In general, the term SMD (from the English. Surface Mounted Device) can be attributed to any small-sized electronic component designed to be mounted on the surface of the board using SMT technology (surface mount technology).
SMT technology (from the English. Surface mount technology) was developed in order to reduce the cost of production, increase the efficiency of manufacturing printed circuit boards using smaller electronic components: resistors, capacitors, transistors, etc. Today we will consider one of these - SMD resistor.
SMD resistors
SMD resistors- These are miniature, designed for surface mounting. SMD resistors are significantly smaller than their traditional counterpart. They are often square, rectangular, or oval in shape, with a very low profile.
Instead of the wire leads of conventional resistors, which are inserted into holes in the PCB, SMD resistors have small contacts that are soldered to the surface of the resistor body. This eliminates the need to make holes in the printed circuit board, and thus allows more efficient use of its entire surface.
Sizes of SMD resistors
Basically, the term frame size includes the size, shape, and pin configuration (package type) of an electronic component. For example, the configuration of a conventional chip that has a flat package with double-sided pinout (perpendicular to the plane of the base) is called a DIP.
Size of SMD resistors are standardized and most manufacturers use the JEDEC standard. The size of SMD resistors is indicated by a numerical code, for example, 0603. The code contains information about the length and width of the resistor. So in our example, code 0603 (in inches), the case is 0.060 inches long by 0.030 inches wide.
The same size resistor in the metric system will have code 1608 (in millimeters), respectively, the length is 1.6 mm, the width is 0.8 mm. To convert the dimensions to millimeters, it is enough to multiply the size in inches by 2.54.
Sizes of SMD resistors and their power
The size of the SMD resistor depends mainly on the required power dissipation. The following table lists the sizes and specifications of the most commonly used SMD resistors.
Marking SMD resistors
Due to the small size of SMD resistors, it is almost impossible to apply traditional resistor color markings to them.
In this regard, a special marking method was developed. The most common marking contains three or four numbers, or two numbers and a letter, which has the name EIA-96.
Marking with 3 and 4 digits
In this system, the first two or three digits indicate the numerical value of the resistance of the resistor, and the last digit indicates the multiplier. This last digit indicates the power to which 10 must be raised to get the final multiplier.
A few more examples of determining resistance within this system:
- 450 \u003d 45 x 10 0 is equal to 45 ohms
- 273 \u003d 27 x 10 3 is equal to 27000 ohms (27 kOhm)
- 7992 \u003d 799 x 10 2 is equal to 79900 ohms (79.9 kOhm)
- 1733 \u003d 173 x 10 3 is equal to 173000 ohms (173 kOhm)
The letter “R” is used to indicate the position of the decimal point for resistance values below 10 ohms. Thus, 0R5 = 0.5 ohm and 0R01 = 0.01 ohm.
SMD resistors of increased accuracy (precision), combined with small sizes, have created a need for a new, more compact marking. In this regard, the EIA-96 standard was created. This standard is for resistors with a resistance tolerance of 1%.
This marking system consists of three elements: two digits indicate the code, and the letter following them determines the multiplier. The two digits are a code that gives a three-digit resistance number (see table)
For example, code 04 means 107 ohms and 60 means 412 ohms. The multiplier gives the final value of the resistor, for example:
- 01A = 100 ohm ±1%
- 38C = 24300 Ohm ±1%
- 92Z = 0.887 ohm ±1%
Online SMD resistor calculator
This calculator will help you find the resistance value of SMD resistors. Just enter the code written on the resistor and its resistance will be displayed at the bottom.
The calculator can be used to determine the resistance of SMD resistors that are marked with 3 or 4 digits, as well as according to the EIA-96 standard (2 digits + letter).
Although we have done our best to test the function of this calculator, we cannot guarantee that it calculates the correct values for all resistors, as sometimes manufacturers may use their own custom codes.
Therefore, to be absolutely sure of the resistance value, it is best to additionally measure the resistance with a multimeter.
A resistor is an element that has some kind of resistance and is used in electronics and electrical engineering to limit current or obtain the necessary voltages (for example, using a resistive divider). SMD resistors are surface mount resistors, in other words, mounting on the surface of a printed circuit board.
