Taconic RF-35 PCB | Low-Cost Rogers Alternative

What Is Taconic RF-35 and Why Consider It?

Taconic RF-35 is a woven-glass-reinforced PTFE composite laminate with a dielectric constant (Dk) of 3.50 ± 0.05 and a dissipation factor (Df) of 0.0018 at 10 GHz. Those numbers put it in the same electrical neighborhood as Rogers RO4350B (Dk 3.48, Df 0.0037) while delivering meaningfully lower dielectric loss—roughly half the Df—at a price point that typically falls 15–30 % below Rogers depending on panel size and order volume. For engineers designing filters, couplers, power amplifiers, or antenna feed networks up to about 40 GHz, RF-35 is one of the most cost-effective paths to controlled-impedance PTFE performance.

The material is manufactured by Taconic Advanced Dielectric Division, a U.S.-based producer with decades of heritage in PTFE laminates. RF-35 is available in thicknesses from 5 mil (0.127 mm) to 60 mil (1.524 mm) with standard 1 oz (35 µm) or ½ oz (18 µm) electrodeposited copper cladding, and it can be ordered with rolled copper for applications where conductor-surface roughness drives insertion loss, such as designs above 20 GHz where HVLP copper foil becomes relevant.

Key Electrical and Mechanical Properties

Two numbers jump out. First, the Df of RF-35 is roughly half that of RO4350B. In a 50 Ω microstrip at 24 GHz on 10 mil core, that difference translates to about 0.15 dB/inch less dielectric loss—significant in a multi-coupler feed network or a long antenna corporate feed. Second, the z-axis CTE of 173 ppm/°C is far higher than RO4350B’s 32 ppm/°C. That high CTE is typical of PTFE composites and means plated-through-hole reliability under thermal cycling needs careful attention—more on that below.

RF-35 vs. RO4350B: Where Each Material Wins

Choose Taconic RF-35 when…

• Insertion loss is the primary driver and cost is constrained—RF-35’s lower Df delivers measurably better performance in filters and long feed lines.
• The design is a single- or double-sided board, or a simple 4-layer hybrid stackup, where z-axis CTE is manageable because via aspect ratios stay low.
• Moisture stability matters: 0.02 % absorption keeps Dk stable in outdoor or humid environments, useful for base-station antennas and marine radar.

Choose Rogers RO4350B when…

• You need a high-layer-count multilayer (≥ 6 layers) with dense via fields. RO4350B’s thermoset chemistry and low z-CTE make it far friendlier to standard FR-4 lamination and drilling processes.
• Lead-free assembly is required and you want the broadest fabricator qualification base. RO4350B is processable on standard epoxy-glass lines without PTFE-specific tooling.
• The design frequency is below 6 GHz and the Df difference is electrically negligible—RO4350B’s easier processing wins on total cost of ownership.

If your project sits between these extremes—moderate frequency, moderate layer count, tight budget—use the cross-reference tool below to compare RF-35 against both Rogers and other alternatives like Shengyi S7136 or Wangling TP-2.

Enter RF-35’s Dk of 3.50 and Df of 0.0018 and the tool will list laminates with matching or near-matching electrical properties. You will typically see RO4350B, Isola I-Tera MT40, and several lower-cost Asian-manufactured PTFE grades. Comparing the full parameter set—CTE, thermal conductivity, moisture absorption—alongside Dk and Df lets you shortlist materials that are both electrically equivalent and mechanically compatible with your fabrication process.

Fabrication Considerations for Taconic RF-35 PCBs

Drilling and Via Reliability

PTFE composites are softer than thermoset resins, so RF-35 requires sharp carbide drill bits and reduced chip loads to avoid smearing the hole wall. Most experienced RF fabricators use entry and backer boards optimized for PTFE and run spindle speeds 10–20 % higher than for FR-4 at the same drill diameter. The high z-axis CTE (173 ppm/°C) means plated through-holes expand significantly during reflow. For boards thicker than 30 mil (0.76 mm), specify a minimum copper plating thickness of 1 mil (25 µm) in the via barrel and consider via-in-pad with filled and capped vias to improve thermal-cycle reliability per IPC-6012 Class 3 requirements.

