IsoClad 933 PCB | Dk 2.33 Random Glass PTFE Guide

What Is Rogers IsoClad 933?

Rogers IsoClad 933 is a random-glass-fiber-reinforced PTFE laminate with a nominal dielectric constant (Dk) of 2.33 ± 0.02 at 10 GHz. Its random, non-woven glass reinforcement eliminates the knuckle effect found in woven-glass PTFE laminates, delivering a more isotropic Dk across the panel and reducing impedance variation along a transmission line. IsoClad 933 targets microstrip and stripline circuits from UHF through Ku-band, including feed networks, couplers, power dividers, and antenna substrates where consistent phase behavior matters.

The material was developed as part of Rogers Corporation’s IsoClad family, which uses a proprietary random-fiber mat instead of the standard E-glass weave. This distinction is the single most important thing to understand about IsoClad 933: the reinforcement geometry, not just the resin system, defines the laminate’s RF performance.

Key Electrical and Mechanical Properties

Two numbers stand out. First, the Df of 0.0013 at 10 GHz places IsoClad 933 among the lowest-loss reinforced PTFE laminates available—comparable to Rogers RT/duroid 5870, which uses woven glass at the same Dk. Second, moisture absorption below 0.1 % means the Dk stays stable in humid environments, a practical advantage for outdoor antenna radomes and marine radar applications.

Why Random Glass Reinforcement Matters

In a woven-glass PTFE laminate, the glass yarns cross over and under each other in a regular pattern. Where a yarn crosses (the “knuckle”), the local glass-to-resin ratio is higher, creating a region of elevated Dk. A microstrip trace routed over these knuckles sees a periodic impedance ripple whose spatial frequency depends on the weave pitch—typically 0.5–1.0 mm (20–40 mil). At frequencies above a few gigahertz this ripple produces measurable phase scatter and amplitude modulation.

IsoClad 933’s random glass mat distributes fibers without any repeating pattern. The result is a statistically uniform Dk in the x-y plane. For phase-sensitive circuits like Butler matrices, Rotman lenses, and corporate feed networks, this uniformity translates directly into tighter phase matching between channels. Designers working with glass-reinforced PTFE substrates should weigh this isotropic advantage against the slightly lower dimensional stability that comes with the random mat structure.

Dimensional Stability Trade-Off

Woven glass constrains CTE along the warp and fill directions, giving the laminate predictable dimensional behavior during thermal cycling. A random mat provides less constraint, so IsoClad 933 exhibits somewhat higher in-plane CTE variability than, say, RT/duroid 5880 (woven glass, Dk 2.20). In practice, this means tighter registration tolerances are harder to hold on large panels (> 18 × 24 in). For multilayer builds requiring precise layer-to-layer alignment, consider hybrid stackups that pair IsoClad 933 signal layers with more dimensionally stable bonding films.

Dk Drift with Temperature and Frequency

Every PTFE laminate’s Dk shifts with temperature and frequency. For IsoClad 933, the thermal coefficient of Dk (TCDk) is approximately −104 ppm/°C over the −55 °C to +125 °C range. This negative coefficient means the Dk decreases as temperature rises—a behavior common to PTFE-based systems because the polymer’s molecular motion increases with heat, lowering its effective polarizability.

Use the estimator below to see how much the Dk of IsoClad 933 (or any laminate you specify) shifts from its datasheet value at a different operating temperature. Enter the nominal Dk, the TCDk in ppm/°C, the reference temperature (typically 25 °C), and your operating temperature.

For example, entering Dk = 2.33, TCDk = −104 ppm/°C, reference 25 °C, and operating temperature 85 °C returns a shifted Dk of roughly 2.3285. That 0.06 % drop may seem trivial, but in a 10 GHz narrowband filter with a 2 % fractional bandwidth, even 0.05 % Dk error shifts the center frequency by about 2.5 MHz—enough to move the passband edge into the rejection band. If your design cannot tolerate that, either add a temperature-compensation network or select a laminate with a lower TCDk.

With respect to frequency, IsoClad 933’s Dk remains within ± 0.02 of 2.33 from 1 GHz to at least 10 GHz. Above 10 GHz the published data thins out, and designers pushing into Ku-band (12–18 GHz) should request characterization data from Rogers or perform their own ring-resonator measurements per IPC-TM-650 method 2.5.5.5.

Fabrication Guidelines for IsoClad 933 PCBs

Drilling

PTFE laminates are softer and more prone to smear than FR-4. Use carbide drill bits with a positive rake angle, spindle speeds of 60,000–80,000 RPM, and controlled infeed rates around 0.001–0.002 in per revolution. Back-up boards should be rigid aluminum or phenolic—not the standard FR-4 entry/exit material—to prevent burring at the hole exit.

Copper Adhesion and Surface Preparation

IsoClad 933 uses electrodeposited (ED) copper foil as standard. Peel strength after solder float is ≥ 6 lb/in, which is adequate for most single- and double-sided designs. For multilayer builds or applications requiring wire bonding, specify the optional sodium-naphthalenide etch treatment on the PTFE surface before lamination. This chemical treatment micro-roughens the fluoropolymer, improving bond strength to prepreg or adhesive layers by 30–50 %.

