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 can 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.
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.
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.