Taconic TLY-5 PCB | Dk 2.20 PTFE Fabrication Guide

What Is Taconic TLY-5?

Taconic TLY-5 is an unreinforced PTFE (polytetrafluoroethylene) laminate with a dielectric constant (Dk) of 2.20 and a dissipation factor (Df) of 0.0009 at 10 GHz. Because it contains no woven glass reinforcement, it delivers the lowest insertion loss available in the Taconic TLY family, making it a go-to substrate for millimeter-wave filters, satellite transponders, and test fixtures above 20 GHz. Its isotropic dielectric structure also eliminates the weave-related Dk variation that plagues glass-reinforced laminates at high frequencies.

Key Electrical and Mechanical Properties

The table below summarizes the published parameters that drive design decisions for a Taconic TLY-5 PCB. All electrical values are at 10 GHz unless noted.

The Dk of 2.20 is among the lowest available in commercial laminates, exceeded only by expanded-PTFE composites and foam dielectrics. A lower Dk means wider traces for a given impedance, which relaxes fabrication tolerances and reduces conductor loss — both significant advantages above 30 GHz.

Why Unreinforced PTFE Matters at Millimeter-Wave

Woven-glass reinforcement improves dimensional stability and CTE control, but it introduces periodic Dk variation at the scale of the weave pitch (typically 0.5–1.0 mm). At frequencies where the guided wavelength approaches the weave pitch, this variation causes amplitude ripple and phase distortion. TLY-5 eliminates that problem entirely because its dielectric is homogeneous PTFE with no glass content.

The trade-off is mechanical: unreinforced PTFE is soft, dimensionally less stable, and more prone to cold flow under clamping pressure. For comparison, a glass-reinforced PTFE PCB like the Taconic TLX series offers a CTE z-axis roughly half that of TLY-5, at the cost of slightly higher loss. If your application is below 15 GHz and dimensional stability matters more than the last tenth of a dB of loss, a woven-glass grade such as Taconic TLX-0 (Dk 2.45) may be the better engineering choice.

Dk Drift Across Temperature and Frequency

Unreinforced PTFE exhibits a well-known Dk transition near 19 °C caused by a crystalline phase change in the polymer. The Dk can shift by roughly 0.01 over a 5 °C window around that transition. Above 25 °C, the thermal coefficient of Dk settles to approximately −125 ppm/°C — meaning the Dk drops slightly as temperature rises.

For narrowband filter designs, this drift can shift the center frequency by several MHz per degree at Ka-band (26–40 GHz). Use the estimator below to see how much Dk shift to expect for your operating temperature range and how it translates to a percentage change in effective dielectric constant.

For example, a TLY-5 board operating at 35 GHz with a temperature swing from 25 °C to 70 °C would see a Dk decrease of roughly 0.012 (from 2.200 to 2.188). That shifts a 35 GHz bandpass filter center frequency up by approximately 100 MHz — enough to matter in a satellite downlink channelizer. If that drift is unacceptable, consider temperature-compensating the circuit or switching to a ceramic-filled PTFE with a near-zero thermal coefficient of Dk.

Comparing TLY-5 to Other Taconic Low-Dk Laminates

Taconic offers several PTFE-based laminates in the Dk 2.2–2.6 range. Choosing among them is a balance of loss, dimensional stability, cost, and processability.

The TLX-8 laminate and TLX-9 laminate are the most common alternatives when you need the mechanical confidence of glass reinforcement but still want low loss. For applications requiring Dk above 3.0, the TLC-30 PCB is a cost-effective step up.

Use the selector below to compare TLY-5 against the full Taconic portfolio filtered by Dk range, frequency band, and reinforcement type.

If the selector returns TLY-5 alongside TLX-0, evaluate whether your circuit’s loss budget or its dimensional tolerance is the tighter constraint. For a 77 GHz automotive radar prototype, TLY-5 wins on loss; for a volume GPS antenna panel at 1.575 GHz, TLX-0 wins on registration and cost.

Fabrication Guidelines for TLY-5 PCBs

Drilling and Routing

Unreinforced PTFE is soft (Shore D hardness ~55) and tends to smear during drilling. Use sharp carbide drill bits with a low chip load (0.001–0.002 in/rev) and moderate spindle speed (40,000–60,000 RPM). Entry and backer materials should be aluminum entry sheet over a rigid phenolic backer to prevent burring. For plated through-holes, plasma desmear or sodium etch is required because PTFE is chemically inert and will not accept electroless copper without surface activation.

Surface Preparation and Plating

The PTFE surface must be etched — typically with a sodium-naphthalenide solution or plasma treatment — before any metallization step. This creates a micro-rough, chemically active surface that allows electroless copper to nucleate. Skipping or under-processing this step is the single most common cause of delamination on PTFE boards. After surface activation, standard electroless-copper and electrolytic-copper plating processes apply.

Lamination (Hybrid Stackups)

TLY-5 is frequently combined with FR-4 or higher-Dk PTFE layers in hybrid multilayer builds. Because PTFE has a much higher CTE z-axis than FR-4, the bonding layer must accommodate differential expansion. Taconic’s FastRise 27 or FEP (fluorinated ethylene propylene) bondply films are typical choices, laminated at 290–315 °C under 200–400 psi. Register accuracy suffers compared to all-FR-4 builds; allow ±3 mil (0.076 mm) minimum for layer-to-layer registration on hybrid stackups.

