Taconic RF-35TC and RF-35HTC high thermal conductivity RF laminates explained — specs, Df, thermal conductivity, design tips, and applications for power RF.

When you move from small-signal RF design into power RF — base-station amplifiers, high-power antenna arrays, radar transmit stages — the PCB substrate stops being “just the dielectric” and becomes part of your thermal management system. The laminate under that 50W LDMOS transistor has to get heat out of the component, not trap it. That’s the problem Taconic RF-35TC was engineered to solve, and its sibling RF-35HTC takes the idea even further.

This is a working engineer’s walkthrough of what Taconic RF-35TC and RF-35HTC actually are, how they differ from standard RF-35, the numbers on the datasheet that drive design decisions, and where each one fits in real RF power architecture. For manufacturing capability using these materials, the Taconic PCB production page covers stack-ups and processing notes.

Why Thermal Conductivity Matters in RF Laminates

Standard RF-35 has a thermal conductivity of about 0.24 W/m·K — typical for PTFE-based laminates. For small-signal RF at a few hundred milliwatts that number is fine. Push past 5–10 watts dissipated in a single device, and heat starts to pool directly under the component, spiking junction temperature.

Three things happen when the laminate can’t move heat efficiently:

• Device junction temperature rises — every 10°C above rated junction temperature roughly halves the MTTF of power transistors.
• Dielectric constant drifts with local temperature — shifting impedance under the device and de-tuning matching networks.
• Passive components de-rate — chip capacitors lose capacitance and Q as they heat.

The answer isn’t always a bigger heatsink. For high-density RF modules and low-profile radar tiles, you need the substrate itself to spread heat laterally and conduct it vertically to the heatsink. That’s where the “TC” (Thermally Conductive) and “HTC” (High Thermal Conductivity) variants of the ORCER family come in.

Taconic RF-35TC: The Thermally Conductive Low-Loss Laminate

Taconic RF-35TC is a PTFE-based, ceramic-filled, fiberglass-reinforced substrate engineered specifically for high-power RF applications. Electrically, it behaves like standard RF-35 with Dk 3.5 — so existing RF-35 designs migrate to RF-35TC without redoing impedance calculations. The difference is in two places: Df drops from 0.0019 to 0.0011 at 10 GHz, and thermal conductivity jumps from ~0.24 W/m·K to 0.87–0.92 W/m·K (measured with copper cladding).

That Df improvement is significant. Insertion loss in high-power transmission lines is a thermal problem as much as an electrical one — every dB lost in the dielectric becomes heat you now have to dissipate. Cutting Df nearly in half means less heat generated in the line itself, on top of the better thermal conductivity to move whatever heat is generated.

Taconic RF-35TC Key Specifications

Parameter	Value	Test Method / Notes
Dielectric Constant (Dk)	3.50	IPC-TM-650 2.5.5.5 at 10 GHz
Dissipation Factor (Df)	0.0011	At 10 GHz
Thermal Conductivity	0.87–0.92 W/m·K	With copper cladding
X-axis CTE	11 ppm/°C	Woven glass controlled
Y-axis CTE	13 ppm/°C	—
Z-axis CTE	34 ppm/°C	Substantially lower than RF-35’s 64 ppm/°C
Peel Strength	Bonds well to low-profile copper	Optimized for VLP/RTF foil
Moisture Absorption	<0.04%	PTFE base
Flammability (UL 94)	V-0	—
Construction	PTFE + ceramic + woven glass	Same family as RF-35
Oxidation Behavior	Does not yellow or drift	PTFE is oxidation-resistant

Note that the X and Y CTE values on RF-35TC (11 and 13 ppm/°C) are notably lower than standard RF-35 (19 and 24 ppm/°C). That matters for printed filters — trace-to-trace distances stay constant across temperature, keeping filter center frequencies stable.

