RF-35 vs RO4350B head-to-head for RF engineers: Df, Dk, CTE, peel strength, cost, and decision criteria. Taconic vs Rogers laminate selection made simple.

If you have ever sat in a design review arguing whether to spec Taconic RF-35 or Rogers RO4350B for a 5G amplifier board, you know these two laminates occupy almost the exact same slot in the RF material catalog. Both sit at Dk ≈ 3.5, both use ceramic-filled chemistry with woven glass reinforcement, both are UL 94 V-0 rated, and both bond to FR-4 in hybrid stack-ups. On paper they look like twins.

They are not. After dozens of RF boards designed on both materials, I can tell you the RF-35 vs RO4350B choice has real consequences — in moisture stability, fabrication process, peel strength, and cost per square foot. Some differences favor Taconic, some favor Rogers, and knowing which is which saves you a respin. This is the honest engineer-to-engineer comparison.

Why the RF-35 vs RO4350B Question Keeps Coming Up

Both laminates target the same sweet spot: RF and microwave circuits from about 1 GHz to 20 GHz where FR-4 loss becomes unacceptable but full PTFE is overkill. This band covers most 5G sub-6 GHz base stations, Wi-Fi, cellular amplifiers, GPS modules, commercial radar up to K-band, and the RF portions of mixed digital/RF boards.

At Dk 3.48–3.50, both produce similar trace widths for 50-ohm impedance. At Df values in the 0.0018–0.0037 range at 10 GHz, both have acceptable insertion loss for commercial microwave work. The competition is real — these are the two default answers when an engineer asks “what do I use for my 5G antenna board?”

Where they diverge is in chemistry. RF-35 is a ceramic-filled PTFE (organic-ceramic) with woven glass. RO4350B is a ceramic-filled hydrocarbon resin with woven glass — no PTFE at all. That difference drives almost every other difference in the comparison. A detailed overview of the full Taconic PCB product line shows where RF-35 sits within Taconic’s broader portfolio; RO4350B has an equivalent position in the Rogers RO4000 series.

RF-35 vs RO4350B: Head-to-Head Specifications

The datasheet numbers first, then context for what they mean on a real board:

Property	Taconic RF-35	Rogers RO4350B
Dielectric constant (Dk) @ 10 GHz	3.50 ± 0.05	3.48 ± 0.05
Dissipation factor (Df) @ 10 GHz	0.0018	0.0037
Dissipation factor (Df) @ 2.5 GHz	0.0025	0.0031
Base resin	Ceramic-filled PTFE	Hydrocarbon/ceramic (thermoset)
Reinforcement	Woven fiberglass	Woven fiberglass
Thermal conductivity (W/m·K)	0.24	0.69
Glass transition temperature (Tg)	>315°C	>280°C
Z-axis CTE (ppm/°C)	280 (PTFE-dominated)	32
X/Y CTE (ppm/°C)	9/12	10/12
Moisture absorption (%)	0.03	0.06
Peel strength (1 oz Cu, lbs/in)	12	5
UL 94 rating	V-0	V-0
Standard thickness range	5–125 mil	4–60 mil
Typical frequency range	Up to 22 GHz	Up to 40 GHz (VF variant: 77 GHz)

The shorthand I use: RF-35 wins on Df, peel strength, and moisture absorption. RO4350B wins on thermal conductivity, Z-axis CTE, and fabrication processing. Everything else is close enough that it rarely drives the decision.

Dielectric Performance: Where RF-35 Gets an Edge

The Df difference is significant and often overlooked in datasheet-level comparisons. At 10 GHz, RF-35 sits at 0.0018 while RO4350B is at 0.0037 — roughly half the dissipation. For a 10-inch trace on a typical 20-mil substrate at 10 GHz, that difference works out to about 0.3 dB of additional insertion loss on the RO4350B board. Not catastrophic, but real, and it compounds on longer feed networks and higher frequencies.

Why does RF-35 have lower Df despite similar Dk? The PTFE content. Even though RF-35 is a ceramic-filled PTFE variant rather than pure PTFE, it retains more of PTFE’s intrinsically low-loss character than RO4350B’s hydrocarbon resin system. For designers building long feed networks on power amplifier inputs or precision coupler circuits, this Df delta is the single biggest technical reason to specify RF-35 over RO4350B. Dk stability across temperature is comparable — both hold Dk within about ±1% from -40°C to +125°C.

