Introduction to Rogers CLTE-AT

Rogers CLTE-AT is a ceramic-filled thermoset laminate material designed specifically for applications requiring excellent dimensional stability and reliability under temperature cycling.

With a low coefficient of thermal expansion (CTE) in the X, Y, and Z directions, Rogers CLTE-AT prevents expansion or contraction of printed circuit boards (PCBs) over wide temperature ranges. This makes it an ideal choice for mission-critical electronics exposed to high temperatures or extreme thermal shock.

Some key features of Rogers CLTE-AT laminates include:

• X,Y CTE of 10 ppm/°C
• Z-axis CTE of 30 ppm/°C
• Thermal conductivity of 1.44 W/mK
• Low dielectric loss for high frequency performance
• Excellent adhesion to copper for reliable multilayers

Rogers CLTE-AT enables PCB designs that can withstand rigorous temperature environments while preventing solder joint cracking, layer delamination, and other thermomechanical failures.

Rogers CLTE-AT Material Properties

Rogers CLTE-AT possesses a unique set of properties that provide enhanced reliability and dimensional stability compared to conventional circuit laminates:

Low, Matched Coefficients of Thermal Expansion

• X,Y CTE: 10 ppm/°C
• Z-axis CTE: 30 ppm/°C
• Tight CTE match minimizes thermomechanical stress

High Thermal Conductivity

• 1.44 W/mK thermal conductivity
• Allows efficient heat spreading in the PCB

Stable Dielectric Constant

• Dielectric constant of 3.9 ± 0.05
• Stable across temperature range
• Provides consistent electrical performance

Low Loss for High Frequency Operation

• Loss tangent of 0.0020 at 10 GHz
• Supports applications above microwave frequencies

High Adhesion and Bond Strength

• 1.1 kN/m adhesion to copper foil
• Excellent for reliable multilayer circuits

Key Material Properties Summary

Property	Value
Dielectric Constant	3.9 ± 0.05
Loss Tangent	0.0020 at 10 GHz
CTE X,Y	10 ppm/°C
CTE Z	30 ppm/°C
Thermal Conductivity	1.44 W/mK
Copper Adhesion	> 1.1 kN/m

Rogers CLTE-AT Laminate Copper Cladding

Rogers CLTE-AT laminates are typically clad with electrodeposited copper foil on one or both sides. Some common foil options include:

• Standard 1⁄2, 1, 2 oz copper foils
• Low profile foils for high frequency applications
• Reverse treat foils for improved adhesion
• Double treat foils for excellent bond strength

Heavier copper weights are available for applications requiring high current capacity or thick copper heat sinking.

PCB Design with Rogers CLTE-AT

To take advantage of the unique properties of Rogers CLTE-AT material, printed circuits should be designed with the following considerations:

Account for Low CTE

• Adjust layout for differential expansion against components
• Watch pad spacing and trace geometries
• Partition board into low CTE sections if necessary

Utilize Thermal Vias

• Place thermal vias under hot components
• Connect to backside thermal pads where applicable
• Provide heat sinking to internal board layers

Control Impedances

• Use impedance calculators to achieve 50Ω, 75Ω, etc.
• Adjust trace geometry based on material Dk
• Simulate across temperature range

Ensure Adequate Reliability

• Perform thermal cycling, shock, and stress analyses
• Verify solder joint integrity, layer adhesion, and performance

Proper modeling and simulation helps assess the thermal mechanical response and electrical performance of Rogers CLTE-AT designs.

PCB Fabrication with Rogers CLTE-AT

Standard PCB processing techniques are compatible with Rogers CLTE-AT laminates:

Imaging and Etching

• Compatible with liquid photoresists and methods
• Can be etched in ammoniacal or cupric chloride chemistries

Hole Drilling

• Use mechanical drilling or laser ablation
• Plasma provides excellent results for small vias

Plating and Outerlayer Imaging

• Electroless copper or direct metallization plating
• Requires sufficient capture pad geometries

Soldermask

• Liquid photoimageable (LPI) soldermask recommended

Final Finishes

• Immersion silver, immersion tin, ENIG, HASL, and others

Rogers provides additional guidelines on chemical solutions, process temperatures, and handling requirements.

Rogers CLTE-AT Material Availability

Rogers CLTE-AT laminates are available under the RO4350bTM product designation in a variety of dielectric thicknesses and panel sizes:

Material	Description
RO4350b(5)	0.005” (0.125mm) dielectric
RO4350b(10)	0.010” (0.250mm) dielectric
RO4350b(20)	0.020” (0.500mm) dielectric
RO4350b(30)	0.030” (0.750mm) dielectric
RO4350b(40)	0.040” (1.00mm) dielectric
RO4350b(50)	0.050” (1.25mm) dielectric

• Sheet sizes up to 18” x 24”
• Cut to customer requirements
• Prepregs available for multilayer circuits

Quick-turn fabrication in as little as 5 days helps accelerate prototyping and development.

Rogers CLTE-AT Laminate Applications

The excellent thermal mechanical stability and reliability of Rogers CLTE-AT make it well suited for:

Aerospace and Defense

• Missile guidance systems
• Radars and electronic warfare boards
• Ruggedized electronics enclosures

Downhole Oil and Gas

• Downhole logging tools
• Wellhead instrumentation

Automotive Electronics

• Engine control units and powertrain circuits
• ADAS sensor PCBs
• Infotainment modules

Industrial Equipment

• Process control boards
• Power conversion systems
• Medical and test equipment

High Reliability Commercial

• Railway electronics
• 5G telecom equipment
• Networking hardware

Considerations for Using Rogers CLTE-AT

While Rogers CLTE-AT provides unmatched thermal mechanical stability, there are some considerations when selecting it:

• Higher material cost compared to FR-4
• More difficult hand soldering if Tg exceeds 250°C
• Lead times may be longer than standard materials
• Requires tight process controls to achieve consistency

For applications requiring maximum reliability under extreme conditions, Rogers CLTE-AT remains an optimal choice to prevent field failures.

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Frequently Asked Questions

What is the Z-axis CTE of Rogers CLTE-AT material?

The Z-axis coefficient of thermal expansion (CTE) for Rogers CLTE-AT laminates is 30 ppm/°C. This is well matched to the 10 ppm/°C CTE in the X and Y directions.

What is the dielectric constant stability of CLTE-AT over temperature?

The dielectric constant of Rogers CLTE-AT material varies less than ±0.05 over a wide temperature range from -55°C to 125°C. This exceptional stability facilitates consistent electrical performance over extreme temperature swings.

Can Rogers CLTE-AT laminates be used for multilayer boards?

Yes, Rogers CLTE-AT laminates are very well suited for multilayer board designs thanks to the excellent adhesion to copper and matched CTE in all directions. This prevents delamination between layers and internal separation during thermal excursions.

What chemical etchants work best with Rogers CLTE-AT laminates?

Ammoniacal etchants are typically used to fabricate Rogers CLTE-AT PCBs, providing good copper etching with minimal undercutting. Cupric chloride can also be used but may require additional process controls.

Is Rogers CLTE-AT compatible with lead-free soldering?

Yes, Rogers CLTE-AT laminates are fully compatible with lead-free soldering processes, including reflow and wave soldering. The high maximum Tg of 280°C allows exposure to lead-free soldering temperatures with ample margin.