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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Layout of circuit elements. Printed circuit boards
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies 6.1. Breadboard Circuit Board used when prototyping a circuit and preparing a sketch of a printed circuit board and can be made on the basis of sockets of multi-pin connectors MRN-22, MRN-44, GRPM-45, GRPM-61, etc. The design consists (Fig. 6.1) of two rails and two rectangular plates , duralumin, getinaks or textolite. Sockets are mounted on the plates for connecting the prototyped circuit to power sources, to other devices, and for connecting large-sized parts to the circuit that cannot be fixed on the “board” itself. A series of holes with a diameter of 3,5 mm with a pitch of 10 mm are made in the slats for installing pads and holes of the corresponding diameter for installing toggle switches, variable resistors, etc. The slats are attached to the plates at a distance from each other corresponding to the distance between the mounting holes of the selected pads. Then the pads are attached to the rails, taking into account the distances between the current-carrying terminals of the radio element or microcircuit. The circuit elements are inserted with their pins into the connector sockets. If the lead fits into the socket too freely, then bend it slightly (for example, using the device described in paragraph 5.4). It is equally convenient to install a variety of radio elements (resistors, capacitors, transistors) and microcircuits on the circuit board. All necessary connections are soldered on the bottom side of the “board” - on the connector pins. Since the pins of the parts are inserted into the sockets without soldering, replacing elements when debugging the prototyped circuit is extremely simplified. 6.2. Making a PCB layout It is convenient to use boards with printed conductors and contact pads in amateur practice only when the device has been thoroughly tested beforehand. During the setup process, it is necessary to dismantle individual parts several times and install others, and printed contact pads, as a rule, peel off under the influence of repeated thermal and mechanical loads. Therefore, at the stage of debugging the circuit, it is better to use circuit boards, which are like a layout of the future printed circuit board. A plate of the required dimensions made of non-foil insulating material (textolite, getinax, plywood) is treated on one side with fine-grained sandpaper, degreased and strengthened with the untreated side on a wooden board 15-20 mm thick. A sheet of paper with a sketch of the future printed circuit board is placed on top of the plate and glued at several points. At the points of attachment of the leads, bending of the circuit conductors, lead contact pads, holes are drilled with a 0 1-1,5 mm drill so that the drill, having passed through the plate, goes 10-12 mm deep into the board. Metal pins of suitable diameter are inserted into the resulting holes so that they protrude 5-10 mm above the surface of the plate. You can use small nails or pieces of stiff wire. Then, board conductors are made from tinned single-core wire with a diameter of 0,3-0,5 mm. To do this, the wire, in accordance with the sketch, is pulled from pin to pin, wrapping each of them with one or two turns. When all connections are made, the sketch is broken and removed with tweezers. The conductors must be pressed tightly to the surface. After this, epoxy glue is carefully applied with a brush to the areas of the conductors located between the pins in such an amount that the conductors are glued to the surface of the board. It is necessary to ensure that the glue does not get on the pins and the turns of wire wound on them. After the glue has completely hardened, the pins are removed and the finished board is removed from the board. The wire loops formed on the board will be convenient contact pads for connecting the terminals of radio elements. Having finished debugging the circuit, they work out the rational arrangement of the elements and refine the sketch. 6.3. Layout of elements on a breadboard The work of placing elements on the board is greatly simplified if you use the following technique. A layer of plasticine 2-4 mm thick is applied to a sheet of whatman paper with the dimensions of the future board. This sheet is glued at several points to another sheet of whatman paper or graph paper. Radioelements and microcircuits are installed into the plasticine, slightly pressing the leads. It is necessary to take into account the fundamental features of the device (mutual influence of circuits, temperature conditions of elements, etc.), reduce the length of connecting conductors, and not make jumpers. The terminals of the elements are pre-bent accordingly (formed). The lines of