Thermal Performance: Where RO4350B Pulls Ahead

RO4350B at 0.69 W/m·K has nearly three times better thermal conductivity than RF-35’s 0.24 W/m·K. For passive RF circuits this does not matter. For anything involving a power amplifier, a Doherty module, or a high-current LDMOS FET, it matters a lot.

When a power amplifier dissipates several watts into the board, that heat has to reach the heat sink somehow. On RO4350B, the substrate itself conducts a meaningful fraction of the heat to thermal vias and back-side copper. On RF-35, you rely almost entirely on thermal vias — the substrate is a thermal insulator. For RF-35 users who need PA-grade thermal performance, Taconic offers RF-35TC with thermal conductivity boosted to 0.71 W/m·K at higher cost.

The CTE mismatch is equally important for reliability. RO4350B’s Z-axis CTE of 32 ppm/°C is close to copper’s 17 ppm/°C, meaning plated through-holes see low stress during thermal cycling. RF-35’s Z-axis CTE of 280 ppm/°C is PTFE-dominated — it expands much more aggressively in the Z direction, and through-hole barrels see more stress cycling through AEC-Q thermal profiles.

Thermal Parameter	RF-35	RO4350B	Impact
Thermal conductivity	0.24 W/m·K	0.69 W/m·K	Matters for PA and high-current designs
Z-axis CTE	280 ppm/°C	32 ppm/°C	PTH reliability in thermal cycling
Glass transition	>315°C	>280°C	Both survive lead-free reflow easily
Max operating temp	260°C	280°C	Both exceed typical RF requirements

Fabrication and Processing: The RO4350B Advantage

This is where Rogers specifically designed RO4350B to compete with PTFE materials like RF-35 on processing cost. The RO4350B datasheet’s key claim is that it uses the “same processing method as standard epoxy/glass” — no sodium-naphthalene etching, no special through-hole preparation, no exotic lamination cycles.

RF-35, being PTFE-based, does require PTFE-specific processing. Before plating, via walls need sodium etching or plasma activation to get copper to bond. Lamination cycles run longer and hotter. Drilling parameters differ from FR-4 norms. None of this is a showstopper — any serious RF fabricator runs RF-35 every day — but it limits the number of shops that can reliably build it and adds process overhead.

Fabrication Factor	RF-35	RO4350B
Requires sodium/plasma etching	Yes	No
Uses standard FR-4 lamination cycle	No (longer, hotter)	Yes
Drilling parameters vs FR-4	Different (slower feed)	Similar
Fabricator availability	Good (most RF shops)	Excellent (nearly all RF shops)
Typical fabrication cost premium vs FR-4	~5x	~3x
Prototype lead time	10–15 days	7–10 days

For prototype quick-turn work and production runs at fabricators that are not PTFE-specialized, RO4350B is meaningfully easier to source. For high-volume production at a qualified PTFE fabricator, the process difference is invisible in the final invoice.

Peel Strength and Mechanical Properties

One area where RF-35 is genuinely superior is copper peel strength. Taconic lists 12 lbs/in for 1 oz copper on RF-35; RO4350B typically measures around 5 lbs/in. That 2.4x difference shows up in rework, through-hole connector reliability, and any application with mechanical stress on pads. For boards with heavy connector cycling or surface-mount components reworked multiple times during development, RF-35’s peel strength is a real advantage. For final assembly boards that get soldered once and shipped, neither material is peel-limited in practice.

The fiberglass weave also makes both materials more dimensionally stable than chopped-fiber PTFE composites. Both hold registration well through multilayer lamination and support laser drilling of microvias.

Moisture Absorption and Environmental Stability

RF-35 shows moisture absorption around 0.03%; RO4350B measures around 0.06%. Both are excellent compared to FR-4 (0.1–0.3%), but RF-35 has a roughly 2x advantage. Absorbed moisture shifts Dk upward and increases Df — over the operating life of a board in humid or outdoor environments, an RF-35 board drifts less than RO4350B. For indoor, climate-controlled applications (telecom racks, test equipment), neither is moisture-limited in practice. For outdoor antennas, under-hood automotive, and avionics where the enclosure is not hermetic, RF-35’s moisture immunity is a meaningful reliability advantage.

