Rogers CLTE-AT PCB | Dk 3.00 Low Loss Fabrication

What Is Rogers CLTE-AT?

Rogers CLTE-AT is a ceramic-filled, woven-glass-reinforced PTFE composite laminate with a nominal dielectric constant (Dk) of 3.00 ± 0.04 at 10 GHz and a dissipation factor (Df) of 0.0013 at the same frequency. Its defining feature is a coefficient of thermal expansion (CTE) that is closely matched in the X, Y and Z axes—roughly 10–12 ppm/°C in-plane and 16 ppm/°C through-thickness—making it far more dimensionally stable than conventional PTFE laminates during thermal cycling. That Z-axis CTE, less than half the value of many unfilled PTFE materials, dramatically reduces via barrel stress in multilayer microwave PCBs.

The material targets applications from 1 GHz through Ku-band and beyond: radar front ends, phased-array antenna feed networks, satellite communication modules, and any design where plated-through-hole reliability matters as much as RF performance. It is available in standard thicknesses from 5 mil (0.127 mm) to 60 mil (1.524 mm) and can be clad with electrodeposited (ED) or rolled copper in ½ oz to 2 oz weights.

Key Electrical and Thermal Properties

A Df of 0.0013 places CLTE-AT among the lowest-loss reinforced PTFE laminates, comparable to unreinforced PTFE substrates while offering much better dimensional stability for drilling, plating and multilayer registration. Moisture absorption of only 0.02 % keeps Dk stable in humid environments—an advantage over many thermoset-resin low-loss alternatives.

Why the Matched CTE Matters for Multilayer RF Boards

Standard PTFE laminates often exhibit Z-axis CTE values of 50–250 ppm/°C. During lead-free reflow (peak ~260 °C), that expansion can stress plated-through-hole barrels beyond their fatigue limit, especially in boards thicker than 60 mil. CLTE-AT’s 16 ppm/°C Z-axis CTE is close to the 14–17 ppm/°C range of copper, which means the barrel and surrounding dielectric expand almost in unison. The result is significantly higher interconnect reliability across thermal cycles—often exceeding 500 cycles at –55 °C to +125 °C in qualification testing per IPC-6012 Class 3 requirements.

The in-plane CTE of 10–12 ppm/°C also matches standard FR-4 prepregs reasonably well, simplifying hybrid stackups where CLTE-AT core layers are bonded with low-loss thermoset prepregs or Rogers CuClad bondply. For designs needing an even lower Dk with similar CTE behavior, the closely related CLTE-XT variant offers Dk 2.94 with comparable Z-axis expansion control.

Dk Drift Across Temperature and Frequency

CLTE-AT’s ceramic-PTFE formulation yields a temperature coefficient of Dk (TCDk) that is among the flattest in the PTFE family—typically within ±50 ppm/°C from –40 °C to +125 °C. Over frequency, Dk stays within ±0.02 of the nominal 3.00 from 2 GHz through 20 GHz. Beyond 20 GHz, a slight downward trend is common but remains well within the ±0.04 tolerance window up to 40 GHz.

Use the estimator below to model how Dk shifts with temperature for a given operating range. Enter the nominal Dk (3.00), the TCDk (±50 ppm/°C), and your expected temperature excursion to see the effective Dk at your hot and cold extremes.

For example, a system operating from –40 °C to +85 °C (a 125 °C swing) sees Dk shift by roughly ±0.019—small enough that a 50 Ω microstrip designed at room temperature stays within ±0.5 Ω across the full range. If your link budget cannot tolerate even that variation, consider narrowing the operating band or adding a tuning element rather than switching materials, because few laminates beat CLTE-AT on TCDk stability.

Copper Roughness and Its Effect on Insertion Loss

CLTE-AT’s bulk Df of 0.0013 sets the dielectric loss floor, but at frequencies above 5 GHz copper roughness increasingly dominates total insertion loss. Standard 1 oz ED copper has an Rz (peak-to-valley roughness) around 5–8 µm. At 10 GHz a microstrip on CLTE-AT with standard ED copper may show 0.15–0.20 dB/in of additional conductor loss beyond the smooth-copper baseline. Switching to HVLP (hyper-very-low-profile) copper foil with Rz ≤ 2 µm can recover 30–40 % of that penalty.

Enter your copper roughness, frequency and trace geometry below to estimate the roughness-related loss contribution on a CLTE-AT line.

If the calculator shows roughness loss exceeding 0.10 dB/in at your operating frequency, specifying HVLP or RTF (reverse-treated foil) copper is strongly recommended. Keep in mind that smoother foils reduce peel strength—typically to 4–5 lb/in versus 6+ lb/in for standard ED—so confirm the adhesion meets your reliability class. Rogers offers CLTE-AT with optional alternative foil treatments; specify the foil grade at the time of laminate order, not as an afterthought.

Fabrication Guidelines for CLTE-AT PCBs

Drilling

The ceramic filler in CLTE-AT is abrasive. Use carbide drill bits with a fresh re-grind cycle no longer than 250 hits for holes ≤ 0.3 mm. Entry and backer materials should be aluminum entry (0.15 mm) over a standard phenolic backer. Stack height should be limited to two panels for holes under 0.5 mm diameter. Drill speeds of 60,000–80,000 RPM with controlled chip loads of 0.025–0.050 mm/rev produce clean hole walls with minimal smear.

