Application and Introduction of Common Thermal Conductive Materials
Why do you need a heat-conducting medium Some people may think that the CPU surface or the bottom of the heat sink are very smooth, and there is no need for heat conducting medium between them. This view is wrong! Because machining can't make ideal flat surface, there are many ravines or gaps between CPU and radiator, which are all air. We know that the thermal resistance of air is very high, so other substances must be used to reduce the thermal resistance, otherwise the performance of the radiator will be greatly reduced or even unable to play a role. Therefore, the heat-conducting medium arises at the historic moment. Its function is to fill the large and small gaps between the processor and the heat sink and increase the contact area between the heat source and the heat sink. Therefore, heat conduction is only one function of heat conducting medium, and increasing the effective contact area between CPU and radiator is its most important function. What are the heat conducting media? I. thermal conductive silicone grease Heat-conducting silicone grease is the most widely used heat-conducting medium at present. It is an ester formed after heating, decompression, grinding and other processes with silicone oil as the raw material and thickening agents and other fillers. The substance has certain viscosity and no obvious graininess. The working temperature of thermal conductive silicone grease is generally-50℃ ~ 180℃, which has good thermal conductivity, high temperature resistance, aging resistance and waterproof properties. In the heat dissipation process of the device, after heating to a certain state, the heat-conducting silicone grease presents a semi-fluid state, which fully fills the gap between the CPU and the heat sink, so that the two are more tightly jointed, and further heat conduction is strengthened. Under normal circumstances, the heat-conducting silicone grease is insoluble in water, is not easy to oxidize, and has certain lubricity and electrical insulation. II. Thermal Conductive Silica Gel Like heat-conducting silicone grease, heat-conducting silicone is made by adding certain chemical raw materials to silicone oil and chemical processing. However, unlike heat-conducting silicone grease, there is some viscous substance in the added chemical raw materials, so the finished heat-conducting silicone has certain cohesive force. The biggest characteristic of thermally conductive silica gel is its hard texture after solidification, and its thermal conductivity is slightly lower than that of thermally conductive silicone grease. At present, there are two kinds of thermally conductive silica gels on the market: one is a white solid after solidification, and the other is a black solid with luster after solidification. General manufacturers are used to using the first type of silica gel as the adhesive between the heat sink and the heating object. Its advantage is very strong adhesion, but this has become its shortcoming. When we need maintenance, we often find a large amount of solid white silica gel left on the contact surface between the bonded device and the heat sink after we try our best to separate them. These silica gels are quite difficult to clean. In contrast, the second type of silica gel has obvious advantages: firstly, its heat dissipation efficiency is higher than that of the first type; secondly, the black solid generated after solidification is brittle and the residue is easy to remove. In any case, the thermal conductivity of thermally conductive silica gel is not strong, and it is easy to "stick" the device and the heat sink, so it is recommended to users only under special circumstances. Three, graphite gasket This kind of heat-conducting medium is relatively rare and is generally applied to some objects with less heat generation. It is made of graphite composite material and has excellent heat conduction effect after certain chemical treatment. It is suitable for heat dissipation systems of electronic chips, CPU and other products. In the early Intel boxed P4 processor, the substance attached to the bottom of the heat sink was a graphite heat-conducting gasket called M751. The advantage of this heat-conducting medium is that it has no viscosity and will not "uproot" the CPU from the base when removing the heat sink. In addition to the above several common heat conducting media, aluminum foil heat conducting gaskets, phase change heat conducting gaskets (plus protective films) are also heat conducting media, but these products are rare in the market. Four, soft silicone thermal pad The soft silica gel thermal insulation pad has good thermal conductivity and high-grade pressure insulation, thermal conductivity coefficient is 1.75W/mK, and voltage breakdown resistance value is over 4000 V. It is a substitute product for thermal conductive silicone grease. The material itself has certain flexibility, and is well attached between the power device and the heat dissipation aluminum sheet or machine shell, thus achieving the best thermal conductivity and heat dissipation purposes. It meets the requirements of the current electronic industry for thermal conductive materials, and is the best product for the binary heat dissipation system replacing the thermal conductive silicone grease thermal conductive paste and mica sheet. This kind of products can be cut at will, which is beneficial to meet the requirements of automatic production and product maintenance. The technological thickness of the silicone heat-conducting insulation pad varies from 0.5mm to 5 mm, and every 0.5 mm plus, that is, 0.5 mm 15mm 1.5 mm 2 mm to 5 mm, the special requirement can be increased to 15 mm. It is specially produced for the design scheme of using gaps to transfer heat. It can fill gaps, complete heat transfer between heating parts and heat-dissipating parts, and also play the role of shock absorption, insulation and sealing, etc. It can meet the design requirement of miniaturization and ultrathinness of social equipment, and is a new material with high technological property and usability. The flame retardant and fireproof performance meets the requirements of U.L 94V-0 and meets the environmental protection certification of EU SGS.