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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Production of printed circuit boards. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies
Ingredients: Aluminum foil. Bought at a hardware store. There are two types of foil: thick soft and thin hard. Thick foil is probably only made here, but thin foil can be both ours and imported. In this need only thin. It has a mirrored side and a matte side. If you cut a 1 x 10 cm strip of such foil and try to hold it horizontally at one end, the strip will bend under its own weight. If the foil is thick, it will not bend under such conditions. In new packaging, thin foil usually has a serrated sheet edge, and the roll is sealed in a transparent film. Printer laser. I used an HP LJ 6L, but any will do. It is necessary to turn off all economic modes, force the printer to make the drawing darker, i.e. use more toner. It is desirable to pass paper through the printer so that it is less bent. From this point of view, the first HP LJ models are probably better, they seemed to be able to skip the paper with almost no bending. Electric iron. We put the thermostat on one point (synthetics), and begin to conduct experiments for fine adjustment. The iron must not melt the image made by the laser printer immediately. That is, the toner at this temperature should become viscous from a solid, but not liquid. Self-adhesive stickers for printing on them with a laser printer. In principle, you can replace them with something else, but I feel sorry for the printer (see below). Rubber sheet. As smooth as possible, preferably soft. I used porous rubber ~5 mm thick, with a smooth (not porous) top layer. Now we take a sheet of plain paper on which your printer prints. We put a slightly smaller piece of foil on it, matte side up, and carefully but evenly glue it on one short side with strips cut off from self-adhesive stickers. You can’t glue it with adhesive tape, because there is an oven in the printer, on which the adhesive tape will remain. The adhesive surface should not, of course, protrude beyond the edges of the paper. Now we fill this design into the printer, so that the glued edge of the foil comes first, and force the printer to drag this sheet (print a text file from one space:). I find it very difficult to ruin a printer with foil. Well, at least because there is a lot of chalk in the paper, on which it is designed, and it is quite hard. Well, you can fill the printer with foil in the same way as with paper. Therefore, the foil must be glued firmly, evenly, so that wrinkles do not form. Well, there should not be gaps along the edges. The sheet of foil that came out of the printer has obvious stripes from all the wheels with which the printer drags the paper. Remember where these stripes are located, these places will be non-working, it is not possible to make an accurate drawing on them. Maybe something rough will work, but I didn't need it. Now we need the actual drawing of the future board. In anything, practically. If it is a bitmap image, there will be problems with exact dimensions, pixels will be visible, etc., but in principle it is possible. With vector formats (*.wmf, for example), only scale is a hassle. I love AutoCAD most of all, it's easy to draw in it, the dimensions are always accurate, etc. Non-etched places (tracks) must be black, and do not forget that the pattern on the board will be mirrored in relation to the drawing. The board must be surrounded by a 2 mm wide track, which is bad, but protects the rest of the board. But along this path it is convenient to cut the board later. It may be easiest to draw the board on a large sheet of paper to scale and scan it. We fill a sheet of paper in the printer and display our drawing. We look that it was in the correct scale and in the right place on the sheet. Now we make the construction again from a sheet of paper, foil and sticky strip, with the difference that now we know where the drawing will be, and a small piece of foil is needed. There must be clean paper under the foil, otherwise the foil will stick to the paper with the reverse side. We print the drawing of the board and carefully examine it. Surely somewhere a marriage turned out due to uneven foil, a mote, etc., in which case it is better to print everything again, on a new piece of foil. If the whole design has left and stretched, you probably printed it not on the matte, but on the smooth side of the foil. Well, when everything turns out correctly and efficiently, carefully cut off the foil from the paper. Now we put a sheet of rubber on some heat-resistant surface, put the foil on it with the pattern up, and cover it with a piece of carefully cleaned foil fiberglass, with the foil down. We put a hot iron on top, and press it with something heavy. I used a 16 kg pack of ceramic tiles :) After 5 minutes, carefully remove the iron, but in its place we put something cold and heavy, but with a flat