CuClad 6700 Bonding Film | Low-Temp PTFE Bonding

What Is CuClad 6700 Bonding Film?

CuClad 6700 is a fluoropolymer-based bonding film originally developed by Arlon (now part of Rogers Corporation) for laminating PTFE-based substrates into multilayer microwave circuits. It bonds at approximately 250 °C (482 °F)—well below the 370 °C sintering temperature of pure PTFE—so the electrical and dimensional properties of the core laminates are preserved. Its dielectric constant (Dk) is 2.35 ± 0.04 at 10 GHz with a dissipation factor (Df) of 0.0025, making it electrically transparent in most RF stackups from L-band through Ka-band.

The film is supplied uncladded in thicknesses from 1 mil (25 µm) to 4 mil (102 µm). Because it is unfilled PTFE-based, it flows during lamination to fill etched-copper topography and plated-through-hole annular rings, producing a void-free bond line that maintains controlled impedance across the multilayer structure.

Key Electrical and Mechanical Properties

The low Dk and Df are the primary reasons designers specify CuClad 6700 over FR-4-based prepregs or thermoset adhesive films. A conventional low-flow FR-4 prepreg has a Dk around 4.2 and Df above 0.015 at 10 GHz—both of which would create impedance discontinuities and excess insertion loss when used between PTFE cores.

Why Low-Temperature Bonding Matters for PTFE Multilayers

Pure PTFE sinters at roughly 370 °C, but holding an entire multilayer stackup at that temperature causes excessive copper grain growth, z-axis expansion and registration shift. Fusion bonding also demands very high pressures (300–500 psi) that can crush thin dielectric layers. CuClad 6700 solves this by flowing and cross-linking at 250 °C under moderate pressure (typically 100–200 psi), which keeps the PTFE cores dimensionally stable and preserves drilled-hole registration to ±2 mil or better.

This is especially important in designs that mix PTFE cores with plated through vias or blind vias, because excessive thermal excursion can crack barrel plating or delaminate the hole wall. Fabricators working with substrates like Rogers DiClad 527 or DiClad 870/880 laminates routinely pair those cores with CuClad 6700 to build two-to-six-layer RF boards.

Lamination Process Guidelines

Surface Preparation

PTFE surfaces are chemically inert, so inner-layer copper and dielectric surfaces must be treated before bonding. The standard approach is sodium-naphthalene etch (a chemical defluorination treatment) on exposed PTFE surfaces, followed by a micro-etch on copper. Plasma treatment is an alternative that avoids wet chemistry but requires a vacuum chamber. Skipping surface prep is the most common root cause of delamination in PTFE multilayers.

Layup and Press Cycle

1. Stack treated cores with CuClad 6700 film cut to panel size. Align using tooling pins.
2. Place the layup between release film and press pads inside a vacuum press or hydraulic press with vacuum assist.
3. Pull vacuum to < 25 mm Hg before applying heat to remove trapped air.
4. Ramp temperature at 3–5 °C/min to 250 °C. Apply 100–200 psi once the film begins to soften (around 200 °C).
5. Hold at 250 °C and full pressure for 60–90 minutes.
6. Cool under pressure at ≤ 3 °C/min to below 100 °C before releasing.

Faster ramps or premature pressure application can trap volatiles and create voids. A post-lamination bake at 150 °C for 2 hours is sometimes used to relieve residual stress, particularly in boards thicker than 60 mil (1.5 mm).

Drill and Plate Considerations

After lamination, drilling PTFE multilayers bonded with CuClad 6700 follows standard PTFE drilling practice: carbide or diamond-coated bits, controlled chip load (typically 1–2 mil per revolution), and entry/exit materials selected to prevent smear. Desmear is performed with a plasma cycle rather than permanganate, because permanganate does not attack fluoropolymers effectively. Electroless copper adhesion to the treated hole wall should be verified with a thermal-stress solder-float test per IPC-TM-650 method 2.4.13.

Stackup Design with CuClad 6700

Because the bond film’s Dk (2.35) is close to—but not identical to—the Dk of most PTFE cores (2.17 to 2.55 depending on glass content), impedance modeling must treat the bond layer as a distinct dielectric region. Ignoring the bond layer in a field solver can introduce a 3–5 % impedance error on stripline structures, which matters above 10 GHz where tight impedance tolerance (±5 Ω on 50 Ω) is the norm.

A typical four-layer stackup for a Ku-band receiver front end might look like this:

In this stackup, the 3-mil bond layer between the two ground/signal copper planes is thin enough to keep the total board thickness under 30 mil while providing reliable fill around inner-layer etch features. Designers working at millimeter-wave frequencies sometimes prefer 1-mil or 2-mil bond film to minimize the dielectric discontinuity.

