When it comes to cooling systems, many people think of fans and fins. In fact, they ignore a medium that is not impressive but plays an important role - heat conducting medium. Computer CPU is a typical power device that needs good heat dissipation. Let's talk about heat conduction materials. I hope you can discuss and express your own experience and views on heat dissipation of various power devices. Why do you need heat conduction media? Some people may think that the surface of CPU or the bottom of heat sink are smooth, and there is no need for heat conduction media between them. This view is wrong! Because machining can not make an ideal flat surface, there are many gullies or gaps between CPU and radiator, all of which are air. We know that the thermal resistance of air is very high, so we must use other substances to reduce the thermal resistance, otherwise the performance of the radiator will be greatly reduced and can hardly play a role. Therefore, the heat conduction medium came into being. Its function is to fill the large and small gap between the processor and the radiator and increase the contact area between the heat source and the heat sink. Therefore, heat conduction is only a function of heat conducting medium, and increasing the effective contact area between CPU and radiator is its important role.
What are the heat conducting mediums? 1. Heat conducting silicone grease heat conducting silicone grease is a kind of heat conducting medium widely used at present. It is an ester formed after heating, decompression, grinding and other processes with silicone oil as raw material and thickener and other fillers. The material has a certain viscosity and no sense of particle. The working temperature of thermal conductive silicone grease is generally - 50 ℃ ~ 180 ℃. It has good thermal conductivity, high temperature resistance, aging resistance and waterproof characteristics. In the heat dissipation process of the device, after heating to a certain state, the heat conductive silicone grease presents a semi fluid state, filling the gap between the CPU and the heat sink, making the connection between them closer, so as to strengthen heat conduction. Under normal circumstances, the thermal conductive silicone grease is insoluble in water and is not easy to be oxidized. It also has certain lubricity and electrical insulation. (at present, the better brands in the market include Dow Corning, Xinyue, and domestic good thermal conductive silicone grease Youtian Zhongshan (it is said to be a brand in Hong Kong) , Li Feng Electronics, Huaneng Zhiyan, among the domestic brands, I have tried the 7.0 thermal conductivity of tianzhongshan 940 and kuneng Zun. In the early stage, the temperature of kuneng Zun will be slightly better than 940 by 0.5 ℃, but the temperature in Zhongshan will be 1 ℃ higher than that of kuneng Zun two days later. I don't know if it's my method. After asking the manufacturers and peers in the industry, I come to the conclusion that kuneng Zun takes radiator as its core Live, the thermal conductive silicone grease is sub packaged from Dow Corning 5126 and Xinyue 7762, and the other part uses the products of tianzhongshan and Huaneng Zhiyan as raw materials, so they are not put into domestic brands.) 2. Thermal conductive silica gel (thermal conductive adhesive) thermal conductive silica gel adopts a molecular chain based adhesive (107 adhesive) containing c-Si results, and thermal conductive powder is added to the base adhesive. Then the molecular chains are crosslinked by a crosslinking agent to form a thermal conductive adhesive that can bond materials and conduct heat. Its thermal conductivity is slightly lower than that of thermal conductive silicone grease, but it has a bonding function than thermal conductivity. It can be widely used in some electronic thermal components that need bonding. However, because its thermal conductivity is not as high as that of thermal conductive silicone grease and its thermal resistance is higher than that of silicone grease, it can not be used in fields with high thermal conductivity requirements. (at present, there are many brands of thermal conductive silica gel in the market as well as silicone grease, but what I want to say is that the thermal conductivity of thermal conductive silica gel cannot be improved due to its special properties and packaging requirements. Generally, the thermal conductivity at the domestic level is between 0.8-1.5, which is not unknown, but it is often achieved at the expense of other properties, such as viscosity Relay, shear strength. The more important thing is its surface wettability (if you don't understand the importance of surface wettability, you can baidu it, or see my next article report high). At present, there are not many brands in this area because of their application. The brands are: Dow Corning, Xinyue, tensan, and sisun). 