When it comes to cooling systems, most people think of fans and heat sinks, often ignoring one of the less visible but important mediators—the thermal conductive material. So, do you know the types of commonly used thermal conductive materials? What are their advantages and disadvantages? We together look!
Thermal gaskets are referred to as thermally conductive gaskets. They are used to fill the air gap between the heating element and the heat sink or metal base. Their flexible and elastic characteristics allow them to be used to cover very uneven surfaces. Heat is conducted from discrete components or the entire PCB to the metal enclosure or diffuser plate, increasing the efficiency and lifespan of heat-generating electronic components.
In the use of thermal pad, pressure and temperature are mutually restricted. With the increase of temperature, after the equipment runs for a period of time, the thermal pad material will soften, creep and stress relaxation, and the mechanical strength will also be reduced. down, the pressure of the seal decreases.
(1) Pre-formed thermally conductive material with ease of installation, testing, and reusability;
(2) Soft and elastic, good compressibility, able to cover very uneven surfaces;
(3) It has the effect of buffering, shock absorption and sound absorption under low pressure;
(4) Good thermal conductivity and high-grade withstand voltage insulation;
(5) Stable performance, no oil leakage at high temperature, and high cleanliness.
(1) The thickness and shape are preset, and the thickness and shape will be limited when used;
(2) The thickness of the thermal pad with a thickness of less than 0.3mm is complex, and the thermal resistance is relatively high;
Application environment: When the gap between the heat-generating component and the heat sink is large, the heat-generating component and the shell conduct heat.
Thermal grease, also known as thermal conductive grease, thermal paste, etc., is the most widely used thermal conductive medium at present. An ester-like substance formed after decompression, grinding and other processes, the substance has a certain viscosity and no obvious graininess. It can effectively fill various gaps.
(1) Exist in liquid form with good wettability;
(2) Good thermal conductivity, high temperature resistance, aging resistance and waterproof properties;
(3) Insoluble in water, not easy to be oxidized;
(4) It has certain lubricity and electrical insulation;
(5) Low cost.
(1) It cannot be smeared on a large area and cannot be reused;
(2) The product has poor long-term stability. After continuous thermal cycles, it will cause liquid migration, leaving only the filling material, and the surface wettability will be lost, which may eventually lead to failure;
(3) Due to the different thermal expansion rates of the materials on both sides of the interface, a “gas-filled” effect is caused, resulting in an increase in thermal resistance and a decrease in heat transfer efficiency;
(4) It is always liquid and difficult to control during processing, which is easy to cause pollution to other components and waste of materials, increasing costs.
Application environment: Between the high-power heating components and the radiator, the heat-dissipating components need to have their own fixing devices.
Thermal conductive double-sided adhesive
Thermal conductive double-sided tape is referred to as thermal tape, which is composed of acrylic polymer and silicone adhesive.
(1) It has both thermal conductivity and adhesive properties;
(2) It has good caulking performance;
(3) The appearance is similar to double-sided tape, and the operation is simple;
(4) Generally used for some electronic parts and chip surfaces with less heat generation.
(1) The thermal conductivity is relatively low, and the thermal conductivity is general;
(2) It is impossible to glue and fix heavy objects;
(3) Once the thickness of the tape is exceeded, effective heat transfer cannot be achieved with the heat sink;
(4) Once used, it is not easy to disassemble, there is a risk of damage to the chip and surrounding devices, and it is not easy to disassemble completely.
Application environment: It is usually used between a heat source with low power and a small heat sink to fix the LED heat sink, etc.
Thermal conductive gel is a gel-like thermal conductive material made of silica gel composite thermal conductive filler after stirring, mixing and potting. This material has some advantages of thermal pad and thermal grease at the same time, and better makes up for the weaknesses of both. Thermal gel inherits the advantages of good affinity, weather resistance, high and low temperature resistance, and good insulation properties of silicone materials. At the same time, it has strong plasticity and can meet the filling of uneven interfaces, and can meet the heat transfer requirements in various applications.
