PCB Components Deep Dive: Essential Parts, Functions & Smart Selection Guide

PCBs consist of a mixed bag of active, passive, and electromechanical components all working together. Active components are used to either switch and amplify electrical signals. Passive components do not amplify electrical signals but are used for storing and dissipating energy. Electromechanical components like switches and relays which physically connect circuits together or disconnect them using a mechanical device. PCBs generally contain eight families of components with which you will regularly work:

Each family has many members, but these eight categories cover the bulk of what you’ll place on a PCB. Understanding them helps you recognize “what actually lives on the board” and sets the stage for deeper learning.

Active vs Passive vs Electromechanical Breakdown

Active components: These things need a power source and can amplify or switch signals. For example: transistors and semiconductor ICs.

Passive components: They don’t require power to function. A resistor simply limits current by Ohm’s law. On the other hand, a capacitor stores charge in an electric field. Passive parts are the “nuts and bolts” that prepare and shape signals. For example - In a power supply, the large capacitors and inductors filter the voltage. Capacitors absorb and release energy to smooth ripples and inductors resist sudden current changes.

Electromechanical parts: They bridge the gap between electrical and physical action. A PCB connector is literally a plug or socket. An electromechanical component joins circuits or interfaces to cables. For example: A switch mechanically opens or closes a path to turn things on or off. Electromechanical parts let us interact with the board physically.

The 8 Component Families You'll Use Every Day

Every electronic gadget’s PCB is built from a handful of fundamental component families. These families include all the common parts a designer reaches for repeatedly.

• Resistors
• Capacitors
• Inductors
• Diodes
• Transistors
• Integrated Circuits (ICs)
• Connectors
• Relays/Switches

These categories cover almost everything on a board. The bulleted list above highlights their roles. Learning the capabilities and symbols of each family is the first step to effective PCB design.

Basic PCB Components Every Designer Must Master

Resistors, Capacitors, Inductors – Real Functions & Hidden Tricks

Resistors, capacitors, and inductors form the backbone of analog circuitry.

Resistors: These are tiny cylinders or SMD chips that set current and divide voltages. They are used as pull-ups/pull-downs on digital inputs, as voltage dividers to create reference levels, and to limit LED current or protect circuits from overcurrent. In high-speed designs they may act as line terminations.

Capacitors: They come in many forms (ceramic, electrolytic, tantalum, and film) but all share the ability to store and release charge. This makes them excellent for decoupling noise and stabilizing power rails. A decoupling capacitor placed right at an IC’s power pin will supply fast transient currents and reduce voltage spikes. Engineers typically use several capacitors in parallel: a 0.1 µF ceramic for high-frequency noise, a 1 µF–10 µF ceramic for mid-frequency, and larger electrolytics or tantalums (10–100 µF) for low-frequency bulk decoupling. We have covered a full guide on bypassing and decoupling capacitors. Capacitor selection involves value (farads), voltage rating, type, and size to fit the application.

Inductors: They are coils or chokes, less familiar to beginners. But they are crucial in power and RF circuits. They store energy in a magnetic field when current flows through them. Inductors tend to resist changes in current as they pass DC easily but oppose sudden pulses.

For example: In a DC–DC converter the inductor and a capacitor work together to transfer energy. The inductor smooths current to the load while the capacitor smooths voltage.

Diodes, Transistors, MOSFETs & IC Packages Explained

Diodes: They are simple one-way valves for current. A common rectifier diode (1N4007) passes current in forward bias but blocks it in reverse.

• Zener diodes clamp voltage to a fixed level.
• Schottky diodes have a low forward drop (~0.2 V) and are used for fast switching.
• LEDs are also diodes but designed to emit photons.

Diodes also serve as protection. Placing a small signal diode across a regulator input can prevent damage from reverse voltage or spikes.

Transistors: These are three-terminal semiconductor switches and amplifiers. Bipolar Junction Transistors are current-controlled devices. For example, the 2N3904 (NPN) can switch loads up to 200 mA. MOSFETs are voltage-controlled and dominate modern designs. The two types of MOS are:

• N-channel MOSFETs handle high currents at low on-resistance.
• P-channel MOSFETs are used for high-side switching.

IC packages: They can encapsulate entire subsystems. A microcontroller IC contains a CPU, memory, and I/O peripherals in one package. Analog ICs and power ICs similarly combine complex circuitry. Older DIP chips (dual in-line packages) have pins you can plug into sockets or breadboards, but SMD packages offer much higher pin counts in smaller footprints.

Crystals, Connectors, Switches & Protection Devices

1) Crystals and Oscillators: They are timekeepers and are used for precise timing. Most microcontrollers require a clock source which is generated using a quartz crystal between two pins. The crystal vibrates at a fixed frequency, and a minimal internal circuit turns it into a stable clock.

2) Switches: These are mechanical parts that open or close circuits. Push-buttons provide user input by shorting contacts when pressed. On a PCB, they allow a user to control power or mode selection.

3) Connectors: These are electromechanical interfaces on a board. They complete the path between the PCB and the outside world. Always pick connectors rated for the needed current/voltage. We have covered a recent article on all types of connectors used in electronics design.

