SMT PCB assembly uses a different process than through-hole PCB assembly. Likewise, SMT components are also different. This particular post will explore the different types of SMT components, how to identify them and what are their characteristics.
SMT means surface mount technology, which is a type of PCB assembly process that uses solder paste and solder reflow process to attach devices to printed circuit boards. SMT components, therefore, refer to surface-mount technology components.
SMD components are distinguished from through-hole types, which are inserted into holes drilled in PCBs. They are also sometimes called SMD (surface-mount device) components.
As the name suggests, these components are mounted or placed on the surface of a PCB (printed circuit board) instead of through holes. To solder SMD components onto a PCB, special soldering equipment and techniques are required.
The most common method is reflow soldering, which uses heat to melt and flow the solder onto the component leads. The process is automated and typically carried. Surface mount PCB components offer several benefits including:
SMTCs, or SMT components, are many and varied. They represent different functions and come in a variety of shapes, sizes, and materials.
Surface mount components are generally categorized as either active or passive. The main difference between the two is that active SMT components require a power source to function while passive devices do not.
Active SMD components would include integrated circuits (ICs), which are also called microchips that contain transistors, diodes, or other semiconductor devices within them. They also consist of discrete parts such as diodes and transistors. Their main characteristic is that they need a power source, such as electricity, in order to function.
Passive SMD components or components would include resistors, inductors, and capacitors. These do not require a power source to function and they are used to control the flow of current in a circuit. They are also used to store energy in a circuit.
Surface mount component codesSMD component identification can be done in several ways. The most common method is by their physical appearance, such as size and shape. These components will usually either have short legs/leads or no legs at all and tubular or rectangular in shape.
When leadless, the devices will have metal tabs or end caps for attachment. These will be soldered to the PCB surface during assembly. Other ways of identification include:
It’s worth noting that surface mount component codes will usually be printed on the body of the component. They can also be found on the product datasheet, which is a document that contains all the information about that particular component.
Soldering surface mount components onto a PCBThe list of SMD components is long and includes both active and passive devices. However, some of these devices are more commonly used than others. In this SMT components list, we excluded the less popular devices and included only the most commonly used SMD components.
These surface mount components are generally used to control the flow of current in a circuit. They are also used to provide a known resistance value and include both thin and thick film types.
The markings on a surface mount technology resistor will usually consist of 3 digits or 2 digits and 1 letter combination. The first two digits represent the value of the resistor, while the last digit represents the tolerance.
An SMD capacitor is used to store energy in a circuit or to filter power. These surface-mount capacitors come in many different types, such as ceramic, film, and electrolytic.
The markings on an SMD capacitor will usually include 3-figure values just like the SMD resistors. Since they do not use length leads like their through-hole counterparts, the SMD capacitors are well-suited for high-frequency applications.
The SMD inductor is primarily used to store energy in the form of a magnetic field and are made from either ferrite or iron-core materials.
For surface mounting, these SMT PCB components typically come with end caps in place of leads. They also will usually have their values printed on their bodies.
The L in the markings indicates the inductance value, which is measured in Henry (H). For example, a marking of 10L would indicate an inductance value of 10 Henries.
These SMT components, unlike the types already mentioned, will often be large enough to allow the information about them to be printed right on the body.
SMT ICs contain all the circuitry necessary to perform a specific function, such as amplifiers, timers, and microcontrollers. The markings on these devices will often include the manufacturer’s name or logo, the part number, and sometimes the function of the IC.
While integrated circuits (ICs) are the most complex of all the SMT components, discreet SMDs are the simplest. These devices typically consist of a single active or passive element, such as a transistor or diode.
An SMD transistor will either be a 3-pin or 4-pin device. An SMD diode, on the other hand, will have 2 leads. The markings on discreet SMDs will often be codes composed of 2 or 3 symbols.
Surface mount, SMT components represent a huge shift in the way electronic circuits are built. They are smaller, more reliable, and can be placed on the PCB board using automated processes, from start to finish. This guide has covered the most common types of SMT components, their functions, and how to identify them by their markings. With this knowledge in hand, you should be able to tackle your next electronics project with confidence.
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