future printed conductors are drawn on plasticine with an awl. By moving the elements, they find the most rational layout. Then, removing each element from the layout one by one, pierce both sheets with an awl at the points of future holes in the board. Several punctures with a thin needle are made along the future printed conductors. After this, the element is installed in its original place. Peel off the bottom sheet, draw connections on it and indicate the location of the elements. The connection pattern is transferred to the foil blank (clauses 6.6, 6.7). After this, the parts are removed from the breadboard. The development board can be used several times. As a basis for prototyping, you can use a foam plate 25-30 m thick. In this case, the leads of the elements are molded and pressed into the foam. When the most rational placement option has been chosen, two mutually perpendicular baselines are drawn on the foam. Using a drawing meter, the distances from the base lines to the pads are measured and transferred to graph paper. The marks are connected with lines, thereby completing the preparation of the printed circuit board design. A sheet of graph paper can be immediately placed on the plate and, while installing the elements, the paper can also be pierced. After determining the best layout, draw connections on graph paper and remove the elements one by one, marking their circuit number on paper. 6.4. PCB layout for some microcircuits and small-sized elements (miniature transformers, relays, etc.) with end pins is quite labor-intensive. Marking is simplified if a layer of plasticine 0,5-1 mm thick is applied to the surface of the board at the intended installation location. The layer should be smooth and even. Then the element (chip) is prepared: the leads are shortened to the same length (10-12 mm) and bend them so that they are perpendicular to the base of the body. The element (microcircuit) is lowered to the intended installation location and the leads are pressed into the plasticine until they touch the surface of the board, then carefully removed and with an awl or a sharpened center punch, the centers of future holes in the board are marked using the remaining traces of the leads. After marking, the plasticine layer is removed and holes are drilled. This method is also convenient when arranging elements on the board. 6.5. Stencil for the manufacture of printed circuit boards used when it is necessary to produce several identical printed circuit boards. A drawing of the printed circuit board is drawn on tracing paper. Place tracing paper on a sheet of thick contrasting photographic paper on the emulsion side and press it with glass. Light the drawing with an electric lamp. The exposure is selected empirically. Once developed and mounted on photographic paper, a negative image of the printed circuit board design is obtained. Using a punch (it can be a piece of metal tube of the required diameter with sharpened edges), holes are punched at the contact pads and images of the conductors are cut out. The resulting stencil is glued with water-soluble glue (clauses 4.15-4.17, 4.22) at several points on a workpiece made of foil material and several layers of nitro varnish are applied. After this, the stencil is carefully removed by moistening it with warm water and dried. This is how the board is prepared for etching in nitric or hydrochloric acid. If etching is carried out in a solution of ferric chloride, then ordinary plasticine, rather than nitro varnish, can be used as a protective layer. A stencil is applied to the foil material and its holes are filled with plasticine. Excess plasticine is removed with an even scraper or a knife blade. After etching, the board is slightly heated to remove the remaining plasticine. 6.6. "Copying" a PCB design The proposed method is based on the photosensitivity of copper. To transfer the design, the board blank is thoroughly cleaned, degreased and dipped in a ferric chloride solution for 1,5-3 minutes, after which it is washed and dried. On the foil side, apply tracing paper with a drawing of conductors and contact pads made in black ink. The tracing paper is pressed with glass on top and this side of the workpiece is illuminated with a 200-300 W lamp from a distance of 150-200 mm for 10-20 minutes. The exposure is clarified experimentally. Exposed areas of foil darken due to bright lighting; areas covered by the pattern do not change color. The tracing paper is removed, and the design of the board is reproduced on the surface of the foil in the form of light lines. The lines of the drawing are painted over with acid-resistant varnish or some other protective compound and the board is etched in the usual way. It should be borne in mind that the contrast of the pattern reproduced on foil in this way gradually weakens and after a few days the pattern may disappear, so a protective layer must be applied immediately after exposure. 