Plasma Desmear and Plating

PTFE is inherently non-wettable, so a sodium etch (sodium naphthalene or plasma treatment with CF₄/O₂ gas mix) is mandatory before electroless copper deposition. Plasma desmear at 200–400 W for 5–10 minutes using a CF₄/O₂ ratio of 1:4 provides consistent surface activation. Inadequate desmear is the single most common cause of barrel-wall delamination in PTFE multilayers. After activation, electroless copper should be deposited within 30 minutes to prevent re-passivation of the PTFE surface.

Lamination

CLTE-AT cores can be laminated with Rogers CuClad 6700 bondply (PTFE-based, Dk 2.35) or RO4450F thermoset prepreg (Dk 3.52) depending on the target impedance and loss budget. Lamination pressure of 200–400 psi at 370–385 °C for 15–20 minutes is typical for PTFE bondply. Ramp rates should stay below 5 °C/min to avoid delamination from trapped volatiles. For hybrid stackups combining CLTE-AT with thermoset laminates like I-Tera MT40, CTE mismatch analysis is essential—CLTE-AT’s low CTE makes it more compatible than most PTFE options, but the bonding interface still requires careful thermal profiling.

Routing and Scoring

Standard carbide router bits work well. Avoid V-scoring on panels thinner than 30 mil (0.76 mm) to prevent micro-cracking along the ceramic-filled matrix. For thicker panels, V-score depth should not exceed one-third of total board thickness on each side.

CLTE-AT vs. Competing Laminates

Choose CLTE-AT when you need Dk 3.00, ultra-low loss and multilayer PTH reliability across wide temperature ranges—radar, satellite and mil-aero applications are the sweet spot. Choose RO3003G2 when Z-axis CTE of 24 ppm/°C is acceptable and you want the same Dk/Df in a non-woven format for tighter Dk tolerance. Choose Taconic TLY-5 for single- or double-sided boards where the lowest possible Dk and loss matter more than multilayer reliability. Choose Megtron 6 for high-speed digital/RF hybrids where standard FR-4-compatible processing is a priority and Df around 0.004 is acceptable.

Stackup Design Tips

A common four-layer CLTE-AT stackup for a Ku-band feed network uses two 10 mil CLTE-AT cores separated by a 4 mil CuClad 6700 bondply, with 1 oz HVLP copper on all signal layers. This yields a symmetric structure with a total thickness near 40 mil (1.0 mm) and impedance easily targeted at 50 Ω with a microstrip width around 24 mil (0.61 mm) on the outer layers.

For thicker boards—eight or more layers for phased-array beamforming networks—alternating CLTE-AT cores with RO4450F prepreg creates a hybrid that balances RF performance on the CLTE-AT signal layers with the mechanical robustness and lower cost of the thermoset bonding layers. Ensure that impedance calculations use the actual Dk of each dielectric layer, not an average, because the bondply Dk (2.35 or 3.52 depending on type) differs significantly from the core’s 3.00.

Typical Applications

• Airborne and shipboard radar: X-band and Ku-band TR modules requiring –55 °C to +125 °C cycling with high PTH reliability.
• Satellite communication: feed networks and diplexers at C-band through Ka-band where phase stability over temperature is critical.
• Phased-array antennas: multilayer beamforming boards with hundreds of vias that must survive thousands of thermal cycles.
• Test and measurement: calibration substrates and reference boards where Dk tolerance and long-term stability affect measurement uncertainty.

Frequently Asked Questions

Can CLTE-AT be used above 40 GHz?

Yes, but with caveats. The woven-glass reinforcement introduces a periodic Dk variation (fiber weave effect) that can produce impedance ripple on narrow traces at millimeter-wave frequencies. For designs above 40 GHz, consider non-woven alternatives or use trace routing at angles that mitigate weave-aligned coupling. Consult the Rogers CLTE-AT product page for the latest high-frequency characterization data.

Is CLTE-AT compatible with lead-free assembly?

Yes. With a decomposition temperature (Td) of 500 °C and a Z-axis CTE of only 16 ppm/°C, CLTE-AT handles lead-free reflow profiles (peak 260 °C) with a wide safety margin. Standard IPC J-STD-001 Class 3 soldering processes apply without modification.

What bondply works best with CLTE-AT?

Rogers CuClad 6700 bondply (PTFE-based, Dk 2.35) is the most RF-transparent option. RO4450F (Dk 3.52) is easier to process and works well when the bondply layer is thin relative to the core. The choice depends on your impedance targets and loss budget for the bonding layers.

How does CLTE-AT compare to CLTE-XT?

CLTE-XT offers a slightly lower Dk of 2.94 and a comparable Z-axis CTE. CLTE-AT’s Dk of 3.00 is sometimes preferred for designs migrating from RO3003 because the impedance geometry is nearly identical, simplifying layout reuse.

What is the lead time for CLTE-AT laminates?

Lead times vary by thickness, copper weight and order volume. Standard configurations (10–20 mil cores, 1 oz ED copper) are typically stocked or available within 4–6 weeks from Rogers distributors. Non-standard builds or HVLP foil options may extend to 8–12 weeks.