Rogers RO4835T PCB Laminate: Complete Guide to Rogers High-Frequency Material

If you’ve been designing multilayer RF circuits lately, you’ve probably encountered the challenge of finding the right inner-layer material that balances performance with manufacturability. That’s exactly where RO4835T PCB laminate comes into play. As someone who’s worked with various high-frequency materials over the years, I can tell you that Rogers really hit a sweet spot with this one.

In this guide, we’ll dive deep into everything you need to know about RO4835T—from its core specifications to real-world design considerations. Whether you’re working on 5G infrastructure, automotive radar, or mmWave antenna systems, understanding this material will help you make better design decisions.

What Is Rogers RO4835T?

RO4835T is a low-loss, spread glass reinforced, ceramic-filled thermoset laminate manufactured by Rogers Corporation. It belongs to the RO4000® series, which has become something of an industry standard for high-frequency applications that require predictable electrical performance without breaking the bank.

What makes RO4835T particularly interesting is its intended use case. Rogers designed it specifically as an inner-layer material for multilayer board (MLB) constructions. Think of it as the complement to RO4835—when your stackup calls for thinner cores in the inner layers, RO4835T PCB is your go-to option.

The material uses a proprietary filler system combined with a flame-retardant dielectric that delivers consistent performance across a wide frequency range. The spread glass reinforcement isn’t just for structural integrity—it also helps minimize the “fiber weave effect” that can cause signal integrity issues at higher frequencies.

Available Thickness Options

RO4835T comes in three standard core thicknesses:

• 2.5 mil (0.064 mm)
• 3 mil (0.076 mm)
• 4 mil (0.102 mm)

These thin profiles make it ideal for high-layer-count designs where overall board thickness is a concern, particularly in applications like phased array antennas and compact radar modules.

RO4835T Key Specifications and Properties

Let’s get into the numbers that matter. When you’re selecting materials for a high-frequency design, these specifications will determine whether RO4835T PCB is the right fit for your application.

Electrical Properties

Property	Value	Test Condition
Dielectric Constant (Dk)	3.33 ± 0.05	10 GHz, 23°C
Dissipation Factor (Df)	0.0030	10 GHz, 23°C
Dielectric Constant (Process)	3.37	Clamped Stripline
Volume Resistivity	1.7 × 10¹⁰ MΩ·cm	C-96/35/90
Surface Resistivity	4.2 × 10⁹ MΩ	C-96/35/90

The 3.33 Dk value at 10 GHz is particularly noteworthy. This relatively low dielectric constant allows for wider trace geometries at a given impedance, which improves manufacturing yield and reduces conductor losses. The tight Dk tolerance (±0.05) ensures consistent impedance control across your production run—something that’s critical when you’re building precision RF circuits.

Thermal and Mechanical Properties

Property	Value	Test Method
Coefficient of Thermal Expansion (X-axis)	14 ppm/°C	IPC-TM-650 2.4.41
Coefficient of Thermal Expansion (Y-axis)	16 ppm/°C	IPC-TM-650 2.4.41
Coefficient of Thermal Expansion (Z-axis)	35 ppm/°C	IPC-TM-650 2.4.41
Glass Transition Temperature (Tg)	>280°C	IPC-TM-650 2.4.25
Thermal Conductivity	0.62 W/m·K	ASTM D5470
Decomposition Temperature (Td)	390°C	TGA

That Tg value above 280°C is significant. It means the material maintains dimensional stability through multiple reflow cycles—important for lead-free assembly processes where peak temperatures can exceed 260°C. The low Z-axis CTE (35 ppm/°C) compared to standard FR-4 (around 60-70 ppm/°C) improves plated through-hole reliability in your RO4835T PCB designs.

Flame Retardancy and Compliance

Property	Rating/Compliance
Flammability Rating	UL 94 V-0
RoHS Compliance	Yes
Lead-Free Process Compatible	Yes

The UL 94 V-0 flame retardant rating is achieved using RoHS-compliant technology, which matters if you’re designing for markets with strict environmental regulations.

RO4835T vs RO4835: Understanding the Differences

One question I get asked frequently is: “When should I use RO4835T versus RO4835?” The answer comes down to your stackup requirements.

Thickness and Application

RO4835 is available in thicker cores (6.6 mil to 30 mil) and is typically used for outer layers or standalone RF boards. It’s your workhorse for single-layer and simple two-layer high-frequency designs.

RO4835T PCB material, with its thinner profiles (2.5-4 mil), is optimized for inner layers in complex multilayer constructions. When you need to build up a stackup with many RF layers while keeping the total thickness manageable, RO4835T is the logical choice.

