RT Duroid 6202PR PCB: Stackup & Design Guide

What Is an RT Duroid 6202PR PCB?

An RT Duroid 6202PR PCB is a multilayer microwave circuit board that uses Rogers RT/duroid 6202PR PTFE/glass-fiber prepreg to bond RT/duroid 6002 cores into a unified stackup. The prepreg has a dielectric constant (Dk) of 2.94 ± 0.04 at 10 GHz and a dissipation factor (Df) of 0.0028, closely matching the 6002 core (Dk 2.94, Df 0.0012). This Dk match is the central reason the material exists: it lets designers build multilayer stripline and hybrid stackups without the impedance discontinuities that arise when a bonding layer has a different Dk from the core.

Unlike thermoset prepregs such as FR-4 or polyimide, 6202PR is a thermoplastic PTFE-based sheet. It does not cure through a chemical cross-linking reaction; instead, it flows and fuses under heat and pressure, then re-solidifies on cooling. This distinction affects every step of RT Duroid 6202PR PCB fabrication, from lamination profiles to rework constraints.

Key Material Properties for RT Duroid 6202PR PCB Builds

The Df of the prepreg is roughly 2.3× higher than the 6002 core. In practice, this matters most in thick stripline builds where the bonding layers make up a large fraction of the total dielectric between reference planes. For thin bond plies (2–3 mil / 0.051–0.076 mm) sandwiched between 20-mil (0.508 mm) cores, the effective loss contribution of the prepreg is small relative to the core.

The high Z-axis CTE (280 ppm/°C) is typical of unreinforced or lightly reinforced PTFE prepregs. It demands careful via design—shorter aspect ratios and, where possible, back-drilled or blind vias—to avoid barrel cracking during thermal excursions.

Why Dk Matching Matters in RT Duroid 6202PR PCB Stackups

When a stripline trace sits between two ground planes, the effective dielectric constant is a weighted average of every dielectric layer the fields penetrate. If the bonding prepreg has a significantly different Dk from the core, the impedance of the stripline shifts unpredictably depending on how close the trace is to the bond line. Worse, any manufacturing variation in prepreg thickness directly modulates the impedance.

With 6202PR and 6002 sharing a Dk of 2.94, the stripline impedance depends only on the total dielectric height and the trace geometry, not on where the bond line falls. This simplifies impedance modeling and widens the fabrication tolerance window—a real advantage in production.

For comparison, bonding a PTFE core with a thermoset prepreg like FR408HR (Dk ≈ 3.65) introduces a Dk step of roughly 0.7. That step creates a localized impedance dip near the bond line and can excite parasitic modes in wide-bandwidth stripline structures above 20 GHz.

Designing an RT Duroid 6202PR PCB Stackup

A typical multilayer 6002/6202PR stackup is symmetric and uses the prepreg only as a bonding layer between copper-clad 6002 cores. The most common RT Duroid 6202PR PCB configurations are four-layer and six-layer builds for stripline filters, couplers, and feed networks.

Four-Layer Stripline Example

• Layer 1 (Top GND): 1 oz copper on 6002 core, 20 mil
• Bond ply: 6202PR, 3 mil
• Layer 2 (Signal): Etched on inner copper of second 6002 core
• Layer 3 (Signal or GND): Opposite side of same 6002 core, 20 mil
• Bond ply: 6202PR, 3 mil
• Layer 4 (Bottom GND): 1 oz copper on 6002 core, 20 mil

Total board thickness in this example is approximately 66 mil (1.68 mm) before plating. Adjusting the 6002 core thickness (available from 5 to 60 mil) and the prepreg thickness (2, 3, or 4 mil) gives fine control over the dielectric spacing for impedance targeting.

Use the stackup builder below to experiment with layer counts, core thicknesses, and prepreg assignments. Enter your target impedance and frequency band, and the tool calculates the resulting dielectric heights and approximate trace widths.

For a 50 Ω offset stripline in the four-layer example above (total dielectric height between planes = 23 mil with a 3-mil bond ply and 20-mil core, signal offset toward the bond side), expect a trace width around 11–12 mil (0.28–0.30 mm) at Dk 2.94. If you shift to a thinner 2-mil prepreg, the offset changes and the trace narrows to roughly 10.5 mil. These small geometry shifts are exactly why getting the prepreg thickness right matters for any RT Duroid 6202PR PCB.

