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What is the dielectric constant of fr4 sheet

Update:08-01-2021
Summary:

In the fr4 sheet, I also said that this is an epoxy gla […]

In the fr4 sheet, I also said that this is an epoxy glass cloth sheet. The fr4 is insulating. What is the dielectric constant of the fr4 sheet? How to better understand the dielectric constant of the fr4 sheet? 

When it comes to FR4 materials, the usual dielectric constant is between 4.2 and 4.7. The value here is also related to the thickness and temperature of our sheet, as well as frequency and combination.

How to understand the dielectric constant of fr4 sheet

Permittivity is a criterion for the propagation of the plate as a medium in electrical signals in our experiments. Generally, the faster the electrical signal propagation speed, the lower the permittivity, because the signal transmission speed is the square root of the dielectric constant. It is inversely proportional; the dielectric constant is usually related to the properties of our sheet media, as well as the test method and frequency, and temperature and humidity are also affected.

The relationship between the dielectric constant of fr4 sheet and temperature

For fr4 sheet, the temperature will definitely affect the performance. In most cases, the higher the temperature, the greater the delay. For example, if the temperature is in the range of 0 to 70 degrees, the dielectric constant of the fr4 sheet will vary. It can reach 20%, and the change in dielectric constant will cause the line to delay 10%.

The relationship between fr4 board and frequency of use

After all, the fr4 sheet is still used for consumption. The frequency we use must be depleted, and under certain circumstances it still affects the sheet. There are also different dielectric constants depending on the material of the plate. This is the specific situation in different environments after using it in many ways.

Generally, ordinary FR-4 has a tangent loss of 0.025 at 1MHz, while pure Teflon material has a very small loss, generally: 0.0010 @ 10GHz. For the same material, the higher the frequency of use, The greater the loss. Pure Teflon material can be used in millimeter wave products, such as anti-collision radar, etc.;

The ordinary FR-4 can only be used at frequencies less than 800MHz, and its power is very small. The price of pure Teflon is relatively expensive, so currently in the mobile communication market, the dielectric constant of Teflon is between 3.0~3.5 Dragon + ceramic powder materials are widely used, such as TACONIC's RF35(A), etc. Its tangent loss is generally 0.0025 @10GHz. Regarding the dielectric constant, the stability of pure Teflon is generally +/-0.02, Teflon +DK stability of ceramic powder substrate is generally +/-0.05

These are the knowledge about the dielectric constant of fr4 sheet, and different manufacturers make this aspect according to customer needs.

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