(1) Compared with the thermal conductive gasket, the thermal conductive gel is softer and has better surface affinity, and can be compressed to a very low thickness, which significantly improves the heat transfer efficiency, and can be compressed to 0.08mm;
(2) The thermal gel has almost no hardness, and will not cause internal stress to the equipment after use;
(3) The thermal conductive gel can be directly weighed and used. The commonly used continuous use method is the glue dispenser, which can realize fixed-point quantitative control, save labor and improve production efficiency.
(1) The cost is high;
(2) The process is more complicated.
Application environment: between high-power heating components and radiators, it can be used for quantitative control of dispensing machines.
Thermal silica glue ( RTV )
Thermal conductive glue, also known as thermally conductive silica gel, is made of organic silica gel as the main body, adding polymer materials such as fillers and thermally conductive materials, and kneading silica gel, which has good thermal conductivity and electrical insulation properties, and is widely used in electronic components.
(1) Thermal interface material, which will be cured, has adhesive properties and high adhesive strength;
(2) After curing, it is an elastic body, which is resistant to impact and vibration;
(3) The cured product has good thermal conductivity and heat dissipation function;
(4) Excellent high and low temperature resistance and electrical properties.
(1) Not reusable;
(2) The caulking gap is general;
(3) The curing time is longer.
Application environment: thermally conductive silica gel can be widely used in various electronic products, the contact surface between the heating body and the heat dissipation facilities in the electrical equipment, which acts as a heat transfer medium and has the properties of moisture, dust, corrosion and shock resistance.
Thermal potting compound
Thermal potting compound is commonly divided into silicone rubber system and epoxy system, silicone system is soft and elastic, and epoxy system is hard and rigid; it can meet the requirements of large depth of thermal conductivity potting. Improve the resistance to external vibration and improve the insulation and waterproof performance between internal components and circuits.
(1) It has a good waterproof sealing effect;
(2) Excellent electrical properties and insulation properties;
(3) It can be disassembled and repaired after curing.
(1) The heat conduction effect is general;
(4) The process is relatively complicated;
(5) poor bonding performance;
(6) The cleanliness is average.
Application environment: potting protection of power modules.
Thermally conductive silicone cloth
Thermally conductive silicone cloth is a silicone polymer elastomer reinforced with glass fiber cloth as a base material.
(1) It can effectively reduce the thermal resistance between the electronic components and the heat sink;
(2) Electrical insulation, with high dielectric strength, good thermal conductivity, and high chemical resistance;
(3) It can withstand circuit short circuit caused by high voltage and puncture of metal parts. It is an excellent thermal insulation material to replace traditional mica and silicone grease.
(1) The thermal conductivity is not high;
(2) The thickness and shape are preset, and the thickness and shape will be limited when used.
Application environment: filling between heat source and heat dissipation module or shell, insulation filling between live heating element and shell, etc.
Phase change material ( PCM )
Phase change materials refer to substances that change shape with temperature changes and can provide latent heat. The process of a phase change material from solid to liquid or from liquid to solid is called a phase change process.
(1) It can be repaired and reused, and the coating thickness and shape can be controlled as needed;
(2) It is solid at room temperature, but melts to fill the micro-gap during the operation of the equipment (no vertical flow);
(3) The thermal conductivity is equivalent to the traditional thermal grease, with better performance;
(4) Excellent substitute for silicone grease, there is no phenomenon of traditional silicone grease and silicone oil volatilizing, drying and aging.
(5) There is no glue overflow phenomenon of general silicone grease.
(6) Compared with thermal grease, there is no “inflatable” effect, and it has high reliability for long-term use;
(7) It can be dispensed, screen printed, and manually coated, and can be fully automated to greatly increase production;
(8) Environmentally friendly, in line with Rohs standards.
(1) It is not easy to store;
(2) Transportation, the cost is relatively high.
Application environment: on the cooling module.
Different thermal conductive materials have their own characteristics. No matter which thermal conductive material is used, there is no way to meet the heat dissipation needs of all electronic devices, and it has more or less some of its shortcomings. The advantages are magnified.