We have already become acquainted with the main radio components: resistors, capacitors, diodes, transistors, microcircuits, etc., and also studied how they are mounted on a printed circuit board. Let us once again recall the main stages of this process: the leads of all components are passed into the holes in the printed circuit board. After which the leads are cut off, and then soldering is done on the back 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, they can be soldered even with a large “Soviet” soldering iron without the help of a magnifying glass or microscope. That is why all Master Kit kits for do-it-yourself soldering involve DIP mounting.
Rice. 1. DIP installation
But DIP installation has very significant disadvantages:
Large radio components are not suitable for creating modern miniature electronic devices;
- output radio components are more expensive to produce;
- a printed circuit board for DIP mounting is also more expensive due to the need to drill many holes;
- DIP installation 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Therefore, DIP mounting is practically not used in the production of modern electronics, and it has been replaced by the so-called SMD process, which is the standard of today.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 components of an electronic circuit printed on a printed circuit board using surface mounting technology - SMT technology. 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 correctly called the SMT process. Saying “SMD installation” is not entirely correct, but in Russia this version of the name of the technical process has taken root, so we will say the same.
In 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 installation has undeniable advantages:
Radio components are cheap to produce and can be as miniature as desired;
- printed circuit boards are also cheaper due to the absence 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 cutting leads.
SMD resistors
It is most logical to start getting acquainted with chip components with resistors, as the simplest and most widespread radio components.
The SMD resistor is similar in its physical properties to the “conventional” output version that we have already studied. All its physical parameters (resistance, accuracy, power) are exactly the same, only the body is different. The same rule applies to all other SMD components.
Rice. 3. CHIP resistors
Standard 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.
A standard grid of standard sizes is also available for chip resistors, only in this case the standard 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 Basic sizes and parameters of chip resistors
Marking of SMD resistors
Resistors are marked with a code on the case.
If the code has three or four digits, then the last digit means the number of zeros. In Fig. 5. resistor with code “223” has the following resistance: 22 (and three zeros to the right) Ohm = 22000 Ohm = 22 kOhm. Resistor code "8202" has a resistance of: 820 (and two zeros on the right) Ohm = 82000 Ohm = 82 kOhm.
In some cases, the marking is alphanumeric. For example, a resistor with code 4R7 has a resistance of 4.7 Ohms, and a resistor with code 0R22 has a resistance of 0.22 Ohms (here the letter R is the separator character).
There are also zero resistance resistors, or jumper resistors. They are often used as fuses.
Of course, you don’t have to remember the code system, but simply measure the resistance of the resistor with a multimeter.
Rice. 5 Marking of chip resistors
Ceramic SMD capacitors
Externally, SMD capacitors are very similar to resistors (see Fig. 6.). There is only one problem: the capacitance code is not marked on them, 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. Ceramic SMD capacitors
Electrolytic SMS capacitors
Fig.7. Electrolytic SMS capacitors
These capacitors are similar to their lead-out counterparts, and the markings on them are usually clear: capacitance and operating voltage. A stripe on the cap 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 markings, and there is no international standard for designations. For example, code 1E may indicate the type of transistor BC847A, or maybe some other one. But this circumstance does not bother either manufacturers or ordinary consumers of electronics at all. 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
The polarity must be indicated on the diode body in the form of a stripe closer to one of the edges. Usually the cathode terminal is marked with a stripe.
An SMD LED also has a polarity, which is indicated either by a dot near one of the pins, or in some other way (you can find out more about this in the documentation of the component manufacturer).
Determining the type of SMD diode or LED, as in the case of a transistor, is difficult: an uninformative code is stamped on the diode body, and most often there are no marks at all on the LED body, except for the polarity mark. Developers and manufacturers of modern electronics care little about their maintainability. It is assumed that the printed circuit board will be repaired by a service engineer who has complete documentation for a specific product. Such documentation clearly describes where on the printed circuit board a particular component is installed.
Installation and soldering of SMD components
SMD assembly is optimized primarily for automatic assembly by special industrial robots. But amateur radio designs can also be made using chip components: with sufficient care and attention, you can solder parts the size of a grain of rice with the most ordinary soldering iron, you only need to know a few subtleties.
