Basic overview of thermal interface materials | Analyzes the role, types, characteristics and selection of thermal interface materials

Thermal interface material background

Heat dissipation has always been a key research work in the electronics industry, and the actual operating temperature of electronic components is one of the key factors affecting their reliability. With the development of electronic equipment towards miniaturization and high power consumption, its power consumption density gradually increases, and the heat output of electronic equipment also increases exponentially, which also puts higher requirements on the heat dissipation performance of the system; Thermal conductive interface materials were born.

Basic overview of thermal interface materials

Thermal Interface Materials, English thermal interface materials, TIM for short, also known as thermal interface materials or interface thermal materials, is a kind of widely used IC packaging and electronic heat dissipation materials, mainly used to fill the micro-gaps and surface uneven holes generated when the two materials join or contact. Reduce heat transfer contact resistance and improve device heat dissipation performance.

There is a very fine uneven gap between the surface of the microelectronics material and the radiator, and if they are directly installed together, the actual contact area between them is only 10% of the radiator base area, and the rest is the air gap. Because the air thermal conductivity is only 0.024W/(m*K), it is a poor conductor of heat, which will cause the contact thermal resistance between the electronic components and the radiator to be very large, seriously hindering the conduction of heat, and ultimately resulting in low efficiency of the radiator. The use of thermal interface materials with high thermal conductivity to fill these gaps, eliminate the air in them, and establish an effective heat conduction channel between the electronic components and the radiator can greatly reduce the contact thermal resistance, so that the role of the radiator can be fully played. Thermal interface (contact surface) materials play a very key role in thermal management and are an important branch of this discipline.

In order to meet the heat dissipation needs of electronic products, thermal interface materials are also a wide variety of thermal interface materials commonly used on the market are: Thermal conductive silicone sheet, thermal conductive mud, thermal conductive gel, thermal conductive double-sided adhesive, thermal conductive silicone grease, thermal conductive potty sealant, thermal conductive adhesive, thermal conductive graphite sheet, thermal conductive silicon tape, thermal conductive phase change material, etc., that today, NFION thermal conductive interface material manufacturers come to tell you what are the key characteristics of thermal conductive interface materials?

one. Thermal characteristic

1 Thermal impedance

The thermal resistance is equal to R=d/k, and this equation shows that the thermal resistance is inversely proportional to the thermal conductivity k and proportional to the thickness of the material. That is to say, the thermal conductivity of the material is a constant, and the thermal resistance is only related to the thickness of the material, the thicker the thickness, the greater the thermal resistance, and the smaller the vice versa.

Contact thermal resistance can be artificially controlled, according to the contact surface to choose the appropriate thermal interface material. In this way, the total thermal impedance can be controlled.

2 Thermal conductivity

Thermal conductivity is a sign to determine the thermal conductivity of thermal interface materials. The higher the thermal conductivity, the better the thermal conductivity.

Two electrical characteristics

1 Breakdown voltage

Breakdown voltage is the measurement of how much voltage the thermal conductivity material can withstand under certain conditions. This value indicates the electrical insulation ability of the thermal interface material. This value is affected in humid, high-temperature environments because the heat-conducting interface material absorbs moisture from the air.

2 Volume resistivity

Volume resistivity is a measure of the volumetric electronic resistance per unit volume of a material. Volume resistivity is the ability of a thermal interface material to direct current leakage between an energized component and a metal cooling device. As well as breakdown voltage, it is also affected by humidity and high temperature and decreases the volume resistivity.

Three elastomer properties

1 Compression deformation

Compressive deformation refers to the resultant force applied during deflection. When a compression load is applied, the elastomer material deforms, but the volume of the material remains unchanged. The compression deformation characteristics may vary depending on the geometry of the part, the deflection rate and the size of the probe.

2 Stress relaxation

When pressure is applied to the thermal interface material, after the initial deformation, a slow relaxation process will occur, followed by the removal of pressure, which will continue until the pressure load reaches equilibrium with the intrinsic strength of the material.

3 Compression deformation

Compressive deformation is the result of stress relaxation. If the thermal conductive interface materials endure the pressure load for a long time, part of the deformation will become a long-term deformation, which can not be recovered after the load is reduced.

How to select thermal interface materials?

After we understand the basic introduction of thermal interface materials, how to choose the appropriate thermal interface materials? First of all, according to the customer's application to determine the type of thermal interface materials; Secondly, according to the thermal conductivity of the product, thickness, size, density, voltage resistance, use temperature and other parameters to select the appropriate thermal interface material.

The choice of thickness is related to the gap size of the TIM position of the product that the customer needs to solve the heat dissipation and the density, hardness, compression ratio and other parameters of the TIM product itself. It is recommended to determine the specific parameters after sample testing. The selection of thermal conductivity mainly depends on the heat source power consumption of the product that needs to solve the heat dissipation, and the heat dissipation capacity of the radiator or heat dissipation structure.

The size is the best choice to cover the heat source, rather than covering the contact surface of the radiator or heat dissipation structure, and choosing a size larger than the heat source will not greatly improve or improve the heat dissipation. When selecting the best matched thermal conductivity interface material, you can first select at least two thermal conductivity interface materials, and then determine which thermal conductivity interface material is the most matching by doing thermal conductivity performance tests.