Cost Comparison: RF-35 vs RO4350B Pricing Reality

Pricing varies by fabricator and volume, but the typical relationship in production:

Quantity	RF-35 Relative Cost	RO4350B Relative Cost
Prototype (5–10 panels)	1.0x (baseline)	0.9–1.0x
Small production (100 panels)	1.0x	0.85–0.95x
Large production (1000+ panels)	1.0x	0.80–0.90x

The gap closes at volume because RO4350B’s easier processing reduces fabrication overhead, while RF-35 remains in PTFE-premium territory regardless of volume. At small prototype quantities the price difference is often negligible; at high production volumes RO4350B typically runs 10–20% cheaper delivered.

This is one reason RO4350B dominates high-volume 5G and automotive applications while RF-35 sees more use in test equipment, aerospace, and applications where the Df advantage or peel strength justifies the premium.

When to Choose RF-35 Over RO4350B

Based on the specs and real-world experience, RF-35 is the better choice when:

• Insertion loss budget is tight. The 2x Df advantage at 10 GHz compounds on long traces; applications with long feed networks benefit measurably
• The board will see humidity or outdoor exposure. RF-35’s 0.03% moisture absorption preserves electrical properties over the product lifetime
• Through-hole connectors or heavy rework is expected. The 12 lbs/in peel strength survives mechanical cycling better than RO4350B’s 5 lbs/in
• The frequency is at or above 20 GHz. RF-35’s Df advantage widens at higher frequencies; RO4350B’s Df climbs more steeply with frequency
• You have a qualified PTFE fabricator in your supply chain. No point paying the RF-35 premium if your fab has to sub it out or work around process limitations

When to Choose RO4350B Over RF-35

RO4350B wins the selection when:

• The application involves significant heat dissipation. Power amplifiers, high-current LDMOS, and Doherty modules benefit from the 3x thermal conductivity
• PTH reliability through thermal cycling matters. The 32 ppm/°C Z-axis CTE is far friendlier to plated through-holes than RF-35’s 280 ppm/°C
• Prototype lead time is critical. Most RF fabricators can quick-turn RO4350B on standard FR-4 lines
• Cost at high volume is the primary driver. RO4350B typically runs 10–20% cheaper than RF-35 at production volumes
• You need frequencies above 40 GHz. Rogers RO4350B VF variant extends to 77 GHz; RF-35’s typical spec range stops around 22 GHz

Hybrid Stack-Ups With Each Material

Both RF-35 and RO4350B support hybrid stack-ups with FR-4 for cost-optimized designs. Here the processing advantage clearly favors RO4350B. Because RO4350B laminates into standard FR-4 lamination cycles without modification, hybrid builds are straightforward and widely qualified. RF-35 hybrid builds work fine but require the fabricator to handle the PTFE-FR-4 CTE mismatch carefully during lamination.

A typical 4-layer hybrid comparison:

Layer	RF-35 Hybrid	RO4350B Hybrid
L1 (RF)	RF-35 10–20 mil	RO4350B 10–20 mil
Bonding	HT1.5 or RF-35P prepreg	Standard FR-4 prepreg (4450F or equivalent)
L2–L3 (Digital)	High-Tg FR-4 core	High-Tg FR-4 core
L4 (Return)	FR-4	FR-4
Lamination cycle	PTFE-compatible (longer, hotter)	Standard FR-4 cycle
Fabricator qualification	PTFE-capable shops	Most RF shops

Useful Resources for RF-35 vs RO4350B Selection

Bookmarks worth keeping:

Official datasheets and technical documentation:

• AGC Multi Material technical library (agc-multimaterial.com/agc-downloads) — RF-35 and RF-35TC datasheets, processing guides
• Rogers Corporation technology hub (rogerscorp.com/advanced-electronics-solutions) — RO4350B data sheet, fabrication guide, and Dk vs frequency curves
• IPC-4103 standards for high-frequency materials — slash sheet /11 covers RO4350B, /245 covers RF-35

Comparison and selection tools:

