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How to choose a thermal pad. Professional thermal gel, thermal grease manufacturer
The thermal pad is to fill the air gap between the heating device and the radiator or metal base. Its flexibility and elasticity enable it to cover very uneven surfaces. The heat is transferred from the separate device or the entire PCB to the metal casing or diffuser, thereby improving the efficiency and service life of heating electronic components. There are many thermally conductive silicone gaskets on the market. In the use of gaskets, pressure and temperature restrict each other. As the temperature rises, after the equipment runs for a period of time, the gasket material softens, creeps, and stress relaxes, the mechanical strength decreases, and the sealing pressure decreases.
Thermally conductive gaskets are mainly used for the bottom or frame of radiators, high-speed hard drives, RDRAM memory modules, micro heat pipe radiators, automotive engine control devices, communication hardware portable electronic devices, semiconductor automatic test equipment, etc. So how can we find a suitable thermal pad among many specifications? Mainly considered from the following aspects:
The choice of substrate.
Common thermal pads have three polymer materials as the matrix, silicone, polyurethane and acrylic resin. The latter two are generally called silicon-free thermal pads. Silicone thermally conductive gasket inherits the characteristics of silicone material and is a widely used thermally conductive gasket, but one of its shortcomings is the precipitation of silicone oil, which cannot be used in certain situations (such as optical equipment, hard disks, etc.). The main advantage of silicone-free gaskets is that there is no silicone oil precipitation, and the disadvantages are also obvious, including poor temperature resistance and high hardness.
Select thermal conductivity.
It is necessary to decide which thermal pad to choose according to the application environment and requirements. First look at the heat generation of the component. The second is the design gap thickness, which is expected to reduce the temperature and heat transfer area. According to these, the area thermal resistance is estimated according to the Fourier equation, and then the required product is determined according to the thickness thermal resistance curve of different thermal pads.
Choice of structure.
Generally speaking, adding reinforcing materials will increase the physical strength, but will sacrifice some thermal conductivity. If the specification is relatively large, it will have little effect on thick products, but it will have a certain effect on thin (less than 1mm) products. The gasket without reinforced material will elongate and severely break, while the strength of the gasket with reinforced material will not change. The gasket on the surface of the silicone cloth has puncture resistance and better electrical insulation.
Choice of thickness.
The thickness of the gasket generally needs to be selected according to the designed gap width. It is recommended to compress 20-50% of the thickness to be close to the gap thickness. For example, if the gap thickness is 1.5mm, a 2.0mm product can be recommended because the 2.0 product is the same as the gap thickness after being compressed by 25%. The thickness of the product can not only ensure the filling of the gap, but also will not generate excessive stress. The figure below is the compressibility curve of the thermal pad. From the figure, we can roughly understand the magnitude of the instantaneous compressive stress at a certain compression rate. The good news is that the stress to maintain the compressibility is much smaller than the instantaneous compressive stress.
The hardness of the product has a great influence on the compression performance. Under the premise of ensuring physical strength, it is recommended to give priority to low-hardness products. In addition to lower stress, low-hardness gaskets have better interface affinity and lower interface thermal resistance.
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