Prepreg Thickness Selection

The 6202PR prepreg is available in 2, 3, and 4 mil nominal thicknesses. Choosing the right one involves balancing three factors:

• Copper fill and flow: Inner-layer copper patterns create topography. The prepreg must flow enough to fill the etched channels without leaving voids. Higher copper density (large ground pours) needs less flow; sparse signal layers with deep etch channels may need the 4-mil sheet.
• Impedance sensitivity: Thinner prepreg plies reduce the bond layer’s share of the total dielectric, making impedance less sensitive to prepreg thickness tolerance. The 2-mil sheet has a tighter absolute tolerance window in mils, but its percentage variation is larger.
• Total stackup height: System constraints (connector footprints, housing pockets, weight budgets) often dictate a target thickness. The prepreg plies are part of that budget.

Enter your inner-layer copper weight and etch pattern density below to find the recommended prepreg thickness and expected pressed thickness.

As a rule of thumb, for 1 oz inner-layer copper with ≥ 70% copper retention, a 3-mil 6202PR sheet presses down to roughly 2.4–2.7 mil after lamination. If copper retention drops below 50%, consider stepping up to 4 mil to ensure adequate resin fill. This pressed-thickness result feeds directly back into your impedance calculation—a 0.3-mil difference in bond-ply thickness can shift a 50 Ω stripline by 1–2 Ω, so always update your stackup model with the post-press value. Verify with a cross-section coupon on the first build.

Lamination and Fabrication Guidelines

Lamination Profile

Because 6202PR is a thermoplastic PTFE prepreg, lamination follows a different protocol than thermoset systems. Rogers recommends a peak temperature of 360–380 °C (680–716 °F) with a pressure of 100–300 psi depending on the panel size and layer count. The dwell time at peak temperature is typically 15–20 minutes. Ramp rates should be controlled to 3–5 °C per minute to avoid trapped air and delamination.

Key differences from thermoset lamination:

• No cure chemistry: The bond forms by PTFE flow and re-solidification. There is no gel point or post-cure step.
• Higher temperature: Standard FR-4 prepregs laminate at 175–185 °C. The 360 °C+ profile requires a high-temperature press with accurate zone control.
• Longer cool-down under pressure: Maintaining pressure during cooling prevents delamination caused by the high Z-axis CTE. The panel should stay under pressure until below 200 °C.

Drilling and Plating

PTFE-based materials are notoriously difficult to drill cleanly. The soft PTFE smears rather than chips, leaving residue on the hole wall that resists standard desmear chemistry. Recommended practices include:

• Use carbide or diamond-coated drill bits at controlled feed rates (typically 0.5–1.0 mil per revolution for holes ≤ 20 mil diameter).
• Plasma desmear (CF₄/O₂) rather than permanganate, which is ineffective on PTFE.
• Sodium etch or plasma treatment of the hole wall before electroless copper to promote adhesion. Without this step, plating pull-away is common.

These steps add cost and cycle time compared to standard FR-4 processing. Budget an additional 1–2 days for a PTFE-based multilayer versus an equivalent FR-4 build.

Registration and Dimensional Stability

PTFE laminates exhibit more movement during lamination than woven-glass thermosets. Expect X-Y shrinkage of 0.5–1.0 mil per inch after pressing. Fabricators compensate with artwork scaling, but designers should use generous annular rings (≥ 5 mil / 0.127 mm on inner layers) and avoid placing critical vias at the extreme panel edges where distortion is worst.

When to Use 6202PR vs. Alternative Bonding Approaches

If your design can tolerate a Dk offset, thermoset bonding with a material like FR408HR is cheaper and uses standard press equipment. If you need the absolute lowest loss and can limit yourself to two bonded cores, fusion bonding eliminates the prepreg entirely. The RT Duroid 6202PR PCB approach occupies the middle ground: Dk-matched multilayer builds where three or more bond interfaces are needed.

For high-Dk applications such as miniaturized patch antennas or dielectric-loaded filters, materials like Rogers TMM6 (Dk 6.0) or Arlon AD1000 (Dk 10.2) serve a completely different design space and use their own bonding systems.