• Saturn PCB Toolkit (free) — includes both Taconic and Rogers material presets for impedance calculations
• Polar Si9000 — industry-standard impedance field solver with full laminate libraries
• Microwaves101 material comparison chart — side-by-side parametric tables for all major RF laminates
• Modular Components National comparison PDFs — independent material comparison data

Simulation tools that support both materials:

• Ansys HFSS — 3D EM simulation with vendor-supplied Dk/Df vs frequency models
• Keysight ADS — circuit and EM co-simulation with Taconic and Rogers libraries
• CST Studio Suite — broadband EM simulation including thermal coupling

Where to buy:

• Both materials sell through PCB fabricators rather than direct. Ask your fab which they stock, which they quick-turn, and which they have process-qualified. Authorized distributors for bulk purchase include Insulectro and Transene for North America.

Frequently Asked Questions

Is RF-35 directly compatible with RO4350B in hybrid stack-ups?

They are not interchangeable drop-ins, but both can bond to FR-4 as the inner layers of hybrid stack-ups. You cannot simply swap RF-35 for RO4350B in an existing design without recalculating trace widths — the slight Dk difference (3.50 vs 3.48) shifts 50-ohm line widths by a fraction of a mil, which matters for tight impedance control. You also cannot bond RF-35 directly to RO4350B in the same stack without a compatible prepreg layer; the CTE mismatch and cure chemistries are different. Specify one or the other as your RF material, not both in the same board.

Which material has better long-term reliability in outdoor applications?

RF-35 typically has the reliability edge for outdoor use, driven primarily by its lower moisture absorption (0.03% vs 0.06%). Over a 10-year deployment in a humid outdoor environment, the RF-35 board will see less Dk drift and less Df degradation. RO4350B is still excellent, but if your application is a weather-exposed antenna or an outdoor 5G radio, RF-35 has a measurable advantage. For indoor, climate-controlled deployments the reliability difference is negligible.

Why is RO4350B cheaper than RF-35 at high volume?

Processing. RO4350B uses a hydrocarbon-ceramic resin system that laminates and plates on standard FR-4 equipment without PTFE-specific chemistry. RF-35 is PTFE-based, requires sodium-naphthalene or plasma activation before plating, and uses longer, hotter lamination cycles. Those process differences translate to lower fab overhead for RO4350B at high volume. At prototype quantities the setup cost dominates and the price gap is minimal; at production volumes the process savings accumulate and RO4350B typically delivers 10–20% cheaper.

Can RF-35 be used for automotive radar applications?

Yes, RF-35 is used in 24 GHz automotive radar and some 77 GHz applications, though for 77 GHz the higher-performance Taconic TLY-5 (or RO3003 equivalent) is more common because of its lower Df at millimeter-wave frequencies. For 24 GHz short-range radar and sub-6 GHz V2X applications, RF-35 is well-qualified and cost-competitive. Both Taconic and Rogers offer AEC-Q-equivalent reliability data for their respective materials in automotive qualification packages.

Which is better for 5G sub-6 GHz base station designs?

Both work well at 5G sub-6 GHz (typically 3.4–3.8 GHz). The selection usually comes down to secondary factors: thermal load, fabricator capability, volume cost structure, and moisture exposure. Power amplifier boards favor RO4350B for its thermal conductivity and PTH reliability. Receiver and filter boards favor RF-35 for its lower insertion loss. For high-volume base station production, RO4350B is more commonly specified because of the cost and processing advantages. For smaller-volume precision work or outdoor remote radio heads, RF-35 is defensible.

Final Take

If you need one sentence for your next design review: pick RO4350B for cost-optimized high-volume production, easier fabrication, and applications with meaningful thermal load; pick RF-35 when insertion loss budget is tight, moisture exposure matters, or peel strength is critical.

Neither is universally “better.” These are mature, well-characterized materials with 20+ years of production history each, and both deliver predictable results when paired with a qualified fabricator. The real differentiator is not the material — it is whether your fab has run the specific laminate in the specific stack-up you are designing, whether your impedance tolerance is achievable on their process, and whether the cost delta is worth fighting your procurement team over. Get those questions answered before the material choice, and the RF-35 vs RO4350B decision becomes straightforward.