What is a thermal interface material? What are the properties of TIM?

What is a thermal interface material?

Thermal interface material is a material commonly used in IC packaging and electronic heat dissipation. It is mainly used to fill the micro-voids and uneven holes on the surface when the two materials are joined or contacted, reducing the resistance of heat transfer and improving heat dissipation.

Usually, the heat dissipation of various high-end electronic components generally adopts the method of adding a heat sink, but experiments show that although the contact between the heat source and the fins seems to be in horizontal contact, in fact, the surface of the heat source and the contact surface of the heat sink are approximately 80% is air, and air is a poor conductor of heat. When there is no high-quality interface material filled between the heat source and the heat sink, the efficiency of the heat sink is less than 30%.

Therefore, the material used for filling between the heat source and the heat sink acts to remove the air between the heat source and the heat sink, and such materials are called “thermal interface materials”.

What are the properties of thermal interface materials?

Thermal characteristics

1). Thermal impedance

Thermal impedance (Thermal Impedance) represents the thermal resistance per unit area of the material, and its unit is °C·cm2/W or °C·in2/W. Compared with thermal resistance, the calculation of thermal resistance takes more area into consideration. The thermal resistance is for a single material, and the thermal resistance of the interface material will also depend on the actual assembly conditions.

2). Thermal conductivity

Thermal conductivity is an indicator that determines the thermal conductivity of thermally conductive materials. The larger the thermal conductivity, the better the thermal conductivity.

Electrical Characteristics

1). Breakdown voltage

Breakdown voltage is a measure of how much voltage a thermally conductive material can withstand under specific conditions. This value indicates the electrical insulating ability of the thermally conductive material. This value is affected in humid, high temperature environments because the thermally conductive material absorbs moisture from the air.

2). Volume resistivity

Volume resistivity is a measure of the volumetric electron resistance per unit volume of material. Volume resistivity is the ability of a thermal material to direct current leakage between energized components and metal heat sink components. Like the breakdown voltage, it is also affected by humidity and high temperature and also reduces the volume resistivity.

Elastomer properties

1). Compression deformation

Compression deformation refers to the resultant force exerted upon deflection. When a compressive load is applied, the elastomeric material deforms, but the volume of the material remains the same. Compression deformation properties may vary depending on part geometry, deflection rate and probe size, etc.

2). Stress relaxation

When pressure is applied to the thermally conductive interface material, after the initial deformation, a slow relaxation process occurs, followed by removal of the pressure, which continues until the pressure load and the intrinsic strength of the material reach equilibrium.

3). Compression deformation

Compression deformation is the result of stress relaxation. If the material endures the compressive load for too long, part of the deformation will become permanent deformation, which cannot be recovered after the load is relieved.

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