Printed circuit boards are everywhere. They connect, power, and control nearly every modern device, from industrial equipment to everyday consumer tech. But what are printed circuit boards made of?

Although they often appear as a single flat piece, a printed circuit board (PCB) is actually built from multiple layers of materials, each with a specific role. Those layers form a structure that holds components in place while controlling the flow of electricity through the design. 

In this article, we’ll look at what circuit boards are made of, how each layer contributes to performance, and why those choices matter for both design and manufacturing.

Why PCB Materials Matter

The materials used in a PCB are fundamental to its reliability. They determine how much heat the board can handle, how efficiently signals travel, and how well it stands up to long-term use.

Selecting the right combination of materials is about balancing performance, cost, and application. High-power boards may require thicker copper to carry current safely, while high-speed or RF designs rely on materials that maintain signal integrity. Even the protective coatings on the surface affect how easily a board can be soldered or assembled.

Understanding these PCB circuit board materials early helps ensure that the final electronic device is functional, consistent, and reliable.

What Are PCB Layers?

Every circuit board is built as a stack of thin, specialized layers that together form a solid, functional structure. Each layer has a specific job, like providing mechanical support or creating conductive paths for electricity to flow.

While the number of layers can range from one to dozens, depending on complexity, most boards share the same basic elements.

Substrate Layer (Base Material)

The substrate is the foundation of every circuit board. It’s made of a non-conductive material that provides rigidity, insulation, and structural support for the conductive layers above it. Different substrate materials are used depending on the application.

FR-4

FR-4 is the industry standard for most circuit boards. It is an electrically insulating material made of fiberglass-reinforced epoxy that provides a strong base for copper traces. It’s suitable for a wide range of applications, including consumer electronics and industrial equipment. 

CEM-1 / CEM-3

CEM-1 and CEM-3 are composite epoxy materials used in cost-sensitive applications. CEM-1 is typically used for single-sided boards, while CEM-3 is slightly stronger and supports double-sided PCB designs. Both are common in low-power or simple consumer electronics.

Polyimide

Polyimide is a pliable, heat-resistant material often found in rigid-flex or flexible printed circuit boards. It performs well in high-temperature environments, such as those found in automotive, aerospace, or industrial control systems.

Metal-Core (Usually Aluminum) 

Metal-core is used for its thermal properties in designs that generate significant heat, like LED lighting or power supplies. The aluminum base helps conduct heat away from the electronic components, improving thermal management and extending the product’s lifespan. These are often used in single-layer designs.

Copper Layer

Copper layers form the electrical connections that make the circuit work. They’re thin sheets of copper bonded to the substrate, then etched into precise conductive pathways. Copper is used because it’s highly conductive, cost-effective, and easy to process. 

The thickness of the copper depends on the amount of current the board needs to carry: Thicker layers are used for power applications, while thinner layers are used for dense signal routing. 

Solder Mask Layer

The solder mask is the thin, colored coating that covers and protects the copper. This layer prevents oxidation, stops solder from bridging between pads during assembly, and gives the physical circuit board its recognizable appearance (typically green). 

Silkscreen (Legend) Layer

The silkscreen, or legend, is the printed layer that includes labels for the electrical components, test points, and orientation markings on the board surface. It’s made from a non-conductive ink. While it doesn’t affect performance, clear silkscreen markings make assembly and troubleshooting faster and more accurate during and after the PCB manufacturing process.

What Are Surface Finishes? 

Once a PCB’s copper traces and pads are exposed, they need protection. Bare copper oxidizes quickly when exposed to air, making soldering and mounting electronic components more challenging. It also makes the board itself less reliable over time. A surface finish prevents that oxidation and ensures every pad remains solderable during assembly. 

Different finishes suit different needs. Some are chosen for their cost and durability, while others are selected for precision and appearance. The right choice depends on the fineness of the components, the duration of storage, and the specific requirements of the PCB fabrication process. 

Common PCB Finishes

HASL (Hot Air Solder Leveling) 

One of the most widely used finishes, HASL involves coating the board in molten solder and then leveling it with hot air. It’s inexpensive and provides excellent solderability, making it a popular choice for general-purpose boards. 

Lead-free versions are available for RoHS-compliant products. However, the process can create a slightly uneven surface, which may not be ideal for fine-pitch components.

