When it comes to cooling system, a lot of people think that the fan and heatsink. In fact, they ignore and an inconspicuous, but plays an important role in the vehicle - a heat transfer medium. Computer CPU is a typical need for good cooling of power devices, we say this is a thermally conductive material. Hope to talk about, all kinds of power to express their ideas and opinions heat from the device.
Why do we need a heat transfer medium?
Some may think that the surface of the bottom CPU or fins are very smooth, no heat transfer medium between them. This view is wrong! Since the machining is impossible to make a flat surface idealized, so there is a lot of ravines or gaps between the CPU and heat sink, which is air. We know that the high thermal resistance of air, it is necessary to reduce the thermal resistance with other substances, or performance of the radiator will be greatly reduced, or even can not play a role. So the heat transfer medium came into being, its role is to fill the gap between large and small processor and heat sink, increasing the contact area between the heat source and heat sink. Thus, the heat conduction effect is a heat medium, increasing the effective contact area of the CPU and the heat sink is its most important role.
Heat transfer medium have?
1, thermal grease
Thermal grease is the most widely used as a heat transfer medium, which is a silicone oil as a raw material, and a filler such as adding a thickener, an ester was heated after the decompression, grinding and other processes forming the substance have a certain viscosity, not grainy. Thermal grease operating temperature is generally -50 ℃ ~ 180 ℃, it has good thermal conductivity, high temperature resistance, aging and water features.
In the device cooling process, after heating to a certain state, thermal grease will exhibit semi-liquid state, fully fill the gap between the CPU and the heat sink so that the engagement between the two is more compact, thereby strengthening heat conduction. Typically, thermal grease is insoluble in water, easily oxidized, also has some lubricity and electrical insulation.
2, thermal silica
And as thermal grease, thermal silica also add certain chemicals from the oil, and chemically processed. But with thermal grease it is different, in that it has added some chemicals goo, so thermal silica bonding finished product has a certain power.
Thermal silica biggest feature is solidified hard, slightly lower than its thermal performance thermal grease. At present, there are two thermal silica: A solidified as a white solid, after solidification another with a shiny solid black. Most manufacturers are accustomed to using silica gel as a first adhesive between the heat sink and hot objects, and it has the advantage of stickiness very strong, but this has just become its shortcomings. We need to repair, often at tremendous efforts after the bonding of the separation device and the heat sink, you will find the contact surface of both the residual quantities of solid white silicone, the silicone is quite difficult to clean.
In contrast, the second silicone advantage is more obvious: one to its thermal efficiency than the first, second, after its solidification generates more brittle black solid residue was easily removed. In any case, the thermal efficiency of thermal silica is not strong, and easy to put the device and the heat sink "dead stick" unless special circumstances therefore recommended to be used.
3, soft silicone thermal pad
Soft silicone thermal insulation mat with good thermal insulation capacity and a high level of pressure, thermal conductivity 1.75W / mK, anti-breakdown voltage of 4000 volts or more is to replace the thermal grease replacement products, the material itself has a certain flexibility, good fit, so as to achieve the best thermal conductivity and heat dissipation purpose power devices and cooling aluminum or machine housing between the electronics industry in line with the current requirements of thermally conductive material, is an alternative to thermal grease thermal paste plus mica Best Product sheet dual cooling system. These products can be cut, which will help to meet the automation of production and product maintenance.
Silicone thermal insulation pads process thickness ranging from 0.5mm ~ 5mm, one plus every 0.5mm, namely 0.5mm 1mm 1.5mm 2mm ~ 5mm, special requirements may be increased to 15mm, specifically for the use of the gap heat transfer design production, can fill the gap, complete heating and cooling parts of the heat transfer site, but also play the role of shock absorption insulation sealing to meet the community miniaturization slim design requirements, it is very technology and use of new materials.
Fire retardant performance meets UL 94V-0 requirements, and comply with EU SGS environmental certification
4, graphite gasket
This heat transfer medium rare, generally less heat is applied over a number of objects. It uses a graphite composite material, after a certain chemical treatment, with excellent thermal conductivity for electronic chips, CPU and other products of the cooling system. In the early boxed Intel P4 processor, the attachment material is graphite thermal pads on the bottom of the radiator called M751, the advantages of the heat medium is not sticky, does not remove the radiator when The CPU from the base "uprooted."
These several common heat transfer medium, aluminum foil thermal pads, phase change thermal pads (plus protective film), also belong to the heat transfer medium, but these products are rarely seen in the market.
5, phase change thermal interface material
The phase change material is mainly used for low thermal resistance, high thermal conduction efficiency of high-performance devices, mainly for the microprocessor and requires low thermal resistance of power devices, to ensure good heat dissipation. Phase change thermal material at 45 ℃ -58 ℃ and downstream into the phase change in pressure and irregular filling the gap between the heating element and heat sink, squeeze out the air to form a good thermal interface.
Performance parameters are also thermally conductive material
Since the thermal grease is a kind of chemical substances, it also reflected the characteristics of their work-related performance parameters. As long as we understand the meaning of these parameters, we can determine the level of performance of a heat conductive material.
1, thermal conductivity
Consistent heat transfer coefficients of thermal grease and radiator, its unit is W / mK, ie cross-sectional area of 1 square meter of the temperature difference between the cylinder along the axial distance of 1 m is 1 Kelvin (1K = 1 ℃) when heat conduction power. The larger the value, indicating that the heat transfer rate of the material, the faster, the better the thermal performance. Currently the mainstream of thermal grease thermal conductivity of greater than 1.134W / mK.
2, operating temperature
Operating temperature is an important parameter to ensure thermal conductive material in solid or liquid, high temperature, thermally conductive material due to be converted to liquid; temperature is too low, it will become solid due to increased viscosity, neither of which is conducive to heat . Thermal grease operating temperature is generally -50 ℃ ~ 180 ℃. For thermal grease operating temperature, we should not worry, after all it is difficult to CPU temperature exceeds this range by conventional means.
3, thermal resistivity
Resistance to heat transfer coefficient means that something is hampered results. The concept of thermal resistance is very similar, but also with similar units (℃ / W), that is, when the object continuous heat power is 1W, the temperature difference across the heat conduction path. Thermal resistance is clearly better, since the same ambient temperature and thermal power, the lower the resistance, the lower the temperature of hot objects. Material size and thermal grease thermal resistance used in a great relationship.
4, the dielectric constant
For some there is no metal cover to protect the CPU, the dielectric constant is a very important parameter, which is related to whether the computer's internal short circuit problems. Ordinary thermal grease is used insulating material better, but some special grease (such as silver grease, etc.) may have some electrical conductivity. Now a lot of CPU are fitted with a metal roof for heat conduction and protecting the core, so do not worry thermal grease overflow problem caused a short circuit. The current mainstream radiator used thermal grease dielectric constant greater than 5.1.
5, viscosity
That guidance viscosity hot viscosity grease. In general, thermal grease viscosity at 68 or so. |
