Selecting the right PCB material for an RF or microwave design is one of those decisions that shows up in every measurement afterwards. High-frequency circuits leave little margin — signal loss, phase drift and unstable electrical properties all trace back to the laminate. The six tips below cover the properties worth checking before you commit.
The dielectric constant (Dk) describes how much a material slows an electrical signal down. Lower Dk means faster signal propagation — and in high-frequency work, that matters. A high Dk introduces signal delay, which hurts RF circuits where timing and phase accuracy decide whether the design works at all. Consistency matters as much as the number itself: even a small shift in Dk across frequencies can distort a signal.
Stable Dk prevents dispersion, where different frequency components of a signal travel at different speeds. Laminates with low, stable Dk — PTFE-based materials and certain ceramic-filled systems, for example — keep loss down and carry signals accurately over distance.
Dissipation factor (Df) is the share of signal energy a material converts to heat. The lower the Df, the less energy you lose — and the effect grows with frequency. Keeping Df below 0.005 preserves signal strength and keeps RF and microwave circuits efficient.
As frequency climbs, a high Df costs more: more power loss, more heat, less stable signals. Low-loss PTFE holds a steady Df even at GHz frequencies, which is why it appears so often in high-frequency stack-ups.
Thermal expansion in the Z-axis should stay low — roughly 10 to 20 ppm/°C. A material that barely expands when heated keeps the board dimensionally stable through thermal cycles. Thermal conductivity between 0.3 and 0.6 W/m·°C helps too, moving heat out of the board before it becomes a reliability problem.
Temperature swings shift impedance and degrade the signal. Boards with high CTE can delaminate or crack, leading to open or short circuits in high-frequency designs. Ceramic-filled PTFE offers both low CTE and good thermal conductivity, which makes it a natural fit for RF work.
Substrate thickness directly affects signal integrity, especially above 10 GHz. Thin substrates — 10 to 20 mils — shorten the signal path, cut loss, and reduce unwanted coupling between layers. They also make impedance easier to control precisely.
Thin laminates limit dielectric loss and keep attenuation low, while thick ones add propagation delay and loss as frequency rises. Rogers RO4350B and Taconic TLY series are common picks when a design needs both thinness and stability.
Conductor loss comes from the resistance of the copper traces themselves. Low-profile copper — very low profile (VLP), hyper very low profile (HVLP), or reverse-treated foil (RTF) — reduces surface roughness, which matters because high-frequency current flows mostly near the conductor surface (the skin effect). Smoother copper keeps signal strength up over distance.
Smooth foil surfaces reduce scattering and loss at high frequency, and HVLP copper also bonds better to the dielectric, so the stack-up resists delamination. Many RF fabricators pair materials like the Rogers RO3000 series with low-profile copper foil for exactly this reason.
Volume resistivity measures how well a material resists current flow. In RF and microwave PCBs, high resistivity keeps current where it belongs — in the intended signal paths — instead of leaking through the substrate.
Leakage current creates interference and weakens signal isolation, which degrades output quality. Ceramics and PTFE-based laminates with high resistivity close off those leakage paths and preserve signal integrity.
No single property makes a good RF material — the low Dk, low Df, low CTE, thin substrate, low-profile copper and high resistivity covered here work as a set. Checking all six before finalizing a stack-up is what separates a design that simulates well from one that performs in the field.
Quick answers from HF PCB PRO engineering — for project-specific advice, contact our team directly.
Below 4 at your operating frequency is the usual target for RF and microwave work; millimeter-wave designs often go lower. Dk consistency across frequency matters as much as the absolute value, because shifts cause dispersion and phase error. Always quote Dk at the design frequency, not at 1 MHz.
Df is the fraction of signal energy converted to heat. At GHz frequencies even small Df differences compound into noticeable insertion loss across a board. Below 0.005 keeps attenuation manageable; PTFE laminates typically reach 0.001–0.003.
Below roughly 1 GHz, sometimes. Above that, FR-4's higher Df (around 0.02), unstable Dk and high Z-axis CTE cost you loss, phase stability and reliability. For anything beyond a few GHz, a low-loss laminate is the safer call.
VLP, HVLP and RTF foils have smoother surfaces than standard electrodeposited copper. Above a few GHz, where current crowds toward the conductor surface, roughness drives conductor loss. Low-profile foil cuts that loss, at some cost in adhesion.
Typically 10–20 mil. Thin substrates shorten the signal path, reduce dielectric loss and tighten impedance control. Very thin laminates trade away mechanical strength, so confirm handling and rigidity requirements with your fabricator.
Send us your frequency band, stack-up and performance targets — our engineers will shortlist laminates, flag DFM risks and quote your build.
Get A Material Recommendation → Fast Reply on WhatsApp