bottom surface. I put all the same pack of tiles. After 10 minutes, the structure will finally cool down, then the fiberglass with the foil adhering to it will be etched. Thin aluminum foil is etched in ferric chloride very quickly, leaving, however, some tatters that prevent copper from being etched normally. Therefore, the board must be washed with water, at the same time you can look at the quality of the resulting pattern, and, if necessary, retouch. If the tracks are lubricated, you inaccurately removed the iron or put a cold load on it. If the tracks are missing somewhere, the iron is too cold, or the gas released during etching of the aluminum has torn off the aluminum along with the paint. If the tracks become wide, the iron is too hot, or the board has been heated for too long. Well, after etching, you will have a one-sided board. How to synchronize the drawing on the second side, if it is needed, I do not know yet. It's easier to make two boards and glue them with reverse toons. The accuracy I got was 0.3 mm, although this is not accuracy, but is somehow called differently. Paths or spaces between them are already (emphasis on the first syllable) 0.3 mm are obtained with difficulty. For example, I made a small board on which SOICs with a different number of legs and chip elements stand, and the accuracy turned out to be quite sufficient. Method 2: Making with a laser printer True, there is an even simpler way to make boards with a pitch of 1.25 mm, paper with some kind of shiny coating is used as a carrier, it is sold in stores on a par with ordinary office paper, in such unsightly gray packs of 250 sheets. It's quite thin, one side looks like it's coated, and that side has a little sheen. Heat shrinkage, of course, is, but acceptable. So, I’m making scarves on OrCad PCB 4.42 (386+), you can immediately print from it on any HP LaserJet (there are options for a mirror, negative, etc.), but I print to a file (300DPI), and then I convert it to PCX with the HP2PCX lotion (it was in the PaintBrush 4.5 kit), and then I compose a sheet of several handkerchiefs with any graph. editor. Next - the usual printing process (I prefer the same PB4.5 - simple and one to one) on a shiny layer, one pass is enough if the board is double-sided, both sides should be on the same sheet to avoid strong misalignment due to different heat shrinkage paper. By the way, if you run it with a blank sheet on a laser before printing, then this glitch tends to zero. Then the fat-free board is placed copper up on a flat surface, with the imprint facing down on top. All this is pressed with an iron heated to the temperature of ironing crepe de chine (ask the ladies), you can first through a thin dry cotton cloth, and then you can gently smooth the paper until the toner completely sticks to the board, then it does not lag behind. Then the board cools down, it needs to be lowered into water heated to about 40 C, hold it there for a couple of minutes (it will be seen how the paper becomes limp), everything is easily peeled off, the rest is just rolled up with your finger. Because of the coating, there will be no lint on the board, as with ordinary paper, when the board dries, you can see that a whitish coating from the paper remains on top of the toner layer. If the board is double-sided, then first both pieces of paper of the sides are combined through the gap, two technological holes are pricked with a needle in any free opposite places, the first side of the board is “ironed” as usual, then drilled according to those. resp. with a thin drill, and on the other hand, through them, it is combined with a piece of paper on the other side, which can be fixed and then “smoothed” in the same way as the first side, there will be no harm to the opposite side. It is natural to soak the board when both sides are already smoothed. It was all etched both with FeCl3 and with hydroperite hodgepodge without any problems. All this was checked even on getinax, there are no delaminations of the tracks. After etching, I drill, OrCad set it up so that when printing, unpainted dots remain inside the pads, which after etching will be instead of punching. The result was a line 1 pixel wide at 300DPI, of course, it was a little wider, but the fact is there. I heard that people used fluoroplastic film instead of paper, but they did not say where to get it. Method 3: Making with a laser printer One more way. Iron. I use an ordinary old electric iron with a thermostat, I put the regulator on "flax". Laser printer or copier with one-component toner. HP LJ3P and LJ4L were tested with complete success, nothing happened with QMS and Mita copiers - the toner layer is very thin. When printing from Windows, I set the contrast to the maximum, while the toner layer is easily felt with a finger. I have not tried it with refilled cartridges, although according to my observations, they sometimes give an even thicker layer of toner. Fine sandpaper, refined gasoline or acetone for