But this is a topic for a separate large lesson, so more details about automatic and manual SMD installation will be discussed separately.
A resistor is an element that has some kind of resistance, used in electronics and electrical engineering to limit current or obtain the necessary voltages (for example, using a resistive divider). SMD resistors are resistors for surface mounting, 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 depending on the thickness, length and materials of the resistive layer, as well as power dissipation.
Electronic components for surface mounting are small in size due to the fact that they either do not have pins for connection in the classical sense. Elements for volumetric installation have long leads.
Previously, when assembling electronic devices, they connected circuit components to each other (hinged mounting) or threaded them through a printed circuit board into the corresponding holes. Structurally, their leads or contacts are made in the form of metallized pads on the body of the elements. In the case of surface-mount microcircuits and transistors, the elements have short, rigid “legs”.
One of the main characteristics of SMD resistors is their size. This is the length and width of the case; according to these parameters, elements corresponding to the board layout are selected. Typically, dimensions in documentation are written abbreviated as a four-digit number, 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=0.6 mm; W=0.3 mm; H=0.23 mm; L1=0.13 m.
Rated power: 0.05W
Operating voltage: 15V
Maximum permissible voltage: 50 V
2. SMD resistors 0402 :
L=1.0 mm; W=0.5 mm; H=0.35 mm; L1=0.25 mm.
Nominal range: 0 ohm, 1 ohm - 30 MOhm
Permissible deviation from nominal value: 1% (F); 5% (J)
Rated power: 0.062W
Operating voltage: 50V
Operating temperature range: –55 - +125 °C
3. SMD resistors 0603 :
L=1.6 mm; W=0.8 mm; H=0.45 mm; L1=0.3 mm.
Nominal range: 0 ohm, 1 ohm - 30 MOhm
Permissible deviation from nominal value: 1% (F); 5% (J)
Rated power: 0.1W
Operating voltage: 50V
Maximum permissible voltage: 100 V
Operating temperature range: –55 - +125 °C
4. SMD resistors 0805 :
L=2.0 mm; W=1.2 mm; H=0.4 mm; L1=0.4 mm.
Nominal range: 0 ohm, 1 ohm - 30 MOhm
Permissible deviation from nominal value: 1% (F); 5% (J)
Rated power: 0.125W
Operating voltage: 150V
Maximum permissible voltage: 200 V
Operating temperature range: –55 - +125 °C
5. SMD resistors 1206 :
L=3.2 mm; W=1.6 mm; H=0.5 mm; L1=0.5 mm.
Nominal range: 0 ohm, 1 ohm - 30 MOhm
Permissible deviation from nominal value: 1% (F); 5% (J)
Rated power: 0.25W
Operating voltage: 200V
Operating temperature range: –55 - +125 °C
6. SMD resistors 2010 :
L=5.0 mm; W=2.5 mm; H=0.55 mm; L1=0.5 mm.
Nominal range: 0 ohm, 1 ohm - 30 MOhm
Permissible deviation from nominal value: 1% (F); 5% (J)
Rated power: 0.75W
Operating voltage: 200V
Maximum permissible voltage: 400 V
Operating temperature range: –55 - +125 °C
7. SMD resistors 2512 :
L=6.35 mm; W=3.2 mm; H=0.55 mm; L1=0.5 mm.
Nominal range: 0 ohm, 1 ohm - 30 MOhm
Permissible deviation from nominal value: 1% (F); 5% (J)
Rated power: 1W
Operating voltage: 200V
Maximum permissible voltage: 400 V
Operating temperature range: –55 - +125 °C
As you can see, as the size of the chip resistor increases, the rated power dissipation also increases. The table below shows this relationship more clearly, as well as the geometric dimensions of other types of resistors:
Table 1 – Marking of SMD resistors
Depending on the size, one of three types of resistor rating markings can be used. There are three types of markings:
1. Using 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 standard size of resistors with this marking is 0603, 0805 and 1206. An example of such marking: 101 = 100 = 100 Ohm
Figure 2 is an image of an SMD resistor with a nominal value of 10,000 Ohms, also known as 10 kOhms.
