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Test standard ASTM D5470 for thermal conductivity.

日期：2018-09-14 20:43:33

Test standard ASTM D5470 for thermal conductivity.

Answer: ASTM D5470 is based on ideal thermal condition: place test sample in appointed thickness between two parallel and heat isothermal surfaces; thermal gradient brought to the sample by temperature difference of two contact surfaces, which leads to heat flow through the sample. The heat flow passes through the test sample surface perpendicularly and evenly to ensure none transverse heat transfer. ASTM D5470 is used to test thermal impedance of electrical insulation materials in a steady state, mainly including the following materials: viscos liquid deforming infinitely after stress, such as thermal grease, phase change materials, hard rubber, etc., which do not show elastic characteristics and not revert to the original state when stress removed; viscoelastic solids, deformation stress is always balanced with the internal stress of the material, such as gel, soft rubber, which shows the linear elastic characteristics related to the material thickness; elastic solids in tiny deformation, such as ceramics, metal or some plastics.
 

Thermal resistance of interface contact is present between the sample and the testing interface, which is largely affected by the surface properties of the sample and by the pressure on the sample surface brought from the test interface.
 

The requirement for test equipment: there has to be 0.4 micron roughness on test surface and 5 micron parallelism; the heater must be protected with high quality insulation materials to prevent heat flow leakage in the test process.
 

The thermal resistance is apparent tested by this equipment, which means the measured thermal resistance R is the sum of the material thermal resistance R1 and the interface thermal resistance R2 between the equipment and the material.
 

To test material’s thermal conductivity has to remove contact thermal resistance R2. This test method can test the area thermal resistance of the same materials in 3 thickness (H1，Ri1;H2，Ri2；H3，Ri3). The linear relation between thickness and area thermal resistance is as below:

 

 

R2 is the contact thermal resistance between equipment and thermal interface material. The thermal conductivity K is the inverse of the fitting curve slope.
The following is the schematic diagram of ASTM D5470 standard test equipment.
 

 

Due to the presence of contact thermal resistance R2, the product thermal resistance tested by single thickness may be higher and the thermal conductivity calculated as per the thermal resistance may be lower.


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