout lets you draw holes for parts in the pads. These holes should be made with a diameter of at least 0.7 ... 0.8 mm. Then the foil in them will etch to the textolite and you will not need to punch holes: the drill will center in these etched holes. The drilling precision is such that even microcircuits in 40 lead-out cases "sit" in their places without any bending of the legs.

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