Basics of PCB layout. Radioelements produced by printing. Installation of inductors on simple printed circuit boards

Flat printed coils are most often used in the meter and decimeter wavelength ranges to reduce the size of the device. They are usually made with round, square, or meander-shaped coils, although it is also possible in the form of a polygon. Recently, with the advent of multilayer printed circuit board technology, multilayer coils on a printed circuit board have also appeared. The use of a core made of magnetic material is ineffective, since such a core is removed from the turns of the coil and can change its inductance by 3 - 5%, which in most cases is not enough. Therefore, printed inductors are used in most cases when adjustment is not required and the inductance value does not exceed microhenry units.

On our website you can use an online calculator to calculate coils on a printed circuit board

In the Coil32 program, starting from version 9.6, flat printed coils with round and square turns are calculated using the general empirical formula:

• L- inductance (µH)
• D- outer diameter of the spiral (mm)
• d- internal diameter of the spiral (mm)
• N- number of turns
• D avg- average coil diameter (mm)
• φ - fill factor

The coefficients c 1 - c 4 are summarized in the table:

The winding pitch in the figure is indicated as " s". With unchanged " s", if you increase the width of the turn, the quality factor of the coil and its own capacitance increases. Usually, to minimize the size of the coil, the width of the printed conductor is made close to the distance between the conductors, so in the formula the influence of " s" the amount of inductance is not taken into account. The optimal value d/D = 0.4 for a round coil and the program selects it automatically. For a square coil, the optimal value is d/D = 0.362 and the program also selects it automatically.

The error in calculating inductance using this formula does not exceed 8% when s is no more than 3w, i.e. if the gap between the strips is no more than twice the width of the strip.

An inductive element in the form of a direct printed conductor is calculated using the following empirical formula:

, Where:

• L- inductance (µH)
• l- conductor length (mm)
• b- conductor width (mm)

Such inductive elements are often used in UHF filters. Since the intrinsic capacitance of such an inductive element is quite large, it must be borne in mind that it is more correct to represent it as a segment of a long line with distributed parameters. However, for approximate calculations the simplification of the model adopted here is quite acceptable.

Many circuit elements can be produced by printing: resistors, capacitors, inductors, multi-turn coils of transformers and chokes, switches and plug connectors.

Printed resistors are made by applying thin varnish films to the surface of the board.

Their configuration (Fig. 35, a) can be very diverse and depends on the possibility of ensuring mechanical strength and heat transfer conditions. Variable resistors are also produced by printing, which consist of a conductive carbon or metal layer of an arc-shaped shape and a contact slider sliding along the surface of the conductive element. The resistance value of the printed resistor depends on the composition of the suspension, the shape of the pattern and the thickness of the film.

Film composite resistors of the SZ-4 type are widely used. These resistors are manufactured directly on the surface of the microboard. They can be used in the temperature range from -60 to +125°C, and the power dissipated by microresistors does not exceed 0.25 W.

Printed capacitors are made by applying two conductive plates to both sides of the insulating base (Fig. 35, b). The capacitance of a capacitor is determined by the area of ​​its plates and the thickness of the dielectric (board). In Fig. 35, c shows a semi-alternating printed capacitor, in which the stator plate is applied directly to the insulating base of the board, and the rotor plate is applied to a ceramic disk, which can rotate around an axis parallel to the plane of the board, changing the value of the capacitance. The use of ceramic materials makes it possible to obtain stable capacitors with ratings from a few to several hundred picofarads and an operating voltage of 100V or more.

Printed inductors (Fig. 35, d) are made in the form of flat spiral metallized lines of round, oval, square or other shapes printed on the board. The amount of inductance of such coils depends on the number of turns of the coil, the distance between them and their diameter. To increase the inductance of printed coils, they are made multilayer, with one coil separated from the other by an insulating layer of varnish, and the ends of the coils are connected to each other in series. In some cases, an increase in inductance is achieved by introducing magnetodielectric cores into the center of the spiral or by applying a layer of magnetic paint in the field of the coil. On printed circuits, you can also create variable inductance, for which a copper or aluminum plate is installed above the printed coil, which can be moved.

To increase the quality factor of the coils, a layer of silver with a thickness of 20...50 microns is added to them by galvanic means.

