Thermal Conductivity and Thermal Resistance of TIMs

To ensure optimum performance and prevent premature component failure, heat must be dissipated from electronic devices efficiently and quickly. In addition to LED inverters,  photovoltaic inverters need excellent thermal management, just like CPUs and GPUs.

Thermal Interface Materials

Thermal interface materials (TIMs) are available as tapes, filled elastomer pads, phase-change materials, and greases. To maintain the performance of the thermal joint and to hold the parts together and, a lot of these materials need a mechanical clamping pressure. The applied pressure can help to expel the air and create more complete wetting of the material at the interface.

Measuring Thermal Conductivity Using Laser Flash Technique

The Laser Flash technique (LFA) is frequently used to measure the thermal conductivity (W/(m∙K)) of TIMs. It monitors the thermal diffusivity (mm2/s), which determines how fast a temperature disturbance can propagate through a material.

NETZSCH LFA 467 Hyper Flash.

NETZSCH LFA 467 Hyper Flash.

A special clamping fixture was applied to permit measurement of the thermal resistance and thermal conductivity of interface materials in a sandwich configuration under a known clamping pressure, for LFA measurements (Figure 1). Linear regression is performed by plotting the total thermal resistance as a function of gap thickness at each nominal pressure level.

The y-axis intercept or zero gap thickness resistance represents the contact resistance, and the material bulk thermal conductivity is established by utilizing the reciprocal of the slope. Once a low clamping pressure is applied, the contact resistance is decreased and it is less sensitive to pressure, as shown in the results.

A viable explanation for the heightened thermal conductivity (see Table 1) with clamping pressure would be that there is a little growth in the material density and conductive filler particle-to-particle contact because of constraints in the material flow which are due to surface adhesion to the substrates.

Total resistance versus gap thickness under different pressures calculated by LFA measurements of a 3M 5590H pad (thickness 0.5 mm, 1 mm an.

Figure 1. Total resistance versus gap thickness under different pressures calculated by LFA measurements of a 3M 5590H pad (thickness 0.5 mm, 1 mm an.

Table 1. LFA measurement results of a TIM: Thermal conductivity and thermal resistance as a function of clamping pressure 1.5 mm

This information has been sourced, reviewed and adapted from materials provided by NETZSCH-Gerätebau GmbH.

For more information on this source, please visit NETZSCH-Gerätebau GmbH.

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