Identifying Electronic Components on a Circuit Board
Key Takeaways
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Identifying the electronic components on a circuit board is important during the designing, assembling, deployment, and troubleshooting stages of the PCB production process.
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A reference designator is a set of alphanumeric codes used to identify a specific component on the PCB board.
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The signs + and - are usually marked on the circuit board to identify the positive and negative leads of polarized components.
In an electronic circuit, there are a variety of different components: resistors, capacitors, inductors, diodes, transistors, ICs, connectors, etc.
Perfecting the art of identifying electronic components on a circuit board requires years of experience. As you begin to see PCBs regularly, you will naturally begin to develop the ability to identify electronic components on the circuit board. In this article, we will cover the most basic electronic components on a board and how to identify them.
Identifying Electronic Components on a Circuit Board
Electronic components contain some marking or writing on their body or packaging to represent their value or part number, respectively. From the specific marking on the body of the component, identification is possible. For example, in color-coded resistors, the bands of color give the value of the resistor. In ceramic capacitors, the component value can be calculated from the writings on the body. In ICs, MOSFETs, IGBTs, etc., the part number is printed on the body. If you know the part number of the component and have a magnifying glass, then you can identify the component.
Circuit Board Components
In an electronic circuit, there are different components, including resistors, capacitors, inductors, diodes, transistors, ICs, connectors, etc. Each of these components performs in a specific way so the desired output of the circuit board is achieved.
Active and Passive Elements
In an electronic circuit board, components can be broadly classified into passive elements and active elements. Resistors, capacitors, and inductors are passive elements, whereas transistors, diodes, and ICs are active elements. There are other, less notable categories of elements also present in a PCB. For example, connectors are used to establish electrical connections between a circuit board and an external source. Together, all the components form a complete circuit.
Through-Hole and Surface-Mount Components
PCB boards use two types of mounting technology: through-hole components and surface-mount components.
Through-hole components -
Through-hole components have leads that are soldered to the circuit board by inserting through-mounting holes. The through-hole components can be avail or radial, depending on where the leads extend from the component's body.
It is not necessary to have leads in surface-mount components; there are surface-mount components without leads. All surface mount components need to be mounted to the PCB precisely.
Reference Designators
A reference designator is a set of alphanumeric codes that are used to identify a specific component on a PCB board. The reference designator follows a specific format. There are general rules followed in assigning the reference designator to a component.
Key Rules for Assigning Reference Designators to Components
A resistor reference designator starts with R, capacitors start with C, inductors start with L, relays start with K, transistors start with Q, etc. The letters are usually followed by numbers, which help in easily identifying the component from the group of similar ones. Commonly used reference designators are shown in the table below.
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Reference Designator |
Component |
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A |
Sub-assembly |
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C |
Capacitor |
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D |
Diode |
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F |
Fuse |
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FB |
Ferrite bead |
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FC |
Filter |
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J |
Jack connector |
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K |
Relay |
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L |
Inductor |
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M |
Motor |
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P |
Plug |
|
PS |
Power supply |
|
Q |
Transistor |
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R |
Resistor |
|
S |
Switch |
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T |
Transformer |
|
TP |
Test point |
|
U |
Integrated circuit |
|
Y |
Crystal for oscillator |
|
Z |
Zener diode |
Identifying Polarized Electronic Components on a Circuit Board
Polarized capacitors on a circuit board
You may come across polarized components and non-polarized components on your circuit board. The soldering of these components needs to be done according to their polarity. The signs + and - are usually marked on the circuit board to identify the positive and negative leads.
Similarly, in the case of unidirectional components such as diodes, + and - or A and K are marked to identify the anode or cathode, respectively. This is a method to identify the terminals of polarized components.
Identifying the Orientation of Electronic Components on a Circuit Board
In components like SOC ICs or QFP packages, component orientation is important for the installation process. For such components, installation or assembly is made easier by putting the pin 1 number or a solid dot to specify the first pin. The pin 1 number or dot can help you quickly pick the ICs in an assembled PCB, with the additional knowledge of where the first pin starts.
Identifying the electronic components in a circuit board is important during the designing, assembling, deployment, troubleshooting, and repairing stages of the PCB production process. Cadence’s PCB design software offers you the ability to rename component reference designators. With Cadence OrCAD, it is possible to import changes to the layout, allowing you to easily identify the electronic components on the circuit board.
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