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.

Thermal Pad Vs Paste

Many customers often can’t tell the difference between thermal pad and thermal paste, and do not know how to choose when purchasing? Friends who have not contacted this line believe that they may think that thermal pad and thermal paste are the same product, but they are not. Although there is only one word difference, the difference is a thousand miles away. Although thermal pad and thermal paste are both thermal gap filler, but the performance is still different, let’s distinguish the difference between thermal pad and thermal paste.

Thermal paste and thermal pad have similar properties and similar production processes, except that a viscous substance is added to the formula to make it have better bonding properties.

Thermal gel is a one-component dealcoholized room temperature curing silicone rubber. The condensation reaction of moisture in the air releases low molecules to cause cross-linking and curing. It can be cured into an elastomer with high hardness in a short time. It has the functions of cooling and bonding electronic devices. After curing, it is closely attached to its contact surface to reduce thermal resistance, which is beneficial to the heat conduction between the heat source and its surrounding heat sinks, motherboards, metal shells and outer casings. Thermal silicone series products have the advantages of high thermal conductivity, good insulation performance and easy to use. Thermal silicone products have good adhesion to metals including copper, aluminum, stainless steel, etc. Does not produce corrosion.

And what we usually call thermal grease is a kind of grease paste, which has no adhesive properties and will not dry. It is produced with a special formula, using metal oxides and organosiloxane with good thermal conductivity and insulation. compound. Thermal grease has excellent thermal conductivity, good electrical insulation, wide operating temperature (working temperature -50 ℃ ~ 200 ℃), stable heat dissipation, low consistency and good construction performance, thermal grease is non-toxic , Non-corrosive, odorless, non-drying, insoluble.

Through the introduction of the above content, I believe that everyone has a certain understanding of the difference between thermal pad and thermal paste. Although silicone grease and silicone are only literally one word apart, and they are both thermal conductive materials, they are completely different. Two things. Relatively speaking, silicone grease has a wider scope of application and is almost suitable for the heat dissipation conditions of any electronic product; and thermal pad is difficult to remove once attached, so it is mostly used in some occasions that only require one-time bonding .

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.

Can Thermal Gel Replace Thermal Grease?

With the development of the times, people’s life is inseparable from the existence of electricity. All kinds of products that need to be driven by electricity are flooded in all aspects of people’s lives. When electrical appliances are operating, heat is inevitably generated due to resistance. If the heat is not dissipated in time, Electrical appliances may be short-circuited due to excessive temperature, so solving the problem of body heat dissipation has become the focus of thermal design engineers.

As a traditional thermal conductive material, thermal grease has always been popular with thermal design engineers. It is a gap-filled thermal conductive material based on silicone resin. Reduce interface thermal resistance. Under normal storage conditions, it will not dry and hard, and has good thixotropy, which is beneficial to people’s use. Since the production process of thermal grease is simpler than other thermal conductive materials, its price phase change is lower.

After years of development, a variety of new thermal conductive materials have come out one after another, and thermal gel, which is joked by industry insiders to replace thermal grease, has gradually attracted the attention of thermal design engineers. Come down to CoolThermo to explain it to you!

Thermal Gel is a soft silicone resin thermal gap filling thermal conductive material with high thermal conductivity, low interfacial thermal resistance and good thixotropy. It is an ideal material for applications with large gap tolerances. It is also a paste-like mixture. Compared with the flowing shape of thermal grease, the use of thermal gel is more like plasticine, and there will be no flow and sedimentation.

Thermal gel combines the advantages of thermal grease and thermal pad, while avoiding the defects of both. Thermal gel is a silicone grease mixed with high thermal conductivity particles (such as alumina, silver powder, etc.), and then cross-linked with low molecular weight siloxane through a heat treatment process, and then a gel is formed.

Thermal gel is a gel state substance between liquid and solid. It not only has the characteristics of shape recovery, strong material cohesion, high heat resistance, good long-term thermal stability, etc., but also has excellent thermal conductivity like thermal grease. Low thermal resistance, can fill voids, and has high adhesion.

The thermal gel is generally packaged in a syringe, and the thermal gel has no gas. It is very convenient and efficient to use as long as it is installed on the dispenser. Thermal grease is generally packaged by filling. Although it can be adjusted in thickness, it cannot be changed to be fluid. It can be screen printed or manually applied. Although it is convenient, manual operation is still used.

