Printed circuit board drawings. Printed circuit board: description, purpose
Many people are familiar with such technology for wiring and creating printed circuit boards as. But what to do when the scheme is too complex and voluminous? Here you will have to master more modern methods, one of which we will get acquainted with here. Take, for example, the circuit of this sound probe:Device diagram
It makes no significant difference whether we lay out the board on a piece of paper in a checkered pattern, cutting out templates of parts with pins from cardboard (although I deeply doubt that anyone will use this method in the 21st century, when every home has a computer), or use some program for PCB layout, for example sprint layout. Of course, with the help of sprint layout it will be much easier to do this, especially in large schemes. In both cases, first we place on the working field the part with the largest number of pins; in our case it is a transistor, let’s say VT1, this is our KT315. (A link to the sprint layout user manual will be provided below). Moreover, at first, when designing, your printed circuit board may resemble a circuit diagram, that’s okay, I think everyone started out that way. We installed it, then we connect its base and emitter with tracks to resistor R1, we also have the base VT1 connected to the output of capacitor C1 and the output of resistor R2. Instead of lines on the diagram, we connect the pins of the parts with a track on the printed circuit board. I also made it a rule to count the number of pins of parts connected on the diagram and on the printed circuit board; we should get the same number of connected patches.
As you can see, we have 3 more pins connected to the base on the board, just like in the diagram; in the diagram they are marked with red rings. Next, we install transistor VT2 - this is a KT361 transistor, it has a pnp structure, but we don’t care at the moment, since it also has 3 outputs and is in a housing exactly the same as KT315. We installed the transistor, then connect its emitter to the second terminal R2, and the second terminal of capacitor C1 to the collector VT2. We connect the VT2 base to the VT1 collector, install patches on the board to connect the BA1 speaker, we connect it with one terminal to the VT2 collector, the other terminal to the VT1 emitter. Here's what everything I described looks like on the board:
We continue further, we install the LED, connect it to the BA1 pin and to the VT2 emitter. Afterwards we install transistor VT3, this is also KT315 and connect it with the collector to the cathode of the LED, we connect the emitter of VT3 to the minus of the power supply. Next, we install resistor R4 and connect it with tracks to the base and emitter of transistor VT3; we connect the output from the base to probe X1. Let's see what happened on the board:
And finally we install the last few parts. Let's install the power switch, connecting it to the power plus with a path from one patch and to the VT2 emitter, with a path from the other patch connected to the switch. We connect this switch terminal with resistor R3, and connect the second patch of the resistor to the contacts of probe X2.
A printed circuit board is a dielectric plate on the surface of which conductive tracks are applied and places are prepared for mounting electronic components. Electrical radio components are usually installed on the board using soldering.
PCB device
The electrically conductive paths of the board are made of foil. The thickness of the conductors is, as a rule, 18 or 35 microns, less often 70, 105, 140 microns. The board has holes and contact pads for mounting radio elements.
Separate holes are used to connect conductors located on different sides of the board. A special protective coating and markings are applied to the outer sides of the board.
Stages of creating a printed circuit board
In amateur radio practice, we often have to deal with the development, creation and manufacture of various electronic devices. Moreover, any device can be built on a printed circuit board or a regular board with surface mounting. The PCB works much better, is more reliable and looks more attractive. Creating it involves performing a number of operations:
Preparation of the layout;
Drawing on textolite;
Etching;
Tinning;
Installation of radio elements.
Manufacturing printed circuit boards is a complex, labor-intensive, and interesting process.
Development and production of a layout
The board drawing can be done manually or on a computer using one of the special programs.
It is best to draw the board manually on recorder paper on a 1:1 scale. Graph paper is also suitable. Installed electronic components must be displayed in mirror image. The tracks on one side of the board are shown as solid lines, and on the other side as dotted lines. The dots mark the places where radio elements are attached. Soldering areas are drawn around these places. All drawings are usually made using a drawing board. As a rule, simple drawings are made by hand; more complex printed circuit board designs are developed on a computer in special applications.
