Rogers RO4835T PCB: Properties & Design Guide

What Is a Rogers RO4835T PCB?

A Rogers RO4835T PCB uses a thin, spread-glass-reinforced thermoset laminate with a dielectric constant (Dk) of 3.48 ± 0.05 at 10 GHz and a dissipation factor (Df) of 0.0037 at the same frequency. It is specifically engineered as a thin core or sub-laminate for hybrid multilayer PCB constructions, available in thicknesses from 2 mil (0.051 mm) to 6 mil (0.152 mm). Because it shares the same resin system and Dk as the standard RO4835, it bonds directly with Rogers RO4450T or RO4450F prepregs and processes on standard FR-4 equipment—eliminating the need for specialized PTFE lamination cycles.

Key Electrical and Mechanical Properties

The table below summarizes the critical parameters from the Rogers RO4835T datasheet. These values drive impedance calculations, loss budgets and thermal reliability assessments for any Rogers RO4835T PCB design.

The Tg above 280 °C and low moisture absorption of 0.06 % make RO4835T suitable for lead-free assembly profiles (peak reflow up to 260 °C) without delamination risk. Its Z-axis CTE of 46 ppm/°C is moderate; in thin cores the absolute Z-expansion per layer is small, which helps via reliability in high-layer-count builds.

Why Thin Cores Matter in Rogers RO4835T PCB Stackups

Modern radar, satellite and 5G mmWave designs often require eight or more copper layers with tightly coupled stripline pairs, embedded capacitance planes and controlled-impedance routing—all within a total board thickness of 60–90 mil. Achieving that with standard 10–20 mil cores wastes too much of the thickness budget on layers that do not need it. RO4835T at 2–6 mil lets the designer allocate thickness precisely: a thin core for a broadside-coupled stripline pair, a thicker core for a power-distribution cavity, and so on.

Thin cores also tighten the coupling between a signal trace and its reference plane, which lowers the trace width required for a given impedance. A 50 Ω stripline on a 4 mil RO4835T core (Dk 3.48) is roughly 6.7 mil wide—narrow enough to route between 0.5 mm-pitch BGA pads without impedance compromise.

Finding the Right Core Thickness

Use the tool below to compare standard core options for your Rogers RO4835T PCB. Enter your target impedance, dielectric constant, and copper weight to see which available core thickness meets your geometry constraints.

For example, selecting a 3 mil RO4835T core with ½ oz copper and a target of 50 Ω stripline returns a trace width near 5 mil—tight but achievable with laser-direct-imaging (LDI) lithography. If your fabricator’s minimum trace is 4 mil, stepping up to the 4 mil core gives a more comfortable 6–7 mil trace. Always verify the result against your fab’s capability table before committing the stackup.

Hybrid Stackup Strategies with RO4835T

The primary use case for a Rogers RO4835T PCB is as the RF signal core in a hybrid multilayer that mixes high-frequency and conventional materials. The goal is to keep low-loss laminate only where RF energy flows and use lower-cost material everywhere else.

RO4835T + RO4450T/F Prepreg + FR-4

The most common hybrid approach pairs RO4835T signal cores with Rogers RO4450T or RO4450F spread-glass prepreg for bonding, while non-critical power and digital layers use standard FR-4 or a mid-loss material such as Isola FR408HR. Because RO4835T and RO4450T share the same thermoset chemistry, they co-laminate at 375 °F (190 °C) with standard press cycles—no sequential lamination or specialty bonding films required.

All-Rogers Builds

For designs where every signal layer must meet the same loss target—such as phased-array antenna feed networks—the entire stackup can be built from RO4835T cores and RO4450T prepreg. This eliminates any Dk mismatch between core and prepreg layers, simplifying impedance modeling. The trade-off is cost: an all-Rogers 8-layer board can run 4–8× the price of a hybrid with FR-4 inner layers.

Comparison with Related Rogers Laminates

RO4835T sits in a family of thermoset hydrocarbon/ceramic laminates. Choosing the right variant for your Rogers RO4835T PCB—or deciding on an alternative—depends on thickness needs, loss tolerance and whether you need industrial-grade thermal cycling.

RO4835T’s advantage over RO4350B is availability in 2 and 3 mil cores—thicknesses RO4350B does not offer. If your stackup can work with 4 mil minimum cores, RO4350B is more widely stocked and sometimes lower cost. When extended industrial temperature cycling (−40 °C to +150 °C continuous) is required, consider the RO4835IND LoPro variant, which adds LoPro copper for reduced conductor loss.

Fabrication and Processing Guidelines for Rogers RO4835T PCB

Drilling and Via Formation

Thin cores (2–4 mil) are too fragile to survive standard mechanical drilling without support. Best practice is to laminate the thin RO4835T cores into the multilayer first, then drill through the full stackup. For microvias landing on or starting from an RO4835T layer, UV laser drilling (Nd:YAG at 355 nm or CO₂ at 9.4 µm) works well; the spread-glass reinforcement ablates cleanly compared to woven-glass laminates, producing a smoother via barrel.

