Thermal interface material is a new type of industrial material designed in recent years to meet the thermal conductivity requirements of equipment. Through thermal interface material, the heat on the heating components is dissipated faster, ensuring the safe and stable operation of the components.

Thermal interface materials provide powerful assistance for the high integration and ultra small and ultra-thin design of equipment, and are increasingly being applied to many products, improving their reliability.

Thermal interface materials can be divided into organic silicon and non silicon types according to their materials

1. Organic silicon thermal conductive interface material

At present, the mainstream products in the market are organic silicon thermal conductive materials. Because organic silicon is easier to add fillers, most of them use organic silicon as a dispersant, and then add thermal conductive fillers such as alumina and boron nitride to improve the thermal conductivity of the product.

However, silicon-based thermal conductive products can precipitate low molecular weight siloxanes, causing circuit short circuits and affecting conductivity. Therefore, silicon-based thermal conductive products are generally not used in precision components such as semiconductors.

2. Non silicon thermal conductive interface material

This type of material generally uses polyurethane, epoxy resin and other materials as dispersion media, which effectively avoids the problem of low molecular weight siloxane precipitation in silicone products. However, the hardness and viscosity of these materials themselves are much higher, which limits the amount of thermal conductive fillers added. Therefore, non silicone thermal conductive products cannot achieve high thermal conductivity.

Thermal conductive products can be divided into thermal conductive adhesive, thermal conductive gasket, thermal conductive grease, and thermal conductive phase change material according to their form

1. Thermal conductive adhesive

Thermal conductive adhesive is divided into three categories: thermal conductive sealant, thermal conductive adhesive, and thermal conductive potting adhesive.

1.1 Thermally Conductive Adhesive

The thermal conductivity of thermal conductive adhesive is generally not too high, around 0.6~2.0W/mK. Because the addition of thermal conductive filler will affect the adhesive performance of the glue, in order to ensure a higher bonding strength, the amount of thermal conductive filler can only be reduced at the expense of some thermal conductivity. A very small number of thermal conductive adhesive products can also achieve a temperature of over 2W/mK.

1.2 Thermal conductive sealing adhesive

Thermal conductive potting compound is widely used in fields such as electronics and automobiles, with a huge amount of usage. The most common thermal conductive sealant is composed of two components (component A and component B), divided into three categories: organic silicon system, polyurethane system, and epoxy resin system. The thermal conductivity of ordinary thermal conductive sealant ranges from 0.6-2.0W/mK, while products with high thermal conductivity can reach 4.0W/mK or higher.

1.3 Thermal conductive sealant

Heat conduction sealant, also known as heat conduction gel, is a mainstream heat conduction product on the market.

Most of the thermal conductive sealant is made of silicon gel, which has the low stress characteristics of silicon gel, and can reduce the stress caused by temperature and external pressure. At the same time, the soft hardness can also resist a certain degree of vibration and impact.

The emergence of thermal conductive grout is mainly to replace thermal conductive gaskets, improve thermal conductivity efficiency, and achieve automated production. The thermal conductivity of thermal sealant is generally above 2.0W/mK, and some high thermal conductivity products can even achieve 7.0W/mK or above.

Thermal conductive sealant is divided into two types: cured and uncured.

• Curing type thermal conductive sealant is essentially a liquid thermal conductive gasket. After the glue is applied by the machine, the components are assembled before curing, and the heating element is pressed into the thermal sealant to tightly bond the components, thermal sealant, and housing. In this way, the heat generated by the components can be conducted to the housing through the thermal conductive sealant, achieving the purpose of heat dissipation. Compared to solid gaskets, thermal conductive grout not only conducts heat but also has a certain degree of adhesion, fully wetting and contacting the substrate to achieve higher thermal conductivity efficiency. And thermal conductive sealant is more flexible, has a wider range of applications, and can meet the needs of automated production.

• Non curing thermal sealant is similar to thermal grease, but the difference is that thermal sealant has a longer service life and higher reliability, while thermal grease has a short service life and is generally only used in applications with low reliability requirements.

2. Thermal pad

Thermal pad is used to fill the air gap between the heating element and the heat sink or metal base. Heat is conducted from the heating element or the entire PCB to the metal shell or diffusion board, thereby improving the efficiency and service life of the heating electronic component.

Thermal pads are generally made of silicone material, which has a soft texture, good compression performance, and good thermal insulation performance. There are various sizes and thicknesses to choose from, suitable for filling cavities. Both sides have natural viscosity, and are easy to operate and maintain.

The thermal conductivity of thermal pads is generally high, even with thermal pads above 10.0W/mK. However, for thermal gaskets and thermal sealants with the same thermal conductivity, the thermal conductivity of the thermal sealant will be much better. Because the thermal conductive sealant adheres more tightly to the components, while also filling the rough surface of the substrate, squeezing out the air that is not conducive to thermal conductivity, and the thermal conductive gasket cannot achieve such a tight fit with the substrate.

3. Thermal grease

Thermal grease, also known as Paste or Grease in English, is divided into silicone and non silicone types, with thermal grease still being the main type on the market.

Thermal conductive silicone grease, commonly known as heat dissipation paste, is a thermal conductive organic silicone grease composite made from organic silicone as the main raw material and added with materials with excellent heat resistance and thermal conductivity. It is used for thermal conductivity and heat dissipation of electronic components such as power amplifiers, transistors, electronic tubes, CPUs, etc., thus ensuring the stability of electrical performance of electronic instruments and meters.

Thermal conductive silicone grease is prone to powdering, resulting in failure, and needs to be removed and reapplied. At the same time, thermal conductive silicone grease is also prone to contaminating surrounding components.

4. Thermal conductive phase change material

Thermal conductive phase change material refers to a substance that changes shape with temperature and can provide latent heat. The process of a phase change material changing from solid to liquid or from liquid to solid is called a phase change process, during which the phase change material absorbs or releases a large amount of latent heat.

The key performance of thermally conductive phase change materials is their phase transition characteristics: the material is solid at room temperature and easy to use. When the operating temperature of the device is reached, the phase change material becomes liquid. With a little tightening force, it can integrate with the two mating surfaces, completely filling the interface air gap and the gap between the device and the heat sink.

Thermal phase change materials themselves are non-conductive, but due to the phase change experienced by the material during typical heat sink installation, there may be metal to metal contact, so phase change materials cannot be used as electrical insulation.

Thermal phase change materials are widely used in microprocessors, memory modules, DC/DC converters, IGBT components, power modules, power semiconductor devices, solid-state relays, bridge rectifiers, high buffer memory chips, and more.