Most often they use a simple program called Sprint Layout. Only a laser printer is suitable for printing. The paper should be glossy. The main thing is that the toner does not eat into it, but remains on top. The printer must be adjusted so that the toner thickness of the drawing is maximum.
Industrial production of printed circuit boards begins with entering the circuit diagram of the device into a computer-aided design system, which creates a drawing of the future board.
Preparing the workpiece and drilling holes
First of all, you need to cut a piece of PCB with the given dimensions. File the edges. Attach the drawing to the board. Prepare the tool for drilling. Drill directly according to the drawing. The drill bit must be of good quality and match the diameter of the smallest hole. If possible, you should use a drilling machine.
Having made all the necessary holes, remove the drawing and drill out each hole to the specified diameter. Clean the surface of the board with fine sandpaper. This is necessary to eliminate burrs and improve the adhesion of paint to the board. To remove traces of grease, treat the board with alcohol.
Drawing on fiberglass laminate
The board drawing can be applied to the PCB manually or using one of many technologies. Laser ironing technology is the most popular.
Manual drawing begins by marking the mounting areas around the holes. They are applied using a drawing pen or a match. The holes are connected with tracks in accordance with the drawing. It is better to draw with nitro paint in which rosin is dissolved. This solution provides strong adhesion to the board and good resistance to high-temperature etching. Asphalt bitumen varnish can be used as paint.
Manufacturing printed circuit boards using laser-iron technology gives good results. It is important to perform all operations correctly and carefully. The degreased board must be placed on a flat surface with the copper facing up. Carefully place the design on top with the toner facing down. Additionally, add a few more sheets of paper. Iron the resulting structure with a hot iron for about 30-40 seconds. When exposed to temperature, the toner should change from a solid to a viscous state, but not to a liquid. Let the board cool and place it in warm water for a few minutes.
The paper will become limp and tear off easily. You should carefully examine the resulting drawing. The absence of separate tracks indicates that the iron temperature is insufficient; wide tracks are obtained when the iron is too hot or the board is heated for an excessively long time.
Small defects can be corrected with a marker, paint or nail polish. If you don’t like the workpiece, then you need to wash everything off with a solvent, clean it with sandpaper and repeat the process again.
Etching
A grease-free printed circuit board is placed in a plastic container with the solution. At home, ferric chloride is usually used as a solution. The bath with it needs to be rocked periodically. After 25-30 minutes, the copper will completely dissolve. Etching can be accelerated by using a heated ferric chloride solution. At the end of the process, the printed circuit board is removed from the bath and thoroughly washed with water. Then the paint is removed from the conductive paths.
Tinning
There are many methods of tinning. We have a prepared printed circuit board. At home, as a rule, there are no special devices and alloys. Therefore, they use a simple, reliable method. The board is coated with flux and tinned with a soldering iron with regular solder using copper braiding.
Installation of radio elements
At the final stage, the radio components are inserted one by one into the places intended for them and soldered. Before soldering, the legs of the parts must be treated with flux and, if necessary, shortened.
The soldering iron should be used carefully: if there is excess heat, the copper foil may begin to peel off and the printed circuit board will be damaged. Remove any remaining rosin with alcohol or acetone. The finished board can be varnished.
Industrial development
It is impossible to design and manufacture a printed circuit board for high-end equipment at home. For example, the printed circuit board of an amplifier for High-End equipment is multi-layered, copper conductors are coated with gold and palladium, conductive tracks have different thicknesses, etc. Achieving this level of technology is not easy even in an industrial enterprise. Therefore, in some cases it is advisable to purchase a ready-made high-quality board or place an order to carry out work according to your own scheme. Currently, the production of printed circuit boards is established at many domestic enterprises and abroad.
Basic rules for board development
It is most convenient to design printed circuit boards in a 1:1 scale on graph paper or other material on which a grid is applied in 5 mm increments (for example, on a notebook sheet). It is advisable to place all holes for pins of parts in the printed circuit board in grid nodes, which corresponds to the pitch
2.5mm on a real board. The terminals of most microcircuits in a plastic case, many transistors and other radio components are located with this pitch. Less
The distance between holes should be chosen only in cases where it is absolutely necessary.
