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Connect the Dots: What PCB Designers Should Know About Materials

What questions does your manufacturer ask when they receive a design? I can tell you one: “How will we build this?”

Every PCB design has specific parameters for elements such as impedance, thermal conductivity, and SI. Designers choose material properties based on the functionality requirements of the boards they design. Does the PCB have to operate in high heat? Be flexible enough to fit into a tiny device, such as a wearable? Maintain SI without distortion or data degradation?

These are important, foundational considerations for designers. I believe it is also important for designers to consider how a manufacturer thinks about materials. PCBs are manufactured using layers of conductive materials, surface coatings to protect conductive layers from oxidation, and substrates. The materials dictate the board's flexibility, heat dissipation, and electrical performance.

So, it’s important for designers to match design requirements to the manufacturer’s list of materials available for production. Those materials represent a means to an end—the smooth, cost-effective production of a reliable PCB that meets the designer’s requirements. In general, a longer list is better. 

More complex designs, boards, and electronic devices mean material requirements must expand and diversify. Designers working in product development are often called upon to create a wide variety of boards, everything from specialized RF and microwave boards to rigid, flex, and rigid-flex circuits. In those situations, it helps to have a manufacturer with experience in the wide universe of substrates, sizes, and shapes.

Materials manufacturers generally offer similar options for conductors (copper, aluminum, gold, and silver) and surface finishes (e.g., solder mask, nomenclature, HASL, and ENIG).

Things get a little trickier when it comes to substrates, the insulating base material that serves as the foundation for a PCB. A substrate is non-conductive, provides mechanical support to hold electronic components in place, and acts as an electrical insulator to maintain signal integrity.

Breaking Down the Types of Substrates
PCB designers generally know how substrate materials can affect a board’s electrical, thermal, and mechanical performance. The material properties you choose determine signal integrity, impedance, heat dissipation, and reliability under thermal stress.

There are several commonly used substrates in PCB manufacturing. They include:

FR-4 Fiberglass

Commonly used for rigid, multilayer PCBs found in laptops and consumer electronics, FR-4 is composed of woven fiberglass cloth bonded with an epoxy resin. It is favored in these applications for its durability, electrical insulation, and cost-effectiveness.

High Speed Materials

Materials geared toward high speed designs make sense where signal integrity is important. These include PTFE, modified epoxies, and laminates that blend ceramic with hydrocarbon resins. All are expensive compared to standard materials, but they offer improved SI, as well as minimized distortion and signal loss.

Polyimide

If you are designing a flexible PCB, chances are polyimide will be the substrate of choice. Polyimide is comprised of resins instead of epoxies, allowing the board to bend and fold into tight spaces without breaking. It is also lightweight and can withstand extreme temperatures, making it ideal for aerospace applications, motor vehicle electronics, and ultra-compact medical devices.

Metal Core

This substrate is structurally tough and dissipates heat more effectively than other materials. Made from aluminum, copper, or steel, metal core PCBs are often found in high-powered, commercial-grade electronics, high-frequency RF applications, and durable military hardware.

PTFE and Ceramics

For high speed and high frequency RF and microwave applications that require PCBs operating with minimal signal loss, delay, and distortion, there are two primary substrate material classes. They are PTFE (polytetrafluoroethylene, also known as Teflon®) and ceramics.

Both feature very, very low dielectric loss and offer stable dielectric constant at high frequencies, making them ideal for antennas, high-speed data networks, and aerospace applications.

Evaluating Material Properties
For PCB designers, choosing materials depends on how and where the board will operate. Sometimes, it is easy to choose. Other times, it’s more nuanced. Design considerations include:

Cost

Though I often see this at the bottom of the list of evaluation criteria, the cost to produce a PCB design can make or break product development. Specialty materials like polyimide are considered premium for a reason. They are not cheap. During design and prototyping, if your device’s application does not clearly require specialty materials, it can be worthwhile to test the feasibility of cost-effective FR-4.

Electrical Performance

Electrical performance is another important attribute for material selection. The primary considerations regard signal integrity and power distribution. Your choice of substrate directly determines how fast and cleanly signals travel across your circuit.

Heat

Is your board going into space? After assembly, will it have a slew of hot components? I encourage designers to carefully evaluate the temperatures their boards will operate in. High heat environments or multiple soldering passes during assembly can cause certain substrates to soften or expand. It’s also important to recognize how much heat components will create and if those temperatures will make one substrate preferable to another.

Strength

A board’s strength is measured in many ways, but all those measures essentially pertain to the board’s durability. It is important to choose substrates that will ensure the board can withstand everything the environment throws at it. This is especially so for flexible PCBs and those subject to vibration or repeated impacts that are often present in military and aerospace applications. Another consideration is excessive moisture absorption that can degrade board performance.

Availability

Substrate availability issues are becoming more common due to increased demand created by AI-related build-out and geopolitical disruption. Lead times are longer now, and substrate costs are increasing, sometimes even for standard materials. This can extend product development windows and drive up the cost of going to market. We encourage designers to consider materials availability in their design choices.

Manufacturability

Manufacturability is a key concern equal to cost considerations. FR-4 is the go-to for ease of manufacture. Every PCB fabricator works with it. But more designs are requiring other substrate materials that not every manufacturer can offer. Choosing the right manufacturer, one knowledgeable and experienced in the array of substrate materials, ensures the design is functional and structurally reliable, while also helping avoid manufacturing issues.

Why It Is Important to Choose Substrate Wisely
Choosing the wrong PCB substrate can lead to everything from manufacturing failures, such as rework or reduced yield, to boards that operate with excessive signal loss, are susceptible to thermal damage, or are prone to mechanical breakdown in the field.

Signal Integrity Issues

If you are designing boards for RF or high-frequency applications, choosing FR-4 can lead to a slew of issues in the field. FR-4 is a solid, cost-effective base for basic circuits, but it opens the door for signal loss, signal reflections, data corruption, and electromagnetic interference (EMI).

Thermal Failures

If your board needs to operate in a hot environment and you pick the wrong substrate, the result can be solder joint cracking, warping, component failure, and even a melted board. When choosing a substrate, pay close attention to CTE, Tg, and thermal conductivity to avoid such issues.

Mechanical Failures

Polyimide is your best bet for applications requiring a board that can bend or flex. Using rigid materials in these instances can lead to delaminated circuits and broken copper or even cause the board to snap. But if your board is designed for structurally rigid application, flexible material will not work because of challenges associated with securely mounting components.

When your manufacturer gets the first peek at your requirements and design, their job is to ask, “How will we build this?” With modern materials and manufacturing techniques, more is possible than ever before. A good manufacturing team has the experience and capacity to help you select the materials that are optimal for your project.

Matt Stevenson is vice president and general manager of ASC Sunstone Circuits. To read past columns, click here.

Read Matt’s book, The Printed Circuit Designer’s Guide to … Designing for Reality and listen to his podcast series here.

This column originally appeared in the August 2026 issue of I-Connect007 Magazine.