Taconic TLF-35 PCB: Properties, Design & Cost

What Is Taconic TLF-35?

Taconic TLF-35 is a woven-glass-reinforced PTFE laminate with a nominal dielectric constant (Dk) of 3.50 ± 0.05 and a dissipation factor (Df) of 0.0020 at 10 GHz. Engineers choosing a Taconic TLF-35 PCB target planar antenna elements, GPS patch arrays, automotive radar feed networks, and other circuits where low insertion loss and tight Dk tolerance matter more than rock-bottom cost. The material 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.

Key Electrical and Mechanical Properties of Taconic TLF-35 PCB

The table below collects the parameters most relevant to circuit design and fabrication. All electrical values are at 10 GHz unless noted.

A Dk of 3.50 sits in a useful sweet spot for antenna designers: high enough to shrink patch dimensions relative to a Dk 2.2 substrate, yet low enough to maintain acceptable bandwidth and efficiency. Compared to higher-Dk options like the Taconic RF-60A with Dk 6.15, TLF-35 offers wider impedance bandwidth and lower surface-wave excitation, which matters in phased-array feeds and multi-element GPS antennas.

Where TLF-35 Fits: Application Sweet Spots

Planar Antennas and Patch Arrays

At Dk 3.50, a square patch resonant at 1.575 GHz (GPS L1) on 60 mil TLF-35 has a physical edge length of roughly 46 mm — about 15 % smaller than the same patch on a PTFE laminate with Dk 2.20. The 0.0020 Df keeps radiation efficiency above 90 % in most single-patch designs. The woven-glass reinforcement provides dimensional stability that pure PTFE films lack, which is critical when holding element spacing in arrays.

Automotive Radar Feed Networks

For 24 GHz and 77 GHz radar front-ends, the primary radiating substrate is often a very-low-Dk material like Taconic FastRise 27, but the corporate feed network and power-divider layers can use a Taconic TLF-35 PCB to save board area. The tight Dk tolerance of ± 0.05 keeps impedance lines within a few tenths of an ohm of their target.

Satellite and Navigation Systems

Low moisture absorption (< 0.02 %) makes TLF-35 attractive for outdoor and avionics antennas where humidity cycling would shift the Dk of a less hydrophobic laminate. PTFE’s inherent chemical inertness also supports conformal-coating and radome-bonding processes without surface-preparation headaches.

Dk Drift with Temperature and Frequency on TLF-35

Every PTFE laminate exhibits some Dk drift as temperature and frequency change. For a Taconic TLF-35 PCB, expect roughly –50 to –80 ppm/°C in the range of –40 °C to +85 °C — a consequence of PTFE’s negative thermal coefficient of permittivity. Over frequency, Dk falls gently from about 3.52 at 2 GHz to approximately 3.48 at 30 GHz due to reduced dipolar polarization at higher frequencies.

Use the estimator below to see how much Dk shift you can expect over your operating temperature and frequency window. Enter your nominal Dk, the temperature excursion, and the frequency range to get an approximate drift budget.

For example, starting at Dk 3.50 and swinging from +25 °C to +85 °C (a 60 °C excursion), the tool will show a drift of roughly –0.012 to –0.019 in Dk. On a 50 Ω microstrip at 5.8 GHz, that translates to about 0.3 Ω of impedance change — usually acceptable for a matched antenna feed, but worth budgeting into your return-loss margin. If the predicted drift exceeds your tolerance, consider a hydrocarbon ceramic laminate, which typically has a flatter thermal Dk coefficient than PTFE composites.

Fabrication Considerations for Taconic TLF-35 PCB

Drilling and Routing

PTFE-glass laminates are softer than FR-4 and prone to smearing. Use fresh carbide drill bits with a positive rake angle, moderate spindle speeds (40 000–55 000 rpm for vias ≤ 0.4 mm), and controlled chip loads. For panel routing, a two-flute carbide end mill at 24 000 rpm with a feed rate of 40–60 in/min gives clean edges without delamination.

Hole Preparation and Plating

PTFE is non-polar, so bare hole walls will not accept electroless copper without surface modification. Sodium-naphthalenide (sodium etch) or plasma treatment is required to create a wettable surface. Sodium etch is the industry default for TLF-35; plasma is preferred when ionic contamination limits are tight (e.g., IPC-6012 Class 3 requirements). After treatment, standard electroless copper and electrolytic plating follow.

Lamination and Hybrid Stackups

TLF-35 bonds well using Taconic’s TacBond or FR-4-compatible prepregs when building hybrid multilayers. A common stackup pairs TLF-35 as the outer antenna layer with an FR-4 or low-cost RF core for the digital/power layers. Keep the bonding temperature below 260 °C to avoid copper-oxide degradation, and ramp slowly (2–3 °C/min) to let entrapped air escape from the PTFE interface.