First you need to roughly arrange the parts. First of all, draw points for the pins of the microcircuit, then place small elements - resistors, capacitors,
and then the big ones - relays, etc. Their placement is usually related to the overall design of the device, determined by the size! the existing case or free space in it. Often, especially
Especially when developing portable devices, the dimensions of the case are determined based on the results of the printed circuit board layout. Sometimes it is necessary to redo the pattern of printed circuit wires
nicks several times to get the desired result of minification and functionality.
If your homemade product has no more than five microcircuits, you can usually place all printed conductors on one side of the board and make do with a small number of test leads.
jumpers soldered on the parts side.
Attempts to produce a single-sided PCB for a larger number
digital chips lead to a sharp increase
labor-intensive wiring and an excessively large number of jumpers. In these
In some cases, it makes more sense to switch to a double-sided PCB.
We will call the side of the board where the
printed conductors, the side of the conductors, and the reverse -
side of the parts, even if on it together with the parts
Some of the conductors have been laid. A special case is presented by
boards in which both conductors and parts are located on
one side, and the parts are soldered to the conductors without
holes. Boards of this design are rarely used.
The microcircuits are placed so that all connections on the board
were as short as possible, and the number of jumpers was
minimal. In the process of wiring conductors, mutual
The placement of microcircuits has to be changed more than once.
Drawing of printed conductors of analog devices
any complexity can usually be placed on one
side of the board. Analog devices that work with
weak signals, and digital on high-speed
microcircuits (for example, KR531, KR1531, K500, KR1554 series)
Regardless of the frequency of their operation, it is advisable to collect
on boards with double-sided foil. Toy foil
sides of the board where the parts are located will play a role
common wire and screen. The foil of the common wire should not be
use as a conductor for high current,
for example, from the power supply rectifier, from the output
steps, from the dynamic head.
Next, you can begin the actual wiring. It is better to measure and write down the dimensions of the spaces occupied by the elements in advance. MLT-0.125 resistors are installed nearby, observing
the distance between their axes is 2.5 mm, and between the holes for
the terminals of one resistor are 10 mm. Places are also marked
% for alternating resistors MLT-0.125 and MLT-0.25 or
two MLT-0.25 resistors, if slightly bent during installation
one from the other (place three such resistors close to
the board will no longer succeed). With the same distances between
the pins and axes of the elements are installed by the majority
small-sized diodes and capacitors KM-5 and KM-6, up to
KM-66 with a capacity of 2.2 µF. “Thick” parts (more than 2.5 mm)
should be alternated with “thin” ones. Distance between
the contact pads of a particular part can be increased,
if necessary.
In this work it is convenient to use a small plate -
template made of fiberglass or other material, in
in which, in increments of 2.5 mm, holes with a diameter of
1-1.1 mm. On it you can apply the possible
arrangement of elements relative to each other.
If resistors, diodes and other parts with axial
pins should be placed perpendicular to the printed circuit board, you can
significantly reduce its area, however, the pattern of printed
conductors will become more complicated. When wiring you should take into account
restrictions on the number of conductors that fit between
contact pads intended for soldering
terminals of radioelements. For most parts diameter
The holes for the leads can be 0.8 mm. Restrictions
per number of conductors for typical layout options
contact pads with holes of this diameter
are shown in Fig. 8.1 (grid corresponds to 2.5 mm pitch on the board).
Between the contact pads of the holes with
with a center-to-center distance of 2.5 mm, guide the conductor almost
it is forbidden. However, if one or both holes have such
there is no pad (for example, at unused pins
microcircuits), this can be done (see Fig. 8.1 - top center).
It is quite possible to lay a conductor between the contact
platform and the edge of the board, through which at a distance
2.5 mm passes through the center of this area (see Fig. 8.1 - right).
Microcircuits whose pins are located in
body planes (series 133, K134, etc.)" can be mounted,
providing for this purpose the appropriate foil
contact pads with a pitch of 1.25 mm, but this is noticeable
complicates both wiring and board manufacturing. More expedient
alternate soldering of microcircuit pins to rectangular ones
platforms from the parts side and to the round platforms through
holes - on the opposite side (Fig. 8.2 -
The width of the microcircuit pins is not shown to scale). Pay
here it is two-sided.