2. Using 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 whole numbers from fractions. Thus, the marking 4402 stands for 44,000 Ohms or 44 kOhms.
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 indicating the encoded resistance value in Ohms. The third symbol is the multiplier. In this way, resistors of size 0603 from the E-96 resistance series are marked, with a tolerance of 1%. The translation of letters into a multiplier is carried out in the following series: 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 SMD resistor marking codes
Figure 4 is a resistor with a three-character marking 10C; if you use the table and the given series of multipliers, then 10 is 124 Ohms, and C is a multiplier of 10^2, which equals 12,400 Ohms or 12.4 kOhms.
Basic parameters of resistors
Figure 5 - Resistor equivalent circuit
So, inductance and capacitance are elements that influence the total resistance and the fronts of currents and voltages depending on frequency. Surface-mounted elements have the best frequency characteristics due to their small size.
Figure 6 – The graph shows the ratio of resistor to active impedance at various frequencies
Resistor design
Surface mount resistors are cheap and convenient for conveyor automated assembly of electronic devices. However, they are not as simple as they might seem.
Figure 7 – Internal structure of an SMD resistor
The basis of the resistor is a substrate made of Al2O3 - aluminum oxide. This is a good dielectric and a material with good thermal conductivity, which is no less important, since during operation all the power of the resistor is released into heat.
A thin metal or oxide film is used as a resistive layer, for example, chromium, ruthenium dioxide (as shown in the figure above). The characteristics of the resistors depend on the material this film is made of. 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 parameters and the ability to create high-precision elements, an example of such a material is constantan, but the values of such resistors rarely exceed 100 Ohms.
The resistor pads are formed from a set of layers. The internal contact layer is made of expensive materials such as silver or palladium. The intermediate one is made of nickel. And the outer one is lead-tin. This design is due to the need to ensure high adhesion (connectedness) of the layers. The reliability of contacts and noise depend on them.
Figure 8 – shape of the resistive layer
Installation of such elements occurs in furnaces, and in amateur radio workshops using a soldering hair dryer, that is, a stream of hot air. Therefore, during their manufacture, attention is paid to the heating and cooling temperature curve.
Figure 9 – heating and cooling curve when soldering SMD resistors
conclusions
The use of surface-mount components had a positive effect on the weight and size parameters of electronic equipment, as well as on the frequency characteristics of the element. Modern industry produces most of the common elements in SMD versions. Including: resistors, capacitors, diodes, LEDs, transistors, thyristors, integrated circuits.
- Introduction
- SMD component housings
- Standard sizes of SMD components
- SMD resistors
- SMD capacitors
- SMD coils and chokes
- SMD transistors
- Marking of SMD components
- Soldering SMD components
Introduction
The modern radio amateur now has access to not only ordinary components with leads, but also such small, dark parts that you can’t understand what’s written on them. They are called "SMD". In Russian this means "surface mount components". Their main advantage is that they allow the industry to assemble boards using robots that quickly place SMD components in their places on the printed circuit boards, and then mass bake them to produce assembled printed circuit boards. The human share remains with those operations that the robot cannot perform. Not yet.
The use of chip components in amateur radio practice is also possible, even necessary, as it allows you to reduce the weight, size and cost of the finished product. Moreover, you practically won’t have to drill.
For those who first encountered SMD components, confusion is natural. How to understand their diversity: where is the resistor, and where is the capacitor or transistor, what sizes do they come in, what types of SMD parts are there? You will find answers to all these questions below. Read it, it will come in handy!
