Thermal Interface Materials Apply in LED Lighting

Design challenges encountered in high-power LED lighting solutions are thermal design and thermal protection. A power and thermal management system is required for LED light sources because most of the electrical energy supplied to LEDs is converted to heat compared to other light sources. Without proper thermal management, this heat will affect the LED life and color output. Solving the heat dissipation problem of LED lighting fixtures is an indispensable link in the lighting design.

The thermally conductive materials commonly used in LED lighting fixtures are mainly divided into: structural thermally conductive materials and filling thermally conductive materials according to their functions in the lamps.

In addition to the function of the shell of the lamp, the structural thermal interface material is also used for the heat dissipation of the LED light source, such as thermal conductive plastics. The complementary thermal interface material is mainly used between the heating element and the heat dissipation element, as the connection between the two is used for heat conduction. Since the thermal conductivity of the thermal interface material relative to the heating element and the metal heat sink is low, the choice of the thermal interface material is also very important. Crucially, this determines how fast the heat is transferred.

The following are several thermal interface materials for high-power LED solutions:

Thermal grease: It has the characteristics of excellent thermal conductivity, electrical insulation, use stability, high and low temperature resistance, etc. It is a commonly used thermal conductive material for high-power LED lighting;

Thermal silicone pad: fill the air gap between the heating device and the heat sink or metal base to achieve heat transfer between the heating part and the heat dissipation part, and also play the role of insulation and shock absorption, which can meet the requirements of miniaturization and ultra-thin Design requirements, the ease of use is unmatched by thermal grease;

Thermal adhesive tape: Bonding between the heating sheet and the heat sink is simple and convenient to use, which is beneficial to improve production efficiency.

Potting compound: a room temperature curing one-component silicone adhesive sealant, non-corrosive to most metals; has excellent resistance to cold and heat alternating performance, aging resistance and electrical insulation performance, excellent moisture resistance, Shock resistance, corona resistance, anti-leakage performance.

At present, thermally conductive materials such as thermal conductive grease, thermal pads, thermal double-sided adhesive tape, and potting compound have been widely used in LED lighting solutions; CoolThermo, as a thermally conductive material manufacturer, is committed to providing customers with comprehensive solutions for LED lighting. , to meet customer one-stop purchasing needs.

How to apply thermal pad?

Compared with thermal grease, thermal pad is a relatively new type of thermal interface material. It is a thermally conductive interface material processed by a special process using silica gel as the material, adding metal oxides and other auxiliary materials. The shape, soft and flexible, compressible, specially designed for the use of gaps to transfer heat, and also play the role of insulation, shock absorption, sealing and so on.

Nowadays, thermal pads have been widely used in computer mainframes, notebook computers, LED lamps, set-top boxes, routers, DVDs, new energy vehicles, power supplies, transformers, and other electronic and electrical industries that require filling and cooling modules. So how can thermal pads be used to effectively exert its thermal conductivity?

The following CoolThermo details the manual installation and use of thermal pads:

  1. Keep the contact surface with the thermal pad clean to prevent the thermal pads from sticking to dirt, and the dirty thermal pads will have poor self-adhesion and sealing thermal conductivity.
  2. When holding the thermal pads in hand, the thermal pads with a large area should be grasped from the center, and the grasping of the smaller-sized sheet is not required, because the uneven force of the large thermal pads will lead to the thermal pads. Deformation, affecting subsequent operations, or even damaging the thermal pads.
  1. Hold (support) the thermal pads in the left hand, and tear off one of the release protective films with the right hand. You cannot tear off both protective films at the same time, so as to reduce the number and area of ​​direct contact with the thermal pads, and maintain the self-adhesive and thermal conductivity of the thermal pads. Sex is not compromised.

Tips: Tear off the side of the protective film, facing the radiator, first align the thermal pads to the radiator, and be careful to avoid the generation of air bubbles when slowly lowering the thermal pads.

If bubbles are generated during the operation, you can pull up one end of the thermal pads and repeat the above steps, or use a tool to gently remove the bubbles. The force should not be too large to avoid damage to the thermal pads.

  1. Tear off the other protective film, put it into the radiator, and tear off the last protective film with less force to avoid straining or pulling up the thermal pads.​​
  2. After tightening or when using a strong adhesive thermal pads, apply a certain pressure to the radiator and store it for a period of time to ensure that the thermal pad is fixed well.