3. Graphite gasket is a rare heat transfer medium, It is generally applied to some objects with small heat. It adopts graphite composite material, after certain chemical treatment and heat conduction, and is suitable for the heat dissipation system of electronic chips, CPUs and other products. In the early Intel boxed P4 processor, the material attached to the bottom of the radiator was a graphite thermal conductive gasket called m751 (Fig. 2). The advantage of this thermal conductive medium was that it had no viscosity and would not "pull the CPU from the base" when removing the radiator. In addition to the above common heat transfer media, aluminum foil heat transfer gasket and phase change heat transfer gasket (with protective film) also belong to heat transfer media, but these products are rare in the market. 4 soft silica gel thermal conductive pad soft silica gel thermal conductive insulating pad has good thermal conductivity and high-grade withstand voltage insulation, with thermal conductivity of 1.75w/mk and voltage breakdown resistance of more than 4000V. It is an alternative product to replace thermal conductive silicone grease. Its material itself has certain flexibility and fits well between power devices and heat dissipation aluminum fins or machine shell, so as to achieve good thermal conductivity and heat dissipation, It meets the requirements of the current electronic industry for heat-conducting materials. It is a good product to replace the binary heat dissipation system of heat-conducting silicone grease heat-conducting paste and mica sheet. This kind of products can be cut arbitrarily, which is conducive to automatic production and product maintenance. The process thickness of silica gel heat conductive insulating pad varies from 0.5mm to 5mm. It is added every 0.5mm, i.e. 0.5mm1mm1.5mm2mm to 5mm. It can be increased by 15mm for special requirements. It is specially produced for the design scheme of heat transfer through the gap. It can fill the gap and complete the heat transfer between the heating part and the heat dissipation part. At the same time, it also plays the role of shock absorption, insulation and sealing, and can meet the design requirements of miniaturization and ultra-thin of social equipment, It is a new material with processability and usability. Its flame retardant and fireproof performance meets the requirements of u.l94v-0 and meets the environmental protection certification of EU SGS. The brands include: bages, Laird, Fuji glass, tensan, aochuan and boon 5 phase change heat conduction materials. Phase change materials are mainly used for high-performance devices requiring low thermal resistance and high heat conduction efficiency, microprocessors and power devices requiring low thermal resistance, To ensure good heat dissipation. The phase change thermal conductive material changes phase at 45 ℃ - 58 ℃, flows into and fills the irregular gap between the heating body and the radiator under pressure, and squeezes out the air to form a good thermal conductive interface
Thermal conductive materials also have performance parameters. Since thermal conductive silicone grease belongs to a chemical substance, it also has relevant performance parameters reflecting its own working characteristics. As long as we understand the meaning of these parameters, we can judge the performance of a thermal conductive material: bels, Laird 1. Working temperature working temperature is an important parameter to ensure that the thermal conductive material is in solid or liquid state. If the temperature is too high, the thermal conductive material will be transformed into liquid; If the temperature is too low, it will become solid due to the increase of viscosity, which is not conducive to heat dissipation. The working temperature of heat conductive silicone grease is generally - 50 ℃ ~ 180 ℃. We don't have to worry about the working temperature of thermal conductive silicone grease. After all, it is difficult to exceed the temperature of CPU by conventional means. 2. Thermal conductivity the thermal conductivity of the thermal conductive silicone grease is basically the same as that of the radiator. Its unit is w / MK, that is, the heat conduction power when the temperature difference of the cylinder with a cross-sectional area of 1 square meter along the axial direction is 1 kelvin (1K = 1 ℃). The larger the value, the faster the heat transfer rate and the better the thermal conductivity of the material. At present, the thermal conductivity of mainstream thermal conductive silicone grease is greater than 1.134w/mk. 3. Thermal resistance coefficient thermal resistance coefficient represents the obstruction of an object to heat conduction. The concept of thermal resistance is similar to that of resistance, and the unit is also similar (℃ / W), that is, the temperature difference at both 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 heat conduction power, the lower the thermal resistance, the lower the temperature of the heating object. The size of thermal resistance is closely related to the material used in thermal conductive silicone grease. 