The main characteristics for resistors are the nominal resistance, measured in ohms and depends on the thickness, length and materials of the resistive layer, as well as the power dissipation.
Electronic components for surface mounting are small in size due to the fact that they either do not have terminals for connection in the classical sense. Elements for volumetric mounting have long leads.
Previously, when assembling REA, they connected the components of the circuit to each other (hinged mounting) or threaded them through the printed circuit board into the appropriate holes. Structurally, their conclusions or contacts are made in the form of metallized areas on the body of the elements. In the case of microcircuits and surface-mount transistors, the elements have short rigid “legs”.
One of the main characteristics of SMD resistors is the size. This is the value of the length and width of the case, according to these parameters, elements are selected that correspond to the layout of the board. Usually, dimensions in the documentation are written in abbreviated four-digit numbers, where the first two digits indicate the length of the element in mm, and the second pair of characters indicate the width in mm. However, in fact, the dimensions may differ from the markings depending on the types and series of elements.
Typical sizes of SMD resistors and their parameters
Figure 1 - designations for decoding standard sizes.
1. SMD resistors 0201 :
L=0.6mm; W=0.3mm; H=0.23mm; L1=0.13 m.
Rated power: 0.05W
Working voltage: 15V
Maximum allowable voltage: 50V
2. SMD resistors 0402 :
L=1.0mm; W=0.5mm; H=0.35mm; L1=0.25 mm.
Rating range: 0 ohm, 1 ohm - 30 MΩ
Permissible deviation from the nominal value: 1% (F); 5% (J)
Rated power: 0.062W
Working voltage: 50V
Operating temperature range: -55 - +125 °С
3. SMD resistors 0603 :
L=1.6mm; W=0.8mm; H=0.45mm; L1=0.3 mm.
Rating range: 0 ohm, 1 ohm - 30 MΩ
Permissible deviation from the nominal value: 1% (F); 5% (J)
Rated power: 0.1W
Working voltage: 50V
Maximum allowable voltage: 100V
Operating temperature range: -55 - +125 °С
4. SMD resistors 0805 :
L=2.0mm; W=1.2mm; H=0.4mm; L1=0.4 mm.
Rating range: 0 ohm, 1 ohm - 30 MΩ
Permissible deviation from the nominal value: 1% (F); 5% (J)
Rated power: 0.125W
Working voltage: 150V
Maximum allowable voltage: 200V
Operating temperature range: -55 - +125 °С
5. SMD resistors 1206 :
L=3.2mm; W=1.6mm; H=0.5mm; L1=0.5 mm.
Rating range: 0 ohm, 1 ohm - 30 MΩ
Permissible deviation from the nominal value: 1% (F); 5% (J)
Rated power: 0.25W
Working voltage: 200V
Operating temperature range: -55 - +125 °С
6. SMD resistors 2010 :
L=5.0mm; W=2.5mm; H=0.55mm; L1=0.5 mm.
Rating range: 0 ohm, 1 ohm - 30 MΩ
Permissible deviation from the nominal value: 1% (F); 5% (J)
Rated power: 0.75W
Working voltage: 200V
Maximum allowable voltage: 400V
Operating temperature range: -55 - +125 °С
7. SMD resistors 2512 :
L=6.35mm; W=3.2mm; H=0.55mm; L1=0.5 mm.
Rating range: 0 ohm, 1 ohm - 30 MΩ
Permissible deviation from the nominal value: 1% (F); 5% (J)
Rated power: 1W
Working voltage: 200V
Maximum allowable voltage: 400V
Operating temperature range: -55 - +125 °С
As you can see, with an increase in the size of the chip resistor, the nominal power dissipation also increases in the table below, this dependence is more clearly shown, as well as the geometric dimensions of resistors of other types:
Table 1 - Marking SMD resistors
Depending on the size, one of three types of marking of the resistor value can be used. There are three types of markings:
1. With 3 digits. In this case, the first two indicate the number of ohms, and the last number of zeros. This is how resistors from the E-24 series are marked, with a deviation from the nominal value (tolerance) of 1 or 5%. The size of resistors with this marking is 0603, 0805 and 1206. An example of such marking: 101 \u003d 100 \u003d 100 Ohm
Figure 2 is an image of a 10,000 ohm SMD resistor, aka 10 kOhm.