The above is a brief introduction to the manual operation of CoolThermo on how to use the thermal pads. You can refer to it in actual operation. At the same time, you should constantly sum up experience in the actual operation process, which is conducive to improving the operation efficiency and ensuring the thermal pads. The performance of the performance, but also hope that everyone can sum up new experience and share.

What are the test standards for thermal conductivity of thermal pad?

For thermal conductive materials such as thermal pads, thermal grease, and thermal gel, the thermal conductivity tests often used in laboratories include the steady-state hot plate method and the laser flash method. The principles are derived from Fourier’s law. There are many methods to test thermal conductivity. The test methods that have been recognized earlier in the field of thermal conductive materials are ASTM E1530, ASTM D5470, and ASTM E1461.

The international general standard adopts ASTM D5470, ASTM E1461 and ASTM E1530 of the American Society for Testing and Materials (ASTM). The data obtained by various test methods and test standards are quite different. The test values of ASTM D5470 and ASTM E1461 are relatively similar, and the ASTM D5470 standard is used for the thermal pads CoolThermo, because this test method can better simulate the actual use state and reflect the thermal conductivity. Most of the famous foreign manufacturers of thermal pads also use this test method and condition.

ASTM D5470: Standard Test Method for Heat Transport Properties of Thermally Conductive Electrical Insulating Materials

Using the hot plate method/heat flow meter steady-state method, a certain heat flow is applied to the sample, the thickness of the sample and the temperature difference between the hot plate and the cold plate are measured, and the thermal conductivity of the sample is obtained. The sample needs to be a larger block. to obtain a sufficient temperature difference.

ASTM E1461: Test Method for Determining the Thermal Diffusivity of Solids by the Flash Method (Laser Flash Method)

High-intensity energy pulses irradiate small, thin disk samples for short periods of time. The energy of the pulse is absorbed by the front surface of the sample and the resulting temperature rise on the back surface is recorded (temperature autograph). The value of the thermal diffusivity is calculated from the thickness of the specimen and the time required for the rear surface temperature to rise to the maximum value of a certain ratio. The principle is that a laser beam hits the upper surface of the sample, and an infrared detector is used to measure the temperature change of the lower surface. The actual measured data is the thermal diffusivity of the sample.

ASTM E1530: Test Standard for Evaluating Heat Transfer Resistance of Materials Using the Protected Heat Flow Meter Technique.

Although the test standard is the same, the data tested by different equipments are quite different. Most foreign manufacturers of thermal conductive materials use the ASTM D5470 standard, because this test method can better simulate the actual use state and reflect the thermal conductivity. ASTM E1461 is a laser flash method that reflects the thermal conductivity within the material itself, but does not consider the influence of interface contact thermal resistance. ASTM E1530 is a test standard for evaluating the heat transfer resistance of materials. It is generally used less in the field of thermal pads. The measured data is much larger than that of ASTM D5470 and ASTM E1461.

CoolThermo, as a manufacturer of thermal pads with ten years of production experience, adopts ASTM D5470 as the thermal conductivity test standard for thermal pads, because this standard has the advantages that other test standards are incomparable: after simple modification, it can be obtained close to the actual working conditions. It can realize the quasi-in-situ test (In-situ Test), and meet the thermal performance measurement in the whole process of different pressure, different temperature, humidity and temperature aging.

What Is Thermal Grease?

Thermal grease is commonly known as thermal grease, also known as thermal paste. Thermal grease is made of silicone as the main raw material, adding materials with excellent heat resistance and thermal conductivity, and made of thermal grease-like compound for power amplifiers , transistors, tubes, CPU and other electronic components heat conduction and heat dissipation, so as to ensure the stability of the electrical performance of electronic instruments, meters and so on.

Thermal grease is a kind of material used to fill the gap between the CPU and the heat sink, which is also called thermal interface material. Its function is to conduct the heat emitted by the CPU to the heat sink, keep the temperature of the CPU at a level that can work stably, prevent the CPU from being damaged due to poor heat dissipation, and prolong its service life.

In thermal management applications, even two flat surfaces with very smooth surfaces can have voids when they come into contact with each other. The air in these voids is a poor conductor of heat and hinders the conduction of heat to the heat sink. Thermal grease is a material that can fill these voids and make heat conduction more smoothly and quickly.