6.7. Drawing a PCB design Before making the drawing, the foil surface of the board is thoroughly degreased. You can apply the design with indelible drawing ink "Squid" (the most durable design is produced by blue ink) using a student's pen or drawing pen, or with asphalt-bitumen varnish using a pen. To work with asphalt-bitumen varnish or nitro paint, you can make a simple device. The needle from a medical syringe is shortened to 8-10 mm, and the base of the needle is soldered to the end of a student pen. The needle point is ground using fine-grained sandpaper. The base is filled with varnish or nitro paint and a design is drawn. Using needles of different diameters, lines of different thicknesses can be drawn. You can also draw a drawing using glass drawing tubes or empty ballpoint pen refills (the ball is removed from the writing unit of the rod). The tube or rod is filled with dye and a piece of polyvinyl chloride tube about 0,5 m long is put on the non-working end. The end of this tube is taken into the mouth and, by gently sucking, a slight vacuum is created, thereby preventing the dye from spontaneously flowing out of the rod or drawing tube.| It’s good to apply a design to the board using a “drawfeeder” made from a cleaned plastic ballpoint pen. To do this, the rod is heated by rotating a match over the flame, and when it softens, it is slightly stretched. At the place of heating, a narrowing is formed - a constriction. After the rod has cooled, use a sharp blade to cut the waist, choosing the cut locations so as to obtain the desired cross-section of the rod, and therefore the width of future lines (Fig. 6.2). Such “resishers” are written “softer” compared to metal or glass tubes. For a more uniform flow of paint, a wedge-shaped groove should be made. It is also convenient to use a container for refilling pens with ink when applying a design. No alterations are required, and the container can be filled with both Squid ink and asphalt-bitumen varnish or nitro varnish. The width of the track applied in one pass is 1-2 mm. At the end of the work, the container is closed with a cap, so that the mascara or varnish does not dry out and the channel does not become clogged. Neat lines of conductors are obtained by drawing them using automatic tubular pens of type ChP 1 or ChP 1B. Depending on the diameter of the writing unit, you can draw lines with a width of 0,3, 0,5 and 0. mm. The fountain pen bottle is filled with Squid ink. 6.8. Drawing a pattern of round contact pads, in the center of which there are holes for fastening the terminals of the elements, it is greatly simplified if you use an awl or a thick needle (they must fit tightly into the hole). After drilling holes in the board, it is cleaned and degreased. Then the tip of the awl (needle) is immersed in the dye, inserted into the hole in the board and turned in it 1-2 times. The concentration of the dye should be such that a drop, flowing from the tip, spreads over the board in the form of a circle. In order to obtain contact pads of the same diameter, you need to dip the awl to the same depth, preferably all the way to the bottom of the vessel with the dye. With this method of applying a pattern of contact pads, etching of the foil directly near the hole is eliminated, since the dye, poured into it, protects the foil from etching. After the dye dries, conductors are drawn on the board. The holes are cleaned of dye residues with a drill of a slightly larger diameter. The rotating drill must be inserted into the hole from the foil side. In this case, it is convenient to use one of the tools, the description of which is given in paragraphs. 5.11, 5.24. 6.9. Drawing a pattern of contact pads for microcircuit pins in packages 401.14-3 or 401.14 for example, "series 133 or 134) is a labor-intensive operation. Its adaptation, made from the body of an unusable microcircuit of the corresponding series, greatly facilitates it. A handle from a piece of copper wire is soldered to the body, and the leads of the microcircuit are molded, as for mounting on a board. If now the leads are dipped in varnish and apply it to the foil side of the board blank, you will get an imprint. In this way, you can easily and quickly “imprint" on the board blank the required number of contact pads for the pins of the microcircuits. The pinout on the board is carried out as usual - with a drawing pen or a pen. 6.10. Drawing a printed circuit board with a cutter The cleaned and degreased surface of the foil side of the workpiece is covered with a thin layer of asphalt-bitumen varnish and dried. A drawing of a printed circuit board is applied to the varnished side of the workpiece and the contours are drawn with an awl. Using a cutter similar to the one described in