When a customer approaches us with a high-frequency application, the conversation rarely starts with price. It starts with the material. In RF and microwave designs, the substrate is not a passive carrier—it is part of the circuit. That is why, when this particular project landed on our desk, the choice of Rogers TMM10 was already made. The real question was whether we could build it exactly to specification.

This is the story of how we manufactured a 2-layer, 5.1mm thick TMM10 PCB for a high-frequency application—and what made it challenging.

The Customer's Requirement

The customer needed a double-sided PCB built on Rogers TMM10, a thermoset microwave material. The finished board thickness was specified at 5.1mm, with a tight dimensional tolerance of ±0.15mm across a compact 63.9mm × 48mm outline.

What made this project unusual was not just the material, but the finish. The board required no solder mask and no silkscreen on either side. For a high-frequency design, this is not a cost-saving decision—it is a performance decision. Solder mask introduces a dielectric layer that can shift impedance and interfere with tuning. Removing it means the copper surface must be flawless, because there is nothing to hide behind.

The application? High-frequency RF work, in the same family as satellite communication systems, GPS and patch antennas, and chip testers.

The Engineering Challenges

A 5.1mm thick board is not standard. Most double-sided PCBs are measured in fractions of a millimeter. At this thickness, several things become difficult at once.

First, the stackup. The board was built as a 2-layer rigid PCB:

• Copper Layer 1: 35 μm (1oz)

• Rogers TMM10 Core: 5.08mm (200mil)

• Copper Layer 2: 35 μm (1oz)

That 5.08mm core is the source of both the board's mechanical rigidity and its manufacturing difficulty.

Second, the drilling. With a minimum hole size of 0.25mm and a board thickness of 5.1mm, the aspect ratio is high. Deep, narrow holes demand precise drilling parameters and clean via walls. We used 13 through-hole vias, all plated to a thickness of 20 μm, with no blind vias. Every connection had to be reliable.

Third, the fine features. The minimum trace and space was 4/7 mils. On a thick, ceramic-filled thermoset material, achieving consistent etching across the panel is not trivial. TMM10 is mechanically stable, but its processing window is narrower than standard FR-4.

Fourth, the finish. With no solder mask and no silkscreen, the surface finish had to be perfect. We specified ENIG (Electroless Nickel Immersion Gold)—a flat, oxidation-resistant finish that supports both soldering and wire bonding. ENIG is a premium choice, and for this board, it was the right one.

One thing worked in our favor: TMM10 does not require sodium naphthalate treatment before electroless plating. That eliminated a hazardous and time-consuming step that is common with PTFE-based materials.

How We Built It

Every project starts with the Gerber data. In this case, the customer supplied artwork in Gerber RS-274-X format, the industry standard. From there, we moved into fabrication.

The stackup was straightforward on paper but demanding in execution. A single 5.08mm TMM10 core, laminated with 1oz copper on both sides, produced a finished thickness of 5.1mm. The material's coefficient of thermal expansion is matched to copper, which helps maintain dimensional stability through thermal cycling—important for an application that may see temperature variation.

Drilling came next. With 13 vias at 0.25mm minimum diameter, we controlled depth, feed rate, and spindle speed to avoid resin smear and ensure clean holes. Plating brought the via walls to 20 μm, providing solid electrical connections between the two copper layers.

The circuit itself was simple in net count—only 2 nets—but dense in pads. The board carries 26 components, 38 total pads, 21 through-hole pads, and 17 top-side SMT pads. There are no bottom-side SMT pads. The layout is a hybrid of through-hole and surface-mount, which is common in RF test and antenna applications where a mix of connector types and tuning components is required.

Patterning the 4/7 mil traces required careful control of exposure and etching. On a material this thick, uneven copper distribution can cause etching inconsistencies. We adjusted the process to maintain trace fidelity across the entire panel.

Finally, ENIG. With no solder mask to protect the copper, the nickel-gold deposition had to be uniform and defect-free. This is where a board like this either passes or fails—there is no cosmetic cover-up.

Quality Verification

Before shipment, every board underwent 100% electrical testing. This is standard practice for us, but it matters more on a project like this, where the customer cannot visually inspect for solder mask defects or silkscreen errors. Electrical test confirms continuity, isolation, and net integrity.

The board was manufactured to IPC-Class-2 standards—the benchmark for dedicated service electronics. It is reliable and durable, built for real-world operation rather than laboratory demonstration.

The Result

The finished board measured 63.9mm × 48mm, within ±0.15mm tolerance. It carried 26 components across 38 pads, connected by 13 vias, with a finished copper weight of 1oz (1.4 mils) on the outer layers.

More importantly, it met the electrical and mechanical requirements of a high-frequency application. The combination of TMM10's electrical properties—a dielectric constant of 9.20 and a dissipation factor of 0.0022 at 10GHz—with a rigid 5.1mm construction makes this board suitable for applications where signal integrity and physical stability are both non-negotiable.

Why TMM10?

For readers unfamiliar with the material, TMM10 is worth understanding. It is a thermoset microwave material that combines the electrical benefits of PTFE with the mechanical advantages of ceramic-filled substrates. It resists creep and cold flow. It withstands process chemicals. It does not require sodium naphthalate treatment. And because it is based on a thermoset resin, it supports reliable wire bonding.

Its typical applications include chip testers, dielectric polarizers, satellite communication systems, and GPS or patch antennas—exactly the kind of high-frequency environments this board was built for.

Final Thoughts

A 5.1mm thick TMM10 board with no solder mask and no silkscreen is not a routine build. It requires the right material knowledge, the right process control, and the willingness to work without a safety net.

If you are working on a high-frequency design and need a manufacturer who understands materials like TMM10, we would be glad to talk. Whether your board is 0.5mm or 5.1mm thick, the conversation starts the same way: with your requirements.

Contact us to discuss your next high-frequency PCB project.