Since thermal grease is a chemical substance, it also has relevant performance parameters that reflect its own working characteristics. As long as we understand the meaning of these parameters, we can judge the performance of a thermal grease.

Thermal conductivity

The thermal conductivity of thermal grease is basically the same as that of the radiator. Its unit is W/mK, that is, the temperature difference of a cylinder with a cross-sectional area of ​​1 square meter along the axial distance of 1 meter is 1 Kelvin (1K=1℃). heat transfer power. The larger the value, the faster the heat transfer rate of the material and the better the thermal conductivity. At present, the thermal conductivity of Novotel thermal grease can reach 5.2W/m.K.

Thermal resistance coefficient

The thermal resistance coefficient expresses the effect of an object on the conduction of heat. The concept of thermal resistance is very similar to that of resistance, and the unit is also similar (℃/W), that is, the temperature difference between the two ends of the heat conduction path when the continuous heat transfer power of the object is 1W. Obviously, the lower the thermal resistance, the better, because under the same ambient temperature and thermal power, the lower the thermal resistance, the lower the temperature of the heating object. The size of the thermal resistance has a great relationship with the material used in the thermal grease.

At present, the thermal resistance coefficient of mainstream thermal grease is less than 0.1°C/W, and the excellent ones can reach 0.005°C/W.

Operating temperature

Due to the characteristics of silicone grease itself, its operating temperature range is very wide. The working temperature is an important parameter to ensure that the thermal conductive silicone grease is in a solid or liquid state. If the temperature is too high, the volume of the thermal silicone grease will expand, the intermolecular distance will increase, the interaction will weaken, and the viscosity will decrease; if the temperature decreases, the fluid volume will shrink and the intermolecular distance will be reduced shortening, the interaction is strengthened, and the viscosity increases, both of which are not conducive to heat dissipation.

The working temperature of thermal grease is generally -40℃~200℃. We don’t need to worry about the working temperature of thermal grease, after all, it is difficult to exceed the temperature of CPU/GPU by conventional means.

Viscosity

Viscosity is a measure of fluid viscosity, which refers to the resistance to flow inside the fluid, expressed by the ratio of the shear stress to the fluid and the shear rate. There are many ways to measure viscosity. For example, the unit of dynamic viscosity is Pa. ·second.
For thermally conductive silicone grease, the viscosity is about 2500 Pa·s, and it has good tiling properties. It can be easily tiled around the surface of the chip under a certain pressure, and a certain viscosity is guaranteed, so that it will not become too thick after extrusion. Excess grease will flow.

Dielectric constant

Dielectric constant is used to measure the performance of insulators to store electrical energy, which refers to the ratio of the capacitance between two metal plates when insulating material is used as the medium to the capacitance between the same two plates when air is used as the medium or vacuum. The dielectric constant represents the degree of polarization of the dielectric, that is, the binding ability to charge. The larger the dielectric constant, the stronger the binding ability to charge.

Ordinary thermal grease uses materials with good insulation, but some special silicone greases (such as silver-containing silicone grease, etc.) may have a certain degree of conductivity. The dielectric constant of air is about 1, and the dielectric constant of common thermal grease is about 5.

Oil separation

Oil separation refers to the precipitation amount of silicone oil after the thermal grease heat-dissipating paste is kept at 200 ℃ for 24 hours, and it is an index to evaluate the heat resistance and stability of the product. Apply the silicone grease heat-dissipating paste on the white paper for observation, and you will see the phenomenon of oil seepage. If the oil separation is high, the oil separation phenomenon is obvious; or open the container containing silicone grease for a long time. Obvious oil separation is seen on the surface of the silicone grease or around the container.

There are many types of silicone greases on the market today, and different parameters and physical properties determine different uses. Thermal grease is a kind of high thermal conductivity insulating silicone material, which is almost never cured, and can maintain the grease state when used for a long time at the temperature of -40℃-200℃. Thermal grease thermal paste has excellent electrical insulation, excellent thermal conductivity, low oil separation (tends to zero), high and low temperature resistance, water resistance, ozone resistance, and weathering resistance. Thermal grease heat dissipation paste can be widely applied to various electronic products, between the heating body (power tube, thyristor, electric heating stack, etc.) and heat dissipation facilities (heat sink, heat dissipation strip, shell, etc.) in electrical equipment The contact surface acts as a heat transfer medium, and has the properties of moisture-proof, dust-proof, anti-corrosion and shock-proof. Thermal grease heat-dissipating paste is suitable for surface coating or overall potting of various microwave devices such as microwave communication, microwave transmission equipment, microwave special power supply, regulated power supply, etc. This kind of silicon material provides excellent heat-generating electronic components. Thermal conductivity.