When to Use Each Material

Design Scenario	Recommended Material
Single or double-sided RF board	RO4835
Inner layers of MLB design	RO4835T
Outer layers of hybrid stackup	RO4835
High layer-count antenna arrays	RO4835T (inner) + RO4835 (outer)
Thin, compact radar modules	RO4835T throughout

Material Compatibility

Both materials share the same resin chemistry, which means they’re fully compatible in hybrid stackups. You can combine RO4835T inner layers with RO4835 outer layers and RO4450T or RO4450F prepregs without worrying about delamination or CTE mismatch issues.

Read more Rogers PCBs:

RO4835T vs Other High-Frequency Laminates

Choosing between RO4835T PCB and other popular RF materials requires understanding the trade-offs. Here’s how it stacks up against common alternatives.

Comparison with FR-4

Parameter	RO4835T	Standard FR-4
Dk @ 10 GHz	3.33	4.2-4.8
Df @ 10 GHz	0.0030	0.020-0.025
Dk Variation with Frequency	Minimal	Significant
Dk Variation with Temperature	±0.05	±0.20+
Cost	Higher	Lower
Processing	FR-4 compatible	Standard

The key advantage of RO4835T is its dramatically lower loss tangent—about 8x better than FR-4. This translates directly to lower insertion loss in your signal paths. At 77 GHz (automotive radar frequencies), the difference between FR-4 and RO4835T can mean the difference between a working design and one that doesn’t meet specification.

Comparison with RO4350B

RO4350B is perhaps the most widely used Rogers laminate. Here’s how RO4835T compares:

Parameter	RO4835T	RO4350B
Dk	3.33	3.48
Df	0.0030	0.0037
Oxidation Resistance	Enhanced	Standard
Thinnest Available Core	2.5 mil	4 mil
Designed For	MLB inner layers	General RF

RO4835T offers slightly better loss performance and superior oxidation resistance, making it preferable for designs that will see elevated temperatures over extended periods. If you’re working on a Rogers PCB project that requires thin inner layers, RO4835T is often the better choice.

Comparison with PTFE Materials

Parameter	RO4835T	PTFE (e.g., RT/duroid)
Dk Stability	Excellent	Excellent
Df	0.0030	0.0012-0.0020
Processing	FR-4 compatible	Specialized
Dimensional Stability	Better	Moderate
Cost	Moderate	Higher

PTFE materials offer lower losses but require specialized fabrication processes. RO4835T provides a compelling middle ground—better than FR-4, processable like FR-4, and significantly less expensive than PTFE systems.

Applications of RO4835T PCB

The real value of any material becomes clear when you understand where it excels. RO4835T PCB has found its way into numerous demanding applications.

5G Wireless Infrastructure

The rollout of 5G networks has created massive demand for high-frequency materials. Base station antennas, particularly massive MIMO arrays operating at 28 GHz and 39 GHz bands, require materials that can deliver consistent performance across many identical elements.

RO4835T’s tight Dk tolerance makes it ideal for these applications. When you’re building an antenna array with 64 or 128 elements, material consistency directly impacts beam-forming accuracy. The thin cores allow designers to create compact feed networks without compromising signal integrity.

Automotive Radar Systems

Modern vehicles use multiple radar sensors operating at 77 GHz (long-range) and 79 GHz (short-range). These systems demand materials with:

• Stable dielectric properties up to 81 GHz
• Good thermal performance (-40°C to +125°C operating range)
• Consistent batch-to-batch properties for automotive-grade reliability

RO4835T PCB meets all these requirements. Its enhanced oxidation resistance is particularly valuable in under-hood applications where temperatures can cycle repeatedly over the vehicle’s lifetime.

Millimeter Wave Antenna Systems

Beyond automotive radar, mmWave applications include:

• Point-to-point wireless backhaul links
• Satellite communication terminals
• 5G fixed wireless access (FWA) systems
• Airport security scanners

At these frequencies, even small variations in dielectric constant can cause significant phase errors. The spread glass construction of RO4835T minimizes the fiber weave effect that can plague woven glass materials at mmWave frequencies.

Aerospace and Defense

Military and aerospace applications have used Rogers materials for decades. RO4835T finds use in:

• Phased array radar systems
• Electronic warfare (EW) systems
• Satellite communication systems
• Unmanned aerial vehicle (UAV) data links

The material’s stability under thermal cycling and resistance to moisture absorption makes it suitable for these demanding environments.

