SpeedWave 300P Prepreg | Low Dk Hybrid Bonding

What Is SpeedWave 300P Prepreg?

SpeedWave 300P is a thermoset prepreg manufactured by AGC (formerly Asahi Glass) that provides a dielectric constant (Dk) of approximately 3.48 and a dissipation factor (Df) of 0.004 at 10 GHz. It is engineered as a bonding ply for hybrid multilayer stackups where low-loss RF cores—such as PTFE or hydrocarbon ceramic laminates—must be laminated together with consistent electrical performance. Because it cures at standard FR-4-class press cycles (around 190 °C peak), SpeedWave 300P lets fabricators build mixed-material boards without exotic lamination profiles.

Key Electrical and Mechanical Properties

The table below collects the published parameters most relevant to stackup design. All electrical values are at 10 GHz unless noted.

A Df of 0.004 at 10 GHz places SpeedWave 300P in the “low-loss” category—comparable to Isola I-Speed or Panasonic Megtron 6 prepregs—while its Dk of 3.48 is close enough to many hydrocarbon laminates (Rogers RO4350B is also 3.48) to simplify impedance matching across a hybrid stackup.

Resin Content and Fill Behavior

Choosing the right resin content is critical when bonding uneven copper distributions or when filling gaps between core layers of different thicknesses. SpeedWave 300P is available in standard-resin (SR) and high-resin (HR) variants depending on glass style. For example, a 1080-SR sheet carries roughly 62–66 % resin by weight, while a 2116-SR sheet is closer to 52–56 %. Higher resin content flows more freely during lamination, filling larger copper voids, but it also increases pressed thickness and slightly shifts the effective Dk of the cured ply.

Enter your target glass style and copper distribution below to estimate whether standard or high resin content is the better fit.

If the advisor suggests that standard resin is marginal—say, for a design with 2 oz (70 µm) copper on the bonding faces—switch to the high-resin variant or double up plies. Starved lamination (insufficient resin to fill voids) causes trapped air pockets that degrade insertion loss and invite delamination during reflow, a failure mode that is especially costly in hybrid RF boards.

Pressed Thickness by Glass Style

Pressed thickness after lamination determines the dielectric spacing that controls impedance. Because SpeedWave 300P is a thermoset system, it compresses during cure; the final thickness depends on the glass style, resin content, surrounding copper weight, and press parameters. Typical single-ply pressed thicknesses are:

• 106 SR: 1.5–2.0 mil (38–51 µm)
• 1078 SR: 2.0–2.8 mil (51–71 µm)
• 1080 SR: 2.8–3.5 mil (71–89 µm)
• 2116 SR: 4.2–5.0 mil (107–127 µm)

Use the thickness finder to look up the expected pressed value for your specific construction.

For a 50 Ω microstrip on a single 2116-SR ply pressing to 4.5 mil with Dk 3.48, the required trace width is roughly 9.5 mil (0.24 mm)—tight but well within standard etch capability. If your stackup needs a thinner bond line, a single 1080 ply at ~3.0 mil brings the 50 Ω width down to about 6.5 mil, which demands tighter etch tolerance. Always confirm pressed thickness with your fabricator’s actual press data before committing the design.

Hybrid Stackup Design with SpeedWave 300P

The primary use case for SpeedWave 300P is bonding dissimilar core materials into a single multilayer. A typical 8-layer hybrid might look like this:

This symmetric construction keeps warpage manageable. The Dk match between SpeedWave 300P (3.48) and RO4350B (3.48) means signal transitions through vias between L1/L2 and L3 see minimal impedance discontinuity at the bond interface—a significant advantage over using standard FR-4 prepreg (Dk ~4.2) as the bonding layer.

For stackups where the RF cores are PTFE-based, SpeedWave 300P’s thermoset chemistry bonds more reliably than trying to fuse two PTFE surfaces. Surface preparation of PTFE cores—typically sodium etch or plasma treatment—is still required for adequate peel strength. The Taconic RF-35 family, for instance, bonds well with SpeedWave 300P after plasma treatment because both materials share compatible Tg ranges.