Plating and Soldering

Standard electroless copper and electrolytic copper plating processes work on IsoClad 933 after plasma desmear. Lead-free soldering (SAC305, peak 260 °C) is compatible with the laminate’s thermal rating, but reflow profiles should minimize time above 250 °C to avoid delamination at the copper-PTFE interface. HASL, ENIG, and immersion silver finishes are all proven on this material.

Etching

Because the Dk is low and the laminate is relatively soft, maintaining etch uniformity is critical. Uneven etch factors widen trace edges on one side, shifting the effective impedance. Alkaline etchants at controlled temperature (48–52 °C) and spray pressure produce the most consistent results on 0.5–1 oz copper. For designs with impedance tolerance ≤ ± 5 %, request cross-section verification coupons on each production panel.

IsoClad 933 vs. Comparable Laminates

Choose IsoClad 933 when you need Dk isotropy across the panel for phase-critical circuits and want glass reinforcement for mechanical handling. Choose RT/duroid 5870 when dimensional stability and multilayer registration outweigh the knuckle-effect concern. Choose Taconic TLY-5 when the lowest possible loss (Df 0.0009) is the priority and you can manage the reduced dimensional stability of an unreinforced PTFE substrate.

Typical Applications

• Antenna feed networks (1–18 GHz): Corporate feeds and series feeds for phased arrays benefit from IsoClad 933’s isotropic Dk, keeping element-to-element phase error below 2°.
• Microstrip filters and couplers: Narrowband bandpass filters at C-band and X-band hold center frequency more tightly on a random-glass substrate than on a woven-glass equivalent.
• Power dividers / combiners: Wilkinson dividers and branch-line hybrids require quarter-wave sections whose electrical length depends directly on Dk uniformity.
• GPS and GNSS patch antennas: The low Dk (2.33) allows wider patch dimensions for a given frequency, easing manufacturing tolerances at L-band (1.575 GHz).
• Marine and outdoor radar: Low moisture absorption keeps Dk stable in salt-spray environments, reducing long-term frequency drift.

Design Tips for Maximizing IsoClad 933 Performance

1. Model with measured Dk, not nominal. Request the actual Dk test report for your production lot. A 0.02 Dk variation at 2.33 represents a 0.86 % change—enough to shift a 10 GHz filter by 43 MHz.
2. Compensate for TCDk in outdoor systems. If the operating range spans −40 °C to +85 °C, the Dk swings by roughly 0.03. Pre-bias the design toward the mid-temperature Dk rather than the 25 °C value.
3. Use ground-plane stitching vias. IsoClad 933’s low Dk means wider traces for a given impedance, which can increase radiation loss at higher frequencies. Dense via fencing along microstrip edges suppresses parasitic modes.
4. Pair with compatible prepregs for multilayer builds. Rogers CuClad 6700 bondply (Dk 2.35) is the intended bonding film for IsoClad 933 stackups, maintaining Dk continuity across layers. Mismatched bondply Dk creates internal reflections at every layer interface.
5. Specify panel orientation. Even with random glass, slight machine-direction fiber alignment can exist. For the most critical circuits, request that the primary transmission-line direction be marked relative to the panel’s machine direction, and characterize both orientations during prototyping.

Designers evaluating other PTFE-class materials with different Dk values for antenna or coupler designs may also want to compare options like the Wangling F4BME enhanced PTFE laminate or the Nelco N9000 PTFE microwave laminate, both of which serve overlapping frequency ranges with different cost and availability profiles.

Standards and Qualification

IsoClad 933 meets Rogers’ published IsoClad series specifications and can be qualified under IPC-6012 Class 3 for high-reliability applications. Designers specifying the material for defense or aerospace programs should call out the Rogers part number, copper weight, and thickness in the fabrication drawing, along with the required IPC class and any MIL-PRF-31032 slash-sheet equivalence.

Frequently Asked Questions

Is IsoClad 933 the same as RT/duroid 5870?

No. Both share Dk 2.33 and use PTFE resin, but IsoClad 933 uses random glass reinforcement while RT/duroid 5870 uses woven glass. The random mat gives IsoClad 933 better Dk isotropy; the woven glass gives RT/duroid 5870 better dimensional stability.

What frequency range is IsoClad 933 suitable for?

IsoClad 933 is characterized up to 10 GHz in standard datasheets and performs well through Ku-band (18 GHz). For millimeter-wave designs above 30 GHz, laminates with tighter Dk tolerance and lower Df—such as Rogers RO3003—are generally preferred.

Can IsoClad 933 be used in multilayer stackups?

Yes, using Rogers CuClad 6700 bondply (Dk 2.35) or FEP bonding film. Sodium-naphthalenide surface treatment of the PTFE is recommended before bonding to achieve adequate peel strength.

How does moisture affect IsoClad 933’s Dk?

Moisture absorption is below 0.1 %. Water has a Dk of roughly 78 at low frequency, so even small absorption can shift Dk. At 0.1 % absorption, the effective Dk increase is on the order of 0.01—negligible for most designs but worth tracking in precision filter applications.

What is the lead time for IsoClad 933?

Lead times depend on thickness, copper weight, and panel size. Standard configurations typically ship within 4–8 weeks from Rogers distributors; non-standard builds may take 10–14 weeks. Always confirm availability before committing a design, as PTFE laminate supply can be constrained during high-demand periods.