Lamination and Hybrid Stackups

RF-35 bonds well to itself and to other PTFE layers using Taconic’s own bonding films (e.g., FR-27 or FastRise 27). For hybrid stackups combining RF-35 signal layers with FR-4 structural layers, a low-flow prepreg such as Taconic’s CER-10 or a thermoset bonding film is used as the adhesive interface. The lamination cycle is typically 370–385 °C at 200–400 psi for PTFE-to-PTFE bonds—well above standard FR-4 press temperatures—so the fabricator needs a high-temperature press capable of controlled ramp and dwell profiles.

For designs that need more layers or tighter via registration, the Taconic family offers related materials: Taconic RF-301 at Dk 2.97 for lower-Dk stripline cores, and Taconic RF-41 at Dk 4.10 for compact antenna elements where size reduction matters.

Surface Finish

ENIG (Electroless Nickel Immersion Gold) is the most common finish for RF-35 boards because it provides a flat, solderable surface and does not degrade RF performance at moderate frequencies. For millimeter-wave designs above 30 GHz, the nickel underlayer adds measurable loss; in those cases, immersion silver or ENEPIG with a thin nickel layer (< 3 µm) is preferred. HASL is generally avoided because the thermal shock of molten solder dipping can stress PTFE-copper interfaces.

Cost Drivers for Taconic RF-35 PCBs

RF-35 raw laminate costs less per square foot than Rogers RO4350B in equivalent thicknesses, but total board cost depends on more than material price. The main cost drivers are:

• Panel utilization: RF-35 is available in standard 12 × 18 inch and 24 × 18 inch panels. Unusual board outlines or small quantities waste material and raise per-unit cost.
• Layer count and bonding: Every additional lamination cycle adds press time and bonding-film cost. A 2-layer RF-35 board is straightforward; a 6-layer hybrid with FR-4 cores doubles the processing complexity.
• Via density and aspect ratio: High-aspect-ratio vias in PTFE require slower drilling, thicker copper plating, and more inspection—each adding cost.
• Surface finish: ENIG adds roughly 8–12 % to bare-board cost versus OSP, but most RF designs need it for wire bonding or repeated reflow.
• Copper weight: 2 oz copper on RF-35 is feasible but requires longer etch times and tighter process control than 1 oz.

Use the cost-driver tool below to see how each of these factors weights against total fabrication cost for your specific design parameters.

After entering your layer count, board dimensions, via count, and surface finish, the tool highlights which factors dominate your cost. For a typical 2-layer RF-35 coupler board (3 × 2 inches, 50 vias, ENIG), the material itself is usually 35–45 % of total cost, with drilling and plating making up most of the rest. Switching from ENIG to immersion tin could save 8–10 %, but only if your assembly process and shelf-life requirements allow it.

Typical Applications

Filters and Couplers (1–20 GHz)

RF-35’s low Df makes it a strong choice for microstrip edge-coupled filters and Lange couplers where passband insertion loss directly affects system noise figure. A 5.8 GHz bandpass filter on 10 mil RF-35 can achieve 0.3 dB lower insertion loss than the same layout on RO4350B—enough to matter in a receiver front end.

Antenna Feed Networks

Corporate-feed patch antenna arrays for WLAN, WiMAX, and point-to-point links at 24–28 GHz benefit from RF-35’s combination of low loss and Dk stability across temperature. The 0.02 % moisture absorption keeps the array’s beam pointing stable in outdoor installations. For higher-Dk antenna elements on the same panel, designers sometimes pair RF-35 feed layers with Taconic RF-41 radiator layers in a hybrid stackup.

Power Amplifier Substrates

At power levels below about 10 W, RF-35’s thermal conductivity of 0.40 W/m·K is adequate. Above that, thermal management becomes the limiting factor; designers should consider adding thermal vias under active devices or moving to a higher-conductivity substrate. For very high thermal loads, materials like aluminum nitride substrates are a better fit.