Similar microcircuits with long leads
(e.g. 100 series), can be mounted in the same way as
plastic, bending the leads and passing them into the holes
fees. In this case, the contact pads are located in
in a checkerboard pattern (Fig. 8.3).
When designing a double-sided board, you should try to leave as few connections as possible on the parts side. This will make it easier to correct possible errors, set up the device and, if necessary, upgrade it. A common wire and a power wire are laid under the microcircuit housings, but they need to be connected only to the power pins of the microcircuits. Conductors to the inputs of microcircuits connected to the power circuit or the common wire are laid on the side of the conductors, and so that they can be easily cut when setting up or improving the device. If the device is so complex that signal circuit conductors have to be laid on the component side, make sure that any of them is accessible for connection to it and cutting. When developing amateur radio double-sided printed circuit boards, one should strive to avoid special jumpers between the sides of the board, using for this purpose the contact pads of the corresponding pins of the mounted parts. In these cases, the leads are soldered on both sides of the board. On complex boards, it is sometimes convenient to solder some parts directly to the printed circuit conductors. When a solid layer of foil is used as a common wire, the holes for terminals that are not connected to this wire should be countersunk from the parts side. Typically, a unit assembled on a printed circuit board is connected to other units of the device using flexible conductors. In order not to damage the printed conductors during repeated soldering, it is advisable to make contact stands on the board at the connection points (it is convenient to use pin contacts with a diameter of 1 and 1.5 mm). The racks are inserted into holes drilled exactly to the diameter and soldered. On a double-sided PCB, the soldering pads for each stand must be on both sides. It is convenient to carry out preliminary wiring of conductors with a soft pencil on a sheet of smooth paper. The side of the printed conductors is drawn with solid lines, the reverse side - with dashed lines, so as not to get confused. Upon completion of the layout and adjustment of the drawing, place carbon paper under it with the ink layer facing up and use a red or green ballpoint pen to trace the contours of the board, as well as the conductors and holes related to the side of the parts. As a result, on the back of the sheet you will get a drawing of conductors for the side of the parts. Next, you should cut out a blank of the appropriate size from the foil material and mark it with a caliper with a grid with a pitch of 2.5 mm. By the way, it is convenient to choose the dimensions of the board in multiples of 2.5 mm. - in this case, you can mark it on four sides. If the board must have any cutouts, they are made after marking. The double-sided board is marked on the side where there are more conductors. After this, use a felt-tip pen to mark the centers of all the holes “in cells”, prick them with an awl and drill all the holes with a drill with a diameter of 0.8 mm. To drill circuit boards, it is convenient to use a homemade miniature electric drill, which can be bought on the radio market. Conventional steel drills become dull rather quickly when processing fiberglass; sharpen them with a small fine-grained whetstone without removing the drill from the chuck. After drilling the board, burrs are removed from the edges of the holes with a larger diameter drill or a fine-grained stone. The board is degreased by wiping with a cloth moistened with alcohol or acetone, after which, focusing on the position of the holes, a pattern of printed conductors is transferred to it using nitro paint in accordance with the drawing. A glass drawing board is usually used for this, but it is better to make a simple homemade drawing tool. To the end of the broken student's pen, solder an injection needle shortened to 10-15 mm with a diameter of 0.8 mm. The working part of the needle must be sanded with fine-grained sandpaper. Nitro paint is poured into the funnel of the instrument in drops and, carefully taking it into the lips, blow lightly so that the paint passes through the needle channel. After this, you just need to make sure that the funnel is at least half filled with paint. The required paint density is determined experimentally by the quality of the lines drawn. If necessary, it is diluted with acetone or solvent 647. If it is necessary to make the paint thicker, it is left for some time in an open container. First of all, the contact pads are drawn, then connections are made between them, starting from those areas where the conductors are closely located. After the drawing is basically ready, you should, if possible, expand the common wire and power conductors, which will reduce their resistance and inductance, and therefore increase the stability of the device. It is also advisable to increase the contact pads, especially those to which racks and large parts will be soldered. To protect large surfaces of the foil from the etching solution, they are sealed with any adhesive film. If you make a mistake when applying a drawing, do not rush to correct everything right away - lay the correct one over the incorrectly applied conductor, and remove the excess paint when finally correcting the drawing (this is done before the paint has dried). Using a sharp scalpel or razor, the area to be removed is cut along the borders, after which it is scraped out. There is no need to specially dry the nitro paint after applying the design. While you are fixing the board, wash the tool - the paint will dry.
