CLTE-MW PCB | Rogers Microwave Grade Laminate Guide

What Is Rogers CLTE-MW?

Rogers CLTE-MW is a ceramic-filled, woven-glass-reinforced PTFE laminate designed for microwave and millimeter-wave circuits that must hold tight electrical performance across wide temperature swings. Its published dielectric constant (Dk) is 2.94 ± 0.04 at 10 GHz, with a dissipation factor (Df) of 0.0012 at the same frequency. The defining feature is an exceptionally low thermal coefficient of dielectric constant (TCDk) of approximately –9 ppm/°C, making it one of the most temperature-stable substrates Rogers offers. If your design must maintain consistent impedance and insertion loss from –40 °C to +140 °C—think outdoor base-station filters, satellite transponders, or airborne radar feed networks—CLTE-MW belongs on your shortlist.

Key Electrical and Mechanical Properties

The table below collects the parameters most relevant to PCB design and fabrication. All values come from the Rogers CLTE-MW product family datasheet.

A Dk of 2.94 positions CLTE-MW between lower-Dk PTFE laminates like CuClad 233 (Dk 2.33) and the common Dk ≈ 3.48 hydrocarbon ceramics such as RO4350B. That middle ground gives moderately compact circuit dimensions while keeping losses very low—useful in filter banks and corporate feed networks where both size and insertion loss matter.

Why TCDk Matters in Microwave Design

Most PTFE laminates exhibit a Dk shift of 50–150 ppm/°C. Over a 100 °C swing, that can move the center frequency of a narrow-band filter by several megahertz at X-band—enough to violate a channelized system’s mask. CLTE-MW’s –9 ppm/°C means the same 100 °C excursion shifts Dk by only about 0.09 %, keeping a 10 GHz filter within roughly ±4.5 MHz. For comparison, standard RT/duroid 5880 (TCDk around –125 ppm/°C) would shift the same filter by approximately ±62 MHz. That single property is the reason CLTE-MW exists.

Where Temperature Stability Is Critical

• Outdoor base-station combiners and duplexers that cycle between sub-zero nights and direct-sun afternoons.
• Satellite payload filters exposed to eclipse thermal transients.
• Military and airborne radar feed networks operating across MIL-STD-810 temperature ranges.
• Automotive 77 GHz radar modules mounted near engine bays (though RO3003 is more common here, CLTE-MW can serve the feed layer in hybrid stackups).

CLTE-MW vs. Other Microwave Laminates

Choosing a high-frequency laminate always involves balancing Dk stability, loss, processability, and cost. The comparison below puts CLTE-MW alongside materials engineers commonly evaluate in the same design trade.

Choose CLTE-MW when your circuit must hold center frequency across temperature extremes and you need woven-glass dimensional stability (better drill registration and plated-through-hole reliability than non-reinforced PTFE). Choose RO4350B when you can tolerate higher loss and moderate TCDk in exchange for standard FR-4 fabrication processes and lower material cost. Choose RO3003 when you need similar thermal Dk stability but prefer a non-woven substrate for the lowest possible Df at millimeter-wave frequencies. For lower-Dk PTFE alternatives, consider CuClad 250 or IsoClad 917, though neither matches CLTE-MW’s TCDk.

Design and Stackup Considerations

Impedance and Line Width

With Dk = 2.94, a 50 Ω microstrip on a 20 mil (0.508 mm) CLTE-MW core requires a trace width of roughly 52 mil (1.32 mm)—slightly narrower than the same line on Dk 2.33 material, and wider than on Dk 3.48 RO4350B. Run your own numbers for the exact stackup you are considering, because copper roughness profile (standard ED vs. rolled) and etch compensation will shift the result by a few mils.

Hybrid Stackups

CLTE-MW layers are frequently bonded to FR-4 or other laminates in hybrid multilayer builds. Rogers recommends their 3001 bonding film for PTFE-to-PTFE bonds and CuClad 6700 prepreg for PTFE-to-FR-4 transitions. Key rules for hybrid stackups:

• Match z-axis CTE as closely as possible between adjacent layers to reduce via barrel stress.
• Keep the RF signal layer on CLTE-MW and route digital/power on FR-4 cores to contain cost.
• Specify sequential lamination if the design requires buried vias between dissimilar materials.

For a broader look at ceramic-filled substrate families and their bonding options, see our guide to hydrocarbon ceramic laminates.

Copper Foil Selection

CLTE-MW ships with electrodeposited (ED) copper in ½ oz and 1 oz weights. For circuits above 20 GHz where conductor loss dominates, specify rolled copper or Rogers’ low-profile HTE foil to reduce surface roughness. The datasheet’s Df of 0.0012 already reflects standard ED copper; switching to rolled copper can lower effective loss tangent by 0.0002–0.0004 at Ka-band, which matters in long feed-line runs.

Fabrication Tips for CLTE-MW PCBs

CLTE-MW is a PTFE-based laminate, so it shares the general processing quirks of the PTFE family. Fabricators experienced with RT/duroid 5870 or 5880 will be on familiar ground, but a few points deserve emphasis.