2. With 4 characters. In this case, the first 3 digits indicate the number of ohms, and the last - the number of zeros. This is how resistors from the E-96 series of sizes 0805, 1206 are described. If the letter R is present in the marking, it plays the role of a comma separating integers from fractions. Thus, the marking 4402 stands for 44,000 ohms or 44 kOhm.
Figure 3 - image of an SMD resistor with a nominal value of 44 kOhm
3. Marking with a combination of 3 characters - numbers and letters. In this case, the first 2 characters are numbers, they indicate the encoded resistance value in Ohms. The third character is the multiplier. In this way, resistors of size 0603 from the E-96 series of resistances are marked, with a tolerance of 1%. Translation of letters into a multiplier is performed in a row: S=10^-2; R=10^-1; B=10; C=10^2; D=10^3; E=104; F=10^5.
The decoding of the codes (the first two characters) is carried out according to the table shown below.
Table 2 - decoding of marking codes for SMD resistors
Figure 4 - a resistor with a three-character marking 10C, if you use the table and the given series of factors, then 10 is 124 Ohms, and C is a factor of 10 ^ 2, which equals 12,400 Ohms or 12.4 kOhm.
Basic parameters of resistors
Figure 5 - Resistor equivalent circuit
So, inductance and capacitance are elements that affect the impedance and the fronts of currents and voltages depending on frequency. The best in terms of frequency characteristics are the elements for surface mounting, due to their small size.
Figure 6 - The graph shows the ratio of the total resistance of the resistor to the active one at various frequencies
Resistor design
Surface mount resistors are cheap and convenient for assembly line automated assembly of electronic devices. However, they are not as simple as they might seem.
Figure 7 - The internal structure of the SMD resistor
The basis of the resistor is a substrate of Al2O3 - aluminum oxide. It is a good dielectric and a material with good thermal conductivity, which is no less important, since during operation the entire power of the resistor is released into heat.
As a resistive layer, a thin metal or oxide film is used, for example, chromium, ruthenium dioxide (as shown in the figure above). The characteristics of the resistors depend on the material of which this film is composed. The resistive layer of individual resistors is a film up to 10 microns thick, made of a material with a low TCR (temperature coefficient of resistance), which gives high temperature stability of the parameters and the ability to create high-precision elements, an example of such a material is constantan, however, the ratings of such resistors rarely exceed 100 ohms.
The contact pads of the resistor are formed from a set of layers. The inner contact layer is made of expensive materials like silver or palladium. Intermediate - nickel. And the outer one is lead-tin. This design is due to the need to ensure high adhesion (cohesion) of the layers. The reliability of contacts and noise depend on them.
Figure 8 - shape of the resistive layer
The installation of such elements takes place in furnaces, and in amateur radio workshops using a blow dryer, that is, a stream of hot air. Therefore, in their manufacture, attention is paid to the temperature curve of heating and cooling.
Figure 9 - heating and cooling curve when soldering SMD resistors
conclusions
The use of surface-mounted components had a positive effect on the weight and size indicators of electronic equipment, as well as on the frequency characteristics of the element. Modern industry produces most of the common elements in the SMD version. Including: resistors, capacitors, diodes, LEDs, transistors, thyristors, integrated circuits.
In our turbulent age of electronics, the main advantages of an electronic product are small dimensions, reliability, ease of installation and dismantling (disassembly of 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 face 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 face M ounted D evice), which is translated from English as “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 board holes. They are soldered onto the contact tracks, which are located directly on the surface of the printed circuit board. In the photo below, there are tin-colored contact pads on the board of a mobile phone that used to have SMD components.
Advantages of SMD components
The biggest advantage of SMD components is their small size. In the photo below, simple resistors and:
Due 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 mounting density increases and, as a result, the dimensions of electronic devices are reduced. Since the weight of the SMD component is several times lighter than the weight of the same simple output radio element, the mass of the radio equipment will also be many times lighter.