Taconic RF-35HTC: Industry-Leading Thermal Conductivity

RF-35HTC pushes the thermal capability further. Where RF-35TC is a reinforced composite with woven glass, RF-35HTC is a non-reinforced ceramic/PTFE composite with very low PTFE content. The result: thermal conductivity of 1.84 W/m·K — roughly 8× higher than standard RF-35 and about 2× higher than RF-35TC.

The other standout spec: Df of 0.0007 at 10 GHz. This is pushing into the ultra-low-loss territory normally reserved for premium PTFE materials — with the thermal performance of a metal-core PCB. There is essentially no other substrate in the commercial RF catalog that combines both at this level.

Taconic RF-35HTC Key Specifications

Parameter	Value	Notes
Dielectric Constant (Dk)	~3.5	Same family Dk positioning
Dissipation Factor (Df)	0.0007	At 10 GHz — ultra-low
Thermal Conductivity	1.84 W/m·K	Industry-leading for low-loss laminates
Construction	Ceramic/PTFE, non-reinforced	No woven glass
X/Y CTE	Low	Uniform ceramic distribution
Z-axis CTE	Low	Stable coupler performance over temp
PTFE Content	Very low	Eases plating and drilling
Abrasive Filler	No alumina	Better drill bit life
Applications	Power amplifiers, couplers, dividers, filters, antennas, satellites	—

The “non-reinforced” aspect is worth calling out. Standard RF-35 and RF-35TC both use woven E-glass fabric for dimensional stability. RF-35HTC drops the glass in favor of a high ceramic filler loading. This means dielectric uniformity is very consistent in X, Y, and Z directions (no fiber weave effect), and the ceramic provides the mechanical stability that glass would otherwise provide.

Taconic specifically avoided using alumina as the ceramic filler because alumina is highly abrasive to mechanical drill bits and router tools. The filler chemistry in RF-35HTC is chosen to be fabrication-friendly while still delivering the thermal conductivity.

RF-35TC vs RF-35HTC vs Standard RF-35: Side-by-Side

This is the comparison I put on the first slide of any material-selection review for high-power RF designs:

Property	RF-35 (standard)	RF-35TC	RF-35HTC
Dk @ 10 GHz	3.50	3.50	~3.5
Df @ 10 GHz	0.0019	0.0011	0.0007
Thermal Conductivity (W/m·K)	0.24	0.87–0.92	1.84
X CTE (ppm/°C)	19	11	Low
Y CTE (ppm/°C)	24	13	Low
Z CTE (ppm/°C)	64	34	Low
Glass Reinforcement	Woven E-glass	Woven E-glass	None (ceramic only)
Relative Cost	1×	2–3×	4–5×
Best For	Commercial RF, filters, antennas	Power amplifiers, high-power filters	Ultra-high-power PAs, radar transmit

The progression from RF-35 to RF-35TC to RF-35HTC is a straight trade: pay more, get dramatically better thermal and electrical loss, with Dk held constant so you can port designs between them with minimal impedance rework. That continuity across the family is what makes the ORCER lineup practical for engineering teams — you don’t have to redesign from scratch when you move up a thermal tier.

Why PTFE Composites Beat Hydrocarbon (Rubber) Laminates for High-Power RF

One of the key design arguments in the RF-35TC and RF-35HTC datasheets is the comparison to hydrocarbon (“synthetic rubber”) composites — the class that includes Rogers RO4000 series materials. It’s worth understanding.

PTFE is a thermoplastic. Once processed, it has no unreacted chemistry. The carbon-fluorine bond doesn’t start to break down until around 600°C. That means PTFE-based laminates resist thermal oxidation almost completely — the dielectric constant and dissipation factor stay stable over operating life, even in hot environments with oxygen exposure.

Rubbers cure by a thermosetting mechanism and never quite reach 100% cure completion. Over years of operation at elevated temperature (typical in base-station amplifier housings or radar enclosures), that unreacted chemistry slowly oxidizes. What you see in practice:

• Visible yellowing of the laminate
• Upward drift in Df (more insertion loss over time)
• Upward drift in Dk (detuning of matching networks)
• Reduced peel strength (rework becomes risky)
• Reduced elongation (mechanical stress cracking)

For a commercial radio that needs to hit 20-year reliability targets in a hot rooftop enclosure, PTFE composites have a measurable long-term performance advantage. RF-35TC and RF-35HTC are formulated specifically for this stability case.