paragraph 5.13, conductors are drawn along the varnished surface, cutting through the varnish layer to the foil. After this, the workpiece is etched in a ferric chloride solution. The use of asphalt bitumen varnish is due to the preservation of its viscosity for a long time. Quick-drying varnishes and paints are not suitable in this case. 6.11. Making a PCB Pattern Using Adhesive Film The printed circuit board drawing made on paper is fixed on the foil side of the workpiece using rubber glue or plasticine and holes for the pins of the parts are marked on it with a center punch through the paper. The holes are drilled with a 0,8-1 mm drill. If it is necessary to make several identical boards, drill the entire stack of blanks at once, having previously clamped it in a vice. Then the foil side of the workpiece is cleaned, degreased and a sticky (“self-adhesive”) light-colored decorative film is glued onto it. The film is pierced through the holes in the workpiece with an awl and the pattern of conductors and contact pads of the printed circuit board is repeated on it with a pencil. Using a scalpel or sharpened knife, cut through the layer of film to the foil along the contour of the pattern. Areas of the film corresponding to the etched areas of the foil are removed and the workpiece is immersed in a solution of ferric chloride. After etching, the workpiece is washed and dried. If, when etching a printed circuit board, a transparent film with an adhesive layer is used as a protective film, then before gluing the film, it is advisable to transfer the board design to the cleaned and degreased surface of the foil through carbon paper. Cutting the film according to the board pattern can be made easier in the following way. A simple pencil with a lead of hardness T or 2T is sharpened sharply at one end, and to the other end, partially exposing the lead, one of the terminals of the incandescent winding (6,3 V) of the transformer is connected using an alligator clip or a wire bandage. The second terminal of the winding is securely connected to the foil of the board blank. The transformer is connected to the network through the LATR and the sticky film is pierced with the tip of a pencil lead. At the point of contact between the lead and the foil, heat is released and the film melts. By selecting the current strength, a good melting of the film is achieved when the pencil tip moves along the contour of the drawing. You can also use PVC insulating tape as a protective layer when etching a printed circuit board. A piece of tape 10-12 cm long is placed with the sticky side on clean organic glass, strips of the required width are cut with a scalpel along a ruler, and then transferred with tweezers to a prepared plate of foil material and glued in accordance with the pattern of the board. When gluing, you need to be especially careful when making joints. If you have a roll of adhesive film (decorative or adhesive tape), you can proceed as follows. On a lathe, “washers” of the required thickness are cut from the roll. From the same film, circles of the required diameter are cut out with a tube. Then they degrease the foil surface of the workpiece, apply a printed circuit board pattern on it with a pencil, drill holes in the places of the contact pads and begin to “glue out” the printed circuit board pattern: cut out circles are glued onto the contact pads and connect them with adhesive tape, rolling a “washer” prepared from a roll along the surface ", (Fig. 6.8). Turns of current-carrying tracks with a large radius of curvature can be “glued out” by deforming the tape, and in case of sudden changes in direction, by cutting the tape and gluing her "butt". 6.12. Etching solutions. - There are various compositions for etching, foil material in the manufacture of printed circuit boards. 1st recipe. For forced (within 4-6 min) etching, you can use the following composition (in mass parts): 38% hydrochloric acid with a density of 1,19 g/cm3 (20), .30% hydrogen peroxide (peroxide), (20), water (60). If hydrogen peroxide has a concentration of 16-18%, then for 20 parts by mass of acid take 40 parts of peroxide and the same amount of water. First, peroxide is mixed with water. and then add acid. Printed conductors and contact pads should be protected with acid-resistant paint, for example nitro enamel NTs-11. 2nd.recipe. Dissolve 4-6 tablets of hydrogen peroxide in a glass of cold water and carefully add 15-25 ml of concentrated sulfuric acid. To apply a printed circuit board design to foil material, you can use BF-2 glue. The etching time in this solution is approximately 1 hour. 3st recipe. In 500 ml of hot (approximately 80 ° C) water, dissolve four tablespoons of table salt and two tablespoons of copper sulfate crushed into powder. The solution becomes dark green in color. Ready for use immediately after cooling. The solution is enough to remove 200 cm3 foil. The etching time is about 8 hours. If the printed circuit board pattern is made with sufficiently heat-resistant paint or varnish, the temperature of the solution can be brought up to about 50 ° C, and then the etching intensity will increase. 