What Is Thermal Conductive Material? What Is The Different?

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 gasket

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.

Advantage:

(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.

Shortcoming:

(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

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.

advantage:

(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.

shortcoming:

(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.

Advantage:

(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.

Shortcoming:

(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 Gel

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.

Advantage:

(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.

Shortcoming:

(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.

Advantage:

(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.

Shortcoming:

(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.

Advantage:

(1) It has a good waterproof sealing effect;
(2) Excellent electrical properties and insulation properties;
(3) It can be disassembled and repaired after curing.

Shortcoming:

(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.

Advantage:

(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.

Shortcoming:

(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.

Advantage:

(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.

Shortcoming:

(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.

How To Apply Thermal Grease?

Thermal grease, also known as thermal conductive grease, thermal paste, or thermal compound, etc., is used to create a thermally conductive layer between the processor and the heat sink. Thermal grease is the link between the cpu and the radiator for heat transfer. It also acts as a heat transfer medium, increases the contact area, buffers vibration and pressure, and fills the pits between the radiator and the cpu. Since thermal grease conducts heat better than air, applying thermal grease between the processor and the heat sink can enhance heat transfer from the processor to the heat sink.

After the influence of the thickness of silicone grease on heat dissipation, the CPU temperature fluctuates between 61-62°C when applying an appropriate amount of silicone grease, and the CPU temperature fluctuates between 63-64°C when a large amount of silicone grease is applied. It can be found that the thickness of the silicone grease layer has an obvious effect on heat dissipation. From this test, there is a 2°C gap between the two.

Therefore, the correct application of thermal grease has a multiplier effect on the heat dissipation of the cpu. Too much or too thick thermal grease is equivalent to adding a heat-conducting medium, which affects the heat transfer of the cpu to the radiator (the heat of the thermal grease the resistance is larger than the thermal resistance of metal), and excess heat dissipation silicone grease will even flow into the CPU socket. Although the current silicone grease is generally insulating and will not cause a short circuit, it flows to the metal contacts of the CPU and the socket. It is easy to cause a short circuit between the cpu pins. In the light of the computer can not be started, in severe cases, it will cause damage to the cpu or other peripheral hardware; too little or uneven application of thermal grease will cause no gap between the cpu and the radiator. The medium of buffering and heat conduction reduces the contact area between the CPU and the heat sink in disguised form, resulting in a decrease in heat dissipation efficiency.

Process plan for applying thermal grease

  1. First clean the surface of the CPU core and the bottom of the heat sink with a high-purity solvent (such as high-purity isoamyl alcohol or acetone) and a lint-free cloth (such as a camera lens cloth), taking care not to let your fingers touch the surface of the core and heat sink.
  2. Determine the area on the heat sink that is in contact with the CPU, and apply an appropriate amount of thermal grease on the CPU. At this time, you can ignore its uniformity, coverage and thickness.
  3. Prepare a moderately soft and hard plastic scraper (or cardboard), spread the thermal grease, and use the scraper to scrape in one direction at an angle of about 45 degrees, so that the thermal grease is evenly formed on the entire surface of the CPU. thin layer.
  4. Apply a small amount of thermal grease to the bottom of the radiator. Similarly, using the method we just applied to the CPU, apply the thermal grease to an area as large as the CPU shell. The purpose of this step is to make the particles in the thermal grease fully Fill the uneven grooves on the bottom of the radiator to make sure that there are no foreign objects on the surface of the radiator base and the CPU core, then install the radiator on the cpu, and fasten the fasteners.