Applications: Where RF-35TC and RF-35HTC Actually Get Used

High-Power Amplifier Stages

The primary use case. LDMOS and GaN power transistors dissipate tens to hundreds of watts, and the substrate under them has to move that heat sideways into the copper pour and vertically through thermal vias to the heatsink. RF-35TC at 0.87 W/m·K gives you 3–4× the lateral heat spread of standard RF-35. RF-35HTC at 1.84 W/m·K is the closest you get to metal-core behavior while keeping low-loss RF properties intact.

Couplers and Power Dividers

For broadband or narrow-band overlay couplers handling high average power, Z-axis CTE is the critical parameter. The low Z-axis expansion of RF-35TC and RF-35HTC keeps the signal-to-ground dielectric thickness stable across temperature, which keeps coupling factor stable. Filters made from printed resonator elements benefit from the low X/Y CTE — trace-to-trace distances hold constant, so filter center frequencies don’t drift.

Antennas and Antenna Arrays

Gain and efficiency of printed antennas depend on maintaining critical spacings between radiating elements. Low X/Y CTE is essential. For high-power transmit arrays (phased arrays in radar or point-to-point telecom), the thermal conductivity handles the heat generated in feed networks and matching components.

Satellite and Aerospace RF

Where the operating temperature range is extreme (-55°C to +125°C) and the performance window is narrow, the temperature stability of PTFE composites wins. Add thermal vacuum cycling survival and 20-year mission life requirements, and RF-35TC or RF-35HTC becomes the sensible base material choice.

Radar Transmit Tiles

Active electronically scanned array (AESA) and modern phased-array radar tiles pack dozens of GaN power amplifiers into a small footprint. The substrate has to handle both the RF signal integrity and the thermal load. RF-35HTC specifically targets this application — ultra-low Df with industry-leading thermal conductivity.

Design and Fabrication Notes for RF-35TC and RF-35HTC

Impedance Calculations Carry Over from RF-35

Because Dk is held constant at 3.5 across the family, microstrip trace widths, stripline calculations, and impedance-controlled routing from an existing RF-35 design transfer directly to RF-35TC or RF-35HTC. That’s deliberate — Taconic designed the family this way to make upgrade paths simple.

Copper Foil Selection for Low Insertion Loss

Both RF-35TC and RF-35HTC bond well to low-profile copper. For frequencies above 5 GHz, specify VLP (very low profile) or reverse-treat copper foil. Standard ED foil has surface roughness of 6–8 µm Rz, which at 10 GHz adds meaningful insertion loss from skin-effect current concentration. VLP foil at 2–3 µm Rz recovers that loss. The datasheet Df of 0.0011 and 0.0007 is only fully achievable with low-profile copper.

Fabrication: PTFE Processing Still Required

Both RF-35TC and RF-35HTC are PTFE-based and require PTFE via-hole preparation. Plasma etch (preferred) or sodium treatment activates the PTFE surface so electroless copper will adhere during plating. This is non-negotiable — skip it and plated-through-holes fail during thermal cycling.

RF-35HTC’s low PTFE content (high ceramic loading) actually makes plating and drilling easier than pure PTFE materials. The ceramic component improves dimensional stability during fabrication and reduces the amount of PTFE that requires activation.

Thermal Via Design

For high-power component sites, thermal vias under the component footprint are standard design practice. With RF-35TC or RF-35HTC you don’t need as dense a thermal via array as on standard RF-35 because the substrate itself is moving heat laterally. A 3×3 or 4×4 array of 0.3 mm vias under a power transistor pad, filled with conductive epoxy or copper, is typically sufficient. Verify with thermal simulation for the specific device dissipation.