ENIG (Electroless Nickel Immersion Gold)

ENIG is a thin layer of gold applied over a nickel barrier. It provides an extremely flat surface and excellent corrosion resistance, making it ideal for higher component density and fine-pitch assemblies. 

ENIG is more expensive than HASL but offers a long shelf life and reliable solder joints, which is why it’s common in high-end and mission-critical electronics. 

ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold)

ENEPIG is a high-performance finish that adds layers of nickel, palladium, and gold to protect copper pads. It provides excellent solderability, corrosion resistance, and long shelf life, making it suitable for demanding applications.

It’s compatible with both soldering and wire bonding, which makes it a preferred choice for fine-pitch components and high-reliability electronics such as sensors and advanced medical equipment.

OSP (Organic Solderability Preservative) 

OSP is a water-based organic coating that protects copper pads from oxidation. It’s cost-effective, very flat, and well-suited for surface-mount technology. 

The trade-off is shelf life: OSP finishes are sensitive to handling and must be assembled relatively quickly after manufacturing. They also offer less corrosion resistance compared to other finishes.

Immersion Silver and Immersion Tin

Both finishes provide a smooth, flat surface at a moderate cost.

Immersion Silver: Offers good conductivity and is often used in high-frequency applications, though it requires careful handling to prevent tarnishing. It’s a good choice for designs that require low-loss connections.

Immersion Tin: Inexpensive and solderable, but can be prone to “tin whiskers” over time if not properly controlled. Tin whiskers are thin, hair-like structures that can grow on the surface of the tin coating and cause short circuits.

Hard Gold (Electrolytic Gold) 

Used in areas that require frequent mechanical contact, such as edge connectors or keypads. 

Hard gold is extremely durable and wear-resistant, but also costly, so it’s typically applied only where needed rather than across the entire board. 

Common Components of Printed Circuit Boards

The materials and finishes form the body of a circuit board, but it’s the board components mounted on top that bring it to life. These small parts control current, store energy, and process electrical signals to make the device function as intended.

While every PCB is unique to its design, most include a few familiar building blocks. 

Capacitors

Capacitors store and release energy as needed. They smooth out voltage fluctuations, filter noise from signals, and provide short bursts of power where necessary, such as when the circuit first turns on. 

Diodes

Diodes allow current to flow in only one direction. They’re used to convert the alternating current (AC) to direct current (DC), prevent reverse voltage damage, and even emit light in the case of light-emitting diodes.

Inductors

Inductors store energy in a magnetic field when current passes through them. They’re used in filters, power supplies, and radio-frequency applications to manage current flow and reduce signal interference. 

Integrated Circuits (ICs)

ICs are complete circuits built into a single chip package. They handle complex tasks like processing, memory, power management, and signal conditioning, and come in packages such as QFN, QFP, and BGA.

Resistors

Resistors limit or control the flow of electrical current. They’re one of the most common components on a PCB and are used to set voltage levels, divide signals, and protect sensitive parts from excessive current. 

Sensors

Sensors detect physical changes such as temperature, light, motion, or pressure, and convert them into electrical signals. They allow devices to interact with their environment, for example, turning on a screen when motion is detected or regulating heat in an industrial system. 

Transistors

Transistors act as electronic switches or amplifiers. They’re the foundation of all modern electronics, from basic circuits to complex processors, controlling how signals are turned on, off, or strengthened. 

Transformers

Transformers transfer energy between circuits and are often used to step voltage up or down. They’re more common in power electronics or devices that connect directly to an AC power source.

Vias

Vias are plated holes that connect copper traces between layers inside the PCB. Common types include through-hole, blind, buried, and microvias, which can also be grouped as thermal vias that pull heat into internal copper planes.

How We Approach Printed Circuit Board Materials at August Electronics

Every layer, coating, and finish in a circuit board plays a role in how that product performs. A deep understanding of involved materials ensures that each of our builds, whether they involve flexible, rigid, or rigid-flex PCBs, is reliable, consistent, and suited to its application. 

Each project we manufacture is evaluated for the best combination of material quality, electrical performance, and production efficiency. Our goal is always the same: to deliver reliable, precisely built circuit boards that meet the demands of their environment.

If you’re planning a new electronic design and want a manufacturing partner who understands how materials affect performance at every stage, connect with us.