Chip component housings
Quite conventionally, all surface-mount components can be divided into groups according to the number of pins and housing size:
| pins/size | Very very small | Very small | Little ones | Average |
| 2 outputs | SOD962 (DSN0603-2) , WLCSP2*, SOD882 (DFN1106-2) , SOD882D (DFN1106D-2) , SOD523, SOD1608 (DFN1608D-2) | SOD323, SOD328 | SOD123F, SOD123W | SOD128 |
| 3 pins | SOT883B (DFN1006B-3) , SOT883, SOT663, SOT416 | SOT323, SOT1061 (DFN2020-3) | SOT23 | SOT89, DPAK (TO-252), D2PAK (TO-263), D3PAK (TO-268) |
| 4-5 pins | WLCSP4*, SOT1194, WLCSP5*, SOT665 | SOT353 | SOT143B, SOT753 | SOT223, POWER-SO8 |
| 6-8 pins | SOT1202, SOT891, SOT886, SOT666, WLCSP6* | SOT363, SOT1220 (DFN2020MD-6), SOT1118 (DFN2020-6) | SOT457, SOT505 | SOT873-1 (DFN3333-8), SOT96 |
| > 8 pins | WLCSP9*, SOT1157 (DFN17-12-8) , SOT983 (DFN1714U-8) | WLCSP16*, SOT1178 (DFN2110-9) , WLCSP24* | SOT1176 (DFN2510A-10) , SOT1158 (DFN2512-12) , SOT1156 (DFN2521-12) | SOT552, SOT617 (DFN5050-32), SOT510 |
Of course, not all packages are listed in the table, since the real industry produces components in new packages faster than the standardization bodies can keep up with them.
The housings of SMD components can be either with or without leads. If there are no leads, then there are contact pads or small balls of solder (BGA) on the case. Also, depending on the manufacturer, parts may differ in markings and dimensions. For example, capacitors may vary in height.
Most SMD component housings are designed for installation using special equipment that radio amateurs do not have and are unlikely to ever have. This is due to the technology of soldering such components. Of course, with a certain persistence and fanaticism, you can solder at home.
Types of SMD housings by name
| Name | Decoding | number of pins |
| SOT | small outline transistor | 3 |
| SOD | small outline diode | 2 |
| SOIC | small outline integrated circuit | >4, in two lines on the sides |
| TSOP | thin outline package (thin SOIC) | >4, in two lines on the sides |
| SSOP | seated SOIC | >4, in two lines on the sides |
| TSSOP | thin seated SOIC | >4, in two lines on the sides |
| QSOP | Quarter size SOIC | >4, in two lines on the sides |
| VSOP | Even smaller QSOPs | >4, in two lines on the sides |
| PLCC | IC in a plastic case with leads bent to form a letter-shaped case J | >4, in four lines on the sides |
| CLCC | IC in a ceramic package with leads bent to form a letter-shaped package J | >4, in four lines on the sides |
| QFP | square flat case | >4, in four lines on the sides |
| LQFP | low profile QFP | >4, in four lines on the sides |
| PQFP | plastic QFP | >4, in four lines on the sides |
| CQFP | ceramic QFP | >4, in four lines on the sides |
| TQFP | thinner than QFP | >4, in four lines on the sides |
| PQFN | power QFP without leads with a pad for a radiator | >4, in four lines on the sides |
| BGA | Ball grid array. Array of balls instead of pins | pin array |
| LFBGA | low profile FBGA | pin array |
| C.G.A. | housing with input and output terminals made of refractory solder | pin array |
| CCGA | CGA in ceramic case | pin array |
| μBGA | micro BGA | pin array |
| FCBGA | Flip-chip ball grid array. Man array of balls on a substrate to which a crystal with a heat sink is soldered | pin array |
| LLP | leadless housing |
From this whole zoo of chip components that can be used for amateur purposes: chip resistors, chip capacitors, chip inductors, chip diodes and transistors, LEDs, zener diodes, some microcircuits in SOIC packages. Capacitors usually look like simple parallelipipeds or small barrels. The barrels are electrolytic, and the parallelepipeds will most likely be tantalum or ceramic capacitors.