4st recipe. Dissolve 350 g of chromic anhydride in 1 liter of hot water (60-70 ° C), then add 50 g of table salt. After the solution has cooled, begin etching. Etching time 20-60 min. If you add 50 g of concentrated sulfuric acid to the solution, the etching will be more intense. 5st recipe. Dissolve 200 g of ferric chloride powder in 150 ml of warm water. 6.13. Preparation of ferric chloride If there is no ready-made ferric chloride (in powder), then you can prepare it yourself. To do this you need to have 9% hydrochloric acid and fine iron filings. For 25 parts by volume of acid, take one part of iron filings. Sawdust is poured into an open vessel with acid and left for a few days. At the end of the reaction, the solution becomes light green, and after 5-6 days the color changes to yellow-brown - the ferric chloride solution is ready for use. To prepare ferric chloride, you can use powdered red lead. In this case, for one volume part of concentrated hydrochloric acid, 1,5-2 parts of red lead are required. The components are mixed in a glass container, adding red lead in small portions. After the chemical reaction stops, a precipitate forms at the bottom and the ferric chloride solution is ready for use. 6.14. galvanic etching This method requires a direct current source with a voltage of 25-30 V and a saturated solution of table salt. The positive pole of the current source is connected to the defatted and dried foil material using an alligator clip. A wire is connected to the negative pole of the source, the end of which is stripped and folded into a loop. Wrap a cotton swab around the loop and soak it generously in a saturated solution of table salt. Lightly pressing the tampon to the foil, move it to the workpiece. In this case, the foil that is not protected by paint is washed off." The tampon is often soaked in the solution and replaced with a new one as it becomes dirty. Galvanic etching can be performed in a slightly different way. The printed circuit board design is transferred onto the workpiece through carbon paper. Then the foil is covered with a thin layer of heated paraffin or wax. The contours of the printed conductors and contact pads are outlined with light pressure with a sharpened awl or needle, and the protective coating is removed from the areas of the foil to be etched. The positive pole of a DC source with a voltage of 4-12 V is connected to the foil. The negative pole of the source is connected to a metal vessel for etching (you can use a vessel made of any metal, for example a tin can). A saturated solution of table salt is poured into the vessel, the board blank is immersed in it and the power source is turned on. At the same time, a greenish coating in the form of scale appears on the areas of the foil from which the protective coating has been removed - the etching process occurs. During etching, the temperature of the solution must not be allowed to rise significantly, otherwise the protective coating may be damaged, so the metal vessel is placed in a bath of running cold water. 6.15. PCB fabrication on non-foil material If there is no foil material at hand, then by galvanic build-up of copper you can make a printed circuit board on getinax, textolite, thick cardboard (pressboard) and even on whatman paper. To do this, the surface of the future board is cleaned on one side with fine-grained sandpaper or a school ink eraser, and a drawing of printed conductors and contact pads is applied to the workpiece with a pencil. After drilling the holes, cover the areas that need to be metalized with a thin layer of BF-2 glue. Since in the future a layer of copper will be applied to the printed wiring using an electrolytic method, the conductors (and pads) must be electrically connected to each other by narrow technological bridges, which are removed after copper plating. To make it easier to separate the temporary jumpers from the board, their lines are first drawn boldly with a soft pencil and only then with glue. After applying the glue, the workpiece is kept for 15 minutes so that the glue dries, then it is placed on a flat stand and bronze powder, used to prepare bronze paint, is poured onto it in a thin layer. The workpiece with the powder is covered with two or three layers of writing paper and pressed with an iron heated to a temperature of 120-150 ° C. After 2-3 minutes, the iron is removed. After cooling, excess powder is removed, the workpiece is washed with a swab under running water and retouched. To increase electrical conductivity. conductors and contact