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92 I-CONNECT007 MAGAZINE I AUGUST 2026 opment 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 manu- facturer 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 mate- rials can affect a board's electrical, thermal, and me- chanical 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 com- posed of woven fiberglass cloth bonded with an epoxy resin. It is favored in these applications for its durability, electrical insulation, and cost-effec- tiveness. High Speed Materials Materials geared toward high speed designs make sense where signal integrity is important. These in- clude PTFE, modified epoxies, and laminates that blend ceramic with hydrocarbon resins. All are ex- pensive 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 aero- space 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 micro- wave 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 Tef- lon®) 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 can make or break product development. Spe- cialty materials like polyimide are considered premium for a reason. They are not cheap. Dur- ing design and prototyping, if your device's ap- plication does not clearly require specialty mate- rials, 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. C O N N ECT T H E D OTS