Standard sizes of SMD components
Chip components of the same denomination may have different dimensions. The dimensions of an SMD component are determined by its “standard size”. For example, chip resistors have standard sizes from “0201” to “2512”. These four digits encode the width and length of the chip resistor in inches. In the tables below you can see the standard sizes in millimeters.
smd resistors
| Rectangular chip resistors and ceramic capacitors | |||||
| Standard size | L, mm (inch) | W, mm (inch) | H, mm (inch) | A, mm | W |
| 0201 | 0.6 (0.02) | 0.3 (0.01) | 0.23 (0.01) | 0.13 | 1/20 |
| 0402 | 1.0 (0.04) | 0.5 (0.01) | 0.35 (0.014) | 0.25 | 1/16 |
| 0603 | 1.6 (0.06) | 0.8 (0.03) | 0.45 (0.018) | 0.3 | 1/10 |
| 0805 | 2.0 (0.08) | 1.2 (0.05) | 0.4 (0.018) | 0.4 | 1/8 |
| 1206 | 3.2 (0.12) | 1.6 (0.06) | 0.5 (0.022) | 0.5 | 1/4 |
| 1210 | 5.0 (0.12) | 2.5 (0.10) | 0.55 (0.022) | 0.5 | 1/2 |
| 1218 | 5.0 (0.12) | 2.5 (0.18) | 0.55 (0.022) | 0.5 | 1 |
| 2010 | 5.0 (0.20) | 2.5 (0.10) | 0.55 (0.024) | 0.5 | 3/4 |
| 2512 | 6.35 (0.25) | 3.2 (0.12) | 0.55 (0.024) | 0.5 | 1 |
| Cylindrical chip resistors and diodes | |||||
| Standard size | Ø, mm (inch) | L, mm (inch) | W | ||
| 0102 | 1.1 (0.01) | 2.2 (0.02) | 1/4 | ||
| 0204 | 1.4 (0.02) | 3.6 (0.04) | 1/2 | ||
| 0207 | 2.2 (0.02) | 5.8 (0.07) | 1 | ||
smd capacitors
Ceramic chip capacitors are the same size as chip resistors, but tantalum chip capacitors have their own size system:
| Tantalum capacitors | |||||
| Standard size | L, mm (inch) | W, mm (inch) | T, mm (inch) | B, mm | A, mm |
| A | 3.2 (0.126) | 1.6 (0.063) | 1.6 (0.063) | 1.2 | 0.8 |
| B | 3.5 (0.138) | 2.8 (0.110) | 1.9 (0.075) | 2.2 | 0.8 |
| C | 6.0 (0.236) | 3.2 (0.126) | 2.5 (0.098) | 2.2 | 1.3 |
| D | 7.3 (0.287) | 4.3 (0.170) | 2.8 (0.110) | 2.4 | 1.3 |
| E | 7.3 (0.287) | 4.3 (0.170) | 4.0 (0.158) | 2.4 | 1.2 |
smd inductors and chokes
Inductors are found in many types of housings, but the housings are subject to the same size law. This makes automatic installation easier. And it makes it easier for us, radio amateurs, to navigate.
All kinds of coils, chokes and transformers are called “winding products”. Usually we wind them ourselves, but sometimes you can buy ready-made products. Moreover, if SMD options are required, which come with many bonuses: magnetic shielding of the housing, compactness, closed or open housing, high quality factor, electromagnetic shielding, wide range of operating temperatures.
It is better to select the required coil according to catalogs and the required standard size. Standard sizes, as for chip resistors, are specified using a four-number code (0805). In this case, “08” indicates the length, and “05” the width in inches. The actual size of such an SMD component will be 0.08x0.05 inches.
smd diodes and zener diodes
Diodes can be either in cylindrical cases or in cases in the form of small parallelipipeds. Cylindrical diode packages are most often represented by MiniMELF (SOD80 / DO213AA / LL34) or MELF (DO213AB / LL41) packages. Their standard sizes are set in the same way as for coils, resistors, and capacitors.
| Diodes, Zener diodes, capacitors, resistors | |||||
| Type of shell | L* (mm) | D* (mm) | F* (mm) | S* (mm) | Note |
| DO-213AA (SOD80) | 3.5 | 1.65 | 048 | 0.03 | JEDEC |
| DO-213AB (MELF) | 5.0 | 2.52 | 0.48 | 0.03 | JEDEC |
| DO-213AC | 3.45 | 1.4 | 0.42 | - | JEDEC |
| ERD03LL | 1.6 | 1.0 | 0.2 | 0.05 | PANASONIC |
| ER021L | 2.0 | 1.25 | 0.3 | 0.07 | PANASONIC |
| ERSM | 5.9 | 2.2 | 0.6 | 0.15 | PANASONIC, GOST R1-11 |
| MELF | 5.0 | 2.5 | 0.5 | 0.1 | CENTS |
| SOD80 (miniMELF) | 3.5 | 1.6 | 0.3 | 0.075 | PHILIPS |
| SOD80C | 3.6 | 1.52 | 0.3 | 0.075 | PHILIPS |
| SOD87 | 3.5 | 2.05 | 0.3 | 0.075 | PHILIPS |
smd transistors
Surface mount transistors can also be of low, medium and high power. They also have matching housings. Transistor cases can be divided into two groups: SOT, DPAK.