The main difference between thermal gel and thermal grease is that the thermal gel does not produce silicone oil precipitation, and the thermal gel can be torn off and reused. The thermal gel only needs a small working pressure when connecting with the heat sink and the chip, generally less than 10psi, low hardness, easy to bend, and has a wide working temperature range.

The thermal gel has very little liquid precipitation during use, and the thermal gel will never be cured after use and will not lose its thermal conductivity. Anyone who has assembled a computer knows that it is necessary to recoat the thermal grease after a period of time. Otherwise, Its dry-solid powdering leads to a significant reduction in thermal conductivity, which also shows that the service life of thermal grease is relatively short among thermal conductive materials.

Although the advantages and performance of thermal gel are different from those of thermal grease, it does not mean that thermal grease should be replaced by thermal gel. Therefore, the areas where thermal gel is generally used are those high-tech products or those with special requirements. Thermal grease is still one of the most widely used thermal conductive materials so far.

What is a potting compound?

Potting is to pour the liquid basic resin compound into the device with electronic components and circuits mechanically or manually, and then solidify it into a thermosetting polymer insulating material with excellent performance under normal temperature or heating conditions. The liquid base resin compound used in this process is the potting compound.

Electronic thermal potting compound is mainly used for bonding, sealing, potting and coating protection of electronic components. The potting compound is liquid before curing and has fluidity. The viscosity of the glue varies according to the material, performance and production process of the product. The potting compound can realize its use value only after it is completely cured.

There are many types of electronic thermal conductive encapsulants. In terms of material types, the most commonly used three are mainly silicone resin thermal conductive encapsulants, epoxy resin thermal conductive encapsulants, and polyurethane thermal conductive encapsulants. The three material potting compounds can be subdivided into hundreds of different products.

Silicone Thermal Potting Compound

There are many types of silicone potting compounds. Different types of silicone potting compounds have great differences in temperature resistance, waterproof performance, insulation performance, optical performance, adhesion and adhesion to different materials, and softness and hardness. Silicone encapsulants can be added with some functional fillers to give them properties such as electrical conductivity, thermal conductivity, and magnetic conductivity. The mechanical strength of silicone encapsulant is generally poor, and it is precisely this performance that is used to make it “breakable” for easy maintenance, that is, if a component fails, you only need to pry open the encapsulant and replace it with a new one. After the original copy, you can continue to use it.

The color of the silicone potting compound can generally be adjusted arbitrarily according to the needs. or transparent or non-transparent or white color. Silicone potting compound performs very well in shockproof performance, electrical performance, waterproof performance, high and low temperature resistance, and anti-aging performance.
Two-component silicone potting glue (or ab glue) is the most common, and this kind of potting glue includes two types: condensation type and addition type. Generally, the condensation type has poor adhesion to components and potting cavity, and volatile low-molecular-weight substances will be produced during the curing process, and there will be a relatively obvious shrinkage rate after curing. Addition type (also known as silicone gel) has minimal shrinkage and no low-molecular-weight formation during curing. It can be cured quickly by heating.

Advantages: The material of the silicone potting compound is soft after curing. There are two forms of solid silicone rubber products and silicone gels, which can eliminate most of the mechanical stress and have the effect of shock absorption and protection. Physical and chemical properties are stable, with good high and low temperature resistance, and can work for a long time in the range of -50~200 °C. Excellent weather resistance, can still play a good protective role outdoors for more than 20 years, and is not easy to yellow. It has excellent electrical performance and insulating ability. After potting, it can effectively improve the insulation between internal components and lines, and improve the stability of electronic components. With rework capability, sealed components can be taken out for repair and replacement quickly and easily.

Disadvantages: The bonding performance is slightly poor.

Application range: suitable for potting a variety of high-end precision/sensitive electronic devices that work in harsh environments. Such as LEDs, display screens, photovoltaic materials, diodes, semiconductor devices, relays, sensors, automotive ballasts HIV, on-board computer ECUs, etc., mainly play the role of insulation, moisture-proof, dust-proof and shock-absorbing.

Epoxy Thermal Potting Compound

Through the EU ROHS standard, the cured product has high hardness, smooth surface, good gloss, and has the characteristics of fixation, insulation, waterproof, oil-proof, dust-proof, anti-theft, corrosion resistance, aging resistance, and thermal shock resistance. It is used for packaging of electronic transformers, AC capacitors, negative ion generators, aquarium water pumps, ignition coils, electronic modules, LED modules, etc. It is suitable for potting of small and medium-sized electronic components, such as automobile, motorcycle igniter, LED drive power supply, sensor, toroidal transformer, capacitor, trigger, LED waterproof lamp, confidentiality, insulation and moisture-proof (water) of circuit board. Potting.