PCB etching
To obtain the conductors after applying the design to the foil, the board must be etched. The main material for etching is a solution of ferric chloride. To obtain it, you need to pour about 3/4 of ferric chloride powder into a glass and fill it with warm water. For etching, use a glass or plastic container, such as a photographic cuvette. Place the board in the solution with the pattern facing up so that the entire surface of the board is covered with the solution. The etching process is accelerated if the vessel is shaken or heated. Pickling produces toxic fumes, so work either in a well-ventilated area or outdoors. Periodically check the condition of the board by lifting it for inspection with wooden or plastic sticks - metal tools and devices cannot be used for this purpose. Once you are sure that the foil in unprotected areas has completely disappeared, stop the etching process. Transfer the board, for example using a clothespin, under running water and rinse thoroughly, then dry it at room temperature. If you intend to reuse the solution, pour it into a tightly sealed container and store it in a cool, dark place. Please note that the effectiveness of the solution decreases with repeated use. When working with ferric chloride solution, remember that it should not get on your hands or other exposed parts of the body, as well as on the surfaces of bathtubs and sinks, since the latter may leave yellow stains that are difficult to wash off. A solution of ferric chloride can be made in another way: treat iron filings with hydrochloric acid. Take 25 parts by weight of 10 percent hydrochloric acid and mix with one part by weight of iron filings. Keep the mixture in a tightly sealed container in a dark place for 5 days. When pouring the solution into a vessel for etching, do not shake it: the sediment should remain in the container in which the solution was prepared. The duration of the board etching process in a ferric chloride solution is usually 40-50 minutes and depends on the concentration of the solution, its temperature, and the thickness of the foil. Solutions for etching boards can be prepared not only based on ferric chloride. For many radio amateurs, an aqueous solution of copper sulfate and table salt may be more accessible. It is not difficult to prepare - dissolve 4 tablespoons of table salt and 2 tablespoons of copper sulfate crushed into powder in 500 ml of hot water (temperature about 80 °C). The effectiveness of the solution increases if it is kept for 2-3 weeks. The etching time of the board in such a solution is three hours or more. A significant reduction in the etching period can be achieved by using acid-based solutions. The process of etching the board, for example, in a concentrated solution of nitric acid, lasts only 5-7 minutes. After etching, wash the board thoroughly with soap and water. Good results are obtained by using a solution of hydrochloric acid and hydrogen peroxide. To prepare it, take 20 parts (by volume) of hydrochloric acid with a density of 1.19 g/cm3, 40 parts of pharmaceutical hydrogen peroxide and 40 parts of water. First mix water with hydrogen peroxide, then carefully add the acid. In this case, the drawing is done with nitro paint. Pour acid-based solutions into glass or ceramic containers; work with them only in well-ventilated areas. Of interest is the method of galvanic etching of boards. To do this, you will need a DC source with a voltage of 25-30 V and a concentrated solution of table salt. Using an alligator clip, connect the positive pole of the source to the unpainted areas of the board’s foil, and attach a cotton swab, generously soaked in salt solution, to the exposed and looped end of the wire coming from the negative pole of the source. Move it along the surface of the board, lightly pressing it against the foil. The movement of the tampon should resemble the drawing of the number 8. In this case, the foil will be “washed off,” as it were. Change the cotton whenever it gets dirty.
