Rogers PCB material dielectric constant

Rogers PCB material dielectric constant

I believe that the most important indicator for most engineers when choosing a sheet of ROGERS high-frequency sheet is the dielectric constant. However, some engineers have a relatively one-sided understanding of the dielectric constant. When selecting rogers high-frequency plates, some problems will be encountered. Through this article, you can better help engineers quickly and accurately select the plate with the appropriate dielectric constant.

definition

When the applied electric field is applied to the medium, the induced electric charge is generated to weaken the electric field. The ratio of the electric field in the medium to the original applied electric field (in vacuum) is the relative permittivity (differential permittivity or dielectric constant), also known as the induced electric rate, which is related to the frequency. . The dielectric constant is the product of the relative dielectric constant and the absolute dielectric constant in vacuum. If a material with a high dielectric constant is placed in an electric field, the strength of the electric field will drop appreciably within the dielectric. The relative dielectric constant of an ideal conductor is infinite.

classification

The polarity of the polymer material can be discriminated based on the dielectric constant of the substance. Generally, a substance having a relative dielectric constant of more than 3.6 is a polar substance; a substance having a relative dielectric constant of 2.8 to 3.6 is a weakly polar substance; and a relative dielectric constant of less than 2.8 is a nonpolar substance.

Manufacturing and design

The manufactured value was tested by Rogers sheet using IPC-TM-650 2.5.5.5 at ~10 GHz, 23 °C. The test was based on a dielectric sheet substrate (no copper foil). The dielectric constant values and tolerances obtained by the IPC-TM-650 method 2.5.5.5 are benchmarks for quality acceptance, but for some products, these values are not necessarily accurate for design or engineering applications, especially for microstrip designs. We recommend that the newly designed proofing prototype board be verified for electrical performance.

The design value is by testing a thick microstrip transmission line circuit, and the Z-axis dielectric constant of the resulting copper foil material is the design DK.

Characteristics

The dielectric constant is related to the frequency, and the thickness of the same sheet sometimes varies. The range of rogers plates is 1.96 (RT/duriod 5880LZ)-13 (TMM13i).

Influencing factor

• Temperature: The inherent property of the material. When the temperature changes, the dielectric constant changes with temperature. The measure is the thermal change rate of εr. Among the Rogers sheets, the CHz series and the TMM series have the lowest εr thermal change rate.

Water absorption rate: Since the dielectric constant of water is about 78, the dielectric sheet will change the dielectric properties of the dielectric sheet after it has absorbed water. Rogers sheet has the lowest water absorption

The RT/duriod 6010LM is 0.01%.

• Copper foil surface roughness: Due to the skin effect, the greater the surface roughness of the copper foil, the lower the transmission rate of electromagnetic waves in the medium, increasing the actual dielectric constant. The lowest roughness of the copper foil is the rolled copper.

Selection considerations

• Impedance: A must-have parameter for designing impedances of 50 ohms, 100 ohms, or other matching impedance.

• Plate size: When designing the antenna, the lower the electromagnetic wave frequency, the larger the wavelength, the larger the corresponding plate size. If a high dielectric constant dielectric plate is used, the plate size can be greatly reduced.

• Transmission speed and delay: The dielectric constant determines the speed at which an electrical signal propagates through the medium. The rate at which electrical signals propagate is inversely proportional to the square root of the dielectric constant. The lower the dielectric constant, the faster the signal transmission speed and the smaller the delay.

• Impedance line width: Design a transmission line with a specific impedance. The lower the dielectric constant, the wider the line width of the transmission line, and the better the circuit performance under the constraints of the minimum processing line width and processing tolerance, if other factors are determined.

There are still many aspects to the influence of dielectric constant on performance. In actual design, it is necessary to consider all aspects and select the most suitable sheet.