For thermal conductive materials such as thermal pads, thermal grease, and thermal gel, the thermal conductivity tests often used in laboratories include the steady-state hot plate method and the laser flash method. The principles are derived from Fourier’s law. There are many methods to test thermal conductivity. The test methods that have been recognized earlier in the field of thermal conductive materials are ASTM E1530, ASTM D5470, and ASTM E1461.
The international general standard adopts ASTM D5470, ASTM E1461 and ASTM E1530 of the American Society for Testing and Materials (ASTM). The data obtained by various test methods and test standards are quite different. The test values of ASTM D5470 and ASTM E1461 are relatively similar, and the ASTM D5470 standard is used for the thermal pads CoolThermo, because this test method can better simulate the actual use state and reflect the thermal conductivity. Most of the famous foreign manufacturers of thermal pads also use this test method and condition.
ASTM D5470: Standard Test Method for Heat Transport Properties of Thermally Conductive Electrical Insulating Materials
Using the hot plate method/heat flow meter steady-state method, a certain heat flow is applied to the sample, the thickness of the sample and the temperature difference between the hot plate and the cold plate are measured, and the thermal conductivity of the sample is obtained. The sample needs to be a larger block. to obtain a sufficient temperature difference.
ASTM E1461: Test Method for Determining the Thermal Diffusivity of Solids by the Flash Method (Laser Flash Method)
High-intensity energy pulses irradiate small, thin disk samples for short periods of time. The energy of the pulse is absorbed by the front surface of the sample and the resulting temperature rise on the back surface is recorded (temperature autograph). The value of the thermal diffusivity is calculated from the thickness of the specimen and the time required for the rear surface temperature to rise to the maximum value of a certain ratio. The principle is that a laser beam hits the upper surface of the sample, and an infrared detector is used to measure the temperature change of the lower surface. The actual measured data is the thermal diffusivity of the sample.
ASTM E1530: Test Standard for Evaluating Heat Transfer Resistance of Materials Using the Protected Heat Flow Meter Technique.
Although the test standard is the same, the data tested by different equipments are quite different. Most foreign manufacturers of thermal conductive materials use the ASTM D5470 standard, because this test method can better simulate the actual use state and reflect the thermal conductivity. ASTM E1461 is a laser flash method that reflects the thermal conductivity within the material itself, but does not consider the influence of interface contact thermal resistance. ASTM E1530 is a test standard for evaluating the heat transfer resistance of materials. It is generally used less in the field of thermal pads. The measured data is much larger than that of ASTM D5470 and ASTM E1461.
CoolThermo, as a manufacturer of thermal pads with ten years of production experience, adopts ASTM D5470 as the thermal conductivity test standard for thermal pads, because this standard has the advantages that other test standards are incomparable: after simple modification, it can be obtained close to the actual working conditions. It can realize the quasi-in-situ test (In-situ Test), and meet the thermal performance measurement in the whole process of different pressure, different temperature, humidity and temperature aging.