CuClad 6700 vs. Alternative PTFE Bond Films

Choose CuClad 6700 when you need a balance of low Dk, low loss and moderate bond temperature for standard PTFE cores. Choose FEP film when the lowest possible loss is required and the fabricator can handle 310 °C without registration issues. Choose a thermoset prepreg (like Gore Speedboard C) when you need the lowest lamination temperature or when hybrid stackups combine PTFE with FR-4 or hydrocarbon layers.

For stackups where thermal management is the priority rather than pure RF transparency, CoolSpan TECA film provides a thermally conductive adhesive option, though its Dk is higher (~3.0) and it serves a different design intent.

Common Applications

• Phased-array antenna feed networks — multilayer stripline distribution networks at X-band and Ku-band where consistent Dk across bond layers maintains beam-pointing accuracy.
• Radar front-end modules — automotive 77 GHz and defense 94 GHz boards where PTFE cores like Rogers RO3003G2 are bonded into four-to-eight-layer stackups.
• Satellite communication diplexers and filters — edge-coupled stripline filters that demand tight Dk tolerance in the bond region to hold center-frequency accuracy.
• Test and measurement fixtures — probe cards and calibration substrates that require stable, repeatable dielectric properties over years of thermal cycling.

Design and Fabrication Pitfalls

Pitfall 1: Ignoring Bond-Layer Dk in Simulation

As noted above, treating the bond film as having the same Dk as the core introduces impedance error. Always model it as a separate dielectric layer in your 2D field solver. If the solver does not support multiple dielectric regions (some free tools do not), use a weighted-average Dk only as a rough check and verify with a full-wave simulation.

Pitfall 2: Insufficient Surface Prep

Peel-strength failures almost always trace back to inadequate sodium-naphthalene treatment or expired chemistry. The treated PTFE surface should show a water-break-free wetting test before layup. If the surface beads water, re-treat it.

Pitfall 3: Excessive Reflow Exposure

CuClad 6700 softens again above its bond temperature. Standard lead-free reflow profiles peak at 245–250 °C, which is right at the bond threshold. For boards that will see multiple reflow cycles, verify bond integrity with a thermal-stress test (288 °C solder float for 10 seconds, six cycles) during qualification. Some designers add mechanical fasteners or edge plating to reinforce the bond in high-vibration environments.

Pitfall 4: Mixing Bond Films in One Stackup

Using different bond films at different interfaces (for example, CuClad 6700 between PTFE layers and a thermoset prepreg between PTFE and FR-4) requires two separate lamination cycles at different temperatures. Plan the press sequence so the higher-temperature bond is cured first, then the lower-temperature bond in a subsequent cycle. Attempting a single-shot press with incompatible films leads to either under-cured or over-cured interfaces.

Sourcing and Availability

CuClad 6700 is available from Rogers Corporation’s Advanced Electronics Solutions division, which absorbed the Arlon product line. It is stocked by major high-frequency laminate distributors in standard panel sizes (12 × 18 in and 18 × 24 in) and can be slit to custom widths for automated layup. Lead times for stock thicknesses (2 mil and 3 mil) are typically four to six weeks; non-standard thicknesses or large-volume orders may require eight to twelve weeks.

When CuClad 6700 is unavailable or cost-prohibitive, fabricators experienced with Taconic RF-35 and similar PTFE-blend laminates can sometimes substitute FEP film or Taconic’s own bonding plies, provided the higher or lower bond temperature is acceptable for the stackup.

Frequently Asked Questions

Can CuClad 6700 bond PTFE to FR-4?

It can, but the CTE mismatch between PTFE (z-axis ~70 ppm/°C for the bond film, ~25 ppm/°C for the PTFE core) and FR-4 (~50–70 ppm/°C below Tg, much higher above) creates reliability risk during thermal cycling. A thermoset prepreg with intermediate CTE is usually a better choice for hybrid PTFE/FR-4 multilayers.

What is the maximum operating frequency for CuClad 6700?

The material’s Dk and Df remain stable through W-band (75–110 GHz) based on published characterization. Practical limits are set by the fabricator’s registration and etching capability at millimeter-wave feature sizes, not by the bond film itself.

Is CuClad 6700 the same as Rogers 6700?

Yes. After Rogers acquired Arlon’s microwave-materials division, the product continued under both legacy (CuClad 6700) and Rogers branding. The datasheet specifications are identical.

How thin can the bond line be?

The thinnest standard film is 1 mil (25 µm). After lamination with typical inner-layer copper (1 oz, 35 µm), the remaining resin thickness over copper features can be as little as 0.3–0.5 mil, which is adequate for bonding but leaves minimal margin for copper-thickness variation. Most designs use 2 mil or 3 mil film for a more robust process window.

Does CuClad 6700 require special storage?

The film should be stored in a clean, dry environment at room temperature. Unlike thermoset prepregs, it has no shelf-life expiration because it is thermoplastic and does not advance in cure. However, surface contamination from handling will degrade bond quality, so gloves and cleanroom-grade packaging are recommended.