4) Protection Components: Every robust design includes parts to guard against faults. TVS/ESD diodes shunt voltage spikes safely to ground. A TVS diode clamps sudden surges on a power rail in nanoseconds, protecting sensitive ICs. See the full detailed working of ESD diodes from a recently posted article.

PCB Component Types by Package & Mounting Style

Through-Hole Era (DIP, Axial, Radial)

Components had wire leads that went through drilled holes in the PCB known as through hole tech.

• Axial-leaded parts have a wire at each end and lie flat along the board.
• Radial-leaded parts have two leads from the same side and stand vertically.

Integrated circuits used to come in DIP forms, with two rows of pins through the board. These chips could be soldered or plugged into sockets. For example, that old “Arduino DIP” board has through-hole resistors and a DIP microcontroller so students can swap parts easily.

SMD Revolution (0402 → 0201 → 01005, QFN, BGA, LGA)

Surface-mount technology puts components directly on pads. Standard chip resistor/capacitor sizes are:

These miniature parts allow extremely compact, high-density PCBs. For example, modern smartphones use 01005 caps under a BGA chip to filter signals in minimal space. SMT ICs come in packages like SOIC/QFP or QFN.

• QFNs often include a central thermal pad on the underside to conduct heat; this pad must align with a matching copper pad on the PCB and usually requires multiple thermal vias to the inner layers.

• Ball Grid Arrays (BGAs) go even further: they have an array of tiny solder balls on the bottom (like micro BGA or flip-chip designs), enabling hundreds of connections.

• LGAs (Land Grid Array) are similar, but use flat pads or a socket instead of balls.

Emerging Packages (WLCSP & SiP)

WLCSP (Wafer-Level Chip Scale Package): It is essentially a die-on-board flip-chip that’s almost the same size as the silicon die. It directly mounts the chip face-down on solder balls, eliminating the conventional substrate.

SiP (System in Package): It combines multiple chips and passives into one module. SiP might include several silicon dies and a handful of capacitors in one package. SiPs allow reusing complex subsystems without designing them from scratch.

How Component Choice Drives PCB Design Decisions

Footprint vs Courtyard Rules

A PCB footprint defines exactly where the pads for a component go. It includes pad shape, size, and spacing as per the component’s datasheet. Beyond the copper pads, each part also has a courtyard. It is an imaginary keep-out area around the footprint. The courtyard ensures there is enough clearance for automated placement and rework.

Modern CAD tools like EasyEDA and Altium handle this by generating land patterns. A good rule is to always use manufacturer or IPC-approved footprints and double-check their pin mappings in the PCB editor.

Thermal Pad, Power Rating & Derating – Real Examples

Power components often have special layout needs, QFN IC or a large MOSFET may have a thermal pad(or multiple pads) underneath that carries heat into the PCB. You must provide large copper areas or thermal vias under these pads to dissipate heat. The PCB copper itself becomes a heatsink.

Similarly, when placing high-power passives (like wirewound resistors or inductors), give them enough copper around them and consider airflow or a heatsink attached. Each component’s power rating is specified for a given ambient temperature and board conditions. Exceeding the rating overheats the part. Designers use derating curves to choose components with more headroom. A common practice is operating a resistor or diode at only 70–80% of its maximum power to increase reliability.

Component Applications on Modern Boards

Minimal MCU Board:

A minimal design often includes an MCU chip (with onboard flash), its required clock source may be an external crystal or the MCU’s internal RC oscillator. A voltage regulator and decoupling caps are on the power pins. A reset pull-up resistor, and maybe one status LED with its series resistor. That can all add up to only about 10–15 parts!

Modern microcontrollers pack so much functionality on-chip that you don’t need many external parts. In fact, integrated circuits on a minimal board replace whole subcircuits. Here is the design of my own MCU board, look at once.

Power Section (Buck/Boost/LDO Layout Secrets)

Power converters are the most layout-sensitive circuits. For a buck or boost regulator, short, tight loops are crucial. In a buck converter, the high-current loop goes through the input capacitor, the switch node of the IC, the inductor, and back via ground. The input capacitor must sit as close as possible to the regulator’s VIN and ground pins to minimize parasitic inductance.

In a boost converter, it’s the output capacitor and diode that need to hug the switch node and ground. Always follow the datasheet’s reference layout. Use plenty of copper and thermal vias under any power IC’s thermal pad to shed heat. Keep sensitive feedback and compensation traces away from the noisy switch node or inductor.

In general, one rule of thumb is to Identify the critical high-di/dt path and make it as short as possible. In practice, that means clustering the switcher IC, input caps, inductor, and diode together, and making feedback and gate drive traces minimal.

Conclusion – Build Better Boards Faster:

Successful PCB design is all about smart component choices and careful layout. As a quick summary, here are 7 golden rules for component selection:

By following these rules and leveraging well-defined component libraries. For example, EasyEDA provides built-in land patterns and 3D models. Well-chosen components and footprints let you “build better boards faster”, with fewer revisions and greater confidence. With this deep dive, you now have the context to understand what lives on your PCB, how to pick it, and how it influences your design. Good luck laying out your next board!