Printed transformers and chokes are made by applying individual spiral coils to a flexible base made of fluoroplastic, varnished fabric, baked paper or other insulating materials. The printed windings are connected to each other in series and placed in a special housing or pressed into a plastic shell.

Printed switches and plug connectors can be made either directly on the printed circuit board of the radio receiver, or on separate boards. A printed switch, even of the highest complexity, is cheaper than one made by any other method. To increase the resistance of the printed switch contacts to abrasion, they are coated with silver, which ensures reliable operation up to several hundred thousand switchings. To ensure increased durability, the copper contacts of the switches are coated with a layer of rhodium with a thickness of 6... 10 microns.

Printed elements are shielded, if necessary, by applying a layer of insulating varnish to the surface of the pattern, which is then covered with a layer of magnetic material. The shielding of conductors is not continuous, but mesh or slot-like.

A bit of antenna theory

At direct current or low frequencies, the active component predominates. As the frequency increases, the reactive component becomes more and more significant. In the range from 1 kHz to 10 kHz, the inductive component begins to take effect and the conductor is no longer a low-impedance connector, but rather acts as an inductor.

The formula for calculating the inductance of a PCB conductor is as follows:

Typically, traces on a printed circuit board have values ​​from 6 nH to 12 nH per centimeter of length. For example, a 10 cm conductor has a resistance of 57 mOhm and an inductance of 8 nH per cm. At a frequency of 100 kHz, the reactance becomes 50 mOhm, and at higher frequencies the conductor will be an inductance rather than a resistive one.

The rule for a whip antenna is that it begins to noticeably interact with the field at about 1/20 of the wavelength, and maximum interaction occurs at a rod length of 1/4 of the wavelength. Therefore, the 10 cm conductor from the example in the previous paragraph will start to become a pretty good antenna at frequencies above 150 MHz. It must be remembered that despite the fact that the clock generator of a digital circuit may not operate at frequencies above 150 MHz, higher harmonics are always present in its signal. If the printed circuit board contains components with pin pins of considerable length, then such pins can also serve as antennas.

The other main type of antenna is loop antenna. The inductance of a straight conductor increases greatly when it bends and becomes part of an arc. Increasing inductance lowers the frequency at which the antenna begins to interact with the field lines.

Experienced PCB designers with a reasonable understanding of loop antenna theory know not to design loops for critical signals. Some designers, however, do not think about this, and the return and signal current conductors in their circuits are loops. The creation of loop antennas is easy to demonstrate with an example (Fig. 8). In addition, the creation of a slot antenna is shown here.


Let's consider three cases:

Option A is an example of bad design. It does not use an analog ground polygon at all. The loop circuit is formed by the ground and signal conductors. When a current passes, an electric field and a magnetic field perpendicular to it arise. These fields form the basis of a loop antenna. The loop antenna rule states that for best efficiency, the length of each conductor should be equal to half the wavelength of the received radiation. However, we should not forget that even at 1/20 of the wavelength, the loop antenna is still quite effective.

Option B is better than Option A, but there is a gap in the polygon, probably to create a specific place for routing signal conductors. The signal and return current paths form a slot antenna. Other loops form in the cutouts around the chips.

Option B is an example of a better design. The signal and return current paths coincide, negating the effectiveness of the loop antenna. Note that this design also has cutouts around the chips, but they are separated from the return current path.

The theory of signal reflection and matching is close to the theory of antennas.

Capacitive coupling occurs between PCB conductors on different layers when they intersect. Sometimes this can create a problem. Conductors placed one above the other on adjacent layers create a long film capacitor. The capacity of such a capacitor is calculated using the formula shown in Figure 10.

For example, a printed circuit board may have the following parameters:
- 4 layers; the signal and ground polygon layers are adjacent,
- interlayer spacing - 0.2 mm,
- conductor width - 0.75 mm,
- conductor length - 7.5 mm.

The typical ER dielectric constant for FR-4 is 4.5.

Substituting all the values ​​into the formula, we get a capacitance value between these two buses equal to 1.1 pF. Even such a seemingly small capacity is unacceptable for some applications. Figure 11 illustrates the effect of a 1 pF capacitance when connected to the inverting input of a high-frequency op-amp.

