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    Affect the thermal silicone sheet and thermal grease the key factor
    日期:2018-02-19   浏览:1193次   来源:怡赛电子
    Influencing factors of thermal silicone sheet material

    Thermally conductive silicone sheet A thermally conductive dielectric material used to fill the air gap between a heat-generating device and a heat sink or metal base. Their flexible, resilient features make them suitable for covering very uneven surfaces. Heat is transferred from the separation device or the entire PCB to the metal case or the diffusion plate to improve the efficiency and the life of the heat-generating electronic component.

    Thermal silicone sheet material of the six key parameters:

     (1) thermal conductivity;

     (2) material thickness;

     (3) material hardness (compression ratio);

     (4) Thermal impedance;

     (5) breakdown voltage (insulation);

     (6) Sustainable work is stable.

    Factors affecting thermal silica film:

      In the use of thermal silica film, the pressure and temperature are mutually constrained, as the temperature increases, the equipment is running for some time, the thermal conductivity of the softening film materials, creep, stress relaxation phenomenon, the mechanical strength will decline , The pressure of the seal decreases, and vice versa.

     (1) Good flexibility and recovery to adapt to pressure changes and temperature fluctuations;

     (2) Proper flexibility, good fit with the contact surface;

     (3) does not pollute the process medium;

     (4) Adequate resilience without breaking due to stress and tightening forces;

     (5) low temperature does not harden, shrinkage is small;

     (6) processing performance, installation, compact convenient;

     (7) non-bonding sealing surface, easy to dismantle;

     (8) Cheap, long service life.

    Influencing Factors of Thermal Grease Material

    (1) Thermal Conductivity

       Thermal conductivity refers to the material in a stable heat transfer, 1m thick material, the temperature difference between the two sides of the surface is 1 degree (K, ℃), within 1 second (1S), through the heat transfer area of 1 square meter W / m · K (here K can be replaced by ℃).

    (2) Thermal Conductance

    Heat transfer coefficient In the past, said the total heat transfer coefficient. The current national standard standard uniform named heat transfer coefficient. The value of heat transfer coefficient K refers to the quantity of heat transferred through an area of 1 square meter within 1 s in a stable heat transfer condition with the air temperature difference of 1 degree (K, ° C) on both sides of the envelope and the unit is W / ㎡ · K Where K can be replaced by ℃).

    (3) Thermal Resistance

       The thermal resistance coefficient indicates the obstruction effect of the object on the heat conduction. The concept of thermal resistance and resistance are very similar, the unit is also similar (℃ / W), that is, the object heat transfer power is 1W, the temperature difference between the two ends of the thermal path. Obviously the thermal resistance is as low as possible, because the same ambient temperature and thermal conductivity, the lower the thermal resistance, the lower the temperature of the hot object. Thermal resistance and the size of the material used in thermal grease has a great relationship.

    (4) dielectric constant

       Dielectric constant is a very important parameter for some CPUs without metal cap protection, which is related to the problem of short circuit inside the computer. Ordinary thermal grease are used by the insulation material is better, but some special grease (such as silver grease, etc.) may have a certain conductivity. Many CPUs are now equipped with metal domes for thermal and core protection so you do not have to worry about the short circuit caused by spills.

    (5) Viscosity

       Viscosity is the two plates with an area of 1m² immersed in a liquid plate, the distance between the two plates is 1m, if the shear stress of 1N, the relative velocity between the two plates is 1m / s, the viscosity of the liquid is 1Pa. s. The flowing liquid is regarded as a lot of liquid layers that move in parallel with each other. The velocity of each layer is different, forming a velocity gradient (dv / dx), which is the basic characteristic of flow. Due to the velocity gradient, the slower flowing liquid layer impedes the faster liquid layer flow and, as a result, the liquid creates resistance to movement. In order for the fluid layer to maintain a certain velocity-gradient motion, it is necessary to apply an opposing force against the fluid to the fluid layer.

    (6) working temperature

       Working temperature is an important parameter to ensure that the thermal conductive material is in the solid or liquid state. When the temperature is too high, the thermal conductive material will be transformed into liquid. If the temperature is too low, it will become solid again due to the increase of the viscosity. . Thermal grease temperature is generally -50 ℃ ~ 230 ℃. For the thermal grease temperature, we do not have to worry about, after all, by conventional means it is difficult to CPU temperature beyond this range.

    (7) Oil off

       Oil release refers to the product at 200 ℃ for 24 hours after the precipitation of silicone oil, is to evaluate the product heat resistance and stability indicators. Will be coated with silica grease observed on white paper, you will see the phenomenon of oil leakage, the oil from the high degree of separation of oil obvious; or open the long-term placement with grease containers, grease away from the large grease, silicon See the oil surface or the container around the obvious oil separation phenomenon.
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