degreasing. Paper. I use sheets from Stereo&Video magazine. It's very thin coated paper. Printing paint does not interfere. I also tried it on ordinary calendered paper, but it turns out disgusting. Finnish chalk (~80 g/m) seems to be suitable, but it soaks too slowly. Process: A mirror-reversed board pattern is printed on thin chalk. Fiberglass is cut out to fit the board with margins of at least a centimeter on each side and cleaned with a sandpaper in a circular motion. The main task is to cover the entire surface of copper with micro-scratches so that it seems to be matte. After sanding, degrease thoroughly, and at the same time remove all dust, even from scratches. Fiberglass is placed with copper on the toner and the paper is wrapped and fixed with adhesive tape so that it does not move out when squashed. A light tightness is needed, but it is harmful to overtighten. Sometimes it is useful to wrap the resulting sandwich with another sheet of writing paper in order to reduce the likelihood that the paper with the toner will "ride" under the iron. The board is placed with the toner side up. A heated iron is placed on it with a plane for 20-30 seconds, so that the fiberglass is warmed up. Then, with the edge of an iron with moderate pressure (here you need to fill your hand experimentally), the entire surface is carefully passed several times. If you squeeze the toner, it spreads to the sides and the drawing will turn out to be smeared; if you don't squeeze it, it may not stick. It takes me about 10-10 minutes to make a 2x3 cm board. After it has cooled down, the board is placed in warm water for 20-30 minutes, after which the soaked paper is easily removed, leaving the toner on the board, and the chalk layer on the toner. If the paper has become sour and left tatters, they can be rolled up with a fingertip under water. Normally adhering toner is hard to scratch even with a fingernail, so if something falls off under your finger, it means that you haven’t warmed up or haven’t reached the point). The chalky layer on the surface of the toner plays the role of an additional mask that closes the pores in the toner, but if it is not soaked, it can also close the holes for subsequent drilling (I always do them, because it then eliminates punching). Dries without heating, the toner tends to fall off if the wet board is dried under a lamp or on a battery. Non-prints are signed with an indelible marker. It is useful to take all the available ones in advance, draw stripes with them on an unnecessary piece of fiberglass and throw them into ferric chloride. Approximately half of the markers I have encountered with a characteristic smell of something like toluene are good for this. In any case, they keep it for 5 minutes, if you don’t rub it. BTW: I get misprints on up to 10 out of 60 boards). If the chalk layer covered the holes somewhere (on a dry board, this can be seen perfectly) - you can carefully remove it from them with a needle. Pickled in a heated solution of ferric chloride. The solution should be sufficiently concentrated, I pour one volumetric part of the crystals by eye with two parts of hot (70-50 degrees) boiled water and filter after complete dissolution ... I have never done a temperature above 40 degrees, already at 50-0.5 it takes only a few minutes, and with a hotter solution, the toner may float. Rubbing the board with a cotton swab is undesirable, it is better to shake it, but you need to make sure that there are no air bubbles left on the surface ... After etching, the toner is removed with something (I used a nail polish remover or Flux-Off aerosol). After that, it is drilled, cut, and so on, as usual. Checked, working. If the ferric chloride is not set, then it is practically never etched. Tracks already 0.8 mm may not work out, I usually do around XNUMX mm. I just didn’t try to make double-sided boards - it wasn’t very necessary, although I don’t exclude that with a certain accuracy and careful alignment of the sheets to the light before laying the textolite between them, it will be possible to make them too ... The only thing - I can’t imagine how to fix it in this case (maybe narrow strips of double-sided tape on the margins). We draw with a plotter rapidograph 0.3 mm at a speed of approximately 5-7 cm/sec. As an ink, I tried everything (zapon, bitumen, nitro enamel), settled on saturated alcohol rosin. The plotter's drawing unit got rid of the pressure spring, but made it heavier - otherwise the previously drawn tracks are scratched. Before drawing, I degrease the board first with acetone, and then with alcohol. Do not ask why - but it affects the result. And no skins. After drawing, I let it dry for an hour or, if patience is not enough, I help with an industrial hairdryer. I etch in a vertical cell 3x40x40 cm with a hot (~50 degrees) solution of ferric chloride. A plastic tube with several small holes was placed along the bottom of the cuvette. I supply air to it for mixing. Etching time 