Matters needing attention after applying thermal grease

  1. The heat-dissipating silicone grease will never be cured after being applied. It should be noted that if the heat-dissipating silicone grease is cured, this heat-dissipating silicone grease is unqualified and cannot be used in industrial manufacturing in large quantities. When buying, you need to pay attention. In order to avoid this situation, users can buy products with word-of-mouth guarantee, which can reduce the chance of this situation. For example, Nuofeng Electronics nfion, which focuses on the R&D and customized production of heat-dissipating silicone grease, can provide different customized solutions.
  2. Apply evenly: For the bottom surface of an ordinary radiator, the thickness of thermal grease applied is about the thickness of a piece of paper. After the thermal grease is applied, place the heat sink on the CPU. At this time, it can only be pressed lightly, and the heat sink cannot be rotated or translated. Otherwise, the thickness of the thermal grease between the heat sink and the CPU may be uneven.
  3. It is necessary to observe whether there are air bubbles after applying the heat-dissipating silicone grease. If there are air bubbles, they can be punctured with a toothpick. Otherwise, these air bubbles will cause uneven application. In addition, there will be air in the air bubbles, which will also increase the thermal resistance and affect heat dissipation. Effect.
  4. The remaining heat dissipation silicone grease needs to be sealed and can be placed in a cool place, so that it can be used up within 12 months. After more than 12 months, the thermal conductivity will decrease and cannot be used again.

Thermal grease is a thermally conductive material with good heat dissipation performance. Thermal grease can be used in various electrical appliances or electronics. There is no change in performance before and after use, and it is always in the state of grease. Thermal grease can only be smeared in the middle of the heating element of the electrical appliance and the heat dissipation facility. Only by mastering the correct operation method when smearing can achieve the purpose of heat dissipation.

What Is Thermal Adhesive? How To Apply?

Thermal adhesive is a one-component, thermally conductive, room temperature curing silicone adhesive sealant. The condensation reaction of moisture in the air releases low molecules to cause cross-linking and curing, and vulcanizes into high-performance elastomers. Thermally conductive adhesive is also known as silicone thermal conductivity. Glue, thermal conductive silica gel, RTV glue, heat dissipation silica gel, heat transfer glue, heat dissipation glue, cooling glue.

Thermally conductive adhesives can be cured at room temperature and have certain bonding properties. Thermally conductive adhesive is a kind of silicone rubber, which is a one-component room temperature vulcanized liquid rubber. Once exposed to air, the silane monomers in it condense to form a network structure, the system is cross-linked, cannot be melted and dissolved, is elastic, becomes rubbery, and adheres to objects at the same time. And once cured, it is difficult to separate the bonded objects.

Thermal adhesive has good thermal conductivity and high-grade pressure resistance. Its function is to fill the large requirements between the processor and the heat sink. It is the best product to replace the binary heat dissipation system of thermal grease and mica sheet. Thermal adhesive has excellent anti-cold and heat alternating performance, anti-aging performance and electrical insulation performance. And has excellent moisture resistance, shock resistance, corona resistance, leakage resistance and chemical resistance properties. It can be used continuously in the environment of -50 ~ 200 ℃ and maintain performance. Non-swelling and good adhesion to most metallic and non-metallic materials.

Thermal adhesive is a new type of adhesive with fast curing speed, easy extrusion and convenient operation, which can meet any working environment and working conditions. So what are the characteristics of thermal adhesive? In which scenarios is it mainly used? Let’s find out together!

Characteristics of thermal adhesives

  1. No need for screws to fix, reduce the cost of low parts and improve production efficiency; thermal adhesive replaces the traditional card and screw connection;
  2. Because the glue has strong adhesion to the metal surface and is not easy to peel off, it is widely used in the bonding and sealing of PTC sheets and aluminum heat sinks;
  3. Comprehensive contact, providing more effective heat dissipation effect, good operating temperature range -50 ~ 200 ℃, short-term high temperature resistance of 300 ℃;
  4. High dielectric strength to ensure electrical insulation properties; single-component, extremely easy to use;
  5. Elastic bonding, shock-proof, shock-absorbing, can be used in electrical equipment of vibration source;
  6. The bonding speed is fast, the bonding force is strong, and the bonding force is lasting; it is suitable for different product designs and technological processes.

Application of Thermal Adhesive

  1. Mainly used in CPU radiator, heat dissipation between thyristor, chip and heat sink, and heat dissipation of electric iron soleplate;
  2. It is used for heat conduction, heat dissipation and insulation between the heat sink and the CPU. Such as: computers and related equipment, audio-visual sound, electronics, electrical appliances, etc.;
  3. It is used for various high power needs to dissipate heat. Heat transfer related electrical appliances such as: semiconductor refrigeration sheet, water dispenser, electric kettle, TV power amplifier tube and heat sink;
  4. It is used for bonding and heat conduction of high-precision DVD decoder boards, heat conduction of transformers and fixing of electronic components, followed by filling;
  5. The heat dissipation bonding of the LED drive module and the shell; high-power LED flood light, LED street light, LED power supply, LED underwater landscape light, LED point light source, LED indoor downlight, etc. are bonded to the bracket.

