What Is a Coil PCB? Types, Functions & Applications

An electronic device that uses coils is referred to as a coil PCB. These coils are essential components in a wide range of applications, including transformers, inductors, motors, wireless charging systems, and RF (radio frequency) circuits. In modern electronics, coils can be directly integrated into printed circuit boards (PCBs) by patterning copper traces into spiral or helical shapes on substrates such as FR4, polyimide, or ceramic.

But what exactly is a coil?

What Is a Coil?

In electronics, a coil—also known as an inductor—is a passive component made by winding a conductive wire (typically copper) into a series of loops or turns. This coiled shape allows it to store energy in the form of a magnetic field when electric current flows through it.

It’s worth noting that the term "coil" is sometimes used more generally. For example, a mechanical coiled spring is also called a "coil spring," though it has no electrical function. In electronics, however, a coil specifically refers to a wound conductor designed to exhibit inductance.

When current flows through a conductor, a magnetic field is generated around it in concentric circles. The direction of this field follows the right-hand rule: if you point your thumb in the direction of current flow, your fingers curl in the direction of the magnetic field.

This magnetic property is the foundation of how inductors (coils) work in electronic circuits.

How Does a Coil (Inductor) Work?

A coil, or inductor, plays two critical roles in electronic circuits:

• Energy Storage: It stores electrical energy in the form of a magnetic field.

• Opposition to Current Change: It resists changes in current, especially in alternating current (AC) circuits

Magnetic Flux and Inductance

When voltage is applied across a coil, current begins to flow, generating magnetic flux—a measure of the total magnetic field passing through the coil. This magnetic flux is similar to that of a permanent magnet and remains for a short time even after the power is removed.

In other words, the coil temporarily magnetizes itself, converting electrical energy into magnetic energy and storing it internally. The ability of a coil to store this energy is called inductance, and it is measured in henries (H), often in millihenries (mH) or microhenries (µH).

• For direct current (DC): Once the current stabilizes, the coil acts like a simple wire with very low resistance.

• For alternating current (AC): The constantly changing current causes the magnetic field to continuously expand and collapse, inducing a voltage that opposes the change in current—this is known as self-inductance.

This opposition increases with frequency, meaning coils block high-frequency AC more effectively than low-frequency or DC signals. This property makes them ideal for use in filters, noise suppression, and power regulation circuits.

Types of Coils Used in Electronics

Coils can be classified based on their construction and integration method. The three main types are:

1. Wound Coils

• Made by winding insulated copper wire around a ferrite core, plastic bobbin, or air core

• Common in power inductors, transformers, and high-inductance applications.

• Offers high performance but larger size.

2. Laminated Coils (Printed or Layered)

• Constructed by stacking multiple layers of patterned conductive traces on a PCB or substrate.

• Compact and suitable for high-frequency applications.

• Often used in RF modules and miniaturized devices.

3. Thin Film Coils

• Fabricated using advanced processes like sputtering or vapor deposition to create ultra-thin, precise coil patterns.

• Extremely accurate and stable, ideal for high-density ICs and medical devices.

• More expensive but offers superior performance in small form factors.

Role of Coil PCBs in Electronic Devices

Coil PCBs are not just add-ons—they are critical components that enable modern electronics to function efficiently and reliably. Whether embedded directly into the board or used as surface-mounted inductors, they serve several key functions:

• Stabilize voltage in DC-DC converters and power supplies.

• Filter out electromagnetic interference (EMI) and high-frequency noise.

• Enable wireless power transfer (e.g., in Qi chargers).

• Support RF communication (e.g., NFC, Bluetooth, and RFID antennas).

• Store and release energy during rapid load changes

From smartphones and laptops to IoT devices and automotive systems, coil PCBs ensure stable, efficient, and compact circuit operation.

While exact component counts vary, inductors typically make up 5% to 15% of all surface-mounted components on a typical PCB—far less than the 30–40% sometimes claimed (which likely includes capacitors).

Coil Structure and Energy Storage Mechanism

A coil consists of a conductive wire wound into multiple turns, often around a magnetic core (e.g., ferrite) to enhance inductance. The core material increases the magnetic flux density, allowing more energy to be stored in a smaller space.

When current flows:

• A magnetic field builds up around the coil.

• Energy is stored in this magnetic field.

• If the current is interrupted, the collapsing field induces a voltage that tries to maintain the current flow—this is why inductors can cause voltage spikes in switching circuits.

The inductance value depends on:

• Number of turns

• Coil diameter

• Core material

• Spacing between windings.

This ability to resist sudden current changes makes coils indispensable in switching power supplies, filters, and resonant circuits.

Common Types of Inductors Used on PCBs

1. Printed Spiral Coils (on PCB)

These are planar coils etched directly onto the PCB using copper traces. Commonly used in:

• Etched directly onto the PCB using copper traces.

• Used in NFC antennas, wireless charging receivers, and RF filters.

• Cost-effective and fully integrable but with lower inductance.

2. Surface Mount Device (SMD) Inductors

Pre-fabricated inductors mounted on the PCB. Types include:

• Wire-wound SMD inductors: High inductance, used in power supplies.

• Multilayer ceramic inductors: Compact, used in high-frequency circuits.

• Thin-film inductors: High precision, used in RF and communication modules.

3. Transformers on PCB

• Consist of two or more coils coupled together.

• Used for voltage conversion, isolation, and signal coupling.

• Common in power supplies and Ethernet interfaces.

Precautions When Mounting Coils on a PCB

If the board is bent while soldering the coil to the printed circuit board or after soldering, the coil may crack.

Therefore, it is necessary to place the coils so that stress is not applied as much as possible due to bending of the printed circuit board.

Placing a coil parallel to the direction of stress, as shown above, will result in direct flexure. Therefore, place the coil perpendicular to the direction in which the stress acts.

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Conclusion

Coil PCBs are more than just passive components—they are enablers of modern technology. From powering your smartphone to enabling contactless payments and wireless charging, integrated coils are at the heart of innovation.

As electronic devices continue to shrink and demand higher efficiency, advancements in embedded coils, thin-film technology, and 3D PCB winding are driving the next generation of compact, high-performance circuits.

Whether you're designing a wearable, IoT sensor, or power module, choosing the right coil integration method can make a significant difference in performance, size, and cost.

Victory PCB specializes in coil PCB design and manufacturing, including: Custom planar spiral coils, Embedded inductors, High-frequency and RF coil PCBs and Flexible and rigid-flex coil circuits. We offer end-to-end solutions from design to production, ensuring high reliability and performance for your application. Contact us by sales@victorypcb.com today to get a free custom quote for your coil PCB project.