How to choose a good thermal conductivity material?

              


When the electronic equipment is working, the components will generate a certain amount of heat, which causes the internal temperature of the equipment to rise rapidly.

If the heat is not dissipated in time, the temperature of the equipment will continue to rise, and the components will also fail due to overheating, which will cause the reliability of the electronic equipment to decrease or damage.


       



The heat dissipation method can be simply divided into active heat dissipation and passive heat dissipation (conduction, convection and radiation).

Thermal design engineers will select appropriate heat dissipation methods and thermal conductivity materials according to the heating conditions.

When choosing a heat transfer medium, not only must consider its heat transfer capacity, but also take into account factors such as production process, convenience in use, maintainability and cost-effectiveness.




Currently commonly used thermal interface materials are:



Thermal Pad, Electrically Insulating Thermal Sheet, Thermal Conductive Gap Filler, Thermal Grease, Thermally Conductive Potting Encapsulant.

The following is a brief description of the characteristics of these types of thermal conductivity materials and the indicators that need to be paid attention to when choosing:

Thermal Pad




       

 A thermal interface material with high softness, high compliance and high compression ratio. It can fill the gap between the heating element and the radiator (shell), improve the heat transfer efficiency, and at the same time have the functions of insulation and shock absorption.


When choosing, you should choose a thermal pad with moderate thickness, thermal conductivity, working temperature range, pressure resistance and other parameters according to the actual situation.


At the same time, we need to pay attention to parameters such as hardness, volume resistivity, dielectric constant, and tensile strength:

Hardness

The lower the hardness, the larger the effective contact area of the thermally conductive silicone sheet and the better the thermal conductivity, and vice versa.

Tensile Strength

High tensile strength, strong resistance to shock and vibration loads.



Thermal Grease




Commonly known as thermal grease and thermal grease, it is a paste-like thermal interface material processed by a specific process with silicone oil as base oil, metal oxide as filler, and various functional additives. It has excellent properties such as high thermal conductivity, low thermal resistance, wide operating temperature range, low volatility, low oil separation, and strong weather resistance.

When choosing, we mainly focus on the following indicators:


Oil separation, thermal conductivity and thermal resistance, viscosity, temperature range, dielectric constant


Oil separation

Refers to the amount of silicone oil precipitated after the product is kept at 200°C for 24 hours. It is an index for evaluating the heat resistance and stability of the product. Good quality thermal conductive silicone grease has very low oil separation, tending to zero.

Thermal conductivity and Thermal resistance

Generally speaking, the thermal conductivity silicone grease with the larger thermal conductivity coefficient is coated with the same thickness of thermal grease, the smaller the thermal resistance, the better the thermal conductivity.

Viscosity

A performance index used to characterize the fluidity and viscosity of thermal grease, which is relatively affected by temperature. In general, the higher the thermal conductivity, the higher the viscosity.

Temperature range

Between -40~200℃, it can meet the working temperature range of electronic components.

Dielectric constant

The dielectric constant is used to measure the performance of an insulator to store electrical energy. It refers to the ratio of the capacitance when the insulating material between two metal plates is a medium to the capacitance between the same two plates when air is the medium or vacuum.


In addition, it is also necessary to consider the volume resistivity coefficient (an indicator of insulation performance), whether it has passed the RoHS environmental certification, and the packaging method (barreled, canned or syringe).


Electrically Insulating Thermal Sheet


                         

Electrically Insulating Thermal Sheet have the characteristics of heat conduction, insulation, high pressure resistance, excellent resistance to mechanical stress and good electrical isolation reliability.


When selecting thermally conductive insulating materials, the parameters that need to be paid attention to are:

Working temperature, thickness, tensile strength, thermal resistance, breakdown voltage.


Thermally Conductive Potting Encapsulant

                  

Thermally Conductive Potting Encapsulant is composed of two components (components A and B). After being mixed and cured at a weight of 1:1, it has dustproof, waterproof and shockproof, flame retardant, sealing, bonding, thermal conductivity and excellent filling Sewing effect.

The parameter indicators that need to be paid attention to when choosing are:


Thermal characteristics

Thermal conductivity: the higher the thermal conductivity, the better the heat conduction and heat dissipation effect

Electrical performance

Breakdown voltage, volume resistivity and dielectric constant, etc., among which the more concerned is the breakdown voltage and volume resistivity.

Physical properties

Fluidity and density: With high popularity, it can be used to fill gaps with smaller pores and increase the volume of thermal and heat dissipation contact surfaces; the same thermal conductivity, the lower the density, which can effectively improve the efficiency of heat dissipation performance when used in automotive power supply industries.



Thermal Conductive Gap Filler


One-part or two-part silicone thermal conductivity products mainly meet the requirements of low stress and high compression modulus when the product is in use.

It shows low contact thermal resistance and good electrical insulation properties. After curing, it is equivalent to a thermal pad, has high temperature resistance and aging resistance, and can work for a long time at -40~200°C. When choosing a thermal gel, it is important to pay attention to its thermal conductivity, anti-cracking, and thermal resistance.


The above are important aspects to judge the quality and performance of thermal conductive materials.

In general, the higher the thermal conductivity of thermally conductive materials, the better the thermal conductivity and the higher the price.

In the process of purchasing various types of thermal conductive materials, factors such as thermal conductivity, price, and usage should be considered.