The above is the detailed introduction of CoolThermo Technology’s definition, characteristics and functions of thermally conductive adhesives. Only with sufficient understanding of thermally conductive adhesives can we more accurately select the adhesive scheme and achieve better performance in practical applications.

Why Do High-Power Led Lamps Need To Be Coated With Thermal Grease?

As an excellent semiconductor optoelectronic device, LED has been unanimously recognized in the market for its advantages of small size, low power consumption, long service life and environmental protection, and has become a new generation of ideal solid-state energy-saving lighting sources.

High-power LED packaging has been a research hotspot in recent years due to its complex structure and process, which directly affects the performance and life of LEDs.

However, with the development of LEDs with high light intensity and high power, the problem of heat dissipation has become increasingly prominent, which seriously affects the light output characteristics of LEDs and the life of the device, and has become a key problem that must be solved in high-power LED packaging. The root cause of the heat dissipation problem of LED is the high power density of the chip, and the heat dissipation efficiency of the chip has not been improved in time.

Heat dissipation is a key problem for LED lamps to solve, and a heat conduction process before this is even more critical. The LED chip will generate a lot of heat when it is working. If it cannot be dissipated quickly and efficiently, the LED chip with too high junction temperature will seriously affect its own service life. At present, there are quite effective means to improve the heat dissipation capacity of LED lamps. We can coat a layer of thermal grease between the LED aluminum substrate and the aluminum heat sink to reduce the thermal resistance of the contact surface between them, thereby improving its own thermal conductivity. heat dissipation capacity.

Why apply a layer of thermal conductive silicone grease to improve the heat dissipation performance of LED lamps? Because the main heat dissipation method of LED lamps is to dissipate heat through the LED radiator. The same is true for the heat generated by the LED chip. The LED chip will first conduct the heat to the aluminum substrate, and then the aluminum substrate will conduct the heat to the aluminum heat sink. However, the aluminum substrate is often fixed on the aluminum heat sink by screws. The structure fixed in this way often forms an air gap between them, and the thermal resistance of the air is very large, which is higher than other thermal resistances. It is dozens of times larger, so it is necessary to apply thermal grease to fill the gap to increase the area of ​​the contact surface, thereby increasing the heat flux, reducing the thermal resistance, and improving the heat dissipation performance of the LED lamp.

In fact, the quality of heat dissipation depends on the material of the heat sink. Thermal grease thermal paste is a thermal medium, the better the thermal conductivity, the more heat is exported, and the better the cooling effect.

What Is Thermal Gel?

Thermal gel is a soft silicone-based thermally conductive gap filler material with high thermal conductivity, low interfacial thermal resistance and good thixotropy. It is an ideal material for applications with large gap tolerances.

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.

Thermal gel mainly meets the requirements of low stress and high compressive modulus during use, and can realize automatic production; it has good contact with electronic products during assembly, showing low contact thermal resistance and good electrical insulation properties. The cured thermal gel is equivalent to a thermally conductive gasket, with good high temperature resistance and aging resistance, and can work at -40~200℃ for a long time.

The thermal gel is filled between the electronic components to be cooled and the radiator/shell, etc., to make them in close contact, reduce thermal resistance, and quickly and effectively reduce the temperature of electronic components, thereby extending the service life of electronic components and improving their reliability. sex. Thermal gels can be applied by hand or by dispensing equipment.

Types of thermal gels

One-component thermally conductive gel is a paste-like gap-filling thermally conductive material, which is formed with the shape of the structure; it has excellent structural applicability and structural surface adhesion for uneven ceramic, heat sink surfaces or irregular cavities. It has good insulation and pressure resistance characteristics and temperature stability, and is safe and reliable to use; it can flow under pressure like thermal grease and thermal paste; it has high reliability under the action of thermal cycles and will not be used. cured.