For a deeper look at unreinforced PTFE processing in general, see our guide to pure unreinforced PTFE PCB fabrication.

Soldermask and Surface Finish

Standard LPI soldermask adheres poorly to PTFE surfaces. Many TLY-5 designs leave the PTFE areas bare and apply soldermask only to the FR-4 portions of hybrid boards. Where a finish is needed directly on PTFE copper, ENIG (electroless nickel immersion gold) or immersion tin are common. HASL is generally avoided because the thermal shock of molten solder can stress the soft dielectric.

Stackup Design Considerations

A typical two-layer TLY-5 board uses a 10 mil (0.254 mm) or 20 mil (0.508 mm) core with ½ oz or 1 oz rolled-annealed copper. For a 50 Ω microstrip on 10 mil TLY-5 (Dk 2.20), the trace width works out to approximately 30 mil (0.76 mm) — comfortably wide for standard etching. That wide trace is one of the practical benefits of the low Dk: it reduces current density and therefore conductor loss, which dominates total loss above 30 GHz.

For stripline builds, TLY-5 can be bonded symmetrically around a signal layer using FEP bondply. The effective Dk of the composite stackup depends on the bondply Dk (typically ~2.1 for FEP) and its thickness relative to the TLY-5 cores. Model the full stackup in a 2D field solver rather than relying on the handbook Dk alone.

Typical Applications

• Satellite transponder filters and multiplexers — Dk stability and ultra-low Df keep passband insertion loss below 0.5 dB at Ku-band and above.
• Millimeter-wave test fixtures and calibration substrates — Isotropic Dk eliminates weave artifacts that corrupt S-parameter measurements.
• Phased-array feed networks (Ka-band and above) — Wide traces and low loss maintain beam efficiency across large corporate feed networks.
• Point-to-point radio front ends (E-band, 71–86 GHz) — At these frequencies, every 0.001 of Df counts; TLY-5 is one of very few solid laminates with Df below 0.001.
• Low-noise amplifier (LNA) matching networks — Low dielectric loss preserves the noise figure advantage of the active device.

Design and Procurement Tips

1. Specify the copper type. Rolled-annealed (RA) copper has lower surface roughness than electrodeposited (ED), reducing conductor loss at mmWave. Ask for RA cladding whenever insertion loss is critical.
2. Account for the PTFE phase transition. If the board will see temperatures cycling through 19 °C (common in outdoor radomes), simulate the Dk shift impact on your circuit’s critical parameters.
3. Use a field solver, not formulas. Closed-form microstrip equations assume a homogeneous dielectric; they are accurate for TLY-5, but any hybrid stackup with bondply layers demands a 2D solver. Altium’s impedance calculation guide walks through setting up a solver-based stackup.
4. Order extra material. PTFE panels are more expensive and lead times can reach 4–6 weeks. Budget for 10–15 % yield loss due to the softer handling characteristics.
5. Confirm sodium etch capability. Not all fabricators have the chemical baths for PTFE surface preparation. Qualify this process step before committing to a vendor.

Standards and Specifications

TLY-5 boards are typically built to IPC-6012 Class 3 for high-reliability applications. Material-level testing follows IPC-TM-650 methods for Dk, Df, moisture absorption, and peel strength. For space-grade builds, additional screening per MIL-PRF-55110 or ECSS-Q-ST-70-60C may apply, including microsection analysis and thermal cycling qualification.

Frequently Asked Questions

Is TLY-5 the same as Rogers RT/duroid 5880?

They target the same niche — unreinforced PTFE with Dk ~2.20 — and are functionally interchangeable in most designs. Both share nearly identical Dk, Df, and CTE characteristics. The choice often comes down to regional availability, pricing, and which material your fabricator has qualified.

Can TLY-5 be used in multilayer stackups?

Yes, but with care. Unreinforced PTFE’s high z-axis CTE and softness make multilayer registration more challenging than with glass-reinforced grades. Hybrid stackups pairing TLY-5 signal layers with FR-4 or ceramic-filled PTFE structural layers are a common compromise.

What is the maximum operating frequency for TLY-5?

There is no hard frequency ceiling imposed by the material itself. TLY-5 has been used successfully in circuits above 110 GHz. The practical limit is set by conductor loss (which scales with the square root of frequency) and by the fabricator’s ability to hold tight trace tolerances at the narrow line widths those frequencies demand.

How does TLY-5 compare to expanded-PTFE laminates?

Expanded-PTFE composites (such as certain Gore products) can achieve even lower Dk (~2.0) and comparable Df, but they are significantly more expensive and harder to source. TLY-5 offers a practical balance of ultra-low loss and commercial availability.

Does TLY-5 need special storage?

PTFE absorbs almost no moisture (< 0.02 %), so humidity-controlled storage is less critical than for hygroscopic laminates. However, the soft material scratches easily; store panels vertically in protective interleaving to prevent surface damage that would affect copper adhesion during processing.