SMD components: How to Identify SMD Components in Circuit Board

Understanding the PCB components is a real struggle for new electronic engineers. So in this article, We will make it simple to understand what SMD components are, the types and how to identify the PCB component. 

Let’s jump right in…

What are SMD Components?

Surface mount devices are electronic components placed directly onto the surface of a PCB. The technology used to mount SMD components in this manner is surface mount technology (SMT).

Before SMT emerged in the 1960s, there was a through-hole technology construction method. It involves using lead on the electronic components to insert them into a hole drilled in a PCB

SMD electronic devices are smaller in size than their through-hole counterparts. Meaning, a lot of them can fit on both sides of the board. So this allows for a much higher component density and more connections per component. 

Other advantages of SMT components over through-hole counterparts include:

  • First, easy manufacturing process 
  • Second, the solder of an adjacent SMT component is not easy to displace during the soldering process. 
  • Finally, autocorrect small errors in component placement.

However, through-hole electronic components also have their advantages, including better stability.  For that reason, you can combine the two technologies for better functionality.

Types of SMD Components

Based on various factors, SMD components can be either active or passive components. These two types of SMD components differ in terms of: 

  • Nature of energy source
  • Functionality
  • Power gain
  • Flow of current
  • Requirement of an external source

Active Components

These are active devices that: 

  • Deliver power or energy to the circuit. 
  • Produce energy form of voltage current.
  • Capable of providing power gain.
  • Can control the flow of current.
  • Require an external source for the operation.

Examples include transistors, diodes, integrated circuits, and SCR among others. 

Passive SMD Components

Passive components are devices that:  

  • First, utilizes power or energy from the circuit
  • Then, store energy in the form of power or circuit
  • Besides, incapable of providing power gain
  • Also, cannot control the flow of the current
  • Finally, do not require any external source to operate

Monolithic ceramic capacitors, thick film resistors, and tantalum capacitors are the main examples.

Circuit Board Components Identification

Well, we are going to show you how to identify SMD components in a circuit board. Given that SMD components are many, we will take you through the most commonly used ones. 

Chip Resistors (R)

SMD components1

Chip resistors are common SMD packages on PCB electronics. The first two or three digits on the body of a chip resistor indicate the resistance value. The last digit is a multiplier with a power of ten. “105” is equivalent to “1 M Ω” and “672” is “6.7K Ω “. 

Network Resistor (RA/RN)

Network resistor chips feature high-grade ceramics with metal electrodes on either end of the chip. The chips consist of a group of resistors that have similar properties. It’s the same as identifying chip resistors.

Ceramic Capacitors

An interlocked ceramic dielectric block has metal electrodes. A layer of plated tin covers the inner electrodes, linked to the end terminations (NiSn). In general, PCB manufacturers utilize SMDs with MLCC. Aside from the COG (NPO) type, there are three more varieties of MLCC: the X7R and Y5V types.

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Diode (D)

Diode (D)
seven color diode on white background

The pin voltage regulation of an SMD diode is similar to the general-purpose SMD diodes in terms of terminals. By just observing the casing, you can identify the positive and negative poles of SMD diodes. But the marks wear out and in that case, we use a multimeter for identification. 

LED

When a current travels through a Semiconductor Crystal, it generates light. The individual product manufacturing guideline determines the polarity of an SMD LED. SMD LEDs are available in different sizes. Like most SMD components, you can identify them in size and numbers.

SMD components5

Transistors (Q)

The most common surface mount device transistor packages are SOT-23 and SOT-223 (larger). The first two letters on the transistors identify them, regardless of the manufacturing code.   

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Inductors

SMD inductors have +ve reactance, and they come in a variety of sizes and shapes. You can see their values on the casings of the components. The value is in standard two-digit and exponent fashion. Example 100 µH would be 101 – 10 x 10^1, and 100 would be 10 x 10^0. 

SMD components7

SMD Transformers

In general, there is a wire wrap around the SMD transformer toroidal core. The design includes surface-mount headers for PCB connectors. The SMD transformer design is different from other types in many ways. They have unique voltage & current output, power rating, bandwidth, and more. 

SMD components8

Crystal Oscillators (X)

Identifying SMD crystal oscillators is simple. If it is within an electrical circuit, you need to locate the position of the crystal oscillators. For a computer motherboard, you will see the label “XTAL”, with the frequency written on top of the device. 

Fuse

SMD fuse helps in surface onboard circuit protection. The voltage rating is sometimes indicated by a voltage code letter. For example, in “F02G1R00A”:

F- fuse

02- Style

G- voltage rating 

1R00-current rating 

A- time delay rating

SMD components9

IC (U)

An integrated circuit is the most functional component of electronic products. Surface-mount packages for ICs come in a variety of shapes and sizes. The waffle pack holds large ICs such as plastic leaded chip carriers (PLCC) and quad flat pack (QFP). 

Leadless ceramic carriers are the main surface-mount technology packages for IC. 

Conclusion

Hopefully, we have made SMD component identification easier during the PCB assembly process. Please feel free to contact us with any questions on SMD components. 

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Emma Lu
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