Radio amateurs advise
Professional radio amateurs offer us the ability to make printed circuit boards quite quickly using a laser printer (or copier), an iron and film from Techniks or DynaArt (everything else - foil PCB, ferric chloride, drills - as usual). Film and iron are needed to transfer the printed circuit board design to copper. Having prepared a drawing of a printed circuit board using any package for developing printed circuit boards or some editor for drawing pictures, we make a test print. We display an image of the printed circuit board on a blank sheet of paper. Then we cut out a fragment from the film with a margin of about 1 cm on each side. Glue it with tape with the glossy side to the paper on top of the drawing. We insert the sheet of film into the printer and print again. We get a film with an image of a printed circuit board printed on it. Then we prepare the textolite. In my opinion, the Surzha cleaning agent is excellent for this (do not neglect basic safety standards - use rubber gloves). After washing and drying the board, apply a film of toner to it and iron it with an iron for 1.5-4 minutes at a temperature of 135-160 °C. When the board cools down, carefully remove the film under running water - the drawing is transferred. We inspect the board and, if there are any flaws, correct them with an alcohol marker. Now you can etch using a ferric chloride solution. You can clean the toner from the finished board with an old blade, using it as a scraper. The same method is suitable for the production of double-sided printed circuit boards. To combine layers, you can use the following trick: draw three anchor points on both layers in the same place - best along the perimeter of the board. After transferring the first layer, drill holes at these points. We combine the points on the film for the second side with the holes. This option is not suitable for Techniks film, since it is opaque. You can do this: add 4 parallel lines to the printed circuit board drawing in both layers at a distance of 5 mm from the board border. After transferring the first layer, apply a ruler over the line and extend it to the end of the workpiece. We make marks on the ends of the workpiece and transfer the lines to the other side of the board. The second film is combined with the lines - you can transfer the second layer. The quality of these boards is very good. There is a technology for manufacturing printed circuit boards using ordinary drawing tracing paper. It differs little from the technology with special film. Before use, tracing paper must be run through a printer or ironed to remove heat shrinkage. Then everything is the same. After cooling, place the board with toner and tracing paper in warm water, wait until the tracing paper gets wet, and carefully roll up the paper with a cloth. After this we correct it with a marker. It should be noted that the quality of the boards is somewhat worse, but much cheaper. To apply a design to the board, you can also use an alcohol marker (preferably a German one), but this is only suitable for simple boards in a single copy. The quality is the same as with tracing paper, but the difficulties are immeasurably greater. But for simple things it will do.
Layout of radio components on the board
We print the board.
Yes, yes, that’s right - we print.
Now we will talk about how to make a good printed circuit board using a laser printer and an iron. In general, let's talk about the currently fashionable laser-iron technology for manufacturing printed circuit boards.
The technology, as it turned out, is not only fashionable, but also very convenient and simple. In order to combine business with pleasure and not make some kind of abstract board, let’s take as an example the circuit from our website. We’ll make a board for her.
First of all, what do we need?
1.
Of course, foil fiberglass - one-sided or two-sided, it doesn’t matter. Now there are no problems with it - it is sold in any radio parts store or on the market.
2.
Any magazine on glossy paper.
3.
A tool for cutting PCB is best a cutter made from a hacksaw blade.
4.
Zero-grit sandpaper or a stiff sponge for cleaning utensils made of steel wire.
5.
From chemistry: alcohol, acetone or solvent, liquid soldering flux, ferric chloride.
6.
And of course a computer, a laser printer, a soldering iron, good lighting and a lot of patience.
Look like that's it.
Naturally, we must start with the design of this very board.
There are a great variety of programs that deal with tracing (that is, routing tracks) of printed circuit boards in manual and automatic mode. Personally, I have settled on the program for now DipTrace domestic manufacturer. It allows you to draw not only boards, but also circuit diagrams and libraries of electronic components. But now we are only interested in boards.
This is what this program looks like and this is what the finished board drawing looks like in it.
Well, then we proceed directly to the manufacturing process and, so as not to get confused in it, we will go in small steps, so:
We need to print the board drawing on a laser printer. In principle, you can use an inkjet printer, but in this case you will need to make a photocopy of the drawing and use it. The idea is simple - we need a print of the drawing on paper made with toner (powder), which is used in laser printers or copiers. We need glossy paper - most often, it is used in computer magazines or various advertising brochures. I used the magazine, which I love and respect very much for its content, and now also for the quality paper on which it is printed.