It can be seen that the amplitude of the output signal doubles at frequencies close to the upper limit of the frequency range of the op-amp. This, in turn, can lead to oscillation, especially at antenna operating frequencies (above 180 MHz).

This effect gives rise to numerous problems, for which there are, however, many ways to solve them. The most obvious of them is reducing the length of the conductors. Another way is to reduce their width. There is no reason to use a conductor of this width to connect the signal to the inverting input, because Very little current flows through this conductor. Reducing the length of the trace to 2.5 mm and the width to 0.2 mm will lead to a decrease in capacitance to 0.1 pF, and such capacitance will no longer lead to such a significant increase in the frequency response. Another way to solve the problem is to remove part of the polygon under the inverting input and under the conductor leading to it.

Signal conductors should not be routed parallel to each other, except in the case of differential or microstrip lines. The gap between conductors should be at least three times the width of the conductors.

Capacitance between traces in analog circuits can create problems with large resistor values ​​(several megohms). The relatively large capacitive coupling between the inverting and non-inverting inputs of an op-amp can easily cause the circuit to oscillate.

Remember that if there are large resistances in the circuit, then special attention should be paid to cleaning the board. During the final operations of manufacturing a printed circuit board, any remaining flux and contaminants must be removed. Recently, when installing printed circuit boards, water-soluble fluxes are often used. Being less harmful, they are easily removed with water. But at the same time, washing the board with insufficiently clean water can lead to additional contamination that worsens the dielectric characteristics. Therefore, it is very important to clean the high-impedance circuit board with fresh distilled water.

SIGNAL ISOLATION

As already noted, interference can penetrate into the analog part of the circuit through the power supply circuits. To reduce such interference, decoupling (blocking) capacitors are used to reduce the local impedance of the power buses.

If you need to lay out a printed circuit board that has both analog and digital parts, then you need to have at least a small understanding of the electrical characteristics of the logic elements.

A typical logic gate output stage contains two transistors connected in series and located between the power and ground circuits (Fig. 14).

These transistors ideally operate strictly in antiphase, i.e. when one of them is open, then at the same moment in time the second is closed, generating either a logical one or a logical zero signal at the output. In the steady state logic state, the power consumption of the logic element is small.

The situation changes dramatically when the output stage switches from one logic state to another. In this case, for a short period of time, both transistors can be open simultaneously, and the supply current of the output stage increases greatly, since the resistance of the current path from the power bus to the ground bus through two series-connected transistors decreases. The power consumption increases abruptly and then quickly decreases, which leads to a local change in the supply voltage and the occurrence of a sharp, short-term change in current. These changes in current result in the emission of radio frequency energy. Even on a relatively simple printed circuit board there may be tens or hundreds of considered output stages of logic elements, so the total effect of their simultaneous operation can be very large.

It is impossible to accurately predict the frequency range in which these current surges will occur, since the frequency of their occurrence depends on many factors, including the propagation delay of switching transistors of the logic element. The delay, in turn, also depends on many random reasons that arise during the production process. Switching noise has a broadband distribution of harmonic components over the entire range. There are several methods for suppressing digital noise, the application of which depends on the spectral distribution of the noise.

Table 2 shows the maximum operating frequencies for common capacitor types.

table 2

From the table it is obvious that tantalum electrolytic capacitors are used for frequencies below 1 MHz; at higher frequencies, ceramic capacitors should be used. It must be remembered that capacitors have their own resonance, and their incorrect choice may not only not help, but also aggravate the problem. Figure 15 shows typical self-resonances of two common capacitors - 10 μF tantalum electrolytic and 0.01 μF ceramic.

Actual specifications may vary between different manufacturers and even from batch to batch within the same manufacturer. It is important to understand that for a capacitor to operate effectively, the frequencies it suppresses must be in a lower range than its own resonance frequency. Otherwise, the nature of the reactance will be inductive, and the capacitor will no longer work effectively.

Do not be mistaken that one 0.1 µF capacitor will suppress all frequencies. Small capacitors (10 nF or less) can operate more efficiently at higher frequencies.

IC power decoupling

The principle of power decoupling for integrated circuits to suppress high-frequency noise is to use one or more capacitors connected between the power and ground pins. It is important that the conductors connecting the leads to the capacitors are short. If this is not the case, then the self-inductance of the conductors will play a significant role and negate the benefits of using decoupling capacitors.