Advantages: Most epoxy resin potting glues are hard, and a few modified epoxy resins are slightly soft. The major advantage of this material is that it has better adhesion to the material and better insulation, and the cured product has good acid and alkali resistance. Epoxy resin generally has a temperature resistance of 100 ℃. The material can be used as a transparent material with good light transmittance. The price is relatively cheap.

Disadvantages: weak resistance to cold and heat changes, cracks are prone to occur after being impacted by cold and heat, resulting in water vapor infiltrating into electronic components from cracks, poor moisture resistance; colloid hardness after curing is high and brittle, high mechanical stress is easy Strain electronic components; epoxy resin cannot be opened due to its high hardness after potting and curing, so the product is a “lifetime” product, and components cannot be replaced; transparent epoxy resin materials generally have poor weather resistance and light exposure. Or yellowing is easy to occur under high temperature conditions.

Scope of application: Generally used for potting of non-precision electronic devices such as LEDs, transformers, regulators, industrial electronics, relays, controllers, power modules, etc.

Polyurethane potting compound

Polyurethane encapsulant, also known as PU encapsulant, is usually composed of polyols and diisocyanates of oligomers such as polyester, polyether and polydiene, and diol or diamine as chain extenders. to make. Potting compounds can generally be prepared using the prepolymer method and the one-step process.

Polyurethane potting materials are characterized by low hardness, moderate strength, good elasticity, water resistance, mildew resistance, shock resistance, transparency, excellent electrical insulation and flame retardancy, no corrosion to electrical components, and resistance to steel, aluminum, copper, tin and other metals, as well as rubber, plastic, wood and other materials have good adhesion. Potting materials can make installed and debugged electronic components and circuits immune to vibration, corrosion, moisture and dust.

Advantages: Polyurethane encapsulant has excellent low temperature resistance, the material is slightly soft, and has good adhesion to general encapsulation materials, and the adhesion is between epoxy resin and silicone. It has good waterproof, moisture-proof and insulating properties.

Disadvantages: poor high temperature resistance and easy foaming, vacuum defoaming must be used; after curing, the surface of the colloid is not smooth and has poor toughness, and the anti-aging ability, shock resistance and ultraviolet rays are weak, and the colloid is easy to change color.

Scope of application: Generally used for potting of electronic components with low heat generation. Transformers, choke coils, converters, capacitors, coils, inductors, varistors, linear motors, fixed rotors, circuit boards, LEDs, pumps, etc.

Instructions for use of thermal potting compound

  1. Before mixing: A and B components should be fully stirred by hand or machine respectively to avoid changes in performance due to filler settling.​​
  2. Mixing: Weigh the two components according to a certain ratio (1:1, 10:1) and put them into a clean container and stir evenly. The error should not exceed 3%, otherwise it will affect the performance after curing.
  3. Defoaming: natural defoaming and vacuum defoaming, natural defoaming: let the mixed glue stand for 20-30 minutes. Vacuum defoaming: the degree of vacuum is 0.08-0.1MPa, and the vacuum is evacuated for 5-10 minutes.
  4. Perfusion: The rubber material should be perfused within the operating time, otherwise it will affect the leveling. Keep the substrate surface clean and dry before potting. The mixed rubber compound is poured into the device to be encapsulated. Generally, vacuum degassing is not required. If high thermal conductivity is required, it is recommended to vacuum degassing and then pour. (Vacuum defoaming: vacuum degree is 0.08-0.1MPa, vacuuming for 5-10 minutes)
  5. Curing: It can be cured at room temperature or by heating. The curing speed of the glue has a lot to do with the curing temperature. It takes a long time to cure in winter. It is recommended to use heating to cure. It takes 15-30 minutes to cure at 80 °C, and it generally takes about 6-8 hours to cure at room temperature.

With its excellent performance, thermal potting compound can well meet the needs of the consumer market, ensure effective bonding, sealing, potting and coating protection between electronic devices and products, and better bring high-quality insulation to the electronics industry. materials, so as to effectively improve its product awareness, so that more areas of awareness, effective use.

