How to Choose and Use Heat Dissipating Materials

Date:10-08-2019

Apply property Regardless of the type of heat dissipati […]

Apply property
Regardless of the type of heat dissipation products chosen, there are also some key attributes that must be considered. These can be fairly simple parameters, such as operating temperature of the equipment, electrical requirements or other constraints, such as viscosity, curing time, etc.
Other parameters are more important for the device, and a single value may not be enough to select the right product. Thermal conductivity is a major example. The unit of thermal conductivity is W/m.K, which represents the thermal conductivity of materials. The accumulated thermal conductivity values are based on most product data tables, which can well reflect the expected thermal conductivity level, and thus can be used to compare different materials.
However, relying solely on the stack thermal conductivity does not necessarily lead to the most effective heat transfer.
The unit of thermal resistance is K. m2/W, which is the reciprocal of thermal conductivity. It takes account of the thickness of the interface. Although the measurement depends on the contact surface and the applied pressure, some general rules can be followed to ensure the minimum thermal resistance and thus maximize the heat transfer efficiency.
For example, a metal radiator has a higher thermal conductivity than a heat transfer compound used at the interface, so only a thin layer of the compound is needed. In this case, increasing the thickness will only increase the thermal resistance. Using the formula in Figure 3, we can compare the difference of thermal resistance between a 50-micron thermal adhesive and a 0.5-mm thickness thermal pad. Therefore, lower interfacial thickness and higher thermal conductivity can improve heat transfer to the greatest extent.
How to choose and use heat dissipation materials for prolonging the service life of LED?
Application Method
Another important factor we need to consider in product selection is the application of heat dissipation management materials. Any gap in the thermal conductive medium will lead to a decrease in the heat dissipation rate, whether for packaging compounds or interface materials.
For thermal conductive packaging resins, the key to success is to ensure that the resin can flow around the unit, including into any small gap. This uniform flow helps remove any air gap and ensures that no heat is generated throughout the unit. In order to achieve this application, the resin needs correct thermal conductivity and viscosity. Usually, as the thermal conductivity of the resin increases, the viscosity also increases.
For interfacial materials, the viscosity of the product or the possible minimum thickness in application have a great influence on the thermal resistance. Therefore, compared with products with low stacking thermal conductivity and low viscosity, compounds with high thermal conductivity and high viscosity can not diffuse uniformly to the surface, but have higher heat resistance and lower heat dissipation efficiency. In order to maximize heat transfer efficiency, users need to address stacking thermal conductivity, contact resistance, application thickness and process.
Table 2 highlights the need to consider these requirements. By measuring the temperature of heating device in use, the potential difference of heat dissipation is compared. These results are based on the work of an end user whose products are all thermal interface materials, using the same thickness and using the same method.
How to choose and use heat dissipation materials for prolonging the service life of LED?
Higher volume thermal conductivity of 12.5 W/m.K is not necessarily more effective than lower volume thermal conductivity of 1.4 W/m.K. This may be because the processing method is not suitable for the product, the product is not easy to use, or the product is not designed for that particular application. Whatever the reason, it highlights the importance of product application and product selection; by finding the right balance between these two parameters, maximum heat transfer efficiency can be achieved.
The original data in "Performance and Life of LED" can draw the conclusion that the use and correct selection of heat dissipation management materials are very important. Products in Table 2 #2. In the test application, the working temperature is reduced by 20%. If a similar percentage reduction is achieved for the LED under discussion, the efficiency can be greatly improved by lowering the operating temperature from 85 C to 68 C. Similarly, the lifetime can be increased from 95,000 hours to 120,000 hours. This is a great improvement.
By reducing the working temperature more, the efficiency can be increased by more than 3%, and the service life can be increased from 95,000 hours to 140,000 hours. Therefore, by choosing the right product and using the best process, the service life can be further increased by 15-20% when product #4 is used instead of product #2.
With the rapid development of electronic industry, more specifically, in the application of LED, the material technology must also meet the increasingly high heat dissipation requirements. The technology has also been transferred to packaging compounds to provide higher filler loads for products, thereby improving thermal conductivity and fluidity.

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