Dielectric constant of thermal conductive pad
[ Date: 2020-12-25 08:57:54 Author: Popularity: ]
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1、What is dielectric constant?

If a piece of dielectric is placed in a parallel electric field, it can be found that a charge is induced on the surface of the medium, that is, the negative charge is induced by the dielectric near the positive plate, and the positive charge is induced on the dielectric surface near the negative plate. The phenomenon that the dielectric produces induced charge under the action of electric field is called dielectric polarization. Under the action of electric field, the material that produces polarization is called dielectric.

The ratio of the decrease of electric field in the medium to the original applied electric field (in vacuum) is the relative permittivity (the relative permittivity of vacuum is 1). For simplicity, the relative permittivity is also called dielectric constant.

                                                                                                     Polarization diagram of dielectric


The physical meaning of dielectric constant can be understood as the ability of dielectric to store charge in the process of polarization. Represents the amount of electrostatic energy accumulated per unit volume in a unit electric field. The dielectric constant of polymer materials is mainly determined by the bond properties and arrangement in the main chain structure.


Dielectric loss refers to the phenomenon of energy loss of dielectric in alternating electric field with internal heating (temperature rise). The reason is that there are carriers in the dielectric which can conduct electricity. Under the action of external electric field, conductive current is generated, which consumes part of electric energy and turns into heat energy. The lower the dielectric loss, the better is. The tangent of loss angle represents the energy consumed to obtain a given storage charge, which is an important evaluation parameter when dielectric is used as insulating material. In order to reduce the dielectric loss, it is expected that the material has smaller dielectric constant and smaller loss tangent.


2 Test method of dielectric constant

We test the dielectric constant according to the American Standard ASTM D150 Standard Test Method of AC loss characteristics and Permittivity (dielectric constant) of solid electrical insulation materials.


3 Influence factors of dielectric constant


The main factors affecting the dielectric constant are: test frequency, test voltage, temperature, humidity, etc. Among them, the dielectric constant measured at different frequencies often has obvious difference. After measuring the dielectric constant and loss index of the pad at several frequencies, we found that the dielectric constant of the pad at high frequency is more stable and has better repeatability.


4 Effect of dielectric constant on properties of thermal conductive pad


Insulating materials are usually used in two different ways, namely:

 (1) It is used to fix the electrical network components and insulate them from each other and ground at the same time;

(2) When it is used to act as the dielectric of a capacitor, a higher value of dielectric constant is required.


Thermal conductive pads are usually used in insulating materials by the first of the above methods, usually requiring fixed capacitance as small as possible and having acceptable and consistent mechanical, chemical and heat resistance properties. Therefore, a low dielectric constant is required.