A decoupling capacitor must be connected to each chip package, regardless of whether there are 1, 2, or 4 op-amps inside the package. If the op amp is dual-supplied, then it goes without saying that decoupling capacitors should be located at each power pin. The capacitance value must be carefully selected depending on the type of noise and interference present in the circuit.

In particularly difficult cases, it may be necessary to add an inductance connected in series with the power output. The inductance should be located before, not after, the capacitors.

Another, cheaper way is to replace the inductance with a resistor with low resistance (10...100 Ohms). In this case, together with the decoupling capacitor, the resistor forms a low-pass filter. This method reduces the power supply range of the op-amp, which also becomes more dependent on power consumption.

Typically, to suppress low-frequency noise in power circuits, it is sufficient to use one or more aluminum or tantalum electrolytic capacitors at the power input connector. An additional ceramic capacitor will suppress high-frequency interference from other boards.

ISOLATION OF INPUT AND OUTPUT SIGNALS

Many noise problems result from directly connecting input and output pins. As a result of the high-frequency limitations of passive components, the response of a circuit when exposed to high-frequency noise can be quite unpredictable.

In a situation where the frequency range of the induced noise is significantly different from the frequency range of the circuit, the solution is simple and obvious - placing a passive RC filter to suppress high-frequency interference. However, when using a passive filter, you must be careful: its characteristics (due to the non-ideal frequency characteristics of passive components) lose their properties at frequencies 100...1000 times higher than the cutoff frequency (f 3db). When using series-connected filters tuned to different frequency ranges, the higher frequency filter should be closest to the source of interference. Also, inductors on ferrite rings can be used to suppress noise; they retain the inductive nature of the resistance up to a certain frequency, and above their resistance becomes active.

The interference on an analog circuit can be so large that getting rid of it (or at least reducing it) is only possible through the use of screens. To operate effectively, they must be carefully designed so that the frequencies that cause the most problems cannot enter the circuit. This means that the screen should not have holes or cutouts larger than 1/20 of the wavelength of the radiation being screened. It is a good idea to allocate sufficient space for the proposed shield from the very beginning of the PCB design. When using a shield, you can optionally use ferrite rings (or beads) for all connections to the circuit.

OPERATIONAL AMPLIFIER CASES

One, two, or four operational amplifiers are usually placed in one package (Fig. 16).

A single op amp often also has additional inputs, for example to adjust the offset voltage. Dual and quad op amps have only inverting and non-inverting inputs and output. Therefore, if it is necessary to have additional adjustments, it is necessary to use single operational amplifiers. When using additional outputs, it must be remembered that by their structure they are auxiliary inputs, so they must be managed carefully and in accordance with the manufacturer's recommendations.

In a single op amp, the output is located on the opposite side of the inputs. This can create difficulties when operating the amplifier at high frequencies due to the long feedback conductors. One way to overcome this is to place the amplifier and feedback components on different sides of the PCB. This, however, results in at least two additional holes and cuts in the ground polygon. Sometimes it is worth using a dual op amp to solve this problem, even if the second amplifier is not used (and its pins must be connected properly). Figure 17 illustrates the reduction in the length of the feedback circuit conductors for an inverting connection.

Dual op amps are especially common in stereo amplifiers, and quad op amps are used in multistage filter circuits. However, there is a rather significant disadvantage to this. Even though modern technology provides decent isolation between amplifier signals on the same silicon chip, there is still some crosstalk between them. If it is necessary to have a very small amount of such interference, then it is necessary to use single operational amplifiers. Crosstalk does not only occur when using dual or quad amplifiers. Their source can be the very close proximity of passive components of different channels.

Dual and quad op-amps, in addition to the above, allow for more dense installation. The individual amplifiers appear to be mirror-image relative to each other (Fig. 18).

Figures 17 and 18 do not show all connections required for normal operation, such as the mid-level driver on a single supply. Figure 19 shows a diagram of such a shaper when using a quad amplifier.