SMD components are much easier to desolder. For this we need a hair dryer. How to solder and solder SMD components, you can read in the article how to solder SMD correctly. Soldering them is much more difficult. In factories, they are placed on a printed circuit board by special robots. No one welds them manually in production, except for radio amateurs and radio equipment repairmen.
Multilayer boards
Since in equipment with SMD components there is a very dense installation, there should be more tracks in the board. Not all tracks fit on the same surface, so printed circuit boards make multilayer. If the equipment is complex and has a lot of SMD components, then there will be more layers in the board. It's like a layered cake. The printed tracks connecting the SMD components are located right 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 Iphone 3g, the green board is the computer motherboard.
All radio repairers know that if you overheat a multilayer board, it will swell up with a bubble. In this case, the interlayer connections are torn and the board becomes unusable. Therefore, the main trump card when replacing SMD components is the right temperature.
On some boards, both sides of the printed circuit board are used, while the mounting density, as you understand, is doubled. This is another plus of SMT technology. Oh yes, it is also worth considering the fact that the material for the production of SMD components takes many times less, and their cost in mass production in millions of pieces costs, literally, a penny.
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, or a capacitor, or even a coil. The Chinese mark as they want. On large SMD elements, they still put a code or numbers to determine their belonging and denomination. 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 denomination.
Sizes of SMD components can be different. Here is a description of the sizes for resistors and capacitors. Here, for example, is a rectangular yellow SMD capacitor. They are also called tantalum or simply tantalum:
And this is what SMD looks like:
There are also these types of SMD transistors:
Which have a large denomination, in the SMD version they look like this:
And of course, how could it be without microcircuits in our age of microelectronics! There are a lot of SMD chip package types, but I mainly divide them into two groups:
1) Microcircuits, in which the leads are parallel to the printed circuit board and are located on both sides or around the perimeter.
2) Microcircuits, in which the conclusions 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 conclusions of such microcircuits are simple solder balls of the same size.
In the photo below, the BGA microcircuit and its reverse side, consisting of ball leads.
BGA chips are convenient for manufacturers in that they greatly save space on the printed circuit board, because there can be thousands of such balls under any BGA chip. This greatly simplifies the life of manufacturers, but does not make life easier for repairmen.
Summary
What do you use in your designs? If your hands are not shaking, and you want to make a small radio bug, then the choice is obvious. But still, in amateur radio designs, dimensions do not particularly 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 chips and SMD components are being developed. Smaller, thinner, more reliable. The future, unambiguously, belongs to microelectronics.
We have already got acquainted with the main radio components: resistors, capacitors, diodes, transistors, microcircuits, etc., and also studied how they are mounted on a printed circuit board. Once again, let's recall the main stages of this process: the leads of all components are passed into the holes available in the printed circuit board. After that, the conclusions are cut off, and then soldering is performed on the reverse side of the board (see Fig. 1).
This process already known to us is called DIP editing. This installation is very convenient for beginner radio amateurs: the components are large, you can solder them even with a large “Soviet” soldering iron without the help of a magnifying glass or microscope. That is why all Master Kits for self-soldering involve DIP mounting.
Rice. 1. DIP mounting
But DIP editing has very significant disadvantages:
Large radio components are not suitable for creating modern miniature electronic devices;
- output radio components are more expensive to manufacture;
- PCB for DIP-mounting is also more expensive due to the need to drill many holes;
- DIP mounting is difficult to automate: in most cases, even in large electronics factories, installation and soldering of DIP parts must be done manually. It is very expensive and time consuming.
Therefore, DIP-mounting is practically not used in the production of modern electronics, and it was replaced by the so-called SMD-process, which is the standard of today. Therefore, any radio amateur should have at least a general idea about it.
SMD mounting
SMD components (chip components) are electronic circuit components applied to a printed circuit board using surface mount technology - SMT technology (Eng. surface mount technology). That is, all electronic elements that are “fixed” on the board in this way are called smd components(English) surface mounted device). The process of mounting and soldering chip components is properly called the SMT process. It is not entirely correct to say “SMD-assembly”, but in Russia this version of the name of the technical process has taken root, so we will say the same.
On fig. 2. shows a section of the SMD mounting board. The same board, made on DIP-elements, will have several times larger dimensions.