5-7 minutes. In general, it has been observed that the thinner the foil on the board, and the more concentrated the solution, the better the result. Ie less undercut. The best results are given by the use of imported fiberglass. The resolution is better than 0.012 inches. Printed circuit boards with photoresist There are such cans of the German company CRAMOLIN with the inscription POZITIV. This is the photoresist. The process is insanely simple - we take a signet, water it from a can - dry it for 15-20 minutes ... then you take the signet itself (you can immediately print it from PCAD), put the film on the dried layer of this resist - and under a kilowatt soffit (a lamp for photographers) for 30-35 minutes. Then you remove the film (a kind of photo negative) and a signet into a solution of caustic potassium (fortunately, it is sold where the spray itself is) - what is lit up is washed off and what remains is what remains. In short, the accuracy and line width are no worse than with factory printing. Method 1: Drawing circuit boards In general, it is more convenient to draw not with a syringe. We take a soft plastic bottle, for example, from under the glue, we close a fairly rigid tube with a diameter of 3-4 mm and a length of 15-20 cm into the lid (I used a plastic tube + a piece of the rod from a fountain pen), we put a needle on its end (reliably :) from a syringe. We first cut the needle at a right angle. With one hand we press on the bottle, with the other we draw. When the bottle is released, the paint is drawn into the needle - there are no drops / blots. Paint - EP52 enamel or similar, diluted as needed. It gives a very dense and even trace, and is easily washed off (does not dissolve, namely, it peels off with a film) after etching with alcohol / acetone, solvent /. After work, the needle is closed with steel wire until the next time, it does not dry out for a long time. Method 2: Drawing circuit boards 1. Reisfeder from a thin (intramuscular) needle from a syringe (slightly shorten and sand the tip) and a well-washed rod from a ballpoint pen (without a writing unit, only a tube). The tube is "thrusted" into the place of the needle, with which it is put on the syringe. Unlike glass, it does not crumble or scratch the board. 2. Another similar option is a disposable syringe with a needle without a plunger. The advantage is a large reservoir, fill it once and draw as much as you like. I got tired of drawing - I stuck the piston and squeezed out the remnants of the varnish back into the vial. Again, it is easy to flush the needle with acetone using the same plunger. 3. The easiest and fastest option (perhaps not the best) is scotch tape. I use it all the time: the technology is trivial - the board is covered with a layer of adhesive tape (not all types are suitable!), Then, according to the pattern applied by something, the tracks are circled either with a sharp knife or a hot burner (with a sharp heating element). It is much more convenient to outline with the latter, then unnecessary areas are simply removed, and the rest - in a solution of chlorine. After etching - a layer of adhesive tape is simply removed, and the finished board. 4. They also draw with glass drawing pen, writing knots from ballpoint pens (after removing the ball with a needle), a match, a pen (antiques), a printer, permanent markers (not all, but there are specially designed for this). For drawing drawing are applied - nitro-paint, toner, ink, bituminous varnish. I personally use nail polish - it is perfectly washed off with hot water. I want to share one tip for speeding up etching. As I understand it, not everyone knows it. And if instead of your favorite ferric chloride you take:
Removing and installing the microchip 1. Hairdryer and sharpened soldering iron. Sometimes it turns out only with a hair dryer. It is possible in another way: we take a needle from a syringe (of a suitable diameter), carefully grind off the tip - and go ahead: after heating up the soldering, with a little effort, put the needle on the leg of the microcircuit (or any other component) and ... everything. This procedure is for each leg. Then everything falls out on its own. 2. Suction. Find a thin rubber tube, put it on the plastic tip of the suction, which should not be pressed tightly against the heated place. Press firmly against the track and soldering tip, then pump out. Pumps out tin at once from various tricky places. 3. Planar microcircuits can be soldered by threading a thread under one row of legs and securing its end on one side. Then we take another and, heating the paws, pull the thread away from the microcircuit. 4. If the board itself or the base is not needed, then you can solder the microcircuit by heating the board over an electric stove or gas burner not from the side of the parts. It takes skill. A very convenient method for removing all parts from the board. Publication: radioradar.net
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