There is no need to clean anything - we just tear out the page and print our drawing directly on top of the source text.
Print a couple of copies at once - it might come in handy.
We printed it, so we move on.
We cut off a piece of PCB to the size we need, prepare sandpaper (sponge) and acetone with a piece of cotton wool or cotton pads.
We take a piece of sandpaper or a sponge and begin to rub our workpiece from the foil side. There is no need to be particularly zealous, but nevertheless, the surface should become smooth and brightly shiny, and not matte, as it was before. Then take a piece of cotton wool, dip it in acetone or solvent and wipe the newly cleaned foil.
It should look something like this:
I must say that after the workpiece has been wiped with acetone, under no circumstances should you grab the foil with your fingers - only by the edges, preferably even with two fingers at the corners. Otherwise, you will have to wipe the foil again with acetone.
Let's move on to the next step.
Before performing this step, read the entire description.
So, from the sheet on which the board drawing is printed, we cut out a piece directly with the drawing, leaving quite large margins along the edges. Then we carefully place our blank on the drawing (with foil to the printed tracks, of course), wrap the fields and fasten them, for example, with masking tape.
You should get an envelope like this:
Done? Great, let's move on to the most important step - ironing.
So, let's take an iron - absolutely any one.
Tefal, Bosch, Belarusian Tractor Plant, with steamer, without steamer. Doesn't matter.
We set the temperature regulator to maximum (if you have the names of fabrics written on your iron, then “linen”). Place the iron on the prepared envelope.
The envelope, of course, must be placed with tape down. We begin to gently iron. This is the most subtle part of the entire procedure and it is impossible to learn it except from your own experience. The pressure on the iron should not be strong - otherwise the toner will spread and smear on the foil, but not weak either - otherwise the toner will not adhere well to the workpiece. In short, there is a wide field for experimentation here. In any case, it is necessary to heat the entire surface of the future board evenly and pay special attention to the edges - there is the greatest risk of non-heating and subsequent peeling of the toner. The same applies to the warm-up time, although this is easier.
Approximately the degree of readiness can be determined by the yellowing of the paper and the appearance of the outlines of paths on it.
It's almost like in the photo.
Well, let's say we decided that everything is ready. Turn off the iron and leave the board for about 10 minutes to cool. Pour water into a suitable container. The temperature of the water should be such that you could barely hold your hand in it. Well, we throw our cooled preparation there.
That's it, let's go smoke, drink tea, chase the cat - anything for 15 minutes. You can even have 20. By the way, you can leave the water on so that it doesn’t cool down.
We come back and begin to carefully separate the paper from the workpiece. Very carefully and slowly. Roll the remaining scraps with your fingers. Under no circumstances should we scrape the board with our claws, but gently, using the pads of our fingers, clean the foil from any stuck paper. After that, we arm ourselves with a hairdryer and dry, dry, dry. In fact, it doesn’t take that long, because it dries in just a minute or two.
Well, we ended up with something like this:
Ugh. We exhaled and moved on to the next step.
At this stage, we need to etch the board - that is, remove all unnecessary foil from the workpiece so that only the tracks we drew remain.
Why use ferric chloride? It is sold in cans - it is such a rust-colored paste and smells terribly disgusting. It is diluted with warm water.
We dilute approximately 100 grams of ferric chloride per 100 grams of water. You can use less water - the main thing is that the solution completely covers our workpiece. So, we dissolve the iron in water, stir thoroughly and throw the future board into it - now it won’t be long before it remains a workpiece.
It is not harmful to stir the solution during the etching process - either by stirring it with a non-metallic rod or by rocking the bath from side to side. Again, you can run warm water under the bottom of the bath so that the solution does not cool down. The etching time depends on the size of the board and the concentration of the solution. Usually about 20 minutes. If during this time the board is not etched, then the concentration of ferric chloride is insufficient and it is worth adding more.