Bonding Films for Multilayer Stack-Ups

Multilayer boards using RF-35TC or RF-35HTC cores need PTFE-compatible bond films. Taconic’s FastRise series and similar products are engineered for this. Standard FR-4 prepreg will not work — the lamination cycle temperatures are too low and the chemistries are incompatible.

Useful Resources and Datasheet Downloads

• AGC Multi Material (Taconic) official page for RF-35TC — agc-multimaterial.com/solutions/rf-35tc/ — current datasheet PDF.
• AGC Multi Material official page for RF-35HTC — agc-multimaterial.com/solutions/rf-35htc/ — datasheet and thermal performance data.
• RF-35TC Technical Data Sheet (PDF) — downloadable from AGC-multimaterial.com/agc-downloads and distributor sites.
• RF-35HTC Technical Data Sheet (PDF) — elcopcb.com/material-docs/taconic/ hosts a mirror.
• IPC-TM-650 Test Methods Manual — ipc.org — reference for all test methods cited in the datasheet (2.5.5.5 for Dk/Df, 2.4.39 for thermal stress, etc.).
• Taconic product selector on PCB Directory and Everything RF — filterable listings for the full ORCER family.
• RayPCB Taconic capability page — https://raypcb.com/taconic-pcb/ — processing, stack-ups, and capability using Taconic high-thermal laminates.

Frequently Asked Questions

Q1: What’s the difference between Taconic RF-35TC and standard RF-35? Dk is the same (3.5), so impedance designs port over directly. The differences are Df (0.0011 vs 0.0019 at 10 GHz) and thermal conductivity (0.87–0.92 vs 0.24 W/m·K with copper). RF-35TC also has much lower CTE in X, Y, and Z — about half the Z-CTE of standard RF-35. Use RF-35TC when you need better heat spreading under power components or lower insertion loss on high-power transmission lines.

Q2: When should I choose RF-35HTC over RF-35TC? When the thermal load is high enough that 0.87 W/m·K of RF-35TC isn’t sufficient. RF-35HTC doubles the thermal conductivity to 1.84 W/m·K and cuts Df further to 0.0007 at 10 GHz. Typical breakpoints: dissipated power density above 5 W/cm², high-power GaN amplifiers, phased-array transmit tiles, and applications where you need metal-core-like thermal performance without giving up low-loss RF characteristics. Cost is roughly 2× RF-35TC, so reserve it for designs where the thermal improvement is the limiting factor.

Q3: Does Taconic RF-35TC require special fabrication equipment? Yes — it’s PTFE-based, so via-hole walls need plasma or sodium treatment before copper plating. Any RF-experienced fab handles this routinely, but generic FR-4 shops may need to subcontract the PTFE processing steps. Drilling and routing use standard carbide tooling at reduced speeds. Soldering uses standard lead-free SMT reflow. RF-35HTC’s low PTFE content actually makes plating easier than pure PTFE.

Q4: Can I mix RF-35TC with standard FR-4 in a hybrid stack-up? Yes, this is a common use case. Put RF-35TC on the power amplifier or high-frequency layers and FR-4 on digital and power-supply layers. Use PTFE-compatible bond films (FastRise or similar) at the interface. CTE mismatch between the sections needs engineering review — large area hybrid boards can warp during lamination. For the critical thermal regions under power devices, keep the build either all RF-35TC or all RF-35HTC to avoid thermal impedance discontinuities.

Q5: Why are PTFE composites like RF-35TC preferred over hydrocarbon (rubber) materials for long-life high-power RF? PTFE is chemically inert after processing — no unreacted chemistry remains, and the material resists thermal oxidation up to around 600°C. Hydrocarbon-based (“rubber”) composites never fully cure and slowly oxidize over years at elevated temperature. The result: hydrocarbon substrates yellow, their Df drifts upward (more loss), their Dk shifts (detuning matching networks), and peel strength degrades. For 20-year mission life in hot RF enclosures, the stability of PTFE-based RF-35TC and RF-35HTC is a measurable reliability advantage.

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