Copper Plating and Surface Finish

RO4835T’s thermoset resin accepts standard desmear (permanganate or plasma) and electroless copper plating without special chemistry. ENIG, ENEPIG, immersion silver and OSP finishes are all compatible. For designs above 20 GHz where conductor surface roughness dominates loss, specify reverse-treated (very-low-profile) foil at order time.

Handling Ultra-Thin Panels

A 2 mil core is only about twice the thickness of standard copper foil. These panels must be vacuum-packed and stored flat. During inner-layer imaging, use vacuum-frame contact exposure or LDI—roller-transport developers can crease a 2 mil core. Many fabricators pre-laminate the thin core onto a carrier before imaging and etching, then remove the carrier after pressing into the final stackup.

Design Tips for RO4835T PCBs

• Model Dk at your frequency, not just 10 GHz. Rogers provides Dk vs. frequency curves; at 28 GHz the effective Dk drops slightly to approximately 3.45. Use the process-specific Dk from Rogers’ Microwave Impedance Calculator (MWI) for accurate trace-width synthesis.
• Account for copper roughness in loss budgets. The Hammerstad-Jensen or Huray roughness models add 0.5–1.5 dB/inch of extra loss at 30+ GHz on standard ED foil. Switching to rolled or very-low-profile foil can recover most of that.
• Keep ground-via spacing below λ/10. On a 3 mil core the fields are tightly confined, but at via transitions and connector footprints, ground vias must stitch the planes together every 15–20 mil at 28 GHz to suppress parallel-plate modes.
• Verify registration tolerances. Thin cores shrink and stretch less during lamination than thick ones, but layer-to-layer registration on a 12-layer hybrid can still drift ±2 mil. Leave adequate annular ring (≥ 4 mil) on all vias.
• Request a stackup review from your fabricator early. Hybrid builds with mixed materials need press-cycle optimization. Sharing your stackup intent at the quoting stage avoids costly respins.

When a Rogers RO4835T PCB Is—and Isn’t—the Right Choice

Choose RO4835T when you need a thin, low-loss core (2–6 mil) that processes like FR-4, bonds with RO4450T prepreg, and fits into a hybrid multilayer without sequential lamination. It excels in 5G mmWave front-end modules, automotive radar (24 GHz and 77 GHz), AESA radar feed boards, and SATCOM phased arrays where layer count is high and total thickness is constrained.

Consider alternatives when:

• You need Dk below 3.0 for wider traces or lower dispersion—look at PTFE options such as RT/duroid 5870 (Dk 2.33).
• Your application is a simple two-layer or four-layer board with cores ≥ 10 mil—standard RO4350B is cheaper and more available.
• You need Dk above 6 for miniaturization—thermoset ceramics like Rogers TMM6 (Dk 6.0) or Rogers TMM10 (Dk 9.2) serve that purpose.
• Cost is the primary driver and frequency is below 6 GHz—a lower-cost woven-glass material may suffice.

Frequently Asked Questions

What is the thinnest RO4835T core available?

The thinnest standard RO4835T core is 2 mil (0.051 mm), copper-clad on both sides with ½ oz or 1 oz foil. This is thinner than any standard RO4350B offering and is designed specifically for tightly coupled stripline pairs in high-layer-count stackups.

Can RO4835T be used with standard FR-4 prepreg?

It can be co-laminated with FR-4 prepreg in a hybrid stackup, but Rogers recommends using RO4450T or RO4450F prepreg for the bond layers adjacent to RO4835T cores. These prepregs match the resin chemistry and Dk, ensuring consistent impedance and reliable adhesion. Standard FR-4 prepreg (Dk ~4.2–4.5) creates a Dk discontinuity at the bond interface that complicates impedance control.

Is a Rogers RO4835T PCB compatible with lead-free soldering?

Yes. With a Tg above 280 °C and a decomposition temperature (Td) above 390 °C, RO4835T withstands standard lead-free reflow profiles with peak temperatures up to 260 °C. It is IPC-6012 Class 3 capable when processed correctly.

How does a Rogers RO4835T PCB compare to RO4350B?

Both share Dk 3.48 and Df 0.0037 at 10 GHz. The key difference is thickness range: RO4835T is available from 2 mil, while RO4350B starts at 4 mil. RO4835T uses spread-glass reinforcement for better thickness uniformity in ultra-thin formats. For standard-thickness cores (≥ 6.6 mil), RO4350B is typically preferred due to wider availability and lower cost.

What prepreg bonds best with RO4835T?

Rogers RO4450T (spread-glass, Dk 3.23 at 10 GHz) and RO4450F (spread-glass, Dk 3.23) are the recommended bonding prepregs. Both cure at the same temperature and pressure as the RO4835T core, and their Dk is close enough to 3.48 that stripline impedance calculations remain straightforward with a simple weighted average.