The diagram shows all the necessary connections to implement three independent inverting stages. It is necessary to pay attention to the fact that the conductors of the half-supply voltage driver are located directly under the integrated circuit housing, which makes it possible to reduce their length. This example illustrates not how connections should be made, but what should be done with component placement and routing. The average level voltage, for example, could be the same for all four amplifiers. Passive components can be sized accordingly. For example, frame size 0402 planar components match the pin spacing of a standard SO package. This allows conductor lengths for high frequency applications to be kept very short.

3D AND SURFACE MOUNTING

When placing op amps in DIP packages and passive components with lead wires, vias must be provided on the printed circuit board to mount them. Such components are currently used when there are no special requirements for the dimensions of the printed circuit board; They are usually cheaper, but the cost of the printed circuit board increases during the manufacturing process due to drilling additional holes for component leads.

In addition, when using external components, the dimensions of the board and the length of the conductors increase, which does not allow the circuit to operate at high frequencies. Vias have their own inductance, which also limits the dynamic characteristics of the circuit. Therefore, overhead components are not recommended for implementing high-frequency circuits or for analog circuits placed next to high-speed logic circuits.

Some designers, trying to reduce the length of the conductors, place resistors vertically. At first glance it may seem that this shortens the length of the route. However, this increases the path of current through the resistor, and the resistor itself represents a loop (turn of inductance). The emitting and receiving abilities increase many times over.

Surface mounting does not require a hole for each component lead. However, problems arise when testing the circuit, and it is necessary to use vias as test points, especially when using small components.

UNUSED OP-AMP SECTIONS

When using dual and quad op-amps in a circuit, some sections may remain unused and must be connected correctly in this case. Incorrect connections can lead to increased power consumption, more heat, and more noise from the op amps used in the same package. The pins of unused operational amplifiers can be connected as shown in Fig. 20a. Connecting pins with additional components (Fig. 20b) will make it easy to use this op-amp during setup.

CONCLUSION

Remember the following basic points and keep them in mind at all times when designing and wiring analog circuits.

Are common:

Think of a PCB as a component in an electrical circuit;
. have an awareness and understanding of sources of noise and interference;
. model and layout circuits.

Printed circuit board:

Use printed circuit boards only from high-quality material (for example, FR-4);
. circuits made on multilayer printed circuit boards are 20 dB less susceptible to external interference than circuits made on double-layer boards;
. use separated, non-overlapping polygons for different lands and feeds;
. Place the ground and power polygons on the inner layers of the PCB.

Components:

Be aware of the frequency limitations introduced by passive components and board traces;
. try to avoid vertical placement of passive components in high-speed circuits;
. For high-frequency circuits, use components designed for surface mounting;
. conductors should be shorter, the better;
. if a larger conductor length is required, then reduce its width;
. Unused pins of active components must be connected correctly.

Wiring:

Place the analog circuit near the power connector;
. never route conductors transmitting logic signals through the analog area of ​​the board, and vice versa;
. make the conductors suitable for the inverting input of the op-amp short;
. make sure that the conductors of the inverting and non-inverting inputs of the op-amp are not located parallel to each other over a long distance;
. try to avoid using extra vias, because... their own inductance may cause additional problems;
. do not route the conductors at right angles and smooth the tops of the corners if possible.

Interchange:

Use the correct types of capacitors to suppress noise in power supply circuits;
. To suppress low-frequency interference and noise, use tantalum capacitors at the power input connector;
. To suppress high-frequency interference and noise, use ceramic capacitors at the power input connector;
. use ceramic capacitors at each power pin of the microcircuit; if necessary, use several capacitors for different frequency ranges;
. if excitation occurs in the circuit, then it is necessary to use capacitors with a lower capacitance value, and not a larger one;
. in difficult cases, use series-connected resistors of low resistance or inductance in power circuits;
. Analog power decoupling capacitors should only be connected to the analog ground, not the digital ground.

Bruce Carter
Op Amps For Everyone, chapter 17
Circuit Board Layout Techniques
Design Reference, Texas Instruments, 2002

We thank the site elart.narod.ru for providing the translation

“Iron-laser” technology for manufacturing printed circuit boards(ULT) has become widespread in amateur radio circles in just a couple of years and allows one to obtain printed circuit boards of fairly high quality. Hand-drawn printed circuit boards require a lot of time and are not immune to errors.