Fig.2. SMD mounting
SMD mounting has undeniable advantages:
Radio components are cheap to manufacture and can be arbitrarily miniature;
- printed circuit boards are also cheaper due to the lack of multiple drilling;
- installation is easy to automate: installation and soldering of components is carried out by special robots. There is also no such technological operation as trimming the leads.
SMD resistors
Acquaintance with chip components is most logical to start with resistors, as with the simplest and most massive radio components.
The SMD resistor in terms of its physical properties is similar to the “usual”, output version we have already studied. All its physical parameters (resistance, accuracy, power) are exactly the same, only the case is different. The same rule applies to all other SMD components.
Rice. 3. CHIP resistors
Sizes of SMD resistors
We already know that output resistors have a certain grid of standard sizes, depending on their power: 0.125W, 0.25W, 0.5W, 1W, etc.
Chip resistors also have a standard size grid, only in this case the size is indicated by a four-digit code: 0402, 0603, 0805, 1206, etc.
The main sizes of resistors and their technical characteristics are shown in Fig.4.
Rice. 4 Main sizes and parameters of chip resistors
Marking SMD resistors
Resistors are marked with a code on the case.
If there are three or four digits in the code, then the last digit means the number of zeros, in fig. 5. The resistor with the code "223" has the following resistance: 22 (and three zeros on the right) Ohm = 22000 Ohm = 22 kOhm. The resistor with the code "8202" has a resistance: 820 (and two zeros on the right) Ohm = 82000 Ohm = 82 kOhm.
In some cases, the marking is alphanumeric. For example, a resistor coded 4R7 has a resistance of 4.7 ohms, and a resistor coded 0R22 has a resistance of 0.22 ohms (here, the letter R is the separator character).
There are also resistors of zero resistance, or jumper resistors. Often they are used as fuses.
Of course, you can not remember the code designation system, but simply measure the resistance of the resistor with a multimeter.
Rice. 5 Marking chip resistors
Ceramic SMD Capacitors
Externally, SMD capacitors are very similar to resistors (see Fig. 6.). There is only one problem: they do not have a capacitance code, so the only way to determine it is to measure it with a multimeter that has a capacitance measurement mode.
SMD capacitors are also available in standard sizes, usually similar to resistor sizes (see above).
Rice. 6. SMD ceramic capacitors
Electrolytic SMS Capacitors
Fig.7. Electrolytic SMS Capacitors
These capacitors are similar to their output counterparts, and the markings on them are usually explicit: capacitance and operating voltage. A strip on the "hat" of the capacitor marks its negative terminal.
SMD transistors
Fig.8. SMD transistor
Transistors are small, so it is impossible to write their full name on them. They are limited to code marking, and there is no international standard for designations. For example, the code 1E may indicate the type of transistor BC847A, or maybe some other. But this circumstance absolutely does not bother either manufacturers or ordinary consumers of electronics. Difficulties can only arise during repairs. Determining the type of transistor installed on a printed circuit board without the manufacturer's documentation for this board can sometimes be very difficult.
SMD Diodes and SMD LEDs
Photos of some diodes are shown in the figure below:
Fig.9. SMD Diodes and SMD LEDs
On the body of the diode, the polarity must be indicated in the form of a strip closer to one of the edges. Usually the cathode output is marked with a stripe.
The SMD LED also has a polarity, which is indicated either by a dot near one of the pins, or in some other way (for details, see the component manufacturer's documentation).
It is difficult to determine the type of SMD diode or LED, as in the case of a transistor: an uninformative code is stamped on the diode case, and most often there are no marks on the LED case at all, except for the polarity mark. Developers and manufacturers of modern electronics care little about its maintainability. It is understood that the repair of the printed circuit board will be a service engineer who has complete documentation for a particular product. Such documentation clearly describes where a particular component is installed on the printed circuit board.
Installation and soldering of SMD components
SMD assembly is optimized primarily for automatic assembly by special industrial robots. But amateur radio amateur designs can also be made on chip components: with sufficient accuracy and care, you can solder parts the size of a grain of rice with the most ordinary soldering iron, you only need to know some subtleties.
But this is a topic for a separate large lesson, so more details about automatic and manual SMD editing will be discussed separately.