I would like to draw your attention to the fact that such packages may also contain assemblies of several components, not just transistors. For example, diode assemblies.
Marking of SMD components
Sometimes it seems to me that the marking of modern electronic components has turned into a whole science, similar to history or archeology, since in order to figure out which component is installed on the board, sometimes you have to conduct a whole analysis of the elements surrounding it. In this regard, the Soviet output components, on which the denomination and model were written in text, were simply a dream for an amateur, since there was no need to rummage through piles of reference books to figure out what these parts were.
The reason lies in the automation of the assembly process. SMD components are installed by robots, in which special reels are installed (similar to the reels with magnetic tapes) in which chip components are located. The robot doesn’t care what’s in the bag or whether the parts are marked. Humans need labeling.
Soldering chip components
At home, chip components can only be soldered up to a certain size; size 0805 is considered more or less comfortable for manual installation. Smaller components are soldered using a stove. At the same time, for high-quality soldering at home, a whole range of measures should be observed.
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 a board using SMT technology (surface mount technology).
SMT technology (from the English Surface Mount Technology) was developed with the aim of reducing the cost of production, increasing the efficiency of manufacturing printed circuit boards using smaller electronic components: resistors, capacitors, transistors, etc. Today we will look at one of these - the SMD resistor.
SMD resistors
SMD resistors- These are miniature ones designed for surface mounting. SMD resistors are significantly smaller than their traditional counterpart. They are often square, rectangular or oval shaped, with a very low profile.
Instead of the lead wires of conventional resistors that are inserted into holes on the printed circuit board, 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.
Standard sizes of SMD resistors
Basically, the term frame size includes the size, shape and terminal configuration (package type) of any electronic component. For example, the configuration of a conventional chip that has a flat package with double-sided pins (perpendicular to the plane of the base) is called DIP.
Size of SMD resistors 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 body length is 0.060 inches by 0.030 inches wide.
The same resistor size 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 dimensions to millimeters, simply multiply the size in inches by 2.54.
SMD resistor sizes 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 of SMD resistors
Due to the small size of SMD resistors, it is almost impossible to apply traditional resistor color coding 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, called EIA-96.
Marking with 3 and 4 digits
In this system, the first two or three digits indicate the numerical value of the resistor, and the last digit indicates the multiplier. This last digit indicates the power to which 10 must be raised to obtain the final factor.
A few more examples of determining resistance within this system:
- 450 = 45 x 10 0 equals 45 ohms
- 273 = 27 x 10 3 equals 27000 ohms (27 kohms)
- 7992 = 799 x 10 2 equals 79900 ohms (79.9 kohms)
- 1733 = 173 x 10 3 equals 173000 ohms (173 kohms)
The letter “R” is used to indicate the position of the decimal point for resistance values below 10 ohms. Thus, 0R5 = 0.5 ohms and 0R01 = 0.01 ohms.
High-precision SMD resistors, combined with small dimensions, have created the need for new, more compact markings. In this regard, the EIA-96 standard was created. This standard is intended for resistors with a resistance tolerance of 1%.
This marking system consists of three elements: two numbers indicate the code, and the letter following them determines the multiplier. The two digits represent 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%
- 38С = 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 reflected below.
The calculator can be used to determine the resistance of SMD resistors that are marked with 3 or 4 numbers, as well as according to the EIA-96 standard (2 numbers + 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 manufacturers may sometimes use their own custom codes.
Therefore, to be absolutely sure of the resistance value, it is best to additionally measure the resistance using a multimeter.