Special requirements for pattern accuracy are imposed in the manufacture of printed inductors for high-frequency circuits. The edges of the coil conductors should be as smooth as possible, as this affects their quality factor. Manually drawing a multi-turn spiral coil is very problematic, and here the ULT may well have its say.

Rice. 1

Rice. 2

So, everything is in order. We launch the computer program SPRINT-LAYOUT, for example, version 5.0. Set in the program settings:

Grid scale - 1.25 mm;

Line width - 0.8 mm;

Board dimensions - 42.5x42.5 mm;

The outer diameter of the “patch” is 1.5 mm;

The diameter of the hole in the “patch” is 0.5 mm.

Find the center of the board and draw a coil conductor template (Fig. 1)along the coordinate grid using the CONDUCTOR tool, twisting the coil in the desired direction (the template requires a mirror image, but it can be obtained later, when printing). We install a “patch” at the beginning and end of the coil to connect the coil with the circuit elements.

In the print settings, we set the number of prints on a sheet, the distance between prints and, if it is necessary to “twist” the spool in the other direction, mirror printing of the design. You should print on smooth paper or special film, setting the printer settings to the maximum toner supply when printing.

Next we follow the standard ULT. We prepare foil fiberglass, clean the surface of the foil and degrease it, for example, with acetone. We apply the template with toner to the foil and iron it with a hot iron through a sheet of paper until the toner adheres securely to the foil.

Afterwards, soak the paper under running tap water (cold or room temperature) and carefully remove it in “pellets”, leaving the toner on the foil of the board. We etch the board and then remove the toner from it with a solvent, for example, acetone. The clear conductor of the high quality printed inductor remains on the board.

Printed coils with spiral turns using ULT are of slightly worse quality. This is due to the square shape of the image pixels, so the edges of the spiral coil conductor are jagged. True, these irregularities are quite small, and the quality of the reel, in general, is still higher than when done manually.

Open the SPRINT-LAYOUT version 5.0 program again. In the toolkit, select SPECIAL FORM - a tool for drawing polygons and spirals. Select the SPIRAL tab. Install:

Starting radius (START RADIUS) -2 mm;

Distance between turns (DISTANCE) - 1.5 mm;

Conductor width (TRACK WIDTH) -0.8 mm;

The number of turns (TURNS), for example, is 20.

The size of the board occupied by such a coil is 65x65 mm (Fig. 2).

Printed coils are usually coupled together in bandpass filters (BPFs) using small capacitors. However, their inductive coupling is also possible, the degree of which can be changed by changing the distance between the planes of the coils or eccentrically rotating one relative to the other. Fixed mounting of the coils relative to each other can be achieved

Build using dielectric struts.

The inductance of the coils can be adjusted by shorting the turns, breaking the printed conductor, or partially removing it. This will increase the circuit tuning frequency. A reduction in frequency can be achieved by soldering small-capacity SMD-type capacitors between the turns.

Manufacturing of VHF coils in the form of a meander, straight and curved lines, comb filters, etc. using ULT also adds elegance to the final product and, as a rule, increases their quality factor (due to the “smooth” edges of printed conductors). However, during production, one should remember the quality of the substrate material (fiberglass), which loses its insulator properties with increasing frequency. In equivalent circuits, the loss resistance in the dielectric should be connected in parallel with the printed coils, and this resistance will be lower, the higher the operating frequency and the worse the quality of the dielectric.

In practice, foil fiberglass can be fully used for the manufacture of printed resonant circuits up to the 2-meter range inclusive (up to approximately 150 MHz). Special high-frequency grades of fiberglass can be used in the range of 70 cm (up to approximately 470...500 MHz). At higher frequencies, foil-coated RF fluoroplastic (Teflon), ceramic or glass should be used.

A printed inductor has an increased quality factor due to a decrease in the interturn capacitance, obtained, on the one hand, due to the small thickness of the foil, and on the other, the “winding” pitch of the coil. A closed frame of grounded foil around the printed coil in its plane serves as a shield from other coils and printed conductors, but has little effect on the parameters of the coil if its periphery is under low RF voltage (connected to a common wire) and its center is under high.

Literature

1. G. Panasenko. Manufacturing of printing reels. - Radio, 1987, No. 5, P. 62.

In our turbulent age of electronics, the main advantages of an electronic product are small size, reliability, ease of installation and dismantling (disassembling equipment), low energy consumption and convenient usability ( from English- Ease of use). All these advantages are by no means possible without surface mount technology - SMT technology ( S urface M ount T echnology), and of course, without SMD components.