Design Tips for Controlled Impedance on RF-35

Because RF-35’s Dk of 3.50 is nearly identical to RO4350B’s 3.48, trace widths for 50 Ω microstrip are almost interchangeable between the two materials at the same substrate thickness. On a 10 mil (0.254 mm) RF-35 core with 1 oz copper (1.4 mil trace thickness after plating), a 50 Ω microstrip is approximately 22.5 mil (0.57 mm) wide—within 0.5 mil of the same calculation on RO4350B.

A few practical guidelines:

• Use the manufacturer’s tested Dk, not the datasheet process Dk. Taconic specifies Dk at 10 GHz using the clamped stripline resonator method. If your design operates at 2 GHz, the effective Dk may be 1–2 % higher due to dispersion; at 30 GHz it may be slightly lower. Always request Dk vs. frequency curves from Taconic for your specific thickness.
• Account for copper roughness. Standard electrodeposited copper on RF-35 has an Rz roughness of about 5–7 µm. At 24 GHz the skin depth in copper is only ~0.4 µm, so surface roughness adds conductor loss. Specifying rolled or reverse-treated copper (Rz < 2 µm) can reduce total line loss by 0.1–0.2 dB/inch at Ka-band.
• Ground-plane continuity matters more than material choice. An impedance discontinuity from a poorly stitched ground plane will cause more reflection loss than the Dk tolerance of any modern laminate. Keep ground-via spacing below λ/20 at your highest operating frequency.

Comparing RF-35 to Other Low-Cost RF Laminates

RF-35 occupies a unique position: it is the lowest-Df option in the Dk ≈ 3.5 bracket. If your loss budget is tight but you cannot justify the cost of ultra-low-loss materials like Taconic TSM-DF, RF-35 is the natural choice. If loss is less critical and you want the easiest possible fabrication, the thermoset-based alternatives (RO4350B, S7136, TP-2) process on standard FR-4 lines and avoid the PTFE-specific handling steps.

Storage and Handling

RF-35 panels should be stored in their original vacuum-sealed packaging in a climate-controlled environment (15–30 °C, < 60 % RH). Although PTFE itself absorbs almost no moisture, the woven-glass reinforcement can wick trace amounts of water along fiber bundles if panels are left unsealed for extended periods. Before lamination, a 2-hour bake at 150 °C is recommended per IPC-4101 guidelines to drive off any absorbed moisture and ensure consistent Dk across the panel.

Frequently Asked Questions

Is Taconic RF-35 a drop-in replacement for Rogers RO4350B?

Electrically, yes—Dk values differ by only 0.02, so 50 Ω trace widths are nearly identical. However, RF-35 is a PTFE composite while RO4350B is a thermoset, so fabrication processes (drilling, lamination temperature, bonding films) differ significantly. You cannot simply swap materials without adjusting the fab process.

What is the maximum usable frequency for RF-35?

RF-35 has been used successfully in production designs up to 40 GHz. Above that, the woven-glass weave pattern can introduce periodic Dk variation (fiber-weave effect), and specifying spread-glass or thinner cores helps mitigate it. For 77 GHz automotive radar, most designers choose non-woven PTFE laminates or LCP films instead.

Can RF-35 be used in lead-free reflow?

Yes. PTFE’s Tg is above 280 °C, so it withstands standard lead-free reflow profiles (peak 260 °C). The concern is not the laminate itself but the copper-to-PTFE bond and via barrel integrity during thermal excursion. Proper sodium-etch or plasma treatment of the PTFE surface before copper plating ensures reliable adhesion.

How does RF-35 compare on moisture absorption?

RF-35 absorbs only 0.02 % moisture (ASTM D570, 24 h immersion at 23 °C), which is among the lowest of any commercial laminate. This makes it well suited for outdoor and marine applications where Dk stability over humidity cycles is critical.

What bonding films work with RF-35 in multilayer stackups?

Taconic’s FR-27 (Dk 2.70) and FastRise 27 (Dk 2.72, very low Df) are the most commonly used bonding plies. For hybrid RF-35 / FR-4 stackups, CER-10 or third-party low-flow thermoset prepregs can serve as the adhesive layer between dissimilar resin systems.