pads, they can be treated with a soft brush with a solution of stannous chloride (3-4 g per 25-30 ml of water) and washed again in running water. A wire is connected to one of the technological jumpers by soldering and the workpiece is placed in a concentrated solution of copper sulfate. The workpiece is a negative electrode; a copper or lead plate serves as a positive electrode. A direct current of 0,5-1,0 A is passed between the electrodes. Copper plating time is about an hour. Instead of a low voltage rectifier, the current source can be two 3336 batteries connected in parallel, or three 373 batteries connected in series. Upon completion of copper plating, the jumpers are removed, the board is washed, dried and kept for 10-15 minutes under a hot iron. This ensures the adhesion of the conductors to the board, since when heated, the glue penetrates into the pores of the deposited copper layer. 6.16. Making a printed circuit board without using chemicals A workpiece of the required dimensions is cut out of foil material, all the necessary holes are drilled and a printed circuit board design is applied to it. The contours are outlined with a sharp awl. For ease of work, the workpiece is fixed on a board clamped in a vice. By hitting a sharp cutter with a light hammer, insulating grooves are cut out along the markings. In this case, the angle of inclination of the cutter is selected such that only the foil layer is removed. Making a board of average complexity using the above method takes 1,5-2 hours. A printed circuit board can be made using a cutter (section 5.13) and a special ruler. To do this, all the necessary holes for the leads of the parts are drilled on a blank made of foil material and the pattern of the insulating grooves is reproduced with a pencil so that the conductors are made up of straight line segments (Fig. 6.4, o). Then, along these lines, using a ruler with a limiting protrusion (Fig. 6.4, b), carefully cut through the foil layer with a cutter to the insulating material. In this case, the protrusion of the ruler is aligned with the end of the groove to prevent erroneous cutting. It is convenient to make a ruler from a transparent material and glue a layer of elastic rubber in several places (shaded in the figure), which improves the fixation of the ruler on the workpiece while cutting grooves. The printed circuit board pattern can also be milled. To do this, you need to attach an adapter sleeve to the shaft of a small electric motor (for example, an AM-OZ-Za DC motor from the Orbita-2 tape recorder) and fix a short drill with a diameter of 1-3 mm in it. The drill is sharpened like a milling cutter. Then turn on the electric motor and, holding it in your hand, mill the foil according to the pattern, right through to the substrate. Unnecessary sections of foil can be removed. Milling is greatly simplified if you use denture burs as a cutter, the rotation of which is transmitted through a flexible shaft from the drill (section 5,24). It is convenient to cut curved paths using a cutter made from a triangular needle file. On the sharpener, the working part of the file is shortened by 20-30 mm and the notch is ground off 20-25 mm from the end. This turned part of the file-blank is released (section 1.3). After tempering, the workpiece is clamped in a vice and its end is processed with the same triangular needle file. The lower edge is rounded: this part of the cutter will be the working part (Fig. 6.5). The end of the workpiece is hardened by heating it to a bright orange color and quickly dipping it into machine oil. A handle is placed on the shank of the file, and the cutting edge is sharpened using a fine-grained emery block. The cutter is taken in the right hand so that the handle rests in the middle of the palm, and the triangular part is held with the fingers. By pressing on the cutter, mounted with its tip on the board, and slightly rocking it along the axis, they cut through the foil, which comes out from under the cutter in the form of long curly shavings. The minimum width of the cut tracks is 0,2 mm. A good cutter can be made from a thick sewing machine needle. Break off the eye and sharpen this end at an angle of 30° so that the end of the needle on the groove side in the sharpening plane takes the shape of the letter M. Sharpen the edge using fine-grained sandpaper. The width of the slot in the foil left by such a cutter is 0,6-0,9 mm. It is convenient to use a plastic handle from an old toothbrush as a handle for the cutter: a hole is drilled at the end of the handle to a depth of 12-15 mm and the cutter is firmly inserted into it. 6.17. PCB tinning... ...before installation, it improves solderability, significantly facilitates and speeds up installation, and reduces the risk of overheating of elements during installation. You can tin in an aluminum bowl (the board should fit flat on the bottom). Glycerin is poured into the dish (layer thickness is about 1 cm) and heated to approximately 60 °C. Then pieces of Rose's alloy are placed in glycerin (see Table 9,1) and heating is continued until it melts. The melt should not be heated above 100 °C. The board is picked out in a 20% solution of hydrochloric acid, washed with water and dipped into the melt for 1-3 s. The removed board is quickly wiped with a foam sponge, removing excess alloy from the surface. The remaining glycerin is washed off with warm water. To reduce the risk of conductors peeling off during soldering of parts, the entire board, with the exception of contact pads, is covered with a layer of BF-2 glue after tinning. Did you know?. 6.18 Marking the conductors on the diagram and printed circuit board will facilitate installation, configuration and troubleshooting. Markings are applied to the printed circuit board along with a protective layer before etching.
6.20 A convenient scraper for retouching a printed circuit board design made with ink or nitro paint can be obtained by inserting a piece of a safety razor blade into the clamp of a collet pencil. If you want to work with a slightly curved blade, choose a collet with an odd number of jaws. 6.21 If, when developing a printed circuit board design, it is difficult to do without the intersection of printed conductors, then one of the conductors is broken, and contact pads with holes are provided at the ends of the break. After manufacturing the printed circuit board, a jumper wire is soldered into the holes on the parts side. 6.22 To apply a design to the board, you can use silicate glue, which is then dried under a lamp for 4-5 minutes. 6.23 Instead of paint, you can use a rosin solution as a protective layer when etching in nitric or hydrochloric acid. в ethyl alcohol. It usually takes 10 minutes for the drawing to dry. 6.24 You can remove ink from tracing paper with a swab moistened with a mixture of BF glue and acetic acid in a ratio of 1:5. 6.25 A breadboard can be quickly made from foil fiberglass or getinax. To do this, the foil is cleaned (clause 6.27) and the arrangement of parts is transferred onto it with a soft pencil. Insulating grooves are made with a cutter or a graver (clauses 5.13, 6.16). 6.26 For prototyping circuits on integrated circuits, it is convenient to use mole rat circuit boards. On such a board there are contact pads for soldering integrated circuits and for soldering connecting conductors. After installing the microcircuits, using a thin mounting wire, perform suspended installation of connections. 6.27 To remove the oxide film from the foil and to degrease it, it is convenient to use a student's ink eraser. 6.28. Small diameter holes in thin circuit boards can be drilled with a sewing machine needle. In this case, the eye of the needle is broken off and the cutting edges are sharpened, like a regular drill. You should work with such a “drill” at increased speeds of the drill chuck. 6.28 Etching of printed circuit boards can be done in a plastic bag. The board is placed in a bag and filled with ferric chloride solution. The sharp corners of the board are first rounded to avoid damaging the bag. Shaking the bag during the etching process, mix the solution. If it is necessary to work at an elevated temperature of the solution, the bag is placed in a vessel with hot water, holding it by the edges. 6.30 Etching a printed circuit board in a concentrated solution of nitric acid takes 1-5 minutes. You need to work outdoors. Wash the finished board thoroughly with warm water and soap. 6.31. С double-sided foil blank when performing single-sided printed installation, it is advisable to remove the second layer of foil (in order to save etching solution). To do this, use a knife blade to carefully separate a corner of the foil and use tweezers or pliers to remove the entire layer. 6.32 The board etching time depends on the intensity of solution exchange at the foil surface. Therefore, to speed up etching, the vessel should be shaken periodically. 6.33 If you cannot find a suitable vessel for etching, you can proceed as follows. Cut the workpiece with an allowance of 6-8 mm around the perimeter. After applying the pattern along the edges of the workpiece, from the foil side, a side with a height of 10-15 mm is formed from plasticine. A solution of ferric chloride is poured into the resulting “cuvette”. In this case, you will have to drill holes for installing parts and for conductors after etching. 6.34 You can clean a cuvette in which etching has been carried out many times using alkaline battery electrolyte: fill the cuvette with the solution for several hours, and then rinse it in running water. Author: tolik777 (aka Viper); Publication: cxem.net
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