RO4450F Bondply | Hybrid RF Lamination Guide

What Is Rogers RO4450F Bondply?

Rogers RO4450F is a thermoset, glass-reinforced hydrocarbon/ceramic prepreg (bondply) engineered to bond RO4000-series core laminates—and, where needed, FR-4 cores—into multilayer RF and microwave PCBs. It has a process dielectric constant (Dk) of 3.52 ± 0.05 at 10 GHz and a dissipation factor (Df) of 0.004 at the same frequency. Because it cures in a standard FR-4 lamination press at temperatures around 190 °C (375 °F), fabricators do not need the high-pressure PTFE bonding equipment that older fluoropolymer bondplies require.

RO4450F fills the same role in a stackup that ordinary epoxy prepreg fills in a digital board—it bonds copper-clad cores together and forms the dielectric between inner-layer copper and adjacent reference planes. The difference is that its Dk is tightly controlled and its loss tangent is roughly four to five times lower than standard FR-4 prepreg at microwave frequencies, so it can carry controlled-impedance transmission lines without the insertion-loss penalty of epoxy glass.

Key Electrical and Mechanical Properties

The Dk of 3.52 sits close to the 3.48 of RO4350B and the 3.66 of RO4003C, which simplifies impedance modelling: the bondply layer between two cores behaves almost identically to the core material itself, reducing the Dk discontinuity at each interface. This is a deliberate design choice by Rogers to keep hybrid stackups predictable. You can verify these values on the Rogers RO4450F product page.

RO4450F vs. RO4450B: What Changed?

RO4450F replaced the older RO4450B bondply in Rogers’ product line. The two share the same resin chemistry family, but RO4450F offers several practical improvements:

• Tighter Dk tolerance — ± 0.05 versus ± 0.05 nominal on RO4450B, but with improved lot-to-lot consistency due to updated filler loading control.
• Lower Df — 0.004 versus 0.004 typical, with narrower distribution tails that matter at millimeter-wave frequencies where the tail of the Df distribution drives yield.
• Better flow characteristics — RO4450F has a more controlled resin flow during lamination, which reduces the risk of resin starvation around dense via fields and improves fill into etched copper patterns.
• Thinner options — The 3.5 mil cured sheet lets designers hit thinner bondply layers for tighter coupling in broadside-coupled stripline structures.

If you are maintaining an existing design that calls out RO4450B, Rogers generally positions RO4450F as a drop-in replacement, but you should re-run impedance modelling and verify lamination profiles with your fabricator before swapping.

Where RO4450F Is Used

Multilayer RO4000-Series Stackups

The most common application is bonding two or more RO4350B or RO4003C cores into a four-to-twelve-layer RF board. Typical examples include phased-array antenna feed networks, power amplifier combiners, and multi-function RF front-ends that integrate filtering, matching and distribution on a single board. The thermoset cure means the finished laminate is dimensionally stable through subsequent reflow cycles—important for BGA and QFN RF components.

Hybrid Rogers / FR-4 Constructions

Cost-sensitive designs often use RO4000 cores for the RF signal layers and standard FR-4 cores for digital and power distribution layers. RO4450F bonds these dissimilar materials together because its cure temperature and pressure window overlaps with both. The CTE mismatch between Rogers hydrocarbon ceramic (X/Y CTE around 10–12 ppm/°C) and FR-4 (14–17 ppm/°C) is modest enough that RO4450F can absorb the stress without delamination, provided the lamination profile is correctly managed. For an alternative bonding approach in hybrid constructions, some designers also evaluate Rogers 2929 bondply, which uses a different resin system optimized for bonding PTFE-based laminates to FR-4.

Automotive Radar and 5G Infrastructure

At 77 GHz automotive radar frequencies, every tenth of a dB matters. Boards built on RO3003G2 cores or RO4835T thin cores sometimes use RO4450F as the bonding layer when the antenna layer sits on a different core than the feed network. The low moisture absorption (0.13 %) also helps in outdoor 5G small-cell radios where humidity cycling can shift Dk in hygroscopic prepregs.

Lamination Process Parameters

RO4450F processes on a standard multilayer press, but the profile differs from FR-4 prepreg in several ways that fabricators must control carefully.

Recommended Press Cycle

Critical Fabrication Notes

• Oxide or oxide-alternative treatment — Inner-layer copper should receive a standard brown or black oxide, or a reduced-oxide alternative, before layup. RO4450F bonds well to treated copper; skipping this step risks adhesion failures at reflow.
• Resin flow management — In areas with heavy copper etch-out (large ground plane voids, dense via arrays), consider using two sheets of 3.5 mil RO4450F instead of one thicker sheet. This provides more resin volume to fill the voids without increasing the nominal dielectric spacing excessively.
• Registration — The low CTE of the RO4000 cores means they shrink less during cool-down than FR-4. If you are building a hybrid stackup, discuss scaling factors with your fabricator. IPC-6012 Class 3 registration tolerances can be met, but the artwork compensation may differ from an all-FR-4 panel.
• Post-lamination bake — A 2-hour bake at 150 °C after lamination drives off residual moisture and completes any marginal cure. This step is especially important for boards that will see lead-free reflow at 260 °C peak.

Fabricators already comfortable with RO4350B multilayer builds will find RO4450F straightforward. The IPC-6012 rigid board qualification specification applies to the finished board just as it does to any other multilayer construction.

