Why Choose Rogers CuClad 217 for High-Frequency PCBs? 

A Look at Dk, Df, and Isotropy

Selecting the right laminate is a primary decision in high-frequency PCB development. Standard materials like FR-4 are not suitable when signal integrity is required above 500 MHz. For radar systems, aerospace communications, or microwave components, the substrate material directly affects circuit performance.

Rogers CuClad 217 is a material used in these applications. This article explains its key properties: Dielectric Constant (Dk), Dissipation Factor (Df), and mechanical isotropy.

1. Dielectric Constant (Dk)

The dielectric constant measures how a material affects the electric field between conductors. It determines signal velocity and transmission line dimensions.

Signal Speed

• Signal propagation speed is inversely proportional to the square root of Dk. A lower Dk allows faster signal transmission. CuClad 217 PCB has a Dk of 2.17. FR-4 typically has a Dk of approximately 4.5.

Trace Geometry

• For a given target impedance, such as 50 ohms, a lower Dk results in wider trace widths. Wider traces are easier to manufacture consistently and contribute to lower insertion loss. On a 0.508 mm (20 mil) core with CuClad 217, achieving 50 ohms results in a practical, manufacturable trace width.

Dk Stability

• CuClad 217 offers a Dk tolerance of±0.02. This means the electrical performance remains consistent across multiple boards and production runs.

2. Dissipation Factor (Df)

Dissipation factor, or loss tangent, quantifies energy loss as heat when a signal passes through the dielectric.

Signal Loss

A higher Df material absorbs RF energy and converts it to heat. This results in:

• -Weaker signal at the receiver
• -Increased thermal noise

CuClad 217 has a Df of 0.0009 at 10 GHz. This is a low value within PTFE-based laminates.

Practical Effect

For a low noise amplifier (LNA), a low Df means the input signal reaches the amplifier with minimal degradation. For a filter, it results in sharper band-pass characteristics and lower in-band loss.

3. In-Plane Isotropy

Isotropy refers to uniform properties in all directions. This is relevant for phase-sensitive circuits.

The Issue with Standard Materials

Standard woven fiberglass laminates have warp and fill directions. Glass fibers run predominantly in these orientations. When a trace runs parallel to the warp versus the fill, the effective Dk can vary slightly. This can affect phase response.

Cross-Plied Construction

CuClad 217 substrate uses cross-plied construction. Coated fiberglass plies are placed at alternating 90-degree orientations. This creates a structure that is mechanically and electrically uniform in the X-Y plane.

Result

Whether a microstrip line runs horizontally, vertically, or diagonally on the board, the dielectric constant it experiences is consistent. This helps prevent phase skew in distributed circuits such as couplers or patch antenna arrays.

Comparison with Other Materials

Typical Applications

These properties make CuClad 217 high frequency PCB suitable for specific applications:

• Electronic Warfare Systems: Systems require consistent performance across wide bandwidths. Low loss helps maintain signal strength. Uniform phase response supports direction-finding accuracy.
• Phased Array Radars: Beam-forming requires consistent phase response across all antenna elements. Material isotropy helps achieve this. 
• Satellite Communications: CuClad 217 has low outgassing (TML 0.01%), which meets requirements for vacuum environments.

Fabrication Considerations

PTFE materials require specific handling during PCB fabrication. A typical 2-layer CuClad 217 board includes:

Layer Count: 2 layers

Core Thickness: 0.508 mm (20 mil)

Copper Weight: 1 oz finished

Surface Finish: Immersion gold (ENIG) to protect copper and provide a flat surface for component assembly

Minimum Hole Size: 0.2 mm

Minimum Trace/Space: 4/5 mils

Quality Standard: IPC-Class 2

Testing: 100% electrical test prior to shipment

Summary

Rogers CuClad 217 PCB offers:

• A Dk of 2.17 with±0.02 tolerance for consistent impedance
• A Df of 0.0009 at 10 GHz for low signal loss
• Cross-plied construction for uniform electrical properties in the X-Y plane

These specifications make it a practical choice for radar, countermeasure, and satellite communication systems where material performance directly affects circuit function.