Duroid PCB Material Selection and Fabrication Guide

Material Choice Sets the Ceiling on RF Performance

Below a few hundred megahertz, laminate choice is mostly a mechanical and cost decision. Above roughly one gigahertz it becomes an electrical one. Dielectric loss converts signal energy into heat, dielectric constant variation shifts impedance, and moisture uptake changes both. A board that performs well in simulation on ordinary FR-4 can miss its loss target by a wide margin once it is built, and no amount of layout tuning recovers that.

Duroid, the PTFE based composite laminate family, exists to remove that limitation. This guide covers what the material does well, how the grades differ, the fabrication and design rules that matter, and where the cost sits.

What Duroid Is

Duroid laminates use a polytetrafluoroethylene matrix reinforced with a filler, usually woven glass or a ceramic powder. The PTFE provides the low loss and the chemical stability; the reinforcement controls mechanical properties and thermal expansion. The result is a laminate with a dielectric constant that can be held between roughly 2.2 and 3.0 depending on grade, with a loss tangent an order of magnitude below FR-4.

That combination is why the material appears in 5G base station antennas, radar and defence electronics, aerospace communication equipment, RF power amplifiers and high frequency test instruments. In each case the requirement is the same: keep the signal intact across a long path, or hold an impedance target tightly enough that a reflected wave does not degrade the link.

Why It Suits High Frequency Work

Five properties explain the choice. Very low dielectric loss, which reduces attenuation along the trace. A stable dielectric constant, which holds impedance consistent from batch to batch and across temperature. Low moisture absorption, which matters in outdoor and humid environments. Good thermal performance for high power RF stages. And better dimensional stability than general purpose laminates, which keeps filter and coupler geometries accurate.

The practical consequence at gigahertz frequencies is a measurable difference in insertion loss over a given path length. That is the figure that decides whether a design meets its link budget.

How Fabrication Differs

PTFE based material does not behave like FR-4 on the shop floor, and the process changes accordingly.

• Panel handling is adjusted to control warp and bow, because the material is softer and more prone to movement.
• Drilling parameters are tuned to reduce burring and damage to the hole wall.
• Copper foil adhesion is treated as a process step in its own right, since PTFE does not bond the way epoxy does.
• Lamination is carried out under vacuum to reduce voiding between layers.
• Tolerances on dielectric thickness are held tightly, because thickness error translates directly into impedance error.

Experience with the material matters more here than on standard boards. A first attempt at a PTFE stackup tends to show up as copper adhesion failures or smeared holes rather than as an obvious outline error.

Design Rules That Matter

Impedance tolerance. Hold impedance to plus or minus five percent or tighter. That depends on dielectric thickness control and on trace width tolerance, both of which are harder to guarantee on PTFE than on FR-4, so the tolerance should be stated on the drawing and verified in test.

Trace geometry. Microstrip and stripline follow different relationships between width, dielectric height and impedance. Set the geometry from the dielectric constant at the operating frequency rather than from a generic table, and confirm it with a field solver. The general principles are shared with any controlled impedance design, as described in our notes on PCB design and layout.

Via design. At gigahertz frequencies a via is a discontinuity. Back drilling removes the unused stub and reduces the parasitic effect. Blind and filled vias reduce reflection further where the layer count justifies them.

Copper weight and finish. Power layers are commonly specified at 1 oz to 3 oz. For surface finish, immersion silver and ENIG are preferred because they present a smoother, lower loss interface than hot air levelling.

Choosing a Grade

The grades are not interchangeable, and selection follows frequency, power and mechanical environment.

• 5880. Dielectric constant around 2.2 and the lowest loss of the common grades. Antennas and satellite systems are its natural home.
• 6002. Dielectric constant around 2.94, a compromise between loss and mechanical stability, widely used in aerospace work.
• 6035HTC. Formulated for high thermal conductivity, which makes it the choice for high power RF modules where heat removal limits performance.
• 6202. Selected for mechanical robustness, including high vibration environments.

Where a design mixes a high frequency front end with ordinary control circuitry, a hybrid stackup is common. FR-4 carries the digital and power sections and the PTFE laminate carries the RF section, bonded together in one board. That approach controls cost and is well established, provided the transition between the two materials is managed carefully.

