Choosing the Right RF PCB Material

When designing RF PCBS applications, the choice of PCB substrate materials is a key performance factor.

For complex microwave structures that are mechanically reliable and electrically stable, an optimal combination of electrical and mechanical properties is required.

The extremely low dielectric constant thermal coefficient provides the electrical stability sought by designers of filters, oscillators, and delay line applications.

Taconic, ISOLA and Rogers all produce PCB laminates designed for high-performance, high-speed /RF/ microwave applications.

Comparison of RF PCB materials

Factors to consider when choosing RF PCB materials

Low Z-axis coefficient of thermal expansion (CTE) is necessary for excellent reliability of electroplated through-holes.

To achieve a narrow range of position tolerances, the X and Y coefficients of the PCB substrate must be expanded to match the copper.

Improving surface mount reliability by reducing stress at solder joints and allowing PCB laminates to expand to a minimum amount of low CTE is an advantage of low tensile modulus materials.

1. Thermal performance

2. Low dissipation factor (Df)

3. Stable Df characteristics

4. Low Z-axis coefficient of thermal expansion (CTE)

5. Migration mitigation characteristic

6. Improved rise time features

7. Jitter reduction

8. Reduce conductor loss

One of the key properties of high frequency laminates is the stability of dissipation factor (Df), as this will tell you how signal losses occur and how they are distributed across the operating frequency band.

In addition, a stable dielectric constant (Dk) and therefore a stable impedance across the length and width of the substrate are also important.

The Dk of hf laminates varies little with temperature over a wide temperature range.

In RF or microwave circuits, the value of permittivity affects the wiring size of the PCB and thus the size of the PCB. High Dk PCB materials can lead to smaller PCBS.

The following table shows the main electrical and mechanical properties of Taconic, ISOLA, and Rogers for comparison purposes.