Briefly introduce several heat-dissipating materials for heat- dissipating materials
When it comes to cooling systems, many people think of fans and heat sinks. In fact, they neglected a medium that is not eye-catching but plays an important role. Computer CPU is a typical power device that needs good heat dissipation. Let's talk about thermal conductive materials. I hope you can discuss and express your own heat dissipation for various power devices.
Why does the heat-dissipating material die-cut require thermal media?
Some people may think that the CPU surface or the bottom of the heat sink is very smooth, and no heat transfer medium is needed between them. This view is wrong! Since machining is not possible to create an ideal flat surface, there are many gullies or voids between the CPU and the heat sink, all of which are air. We know that the thermal resistance of air is very high, so other materials must be used to reduce the thermal resistance, otherwise the performance of the heat sink will be greatly reduced or even impossible to function. Then the heat-conducting medium came into being. Its function is to fill the gap 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 a function of the heat transfer medium, and increasing the effective contact area of the CPU and the heat sink is its most important function.
What are the heat-dissipating materials for heat-dissipating materials ?
1, thermal grease
Thermal grease is the most widely used heat transfer medium. It is a kind of ester formed by using silicone oil as raw material and adding a thickener and other fillers after heating, decompression, grinding and other processes. It has a certain consistency and no obvious graininess. Thermal grease has a working temperature of -50 ° C to 180 ° C. It has good thermal conductivity, high temperature resistance, aging resistance and water resistance.
During the heat dissipation process of the device, after heating to a certain state, the thermal grease exhibits a semi-liquid state, fully filling the gap between the CPU and the heat sink, so that the two are more closely coupled, thereby enhancing heat conduction. Under normal circumstances, thermal grease is insoluble in water, is not easily oxidized, and has certain lubricity and electrical insulation.
2, thermal silica gel
Like thermal grease, thermal silica gel is also made from silicone oil and chemically processed. However, unlike thermal grease, there is some kind of viscous material in the chemical raw materials it adds, so the finished thermal silica gel has a certain adhesive force.
The most important feature of thermal silica gel is that it has a hard texture after solidification and its thermal conductivity is slightly lower than that of thermal grease. At present, there are two kinds of thermal silica gel on the market: one is a white solid after solidification, and the other is a solid black pigment after solidification. The average manufacturer is accustomed to using the first type of silica gel as a bonding agent between the heat sink and the heat generating object. The advantage is that the viscosity is very strong, which is precisely its disadvantage. When we need to repair, often after a lot of effort to separate the bonded device and the heat sink, we will find a large amount of solid white silica gel on the contact surface of the two. These silica gels are quite difficult to clean.
In contrast, the second silica gel advantage is more obvious: first, its heat dissipation efficiency is higher than the first one, and secondly, the black solid formed after solidification is brittle, and the residue is easily removed. In any case, the thermal conductivity of the thermal silica gel is not strong, and it is easy to "stick" the device and the heat sink, so it is recommended to use it unless otherwise specified.
3, soft silicone thermal pad
The soft silicone thermal insulation pad has good thermal conductivity and high-grade pressure insulation, thermal conductivity of 1.75W/mK, and voltage breakdown resistance of 4000 volts or more. It is an alternative to thermal grease, and the material itself has certain The flexibility, good fit between the power device and the heat-dissipating aluminum sheet or the machine casing, so as to achieve the best heat conduction and heat dissipation purposes, in line with the current requirements of the electronic industry for thermal materials, is an alternative thermal grease grease paste plus mica The best product for the binary cooling system. These products can be cut at will, which is convenient for automated production and product maintenance.
The thickness of the silicone thermal insulation mat varies from 0.5mm to 5mm, 0.5mm per mm, ie 0.5mm 1mm 1.5mm 2mm~5mm, and the special requirement can be increased to 15mm. It is specially designed for the transmission of heat through the gap. Filling the gap, completing the heat transfer between the heat-generating part and the heat-dissipating part, and also functioning as a shock-absorbing and insulating seal, can meet the design requirements of miniaturization and ultra-thinness of the social equipment, and is a new material with great processability and usability. Flame retardant fire resistance meets UL 94V-0 requirements and complies with EU SGS environmental certification
4, graphite gasket
Such a heat transfer medium is relatively rare and is generally applied to some objects that generate less heat. It uses graphite composite material, after a certain chemical treatment, the thermal conductivity is excellent, suitable for the heat dissipation system of electronic chips, CPU and other products. In the early Intel boxed P4 processor, the material attached to the bottom of the heat sink was a graphite thermal pad called M751. The advantage of this heat transfer medium is that it has no stickiness and will not be removed when the heat sink is removed. Pull the CPU up and down from the base.
In addition to the above-mentioned several common heat conduction media, aluminum foil thermal conductive gaskets, phase change thermal conductive gaskets (plus protective film), etc. are also heat transfer media, but these products are rare on the market.
5, phase change thermal material
Phase change materials are mainly used in high performance devices requiring low thermal resistance and high heat transfer efficiency. They are mainly used in microprocessors and power devices requiring low thermal resistance to ensure good heat dissipation. Phase change thermal materials are between 45 ° C and 58 ° C. A phase change occurs and flows under pressure to fill the irregular gap between the heating element and the heat sink, and the air is squeezed out to form a good thermal interface.
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