4. Dielectric constant for some CPUs without metal cover protection, dielectric constant is an important parameter, which is related to whether there is a short circuit in the computer. Ordinary thermal conductive silicone grease adopts materials with good insulation, but some special silicone grease (such as silver containing silicone grease) may have certain conductivity. Now many CPUs are equipped with metal top covers for heat conduction and core protection, so there is no need to worry about the short circuit caused by the overflow of heat conduction silicone grease. At present, the dielectric constant of thermal conductive silicone grease used in mainstream radiators is greater than 5.1. 5. Viscosity refers to the viscosity of hot silicone grease. The viscosity of thermal conductive silicone grease is about 68. 6. Insulated heat conducting graphite sheet graphite heat sink is a new heat conducting and radiating material with unique grain orientation and uniform heat conduction along two directions. The lamellar structure can well adapt to the surface, shield heat sources and components, and improve the performance of consumer electronic products. The product not only dissipates heat evenly, but also provides heat isolation in terms of thickness. The molecular structure diagram of heat conducting graphite sheet is as follows: molecular structure diagram of heat conducting graphite sheet. The unique combination of heat dissipation and heat insulation properties of graphite heat conducting sheet (GTS) solution makes (GTS) heat conducting graphite an outstanding material choice for heat management solutions. (GTS) thermal conductive graphite sheet has ultra-high thermal conductivity in the range of 150-1500w / m-K. The chemical composition of (GTS) thermal flexible graphite sheet is mainly a single carbon (c) element, which is a natural element mineral. Thin film polymer compounds can obtain (GTS) graphitized films under high temperature and high pressure by chemical methods, because carbon is a non-metallic element, but it has the conductivity and thermal conductivity of metal materials and plasticity like plastics, Moreover, there are some good process properties such as special thermal properties, chemical stability, lubrication and coating on solid surfaces. Therefore, heat conductive graphite (GTS) has been widely used in many fields such as electronics, communication, lighting, aviation, national defense and military industry. (GTS) graphite heat conductive materials provide a unique solution with comprehensive high performance for the heat management industry. (gtss) heat conducting graphite material brings new technical solutions to the increasingly extensive industrial heat dissipation field through a series of different heat management solutions and applications, (GTS) heat conducting graphite material products provide innovative new technologies for heat management in the electronic industry. (GTS) thermally conductive graphite provides better thermal conductivity by reducing the weight of devices. The (GTS) thermally conductive graphite heat dissipation solution is a new application scheme for thermal design. (GTS) heat conducting graphite can effectively solve the thermal design problems of electronic equipment. It is widely used in electronic products such as PDP, LCDTV, notebook PC, UMPC, flatpaneldisplay, MPU, projector, powersupply, led and so on. Graphite heat dissipation materials have been widely used in communication industry, medical equipment, Sony / Dell / Samsung notebook, ZTE mobile phone, Samsung PDP, PC memory module, led substrate and so on. Comparison of thermal conductivity between GTS thermally conductive graphite and common metal materials: comparison of thermal conductivity between GTS thermally conductive graphite and common metal materials thermal diffusion diagram of GTS thermally conductive graphite sheet: thermal diffusion diagram of GTS thermally conductive graphite sheet characteristics: product characteristics: the surface can be combined with metal, plastic, self-adhesive and other materials to meet more design functions and needs. Low thermal resistance: the thermal resistance is 40% lower than aluminum, 20% lower than copper, light weight: 25% lighter than aluminum, 75% lighter than copper, high thermal conductivity: the graphite heat sink can be smoothly attached to the plane and curved surface, and can be cut according to the needs of customers. The application of heat conducting graphite sheet is widely used in PDP, LCDTV, notebook PC, UMPC, flatpaneldisplay, MPU, projector, powersupply, led and other electronic products. Graphite heat dissipation materials have been widely used in communication industry, medical equipment, Sony / Dell / Samsung notebook, ZTE mobile phone, Samsung PDP, PC memory module, led substrate and so on.