Power Amplifiers and RF Front-Ends

High-power RF applications benefit from RO4835T’s thermal properties. Power amplifier circuits generate significant heat, and the material’s thermal conductivity helps dissipate this heat more effectively than standard FR-4.

RO4835T PCB Stackup Design Considerations

Designing a successful multilayer board with RO4835T requires attention to several factors.

Recommended Stackup Materials

For optimal results, Rogers recommends combining RO4835T PCB with compatible materials:

Layer Type	Recommended Material	Notes
Outer signal layers	RO4835	6.6-30 mil cores
Inner signal layers	RO4835T	2.5-4 mil cores
Bonding layers	RO4450T or RO4450F	Prepreg options
Copper foil	CU4000 or CU4000 LoPro	ED or reverse-treated

Copper Foil Selection

The copper foil choice impacts both electrical and mechanical performance:

CU4000 LoPro (low-profile copper): Recommended for applications above 10 GHz. The smooth copper surface reduces conductor losses at high frequencies where skin effect becomes significant.

Standard ED copper: Acceptable for lower frequencies where cost is a primary concern.

Stackup Example: 8-Layer Automotive Radar Board

Here’s a practical stackup example for a 77 GHz automotive radar application:

Layer	Material	Thickness	Function
L1	Copper (LoPro)	0.5 oz	Top signal
	RO4835	5 mil	Core
L2	Copper	1 oz	Ground
	RO4450T	3 mil	Prepreg
L3	Copper	0.5 oz	Signal
	RO4835T	3 mil	Core
L4	Copper	1 oz	Ground
	RO4835T	3 mil	Core
L5	Copper	1 oz	Power
	RO4450T	3 mil	Prepreg
L6	Copper	0.5 oz	Signal
	RO4835	5 mil	Core
L7	Copper	1 oz	Ground
	RO4450T	3 mil	Prepreg
L8	Copper (LoPro)	0.5 oz	Bottom signal

Sequential Lamination Considerations

RO4835T PCB is well-suited for sequential lamination processes. The fully cured RO4000 products can withstand multiple lamination cycles without degradation—important for designs requiring blind or buried vias.

When planning sequential laminations:

1. Use consistent thermal profiles across lamination cycles
2. Allow adequate cooling time between cycles
3. Consider via reliability when determining via aspect ratios
4. Work closely with your fabricator to optimize the process

Fabrication and Processing Guidelines

One of RO4835T’s biggest advantages is its compatibility with standard FR-4 processing. This means your fabricator doesn’t need specialized equipment or drastically different processes.

Drilling Recommendations

Parameter	Recommendation
Entry material	Standard aluminum entry
Backup material	Phenolic or composite backup
Drill speeds	Standard for glass-reinforced materials
Chip load	0.001-0.003 inches per revolution
Stack height	2-3 panels typical

The ceramic filler content does increase tool wear compared to pure epoxy materials, so factor in higher drill bit consumption when estimating costs.

Plating Considerations

RO4835T PCB materials accept plating well. For best results:

• Use desmear processes appropriate for thermoset materials
• Plasma desmear provides excellent results
• Standard electroless copper deposition works well
• Monitor plating thickness in high aspect ratio vias

Solder Mask and Surface Finish

The material is compatible with:

• LPI (Liquid Photo-Imageable) solder mask
• ENIG (Electroless Nickel Immersion Gold)
• HASL (Hot Air Solder Leveling)
• OSP (Organic Solderability Preservative)
• Immersion silver and tin

For high-frequency applications, ENIG is typically preferred due to its flat surface and consistent skin effect performance.

Lead-Free Assembly Compatibility

RO4835T is fully compatible with lead-free soldering processes. The high Tg (>280°C) and Td (390°C) provide adequate margin for peak reflow temperatures up to 260°C.

Impedance Control and Signal Integrity

Getting impedance control right on RO4835T PCB designs requires understanding a few nuances that differ from standard FR-4 work.

Design Dk vs Process Dk

Rogers specifies two Dk values for RO4835T:

• Design Dk (3.33): Use this for initial impedance calculations and simulations
• Process Dk (3.37): Accounts for the resin-rich regions around traces in actual fabricated boards

For the most accurate impedance predictions, start with the process Dk value and work with your fabricator to fine-tune based on their specific process data. Most experienced RF fabricators have developed correlation data for Rogers materials that improves first-pass yield.

Trace Width Calculations

At higher frequencies, conductor losses become increasingly important. The lower Dk of RO4835T PCB allows for wider traces at a given impedance compared to FR-4:

Target Impedance	RO4835T Trace Width	FR-4 Trace Width
50Ω microstrip (5 mil core)	~11 mil	~9 mil
50Ω stripline (6 mil total)	~7 mil	~5.5 mil

Values are approximate and depend on copper thickness and specific stackup

Wider traces mean lower conductor losses and improved manufacturing yield—a double benefit that’s particularly valuable at mmWave frequencies.