Design Tips and Common Pitfalls

• Do not reflow after lamination. Because 6202PR is thermoplastic, exposing the finished board to temperatures near 360 °C (as in lead-free reflow) risks re-melting the bond layer. Standard SAC305 reflow at 245–250 °C peak is safe, but rework with a hot-air station near the bond line requires care.
• Account for prepreg Df in loss budgets. At 77 GHz automotive radar frequencies, even a 0.0016 difference in Df between core and prepreg becomes significant over long stripline runs. Model the composite loss using the volume-weighted Df, not just the core value.
• Specify plasma desmear on the drawing. Many fabricators default to permanganate. If you do not call out plasma, you may get unreliable plating adhesion.
• Use back-drilling for high-frequency vias. The high Z-axis CTE of the prepreg makes long via stubs both an electrical stub resonance problem and a reliability risk. Back-drill to within 10 mil of the target layer.
• Request cross-section coupons. On the first article, ask for microsection photos at the bond line to verify resin fill, copper adhesion, and absence of voids.

Comparison With Other Low-Dk PTFE Cores and Prepregs

RT/duroid 6002 and its 6202PR prepreg sit in the low-loss, moderate-Dk segment. Designers evaluating alternatives to an RT Duroid 6202PR PCB should consider:

• Rogers RO3003G2 (Dk 3.00, Df 0.0010) — ceramic-filled PTFE with slightly higher Dk but even lower loss, and compatible with RO3003 bondply systems.
• Taconic TLY-5 (Dk 2.20, Df 0.0009) — lower Dk for wider traces and lower loss, but no Dk-matched prepreg from Taconic; bonding typically requires a third-party adhesive or fusion.
• Rogers TMM3 (Dk 3.27) — thermoset ceramic, easier to fabricate, but higher Dk and not bondable with 6202PR.

The right choice depends on frequency, layer count, loss budget, and fabrication infrastructure. For detailed material-level comparisons, the Rogers RT/duroid 6002 product page provides the full datasheet and design guidelines.

Applicable Standards

RT Duroid 6202PR PCB multilayer boards should be specified to IPC-6012 Class 3 for high-reliability applications (aerospace, defense, medical). Key call-outs include:

• Plated-through-hole integrity per IPC-6012 Table 3-5 (minimum copper thickness, void allowance).
• Microsection requirements for bond-line evaluation.
• Impedance tolerance: ± 10% is typical for stripline on PTFE; tighter tolerances (± 5%) require coupon-based verification and may increase cost.

For material acceptance, reference IPC-4103 (Specification for Plastic Substrates, Unreinforced), which covers PTFE-based laminates and prepregs.

Frequently Asked Questions

Can RT/duroid 6202PR bond materials other than 6002?

It can physically bond to other PTFE-based laminates such as RT/duroid 5880, but the Dk match advantage is lost. The prepreg’s Dk of 2.94 is optimized for 6002 cores. Using it with a Dk 2.20 core creates the same impedance-discontinuity problem it was designed to avoid.

Is lead-free assembly compatible with 6202PR?

Yes. Standard SAC305 reflow with a peak temperature of 245–250 °C is well below the 360 °C bond temperature. Multiple reflow cycles (up to 6×) have been demonstrated without delamination, per Rogers application notes.

What is the maximum frequency for an RT Duroid 6202PR PCB?

There is no hard frequency ceiling. The material has been used in designs through W-band (75–110 GHz). The practical limit is set by the prepreg’s Df (0.0028), which contributes progressively more insertion loss as frequency rises. Above 40 GHz, minimize the number and thickness of bond plies, or consider fusion bonding for the most loss-sensitive layers.

How does 6202PR compare to RO4450F prepreg?

RO4450F is a thermoset hydrocarbon prepreg with Dk 3.52 and Df 0.004, designed for the RO4000 family. It laminates at standard FR-4 temperatures (~185 °C) and is far easier to process. However, it does not Dk-match 6002 cores and has higher loss. Choose RO4450F for RO4350B-based builds; choose 6202PR for 6002-based builds.

What panel sizes are available?

Rogers supplies 6202PR prepreg sheets in standard panel sizes of 12 × 18 in and 18 × 24 in. Custom sizes may be available on request with minimum order quantities. Check with your laminate distributor for current availability and lead times.