What is Silicone Adhesive?

Speaking of “adhesive”, many people may be at a loss, and to put it another way “glue”, suddenly realized. Professionally known as adhesives, the range of adhesives is too wide and has been widely used in aerospace, aircraft manufacturing, electronics industry, machining, automobile manufacturing, construction and medical care. Adhesives are used in everything from food, clothing, housing and transportation to aerospace. Silicone is one of them.

Silicone? What is Silicone? Organosilicon compounds refer to compounds that contain Si-C bonds and at least one organic group is directly connected to a silicon atom. It is also customary to use those compounds that connect organic groups to silicon atoms through oxygen, sulfur, nitrogen, etc. Also used as organosilicon compounds. Among them, the polysiloxane composed of silicon-oxygen bond (-Si-O-Si-) as the skeleton is the most numerous, the most deeply studied and the most widely used type of organosilicon compounds, accounting for more than 90% of the total dosage. .

The silicone adhesive is a one-component, translucent paste-like room temperature curing adhesive, which is a high-performance elastomer that is naturally cured. It has excellent heat and cold resistance, aging resistance and electrical insulation properties, and has good adhesion to most metal and non-metal materials.

Silicone adhesives can be divided into two categories: silicone resin-based adhesives and silicone rubber-based adhesives. The chemical structures of the two are different: the silicon-oxygen bond is the main chain of the body structure, which can be further condensed into a high-strength cross-linked hard and brittle resin at high temperature; while silicone rubber is a linear silicone rubber. A relatively high molecular weight elastomer with oxygen bonds as the main chain. The relative molecular weight ranges from tens of thousands to hundreds of thousands, and they must be condensed into elastomers with several cross-linking points under the action of curing agents or catalysts. It can also be divided into two types: condensation type and addition type. The addition type is a silicone adhesive made of cyanopolysiloxane and vinyl polysiloxane as the main material under the action of a catalyst.

Compared with other types of polymer materials, what are the excellent properties of silicone adhesives?

The basic structural unit of silicone products is composed of silicon-oxygen chains, and the side chains are connected to various other organic groups through silicon atoms. Therefore, the structure of silicone products contains both “organic groups” and “inorganic structures”. This special composition and molecular structure make it combine the characteristics of organic substances with the functions of inorganic substances.

Compared with other polymer materials, the most outstanding properties of silicone adhesives are:

  1. Temperature resistance

The silicone adhesive is based on a silicon-oxygen (Si-O) bond as the main chain structure. The bond energy of the C-C bond is 82.6 kcal/mol, and the bond energy of the Si-O bond is 121 kcal in silicone. /molecule, so the thermal stability of the silicone adhesive is high, and the chemical bonds of the molecules are not broken or decomposed under high temperature (or radiation irradiation). Silicone adhesives are not only resistant to high temperatures but also low temperatures, and can be used in a wide temperature range. Whether it is chemical properties or physical and mechanical properties, the change with temperature is very small.

  1. Weather resistance

The main chain of the silicone adhesive is -Si-O-, and there is no double bond, so it is not easy to be decomposed by ultraviolet light and ozone. Silicone adhesives have better thermal stability, radiation resistance and weather resistance than other polymer materials. The service life of silicone adhesives in natural environment can reach several decades.

  1. Electrical insulation properties

Silicone adhesives all have good electrical insulation properties, and their dielectric loss, withstand voltage, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best in insulating materials, and their electrical properties are affected by temperature and frequency. impact is small. Therefore, they are a stable electrical insulating material and are widely used in the electronics and electrical industries. In addition to excellent heat resistance, silicone adhesives also have excellent water repellency, which enables electrical equipment to be used in wet conditions with high reliability.

  1. physiological inertia

Polysiloxanes are among the most inactive compounds known. They are very resistant to biological aging, have no rejection reaction with animals, and have good anticoagulant properties.

  1. Low surface tension and low surface energy

The main chain of the silicone adhesive is very flexible, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it has lower viscosity, weaker surface tension, lower surface energy, and stronger film-forming ability than hydrocarbons of the same molecular weight. This low surface tension and low surface energy are the main reasons for its many applications: hydrophobicity, defoaming, foam stabilization, anti-sticking, lubrication, glazing and other excellent properties.

It is these excellent properties of silicone adhesives that are widely used in military/aerospace/construction/electrical/electronics/automobile/leather/textile/chemical/medical and medical industries.

Language »