Two-component thermal conductive gel is a pre-formed thermal conductive silicone grease product, which mainly meets the needs of low pressure and high compressive modulus when the product is in use. It can realize automatic production, and has good contact with electronic products during assembly, showing a relatively high performance. Low contact thermal resistance and good electrical insulation properties. This material has some advantages of thermal pad and thermal grease at the same time, and better makes up for the weaknesses of both.

Characteristics of thermally conductive gels

  1. Performance characteristics
    Compared with thermal pads, thermal gels are softer and have better surface affinity, and can be compressed to a very low thickness, which significantly improves heat transfer efficiency. The minimum can be compressed to 0.1mm, and the thermal resistance at this time can be 0.08℃·in2/W – 0.3 ℃·in2/W, it can reach the performance of some silicone grease. In addition, the thermal gel has almost no hardness and will not cause internal stress to the device after use.

Thermal gel is easier to handle than thermal grease. The general use of silicone grease is screen or steel plate printing, or direct brushing, which is very unfriendly to users and the environment, and because of its fluidity, it is generally not used for occasions with a thickness of more than 0.2mm.

Thermal gel has a certain degree of adhesion, and there is no problem of oiling and drying out, and it has certain advantages in reliability.

  1. Advantages of continuous operation

The thermal 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. Curing time
    The two-component thermal gel starts from the contact between the A and B glue mixing heads. The viscosity will increase in 5 minutes, and it will dry in 10 minutes. After 30 minutes to 3 hours, the product will gradually harden and become elastic, and the hardness will continue to rise. no longer change.
  2. Reliability
    The cured thermal gel is equivalent to a thermal pad, with good high temperature resistance and aging resistance, and can work at -40~200℃ for a long time.

Pay attention

Unlike adhesives, thermal gels have weak adhesion and cannot be used to fix heat sinks.

Thermal Gel VS Thermal Grease

Thermal gel is an upstart thermal interface material emerging in recent years, while thermal grease is the veteran of the thermal interface material family. Both thermal gel and thermal grease are paste-like, and they represent two different grades. , many people in the industry say that there is a certain connection between the two, and they can make a better choice after understanding the difference and connection between thermal gel and thermal grease; but the production process of both has been improved at present, so it is not There is no obvious advantage or disadvantage, but it has to be said that each has advantages in specific construction and application. In view of this, CoolThermo will explain the difference between thermal gel and thermal grease with you today.

Difference 1: The construction methods of thermal gel and thermal grease are different.

Thermal gel is an ultra-high viscosity thermally conductive material. It is made of a variety of thermally conductive powders and thermally conductive silica gel after being fully matured and mixed. The entire production process is completed in a vacuum state, so there is no air in the thermal gel material. , The packaging of thermal gel is also in syringe packaging, which can be directly dispensed by an automatic glue dispenser during construction, ending the history that thermal interface materials cannot be automated production.

The thermal grease is different from the thermal gel in terms of the formula and the production process of the thermal grease itself, including the packaging method of the thermal grease is also simple canned, the construction method is usually screen printing, and some customers use more For convenience, just apply and scrape evenly. However, such a simple construction method must also be manually operated. Simply put, thermal gel can be constructed by a fully automatic dispensing process, while thermal grease can only be constructed manually.

Difference 2: The working life of thermal gel and thermal grease is different.

The thermal gel is not dry for a long time, can be compressed infinitely, and can guarantee a service life of more than 10 years with customers. Some manufacturers also call the thermal gel a liquid thermal pad. However, the life of thermal grease is the shortest among all thermal interface materials. After 1-2 years of use, thermal grease begins to dry up and pulverize. It can be completely turned into powder in no more than 5 years, and it will become dust when it is pinched by hand, and the thermal conductivity of thermal grease will also be Greatly reduced. This is also the point where thermal grease is often complained about, and it is also a fatal bottleneck for the development of thermal grease.

The thermal resistance, temperature resistance and other technical parameters of thermal gel and thermal grease are different to a certain extent, but it does not mean that any product must use thermal gel instead of silicone grease as a thermal conductive material, mainly based on The customer’s product needs to choose a relatively suitable product; thermal gel has higher requirements on the structure, so thermal gel is also considered to be a more discerning thermal conductive material, so it is used in different occasions and working conditions. limit.

Due to the higher cost of thermal gel compared to silicone grease, the general application fields are some high-tech or products with special requirements, and thermal grease is still one of the most widely used thermal conductive materials.

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