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CPUThermal conductivity of passive means without other auxiliary way of thermal conductivity of thermal conductivity, by conducting strip their contact with the chip, heat conduction take away heat gathering on the chip, but the present computer parts and components manufacturing more and more complex, the instant heat, only a passive thermal far cannot satisfy the needs of CPU heat conduction, so now we can only in the low calorific value control motherboard north and south bridge chip or some graphics display chip calorific value is not high to see this kind of way of thermal conductivity.Air cooling heat conduction is now the most common and the highest utilization of a heat conduction, belongs to the active heat conduction, this heat conduction can solve our usual heat conduction needs, the technology is mature and the price is moderate, so it is widely used in the market. The air-cooled heat conductor is simple in structure, cheap in price, safe and reliable. However, it also has some disadvantages, such as not being able to lower the temperature below room temperature, noise due to the rotation of the fan, and the improper installation of the fan will cause vibration, which will damage the computer components in the long run, and the fan life is also limited.Water cooling heat conduction is the use of water to replace air, through the movement of water in the heat between the heat convection to take away the excess heat.The water cooling system works simply by using pumps to pull water out of the water storage unit, which is then piped into a heat exchanger that covers the CPU. The water then comes out of another opening in the heat exchanger and flows back through the water pipe to the storage tank. The whole water cooling system includes heat exchanger, circulation system, water tank, water pump and so on. The thermal conductivity of the water-cooling system is very strong, which is very suitable for some overclocking enthusiasts. The principle of liquid cooling heat conduction is the same as that of water cooling heat conduction, and the heat conduction method adopted by them is the same. The difference is that the flow in the circulation system is thermal silicone oil instead of water, which has obvious benefits. It will not cause the computer hardware damage due to the damage of the circulation system to the silicon oil flowing out. At present the market for the sale of the aokma liquid cooling thermal conductivity belongs to this type of thermal conductivity. In addition to the above mentioned methods of active heat conduction, there are heat conduction of heat pipe, heat conduction of semiconductor refrigerator, heat conduction of compressor refrigeration, heat conduction of liquid nitrogen, etc.

November 1, 2003 Daniel Blazej, Ph.D.Articles, Design, Materials, Compounds, Adhesives, Substrates, TIMsThermal Interface Materials, TIMIt doesn’t take long for an electronics assembler to realize that a thermal interface material (TIM) is essential when two or more solid surfaces are in the heat path. Standard machined surfaces are rough and wavy, leading to relatively few actual contact points between surfaces. The insulating air gaps created by multiple voids of “contacting” hard surfaces are simply too large a thermal barrier for even modest power applications. The first tactic in overcoming this barrier is to fill the voids and eliminate air by introducing a third material to the heat path that is fluidic and wets the surfaces. For more demanding thermal applications, the second tactic is to use a composite TIM containing fillers that enhance the conduction process of the third material. Yovanovich et al. have calculated that simply replacing air with grease can reduce the thermal resistance by a factor of five or so (depending on the surfaces and contact pressure). As shown in Figure 1, a thermal interface material essentially changes the thermal path between rough-surfaced solids from conduction through point contacts and air to conduction entirely through solids.Figure 1a. Conduction through point contacts and air between hard surfaces.Figure 1b. Conduction through TIM filling gaps.An important property of any TIM is its thermal conductivity, kTIM. Unfilled polymers have a thermal conductivity of about 0.1 W/mK. All modern TIMs are composites containing particulate fillers that push thermal conductivity up to the 7 W/mK range. Inorganic particulate fillers include aluminum oxide, magnesium oxide, aluminum nitride, boron nitride, and diamond powder. Metal fillers, notably silver, are also used. Unfortunately, high thermal conductivity alone is not enough to guarantee optimal system performance, as we will show later. In the descriptions of specific material classes, we will characterize performance with thermal resistance (normalized to a unit area on one square cm) that has units Kcm2/W, obtained from a one-dimensional heat flow calculation. In this way, we can account for the interfacial thickness. The specific value in any given application is highly dependent on the contact surfaces and pressures applied. Nevertheless, the ranges provided are representative of each material class. (Note: Many suppliers report resistance values in the mixed unit of Kin2/W. These need to be multiplied by 6.45 to match the units in this paper.)In addition to thermal performance, TIMs are selected on several other critical criteria as well. Ease of use in assembly and rework are important in high-end applications, as is long-term stability (reliability). The manufacturing process flow often dictates the material selection. In many cases, for example, the TIM is attached to a heat sink in one location while final module assembly occurs in another. Elastomeric pads were developed as an alternative to early grease solutions, largely for the manufacturing advantages they offered. Phase change materials emerged as a technology that captured the thermal performance advantage of grease and combined it with the assembly ease of a solid pad. Often overlooked in the TIM selection process are adhesives and solders. Both offer the unique advantage of secure mechanical bonding, eliminating the need for clamping hardware that the greases, pads, and phase change materials require.

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