• Drilling: Use carbide drill bits with a positive rake angle. PTFE’s low glass transition behavior means aggressive feed rates cause smear. A controlled entry speed of 150–200 surface feet per minute (SFM) with a chip load of 1–2 mil/rev works well for standard 10–20 mil holes.
• Desmear: Sodium-based plasma desmear is the standard method for PTFE. Permanganate desmear used for FR-4 is ineffective on PTFE resin.
• Copper adhesion: The woven-glass reinforcement in CLTE-MW improves peel strength compared to non-reinforced PTFE, but surface preparation before plating still matters. Sodium-naphthalene etch or plasma treatment ensures adequate adhesion for electroless copper.
• Scoring and routing: Score-and-snap panelization works because the woven glass provides a clean break line. V-scoring depth should be 30–40 % of total thickness per side.
• Solder reflow: CLTE-MW withstands standard lead-free reflow profiles (peak 260 °C for 10 s). Its low moisture absorption (0.05 %) makes delamination during reflow extremely rare, but pre-bake panels stored in humid environments for more than 48 hours as a precaution.

IPC’s IPC-6012 rigid board qualification standard applies to CLTE-MW boards the same as any rigid laminate; call out Class 3 if the end use is military or aerospace.

Cost Drivers for CLTE-MW PCBs

CLTE-MW sits at the upper end of the microwave laminate price spectrum. Several factors influence total board cost:

• Raw laminate price: Ceramic-filled PTFE with woven glass and tight Dk tolerance is inherently more expensive than commodity PTFE or hydrocarbon ceramics. Expect a significant premium over RO4350B.
• Panel utilization: Standard panel size is 12 × 18 in (305 × 457 mm). Odd board outlines waste material on a premium substrate; nesting multiple designs on a panel helps.
• Hybrid vs. all-CLTE-MW: Confining CLTE-MW to the RF layers and using FR-4 for non-critical layers can cut material cost by 30–50 % in a multilayer build.
• Volume: Rogers laminates are made to order in thinner gauges. Minimum-order-quantity (MOQ) surcharges apply to non-standard thicknesses below roughly 25 panels.
• Copper weight and finish: ENIG or hard gold adds the same per-area cost as on any substrate, but the base laminate cost makes it a smaller percentage of total.

Use the laminate cost index calculator below to get a relative cost comparison between CLTE-MW and other common microwave substrates for your panel size and layer count.

If the calculator shows CLTE-MW at, say, 3.2× the cost index of RO4350B for a four-layer hybrid stackup, consider whether the temperature stability gain justifies that premium. For a ground-station duplexer that must hold ±2 MHz over –40 to +85 °C, it almost certainly does. For a benchtop test fixture that lives in a lab, it probably does not—an alternative like Taconic TLF-35 at Dk 3.50 may suffice at a fraction of the price.

Typical Applications

Satellite Communication Filters

Ku- and Ka-band multiplexers on CLTE-MW maintain channel-center accuracy through eclipse thermal cycles without the need for active temperature compensation. The woven-glass reinforcement also provides the dimensional stability required for precision edge-coupled filter geometries.

Base-Station Power Amplifier Combiners

Wilkinson combiners and branch-line couplers in macro-cell base stations benefit from CLTE-MW’s low loss and stable impedance. A 1.9 GHz Wilkinson divider on 30 mil CLTE-MW can achieve better than 0.1 dB excess insertion loss per stage.

Phased-Array Feed Networks

Corporate feed networks distributing power to hundreds of elements need uniform phase across temperature. CLTE-MW’s TCDk keeps element-to-element phase error within ±1° over a 100 °C range at X-band, a margin that matters for sidelobe performance in radar and EW systems.

Storage and Handling

Store CLTE-MW panels flat, in sealed moisture-barrier bags with desiccant, at 15–30 °C and below 60 % RH. Although its moisture absorption is only 0.05 %, copper surface oxidation in humid storage degrades solder wetting and peel strength. Once opened, process panels within 72 hours or re-seal. Shelf life in sealed packaging is typically 12 months per IPC/JEDEC J-STD-033 moisture-sensitive handling guidelines.

FAQ

Is CLTE-MW the same as RT/duroid 6002?

No. Both are ceramic-loaded PTFE laminates from Rogers, but RT/duroid 6002 has a Dk of 2.94 without woven-glass reinforcement, resulting in lower dimensional stability and different CTE behavior. CLTE-MW includes woven glass for improved drill registration and plated-through-hole reliability.

Can I process CLTE-MW on a standard FR-4 fabrication line?

Not without modifications. PTFE substrates require carbide tooling, plasma desmear, and sodium-naphthalene surface preparation. Fabricators set up for hydrocarbon ceramics (RO4000 series) will also need to adapt their process for PTFE resin chemistry.

What bonding film works for CLTE-MW multilayer builds?

Rogers 3001 bonding film (PTFE-based, Dk 2.28) is the standard choice for CLTE-MW-to-CLTE-MW bonding. For hybrid builds with FR-4, CuClad 6700 or RO4450F prepreg can be used, though the Dk mismatch at the bond layer must be modeled in the stackup simulation.

What is the maximum operating frequency for CLTE-MW?

Rogers characterizes CLTE-MW up to 40 GHz. Practical designs have been demonstrated through Ka-band (26.5–40 GHz). Above 40 GHz, conductor loss on standard ED copper becomes the dominant loss mechanism; specifying rolled or low-profile foil extends usable performance into the V-band range.

Does CLTE-MW meet UL 94 flammability requirements?

CLTE-MW is not inherently UL 94 V-0 rated. If your end product requires a UL-listed flame rating, verify the specific construction (copper weight, thickness) with Rogers and your UL file holder. Some constructions achieve V-0 with heavier copper cladding.