Graphite sheets are materials with exceptionally high thermal conductivity in the plane direction of the material. At room temperature, they exhibit a thermal conductivity of over 1000 W/m·K, which is more than two to three times that of copper. These sheets are commonly used for heat dissipation in electronic devices such as laptops and smartphones.

In this study, we measured the thermal conductivity using Bethel's thermal diffusivity measurement device, the Thermowave Analyzer. Measuring graphite sheets is particularly challenging, and there are not many devices that can accurately measure them. Bethel’s device is the only one capable of measuring graphite sheets in accordance with the JIS R 7240 standard.

Since standard devices cannot measure at low temperatures, we used a custom device within our company to perform measurements at -40°C to 100°C. The specific heat and density were measured with separate devices to determine the thermal conductivity.

The graph below shows the results of the temperature dependence of the thermal conductivity.

Figure 1. Temperature Dependence of the Thermal Conductivity and Thermal Diffusivity of Graphite Sheets

At -40°C to 0°C, the thermal conductivity is 1400 W/m·K, but as the temperature increases, the thermal conductivity decreases, reaching 1200 W/m·K at 100°C.

This indicates that if the thermal conductivity is not measured at the operating temperature, the desired heat dissipation effect may not be achieved.

Copper, with a thermal conductivity of about 400 W/m·K at room temperature, is less than one-third of that of the graphite sheet. However, even at 300°C, copper maintains a thermal conductivity of 380 W/m·K, showing that its thermal conductivity does not change significantly with temperature.

For appropriate heat dissipation design, it is necessary to carefully evaluate the thermal conductivity of materials in the actual operating environment and select the materials accordingly.

Our company is capable of measuring various materials in special environments. Please feel free to contact us through our inquiry form at any time.