Duroid Against FR-4

Set side by side on the dimensions that matter, the trade is clear. High frequency loss is very low on Duroid and comparatively high on FR-4. Signal integrity is excellent against adequate. Cost is significantly higher against low. The decision rule follows from that: where the operating frequency and link budget demand it, Duroid is the right answer, and where the board runs at low frequency, FR-4 remains the sensible engineering and commercial choice.

Fabrication Challenges to Plan For

Three failure modes recur. Poor copper adhesion, caused by insufficient surface treatment before lamination. Thermal expansion mismatch between layers, which shows up as dimensional drift after assembly. And drilling defects such as burrs or interlayer smear, caused by parameters copied from an FR-4 process. All three are process control problems rather than material limitations, which is why supplier experience is a real selection criterion rather than a marketing point.

Testing

High frequency boards carry a test regime beyond continuity and optical inspection. Time domain reflectometry verifies impedance along the trace, vector network analysis characterises loss and return loss, insertion loss testing confirms the link budget, and thermal shock plus environmental testing covers reliability. Our notes on TDR impedance testing explain what that measurement actually resolves.

Cost

PTFE laminate costs more than FR-4 per square metre, and the fabrication step costs more because it is slower and yields are lower. RF test capacity has to be funded as well. Indicative pricing for small quantities: a two-layer 5880 prototype batch commonly falls between 500 and 1200 US dollars; a four to six layer communication board between 1000 and 3000; a multilayer radar or satellite board from 3000 to 10000 and above. Volume production reduces unit cost substantially, in the same way as on any other laminate, and the reasons are covered in our notes on custom PCB pricing.

Where a project is cost sensitive, the most effective lever is to restrict the high frequency laminate to the area that actually needs it and use FR-4 elsewhere. The second is to fix the grade early, because changing laminate after tooling invalidates the impedance verification.

Selecting a Manufacturer

Five criteria matter. Demonstrated RF and microwave fabrication experience, since the process deviations described above only appear in practice. A traceable supply route for the laminate itself. In house high frequency test capability, because sending boards out for impedance and loss measurement extends the loop and weakens the feedback. Prototype and volume capability on the same site, so the qualified stackup carries through to production. And certifications appropriate to the target market, such as ISO 9001 and IATF 16949 where automotive work is involved.

It is also worth reviewing general PCB prototype turnaround alongside the high frequency capability, because RF development depends on short iteration cycles more than most disciplines, and the wider context sits under PCB manufacturing.

FAQ

Can Duroid be mixed with FR-4 in one board? Yes. Hybrid stackups are common and are usually the most cost effective way to give a mixed design the RF performance it needs without paying PTFE prices for the whole panel.

What is the minimum order quantity? Prototype runs from a single piece are usually possible on PTFE laminates, with volume pricing following after qualification.

Where is the material used? Aerospace, satellite communication, defence electronics, radar and 5G infrastructure are the main sectors.

Why does the impedance tolerance need to be stated explicitly? Because dielectric thickness and trace width both move impedance on PTFE more than on FR-4, so an unstated tolerance is effectively uncontrolled.

Applications Beyond Telecom

Although telecommunications draws most of the attention, the same properties serve other fields. Radar front ends need low loss and phase stability across temperature. Satellite links need dimensional stability in a vacuum and a wide thermal range. Test and measurement equipment needs the board itself to contribute as little uncertainty as possible. In all three cases the laminate is not simply a mechanical carrier; it is part of the electrical design.

Summary

Duroid laminates are chosen when dielectric loss and impedance stability decide whether a design works. The grade follows the frequency, power and mechanical environment: 5880 for antennas and satellite systems, 6002 for aerospace, 6035HTC for high power RF and 6202 for vibration. Success then depends on process discipline, meaning controlled warp, tuned drilling, treated copper adhesion, vacuum lamination and tight dielectric thickness tolerance, plus an impedance and loss test regime that confirms the result. Fix the material and the stackup before tooling, keep PTFE where it earns its cost, and the design will meet its link budget with margin left over.