What is the influence of the dielectric constant of thermal conductive materials on electromagnetic interference radiation

The common source of electromagnetic interference (EMI) in many systems is integrated circuits (ICs). ICs generate heat, which must be effectively dissipated through heat sinks. In order to achieve rapid and efficient heat transfer, a thermal interface material (TIM) should be used between the IC and the heat sink. The ideal characteristics of TIM are high thermal conductivity and flexibility, ensuring good physical contact between the IC, heat sink, and TIM. However, research has found that the electromagnetic properties of TIM materials sometimes increase EMI radiation, leading to non-compliance or a decrease in equipment efficiency. This has led many users to demand the use of TIM materials with lower dielectric constant (dk). The Advanced Institute will study why the dielectric constant of thermal conductive materials affects EMI radiation.

IC radiation

Integrated circuits contain multiple current paths that generate radiated electromagnetic energy. The actual working mode inside the IC is very complex, making it difficult to model and simulate the EMI radiation of the IC. The current is not constant and may vary depending on the IC operating mode. Therefore, in order to simulate ICs, we need to make some simplified assumptions.

source type

All objects or components that radiate electromagnetic energy can be regarded as antennas. Depending on the size, shape, and material properties of the antenna, different antennas will radiate in different ways. Some antennas have good radiation effects, while others do not. In terms of usage, there are only two basic types of antennas: line antennas and loop antennas. In an online antenna, the conductive part is in a straight line shape, similar to the radio antenna on a car. The current is limited by the end of the antenna. In a circular antenna, the current is not restricted and propagates freely from the energy source before returning to the energy source. We have found that the most representative model of IC radiation is a circular (ring-shaped) source perpendicular to the printed circuit board (PCB). The analysis of the influence of dielectric constant in this article is very similar for any type of source.

The model shown in the following figure represents a vertical circular source implemented on a PCB. The current path goes from the source on the left side up through the first conductive pillar, then through the horizontal conductive part, then down through the second conductive pillar, and finally returns to the source through the conductive ground layer. In our model, the antenna height is 2mm, and the antenna length (horizontal portion) may vary.