How SpeedWave 300P Compares to Competing Prepregs

Choose SpeedWave 300P when your stackup already uses Dk ~3.48 cores and you want the bond ply to match. Choose Megtron 8 prepreg when loss is the dominant constraint (Df ≤ 0.001) and Dk matching is secondary. For budget-constrained designs that can tolerate higher Dk mismatch, Nelco N4000-13 prepreg is a proven mid-loss alternative.

Fabrication and Processing Notes

Lamination Profile

SpeedWave 300P cures with a standard high-Tg epoxy press cycle: ramp to 190 °C at 2–3 °C/min, hold 60–90 min under 250–400 psi, cool under pressure. No post-cure bake is normally required, though a 4-hour bake at 150 °C can improve dimensional stability for tight-tolerance designs. The cure profile is compatible with most FR-4 and hydrocarbon cores, which is the whole point of this material.

Drilling and Via Formation

Because the glass styles are conventional E-glass, standard carbide drill bits work without the rapid wear seen in ceramic-filled PTFE prepregs. Laser drilling for microvias is also straightforward; the resin ablates cleanly with CO₂ or UV lasers. Desmear uses standard permanganate chemistry.

Storage

Store SpeedWave 300P at ≤ 5 °C in sealed moisture-barrier bags. Shelf life is typically 6 months refrigerated. Allow the sealed bag to reach room temperature before opening to prevent condensation on the prepreg surface, which degrades bond quality.

Design Guidelines and Common Pitfalls

• Dk mismatch at via transitions: If you bond a Dk 3.48 core to a Dk 4.2 FR-4 core through SpeedWave 300P, the via impedance will shift at each material boundary. Keep high-speed or RF vias away from the FR-4 region, or add back-drill stubs to minimize reflections.
• Resin starvation on heavy copper: For 2 oz copper or thicker, always use high-resin variants or double plies. Confirm with your fabricator’s resin-fill study.
• CTE mismatch management: SpeedWave 300P’s z-axis CTE (~45 ppm/°C) is moderate. In boards exceeding 3 mm total thickness with many via transitions, consider via-in-pad with copper fill to improve z-axis reliability through thermal cycling per IPC-6012 Class 3 requirements.
• Impedance modeling: Use the prepreg’s cured Dk (not the uncured value) in your field solver. For SpeedWave 300P, the cured Dk is essentially the same as the datasheet value (3.48) because the measurement is performed on cured stripline coupons.

When to Specify SpeedWave 300P

SpeedWave 300P earns its place in a bill of materials when three conditions converge: the design mixes RF and digital layers, the RF cores have Dk near 3.48, and the fabricator needs a bond ply that processes like FR-4. Automotive radar front-ends at 24 GHz and 77 GHz, 5G massive-MIMO antenna feed networks, and test-and-measurement backplanes above 20 Gbps are all common applications. For purely digital boards where Dk matching is less critical, a general-purpose low-loss prepreg such as Isola IS680-AG may offer wider availability at a similar price point.

Frequently Asked Questions

Is SpeedWave 300P compatible with lead-free assembly?

Yes. Its Td of ≥ 350 °C and Tg of ≥ 200 °C provide ample margin for lead-free reflow profiles peaking at 260 °C. Multiple reflow cycles (typically 6×) are supported without measurable delamination, consistent with JEDEC J-STD-020 moisture sensitivity expectations for board-level materials.

Can SpeedWave 300P bond Rogers RO4000-series cores directly?

Yes, and this is one of its strongest use cases. Both materials share a Dk near 3.48 and compatible cure temperatures. No special surface treatment is needed on RO4000-series cores beyond standard oxide or oxide-alternative processes.

What is the maximum frequency for reliable performance?

AGC characterizes SpeedWave 300P through 40 GHz, showing Dk stability within ±0.03 and Df remaining below 0.005. For 77 GHz automotive radar, it can serve as a bonding ply in inner layers that carry only DC or low-frequency signals, but the RF signal layer itself should use a lower-loss laminate.

How does SpeedWave 300P differ from SpeedWave 300?

SpeedWave 300 is the copper-clad laminate (core); SpeedWave 300P is the prepreg (bonding sheet). They share the same resin system, so Dk and Df are matched, which is the intended design: use 300 for cores and 300P for bond plies in the same stackup.