Managing Fiber Weave Effects

Even with RO4835T’s spread glass construction, fiber weave effects can impact performance above 30 GHz. Consider these mitigation strategies:

1. Route at angles: Running traces at non-orthogonal angles to the fiber weave pattern averages out the local Dk variations
2. Use wider traces: Wider conductors average over more fiber weave periods
3. Specify spread glass: RO4835T already uses spread glass, but confirm with your fabricator
4. Differential pairs: Tight coupling helps both traces see similar effective Dk

Via Design for High Frequencies

Via transitions become critical above 10 GHz. When using RO4835T PCB in your stackup:

• Back-drill signal vias: Removes the via stub that causes resonances
• Use via fencing: Ground vias around signal vias improve isolation
• Consider blind/buried vias: Eliminates stubs entirely but adds cost
• Optimize via-to-pad ratios: Larger pads increase capacitance; size appropriately

A via stub resonance frequency can be estimated as: f(GHz) ≈ 75 / stub_length(mm). For a 60 mil stub, resonance occurs around 50 GHz—right in the automotive radar band.

Thermal Management Strategies

While RO4835T PCB has reasonable thermal conductivity (0.62 W/m·K), proper thermal design ensures long-term reliability.

Heat Spreading Techniques

For power amplifier and other high-power applications:

1. Thermal vias: Arrays of plated vias under hot components conduct heat to inner ground planes
2. Copper pours: Maximize copper on inner layers to spread heat laterally
3. Component placement: Distribute heat-generating components across the board
4. Heatsink attachment: Plan for thermal interface materials and mechanical mounting

Via Array Calculations

A rough estimate for thermal via array thermal resistance:

For an n×n array of 10 mil diameter vias with 1 oz plating through a 62 mil board:

• Thermal resistance ≈ 50 / n² °C/W (approximate)

This helps size via arrays for specific thermal dissipation requirements.

Temperature-Dependent Dk Considerations

RO4835T’s Dk changes minimally with temperature, but for precision applications, account for this variation:

• Typical Dk temperature coefficient: approximately 40 ppm/°C
• Over a 100°C temperature swing, expect ~0.4% Dk change
• This translates to approximately 0.2% impedance variation

For most applications, this is negligible, but phased array designs with tight beam-pointing requirements may need to account for it.

Oxidation Resistance: A Key Differentiator

One aspect that often gets overlooked in material selection is long-term stability. All hydrocarbon-based thermoset materials can oxidize over time, particularly at elevated temperatures. This oxidation gradually increases both Dk and Df, potentially affecting circuit performance.

Rogers developed RO4835T PCB with enhanced oxidation resistance specifically to address this concern. The proprietary formulation maintains stable electrical properties even after extended exposure to high temperatures.

This matters most in applications where:

• Operating temperatures consistently exceed 85°C
• Product lifetime requirements exceed 10 years
• Reliability testing includes high-temperature operating life (HTOL) testing
• Field returns due to electrical drift are unacceptable

Automotive radar is a prime example. These systems must function reliably for 15+ years while experiencing temperature swings from -40°C to over 100°C. RO4835T’s oxidation resistance provides confidence that the radar won’t drift out of specification over the vehicle’s lifetime.

How to Source RO4835T Laminates

Sourcing considerations for RO4835T PCB material:

Through PCB Fabricators

Most designers don’t purchase laminate directly. Instead, they work with PCB fabricators who maintain relationships with Rogers distributors. When requesting quotes:

• Specify RO4835T by name in your fabrication drawing
• Include the required thickness (2.5, 3, or 4 mil)
• Note any specific copper foil requirements
• Mention if you need low-profile copper for high-frequency applications

Rogers Authorized Distributors

For direct material purchases or large-volume procurement:

• Contact Rogers Corporation directly for regional distributor information
• Major electronics distributors stock popular configurations
• Lead times vary from stock to 8-12 weeks for custom configurations

Material Availability Notes

Standard configurations (3 mil core with 0.5 oz copper) typically have better availability than custom builds. For prototype work, check with multiple fabricators to find one with the specific configuration in stock.

Cost Considerations and Design for Manufacturability

Understanding the cost drivers helps optimize your RO4835T PCB design for both performance and budget.