Solder Mask and Surface Finish

Liquid photo-imageable (LPI) solder mask adheres adequately to PTFE surfaces that have been plasma-cleaned, but adhesion testing per IPC-TM-650 2.4.28 is recommended on first-article builds. ENIG and immersion silver are the most common finishes; HASL is possible but the thermal shock can stress the PTFE-copper interface on thinner cores.

TLF-35 vs. Comparable Laminates

Choosing a Dk ~3.5 laminate means weighing loss, cost, processability, and supply chain. The table below places the Taconic TLF-35 PCB alongside frequently compared alternatives.

Choose TLF-35 when you need the lowest possible Df at Dk ~3.5 and your fabricator already handles PTFE processing. Its 0.0020 Df beats RO4003C’s 0.0027 by roughly 25 %, which adds up in long feed lines and corporate dividers.

Choose RO4003C when you want FR-4-compatible processing and a broader fabricator base, and can tolerate slightly higher loss. For more on thermoset alternatives, see the Taconic TSM-DS3 overview or the Isola Astra MT77 profile.

Cost Positioning and Budgeting

PTFE laminates sit above hydrocarbon-ceramic boards in cost. Taconic TLF-35 PCB panels are typically priced between commodity woven-PTFE grades and premium ultra-low-loss materials like Rogers RT/duroid 5880. The main cost drivers are:

• Panel utilization — standard 12 × 18 in panels; designs that nest poorly waste expensive material.
• Thickness and copper weight — thicker cores and heavier copper increase raw-material cost roughly linearly.
• Sodium-etch processing — adds a wet-chemistry step that not every shop runs in-house, potentially adding lead time and cost.
• Volume — PTFE laminates have longer lead times at low volumes; ordering full-case quantities (typically 10–20 panels) improves pricing.

Use the laminate cost index tool below to compare TLF-35’s relative cost position against other RF laminates in your stackup. Enter the material family and thickness to see an indexed estimate.

If the index shows TLF-35 running 1.5–2× the cost of a hydrocarbon-ceramic baseline, that premium is buying you a 25–30 % reduction in dielectric loss and significantly lower moisture sensitivity. For outdoor antenna products with a 15-year service life, the moisture advantage alone can justify the difference. For a broader look at material pricing trends, consult the RF laminate price guide.

Design Tips for Taconic TLF-35 PCB Layouts

• Use the manufacturer’s Dk at your design frequency. Taconic specifies Dk at 10 GHz; if you are designing at 2.4 GHz, add approximately +0.02 to the nominal value for initial line-width calculations, then verify with a microstrip impedance calculator or full-wave simulation.
• Account for copper roughness. ED copper on PTFE typically has an Rz of 5–8 µm. At 24 GHz and above, this roughness adds 0.1–0.3 dB/in of extra conductor loss. Specify rolled or reverse-treated (RTF) copper if loss budget is tight.
• Keep ground vias tight around transitions. PTFE’s low Dk means the substrate wavelength is longer, but via fences around microstrip-to-stripline transitions should still be spaced at ≤ λ/10 at the highest operating frequency to suppress parallel-plate modes.
• Prototype with the production laminate. Substituting FR-4 for prototyping will shift Dk from 3.50 to ~4.3, moving resonant frequencies by roughly 10 %. The cost of a few TLF-35 prototype panels is far less than a respin.

Frequently Asked Questions

Is TLF-35 the same as TLC-35?

No. Taconic’s TLC series uses a non-woven glass reinforcement, giving slightly different CTE and dimensional stability. TLF-35 uses woven E-glass, which provides better mechanical rigidity and more predictable drilling behavior. Check the Taconic datasheet suffix to confirm which variant you are quoting.

Can a Taconic TLF-35 PCB be processed on a standard FR-4 line?

Not without modifications. The PTFE hole walls require sodium-naphthalenide etching or plasma treatment before plating. Drilling parameters also differ. Fabricators experienced with PTFE materials can handle TLF-35, but a shop that only runs FR-4 will need process development.

What frequency range is TLF-35 best suited for?

TLF-35 performs well from UHF through Ku-band (roughly 0.3–18 GHz). Above 20 GHz, the woven-glass weave pattern can introduce small periodic Dk variations (“fiber-weave effect”), so for millimeter-wave designs consider skewing trace routing at 5–10° to the weave or moving to a non-woven or ceramic-filled alternative.

How does moisture absorption affect TLF-35’s Dk?

With absorption below 0.02 %, the Dk shift from moisture is negligible — typically less than 0.005 even after 24-hour immersion. This is one of TLF-35’s strongest advantages over thermoset laminates, which can absorb 0.05–0.10 % and shift Dk by 0.02 or more in humid environments.

What is the maximum operating temperature?

PTFE remains stable well above 250 °C continuously. The practical limit is usually the copper-laminate bond, which Taconic rates for solder-float survival at 288 °C for 10 seconds. For sustained high-temperature operation, verify copper peel strength at your target temperature on a test coupon.