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How to Identify SMD Components from Appearances

how to identify smd components
PCBONLINE Team Thur, Dec 09, 2021

SMD components, or surface mount components, are electronic components to be mounted on printed circuit boards to function. How to identify SMD components from their appearances? This article will guide you to identify surface mount components quickly and easily.

Part 1: Identify SMD Resistors

identify SMD resistors

SMD resistors are basic surface mount components that limit the current passing through them. "R" stands for resistance, and the unit of resistance is Ohm (Ω). 1KΩ equals to 1000Ω, 1MΩ equals to 1000000Ω.

There are two methods to indicate the resistance value on the SMD resistors' appearance.

1. In Arabic numbers: the first two numbers indicate the absolute numbers of the resistance value, and the last number means the power of 10.

For example, 103 means 10000Ω, 391 means 390Ω, and 473 means 47000Ω.

2. In a combination of Arabic numbers and R: the Arabic numbers before the R stand for the whole part of the resistance value, and those after the R stand for the fractional part of the resistance value.

For example, R100 means 0.100Ω, 5R60 means 5.60Ω, 30R9 means 30.9Ω.

Classification of SMD resistors: according to the use differences, there are normal resistors, precision resistors, power resistors, high voltage resistors, high-resistance resistors, and high-frequency resistors.

Part 2: Identify SMD Capacitors

identify SMD capacitors

SMD capacitors are PCB parts consisting of two metal pieces separated by an insulator and mainly used to store energy. " C" stands for capacitance, and the unit of capacitance is Farad (F).

The unit F is too big for SMDs' capacitance, and we usually use the smaller units μF, nF, and pF. 1μF equals to 1000nF, 1nF equals to 1000pF.

There are two methods to indicate the capacitance value on the SMD capacitors' surface.

1. Directly denote the capacitance and working voltage on the capacitors, for example, 10μF/16V.

2. In a combination of Arabic numbers and working voltage: the first two numbers indicate the absolute numbers of the capacitance value, and the last number means the power of 10.

For example, 107 means 10 × 10^7pF (= 100μF), 225 means 22 × 10^5pF (=2.2μF)

Besides, on SMD capacitors, the capacitance is denoted by a combination of numbers and a letter.

The letter stands for capacitance tolerance. Here is a chart:


For example, 104J means 10 × 104pF (= 0.1μF), and the capacitance tolerance is ±5%.

Classification of SMD Capacitors

SMD ceramic capacitors

Ceramic capacitors: made up of a ceramic insulator with two terminals sprayed with silver and then sintered. On SMD capacitors' surface, C.CAP stands for ceramic capacitors.

SMD aluminum electrolytic capacitors

Aluminum electrolytic capacitors: made up of an aluminum cylinder filled with liquid electrolyte (together as the negative electrode) and a curly aluminum strip (as the positive electrode) covered with an oxide film (as the insulator) plugged in it.

SMD tantalum electrolytic capacitor

Tantalum electrolytic capacitors: made up of tantalum or niobium (as the positive electrode) and dilute sulfuric acid (as the negative electrode), the oxide film covered on tantalum or niobium as the insulator. TAN.CAP or TC stands for tantalum capacitors.

All electrolytic capacitors are polar capacitors. The positive and negative electrodes of polar components can't be reversed during PCB assembly. On tantalum capacitors, the terminal printed with lines is the positive electrode. The sizes of tantalum capacitors from minimum or maximum are denoted by A, B, C, D ... J.

Part 3: Identify SMD Inductors

identify SMD inductors

SMD inductors are basic electronic components that convert electrical energy into magnetic energy and store it. Inductors are made up of an enameled wire winding around an insulator. "L" stands for inductance, and the unit of inductance is Henry (H). 1H equals to 1000mH, and 1mH equals to 1000μH.

The method to indicate the inductance value on the SMD inductors' appearance is below.

In Arabic numbers: the first two numbers indicate the absolute numbers of the inductance value, and the last number means the power of 10.

For example, 470 means 47H, 101 means 100H, and 100 means 10H.

Part 4: Identify SMD Diodes and SMD Triodes

identify SMD diodes

SMD diodes are unidirectional conductive electronic components. Diodes are also polar components, and the positive and negative electrodes can't be reversed. When currents flow from the positive electrode, the diode's resistance is extremely small. Vice versa, the resistance is extremely large. CR or D stands for diodes.

On SMD diodes, the terminal printed with lines is the negative electrode.

SMD triodes

SMD triodes are control components that amplify currents. Q stands for triodes.

Part 5: Identify SMD ICs

identify SMD IC

SMD ICs are surface-mounted integrated circuits that integrate components such as diodes, resistors, capacitors, and inductors on an extremely small semiconductor and then package them. According to the packaging differences, the integrated circuits include PLCC, PPGA, PQFP, QFP, BGA, CSP, SSOP, etc.

Part 6: Identify SMD Crystal Oscillators

identify SMD crystal ocsillators

An SMD crystal is a quartz piece with two terminals polished and sprayed with a silver film. When an IC is packaged with the quartz piece to form the oscillation circuit, it is an SMD oscillator. stands for crystal oscillators.

SMD crystal oscillators provide basic clock signals for the system.

On a component, if you see a combination of numbers and HZ or Z, that is a crystal oscillator.

You can see crystal oscillators in the below image. DIP crystal oscillators have two long pins, and the rest are SMD crystal oscillators. SMD crystal oscillators have two or four pins.

crystal oscillators

Part 7: Identify SMD Connectors

identify SMD connectors

SMD connectors provide temporary or permanent electrical connections for circuits, and they are usually used in pairs.

Part 8: Identify SMD Button Switches

identify SMD button switches

SMD button switches are surface mount switches that use a button to connect or separate the two contacts to realize the circuit switch.

SMD Components Sourcing and PCB Assembly One-Stop Solutions

SMD components sourcing

PCBONLINE provides one-stop-shop solutions for SMD electronic components sourcing, PCB Assembly, and advanced PCB manufacturing. PCBONLINE is an ISO-certified electronics manufacturing services provider founded in 1999.

Relying on our EMS factory for manufacturing, PCBONLINE takes part in joint components procurement with other large EMS and enjoys bargaining power.

From PCBONLINE, you can enjoy these benefits in SMD components sourcing:

  • High-quality SMD components directly sourced from original factories.
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  • You can let PCBONLINE mount SMD components on printed circuit boards, complete all PCBA tests, and do the end-product assembly.

Please feel free to send your BOM to PCBONLINE by email at info@pcbonline.com to get a quote for your electronic components.


This article gives a brief introduction to common SMD components, displays their images, and provides tips to identify components from their appearances. If you have any concerns or needs for SMD components or PCBs, welcome to contact PCBONLINE by email or from the online chat window on the right of our website pages.


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