Stackup Design Considerations

Impedance Modelling

When modelling a microstrip or stripline whose reference plane sits across an RO4450F bondply layer, use Dk = 3.52 at your operating frequency. Because the Dk is close to RO4350B’s 3.48, the trace width difference between a line referenced to the core and a line referenced to the bondply is small—typically under 0.5 mil (0.013 mm) for a 50 Ω microstrip at 10 GHz on a 4 mil dielectric. Still, the difference exists, and ignoring it in a tightly impedance-controlled design (± 5 % tolerance) can push you outside spec.

Most 2D field solvers (Polar Si9000, Altium’s impedance calculator, or the free ATLC open-source field solver) let you assign different Dk values to each dielectric layer in the stackup. Always do this rather than averaging the Dk across the entire cross-section.

Coupling and Spacing

Broadside-coupled stripline pairs—common in Lange couplers and balanced filter topologies—benefit from the 3.5 mil cured thickness option because it enables tight coupling without exotic thin-core laminates. A 3.5 mil RO4450F bondply between two 0.5 oz copper layers gives a coupling gap of roughly 3.5 mil minus twice the copper thickness (0.7 mil each side), yielding about 2.1 mil of pure dielectric separation. That is tight enough for 3 dB coupling in many X-band and Ku-band coupler designs.

Thermal Reliability

The Z-axis CTE of 38 ppm/°C is moderate—lower than most FR-4 prepregs (typically 45–65 ppm/°C below Tg) but higher than the RO4000 core laminates themselves (around 32 ppm/°C). In plated through-holes and vias, the bondply layer contributes to barrel stress during thermal cycling. For designs with high via density and Class 3 reliability requirements (aerospace, defense), keep via aspect ratios below 8:1 and consider via filling or plugging to reduce stress concentrators.

Comparing RO4450F to Other Bonding Options

Choose RO4450F when your signal layers are on RO4350B or RO4003C cores and you want the bondply Dk to match the core Dk as closely as possible. Choose Rogers 2929 when bonding PTFE-based laminates (RT/duroid, TMM) to FR-4 or to each other, because its lower Dk better matches PTFE families. Choose SpeedWave 300P prepreg when you need a Dk around 3.0 in the bondply layer, for example to match RO3003 cores in a hybrid build. Use standard FR-4 prepreg only for non-RF layers in a hybrid stackup, never for layers carrying controlled-impedance RF traces above a few hundred MHz.

Design and Procurement Tips

• Specify the cured thickness, not the raw sheet thickness. RO4450F is sold in uncured sheets that are thicker than the final pressed dimension. Your stackup drawing should call out the cured (pressed) thickness—3.5 or 4.0 mil—so the fabricator knows which product to order.
• Call out the material by full Rogers part number on your fabrication drawing and in the stackup table. “RO4450F” is unambiguous; “Rogers bondply” is not.
• Request a test coupon with impedance verification on every production lot. The coupon should include a stripline referenced to the bondply layer, not just to the core, so you are actually measuring the bondply Dk in production.
• Lead time planning — RO4450F is a specialty material. Lead times range from stock (if your fabricator pre-buys) to 6–8 weeks from Rogers distribution. Confirm availability before committing to a schedule.
• Shelf life — Like all thermoset prepregs, RO4450F has a finite shelf life, typically 6 months at room temperature in sealed packaging. Expired material may under-cure, leading to delamination. Verify date codes at incoming inspection.

When RO4450F Is Not the Right Choice

RO4450F is optimized for the RO4000 family. It is not recommended for bonding pure PTFE laminates such as RT/duroid 5880 or RO3003, because the resin chemistry does not wet PTFE surfaces effectively without a sodium-etch surface treatment that adds cost and process risk. For those materials, Rogers 2929 or a fluoropolymer-based bondply is a better fit.

At frequencies above 40 GHz, the Df of 0.004 may become a limiting factor in long transmission-line runs. Designs at 60 GHz or 77 GHz that require very low loss in the bondply layer should evaluate whether a thinner core approach—using RO4835T thin-core laminates laminated directly—can eliminate the bondply from the critical signal path entirely.

Frequently Asked Questions

Can RO4450F be used with lead-free solder reflow?

Yes. With a Tg above 280 °C and Td of 390 °C, RO4450F withstands standard lead-free reflow profiles peaking at 260 °C. A post-lamination bake at 150 °C for 2 hours is recommended to ensure full cure and moisture removal before reflow.

How many sheets of RO4450F should I use per bondply layer?

One sheet of 4.0 mil cured thickness is sufficient for most inner-layer bonds with moderate copper density. For layers with heavy etch-out (large voids in the copper pattern), use two sheets of 3.5 mil to provide extra resin fill without excessive dielectric thickness.

Is RO4450F compatible with sequential lamination?

Yes. The 190 °C cure temperature and thermoset chemistry allow RO4450F to be used in sequential lamination cycles. Previously cured RO4450F layers will not re-melt during subsequent press cycles, which is essential for HDI-style RF builds with buried vias.

What is the UL flammability rating of RO4450F?

RO4450F meets UL 94 V-0 flammability requirements, making it suitable for commercial, industrial and automotive applications that require V-0 rated materials throughout the stackup.

Does RO4450F require special drilling parameters?

No special drill bits are needed. Standard carbide drill bits used for FR-4 and RO4350B work well. Use entry and backer materials recommended for Rogers laminates, and keep hit counts conservative (under 1,000 hits per bit for holes ≤ 0.3 mm) to maintain hole-wall quality.