By the way! Did you know that used ferric chloride can be recovered? If you are strangled by a large, green toad, the used solution can be reused. To do this, you need to restore it - that is, remove from the solution all the copper that it devoured from the printed circuit board. Look at the photo
Half of this nail was in the used ferric chloride solution. Thus, if you add a handful of nails, all the copper present in the solution will be deposited on them. What is characteristic is that the consumer qualities of the nails will not suffer at all from this.
However, let's return to our sheep. Or rather, to our almost finished board. She's already poisoned.
Now we wash it thoroughly, dry it and this is what happened:
Now again we take cotton wool, dip it in acetone and erase all the toner that now covers the tracks on the board.
Well, almost everything is ready - the last step remains.
Well, now all that remains is to drill holes for the elements and tin the tracks - that is, cover them with a thin layer of solder. We drill, you know, with a drill.
I used a drill with a diameter of 0.9 mm, which I recommend for you, unless of course you have large parts on the board. In general, of course, the diameter of the pins must be taken into account at the design stage of the printed circuit board, so as not to bite your elbows and redo everything later.
As for tinning, everything is quite simple - we cover the board with any liquid flux - the simplest is a 30% solution of rosin in alcohol. We heat up the soldering iron and, taking a minimum amount of solder onto the tip, begin to move it along the board tracks. Then we wipe the board with alcohol to remove excess flux.
A printed circuit board is a structural element that consists of a dielectric base and copper conductors, which are deposited on the base in the form of metallized areas. It provides the connection of all radio-electronic elements of the circuit.
A printed circuit board has a number of advantages compared to volumetric (hinged) installation using cables and wires:
- high installation density of radio components and their connections, resulting in a significant reduction in the dimensions and weight of the product;
- production of conductors and shielding surfaces, as well as radioelements in a single technological cycle;
- stability, repeatability of such characteristics as capacitance, conductivity, inductance;
- high performance and noise immunity of circuits;
- resistance to mechanical and climatic influences;
- standardization and unification of technological and design solutions;
- reliability of components, blocks and the device itself as a whole;
- increased manufacturability as a result of comprehensive automation of assembly work and control and regulatory actions;
- low labor intensity, material intensity and cost.
The printed circuit board also has disadvantages, but they are very few: limited maintainability and high complexity of adding design changes.
The elements of such boards include: a dielectric base, a metallized coating, which is a pattern of printed conductors, contact pads; fixing and mounting holes.
Requirements that GOST imposes on these products
- Printed circuit boards must have a dielectric base that is uniform in color, which must be monolithic in structure and free from internal bubbles, cavities, foreign inclusions, cracks, chips, and delaminations. However, single scratches, inclusions of metal, traces of a single removal of an unetched area, as well as the manifestation of the structure are allowed, which does not change the electrical parameters of the product and does not reduce the permissible distance between the elements of the design.
- The pattern is clear, with a smooth edge, without swelling, tears, peeling, or tool marks. Minor local mordants are allowed, but not more than five points per square decimeter, provided that the remaining width of the path corresponds to the minimum allowable; scratches up to six millimeters long and up to 25 microns deep.
To improve corrosion characteristics and increase solderability, the surface of the board is coated with an electrolytic composition, which must be continuous, without peeling, ruptures or burns. Fixing and mounting holes must be located in accordance with the drawing. It is allowed to have deviations determined by the accuracy class of the board. In order to improve the reliability of soldering, a layer of copper is sprayed onto all internal surfaces of the mounting holes, the thickness of which must be at least 25 microns. This process is called metallization of holes.
What are PCB classes? This concept refers to the accuracy classes of board manufacturing; they are provided for by GOST 23751-86. Depending on the density of the pattern, the printed circuit board has five options, the choice of which is determined by the level of technical equipment of the enterprise. The first and second classes do not require high-precision equipment and are considered cheap to produce. The fourth and fifth classes require special materials, specialized equipment, ideal cleanliness in production premises, and maintenance of temperature conditions. Domestic enterprises mass produce printed circuit boards of the third accuracy class.