What are SMD components

SMD components are used in absolutely all modern electronics. SMD ( S urface M mounted D evice), which translated from English means “surface-mounted device.” In our case, the surface is a printed circuit board, without through holes for radio elements:

In this case, SMD components are not inserted into the holes of the boards. They are soldered onto contact tracks, which are located directly on the surface of the printed circuit board. The photo below shows tin-colored contact pads on a mobile phone board that previously had SMD components.

Pros of SMD components

The biggest advantage of SMD components is their small size. The photo below shows simple resistors and:

Thanks to the small dimensions of SMD components, developers have the opportunity to place a larger number of components per unit area than simple output radio elements. Consequently, the installation density increases and, as a result, the dimensions of electronic devices decrease. Since the weight of an SMD component is many times lighter than the weight of the same simple output radio element, the weight of the radio equipment will also be many times lighter.

SMD components are much easier to desolder. For this we need a hairdryer. You can read how to desolder and solder SMD components in the article on how to solder SMDs correctly. It's much more difficult to seal them. In factories, special robots place them on a printed circuit board. No one solders them manually in production, except for radio amateurs and radio equipment repairmen.

Multilayer boards

Since equipment with SMD components has a very dense installation, there should be more tracks on the board. Not all tracks fit on one surface, so printed circuit boards are made multilayer. If the equipment is complex and has a lot of SMD components, then the board will have more layers. It's like a multi-layer cake made from short layers. The printed tracks connecting SMD components are located directly inside the board and cannot be seen in any way. An example of multilayer boards is mobile phone boards, computer or laptop boards (motherboard, video card, RAM, etc.).

In the photo below, the blue board is the Iphone 3g, the green board is the computer motherboard.

All radio equipment repairers know that if a multilayer board is overheated, it will swell with a bubble. In this case, the interlayer connections break and the board becomes unusable. Therefore, the main trump card when replacing SMD components is the correct temperature.

Some boards use both sides of the printed circuit board, and the mounting density, as you understand, doubles. This is another advantage of SMT technology. Oh yes, it’s also worth taking into account the fact that the material required for the production of SMD components is much less, and their cost during mass production of millions of pieces literally costs pennies.

Main types of SMD components

Let's look at the main SMD elements used in our modern devices. Resistors, capacitors, low-value inductors, and other components look like ordinary small rectangles, or rather, parallelepipeds))

On boards without a circuit, it is impossible to know whether it is a resistor, a capacitor, or even a coil. The Chinese mark as they please. On large SMD elements, they still put a code or numbers to determine their identity and value. In the photo below, these elements are marked in a red rectangle. Without a diagram, it is impossible to say what type of radio elements they belong to, as well as their rating.

The standard sizes of SMD components may be different. Here is a description of the standard sizes for resistors and capacitors. Here, for example, is a yellow rectangular SMD capacitor. They are also called tantalum or simply tantalum:

And this is what SMDs look like:

There are also these types of SMD transistors:

Which have a high denomination, in SMD version they look like this:

And of course, how could we live without microcircuits in our age of microelectronics! There are many SMD types of chip packages, but I divide them mainly into two groups:

1) Microcircuits in which the pins are parallel to the printed circuit board and are located on both sides or along the perimeter.

2) Microcircuits in which the pins are located under the microcircuit itself. This is a special class of microcircuits called BGA (from English Ball grid array- an array of balls). The terminals of such microcircuits are simple solder balls of the same size.

The photo below shows a BGA chip and its reverse side, consisting of ball pins.

BGA chips are convenient for manufacturers because they greatly save space on the printed circuit board, because there can be thousands of such balls under any BGA chip. This makes life much easier for manufacturers, but does not make life any easier for repairmen.

Summary

What should you use in your designs? If your hands don’t shake and you want to make a small radio bug, then the choice is obvious. But still, in amateur radio designs, dimensions do not play a big role, and soldering massive radio elements is much easier and more convenient. Some radio amateurs use both. Every day more and more new microcircuits and SMD components are being developed. Smaller, thinner, more reliable. The future definitely belongs to microelectronics.