Material Cost Factors

RO4835T costs more than standard FR-4 but less than PTFE alternatives. Key cost drivers include:

Factor	Impact on Cost	Mitigation Strategy
Raw material cost	5-10x FR-4	Minimize RF layer count
Copper foil type	LoPro adds 15-25%	Use LoPro only where needed
Core thickness	Standard sizes lower cost	Use 3 mil (most common)
Panel utilization	Larger panels more efficient	Design for standard panel sizes
Layer count	Each RF layer adds cost	Optimize stackup carefully

Hybrid Stackup Strategies

One effective cost optimization technique is hybrid stackup design. Not every layer needs RO4835T PCB:

• Use FR-4 for power and ground: No RF performance needed
• Use RO4835T only for signal layers: Where loss matters
• Consider mixed-material zones: Different materials in different board regions

A well-designed hybrid stackup can reduce material costs by 30-50% compared to all-Rogers construction while maintaining RF performance where it counts.

Panelization Tips

Work with your fabricator on panelization early:

1. Standard panel sizes: 12×18″ or 18×24″ are common
2. Tooling borders: Account for handling areas
3. Array spacing: Allows for routing and V-scoring
4. Orientation: Align to grain direction for consistent properties

First-Article Testing Recommendations

For critical applications, invest in thorough first-article testing:

• TDR measurements: Verify impedance control
• Insertion loss testing: Confirm RF performance
• Cross-sectioning: Validate layer registration and plating
• Dk measurement: Compare actual vs. specified values

This upfront investment prevents costly field failures and production delays.

Useful Resources for RO4835T PCB Design

When working with RO4835T, these resources will help:

Official Documentation

Resource	Description	Access
RO4835T Data Sheet	Complete specifications	Rogers Corporation website
Fabrication Guidelines	Processing recommendations	Available from Rogers
MWI Calculator	Impedance and loss calculations	Rogers online tool
Design DK Calculator	Process Dk estimation	Rogers online tool

Design Tools

Rogers provides several free online tools:

• MWI-2017: Microwave impedance calculator with loss estimation
• TDDK Calculator: Temperature-dependent Dk modeling
• Stackup Planner: Helps visualize multilayer constructions

Technical Support

Rogers offers application engineering support for complex designs. Don’t hesitate to reach out if you’re pushing the material to its limits or working on a novel application.

Frequently Asked Questions About RO4835T PCB

What is the dielectric constant (Dk) of RO4835T?

The dielectric constant of RO4835T is 3.33 at 10 GHz under design conditions. The process Dk (measured using clamped stripline method) is 3.37. Both values include tight tolerance control of ±0.05, ensuring consistent impedance across production lots.

Is RO4835T compatible with standard FR-4 fabrication processes?

Yes, RO4835T PCB can be fabricated using standard epoxy/glass (FR-4) processes. This includes drilling, plating, etching, and lamination. The material was specifically designed to enable high-frequency performance without requiring specialized fabrication equipment.

What thickness options are available for RO4835T?

RO4835T is available in three standard core thicknesses: 2.5 mil (0.064 mm), 3 mil (0.076 mm), and 4 mil (0.102 mm). These thin profiles are optimized for inner-layer use in multilayer board designs where overall thickness must be minimized.

Can RO4835T be used for automotive radar applications?

Absolutely. RO4835T is well-suited for automotive radar operating at 77 GHz and 79 GHz. Its stable Dk across temperature (-40°C to +125°C typical automotive range), enhanced oxidation resistance for long-term reliability, and low loss at mmWave frequencies make it an excellent choice for these applications.

What prepreg materials should I use with RO4835T?

Rogers recommends RO4450T or RO4450F prepreg for bonding RO4835T PCB cores together. These prepregs have matched Dk values and thermal properties, ensuring consistent electrical performance and reliable lamination. The combination creates a material system designed to work together in demanding multilayer applications.

Conclusion

RO4835T PCB laminate represents a thoughtful solution to a real design challenge: how to build high-layer-count RF boards without sacrificing performance or paying PTFE prices. Its combination of low loss, tight Dk tolerance, FR-4-compatible processing, and enhanced oxidation resistance makes it a compelling choice for demanding applications from 5G to automotive radar.

If you’re designing multilayer RF circuits and need thin inner-layer materials that won’t compromise your signal integrity, RO4835T deserves serious consideration. Work with a fabricator experienced in Rogers materials, use the recommended prepregs and copper foils, and you’ll have a solid foundation for your next high-frequency design.The RF and microwave world continues to push toward higher frequencies and more complex multilayer structures. Materials like RO4835T make these advances possible while keeping manufacturability and cost in check. That’s the kind of engineering trade-off that makes our jobs as designers just a little bit easier