Thermal and EMI Performance of Composite Plastic Molded Heat Sinks and Hybrid TIM Materials

Abstract

Heat sinks are widely used in thermal management of electronics. However, it is also well established that a heat sink can couple and radiate electro-magnetic (EM) energy from the same component that it is cooling. As the frequency of these devices continues to increase, it is more crucial to try to suppress the EM radiation at the source. The component suppliers for thermal management and EMI products have been developing materials that are thermally conductive and also have EM absorbing properties. The thermal and EMI material properties of the additives can change the properties of the final material and they may not always be complementary between thermal and EM absorbing behaviors. In this paper, two such hybrid solutions are investigated to understand the thermal and EM absorbing characteristics and interactions. These are: (1) heat sinks made of composite plastic materials; and (2) hybrid RF/thermal interface materials (HRTIMs). For the heat sink study, three heat sinks of the same physical design (40mm square x 8.25mm tall) but with different materials are tested and analyzed. Two of the heat sinks are molded from two different composite plastics (Materials A and B), while the third one is constructed from aluminum and used as the baseline heat sink for comparison. The results presented in Figure 7 show EMI improvement for composite material heat sinks over the traditional aluminum heat sink. Material A provides a broadband reduction of 2–3 dB power whereas Material B heat sink provides significant reduction at lower frequency range of 1–8 GHz. The thermal performance results are plotted in Figure 11 – Figure 14, and the results show that the composite plastic materials are more suitable for applications that have lower power and power density. For the HRTIMs, two different base materials at different thicknesses are investigated and the material details are given in Table 2 . Similar to the heat sink EMI study, Total Radiated Power (TRP) measurements are performed for the HRTIMs in an Electromagnetic Reverberation Chamber in the frequency range of 5–40 GHz show improvement for material TIM 1. The EMI results are plotted in Figure 9 and Figure 10. For thermal performance characterizations, an ASTM D-5470 compliance test stand (Figure 6) is used. The thermal impedance results of these materials are plotted in Figure 15.