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Novel electromagnetic interference and thermal solution for smartphones using composite material
Keywords: electromagnetic interference, thermal interface material, thermal conductivity
In recent years, the capabilities of smartphones have greatly improved, and current models can play 3D movies and record high-definition 4K video while simultaneously uploading it to the Internet. In the LTE Advanced standard, the communication speed is up to 1 Gbps, and this is expected to increase to 10 Gbps in the 5G standard. Hardware demands will also increase as the new 8K video standard is introduced. To meet these challenges, it is necessary to significantly improve the performance of the application processor in smartphones. However, this leads to considerable problems with heat dissipation. In a smartphone, removal of excess heat is achieved mainly by natural air convection, but the area available for this cooling process is extremely small. In addition, in integrated circuits (ICs) using 2.5D or 3D stacking, there is a high thermal resistance between the IC core and the outside of the package, which makes heat removal problematic. Another issue with such devices is that of electromagnetic interference (EMI), which requires that they be enclosed in a metal shield. Overcoming the problems of both heat dissipation and EMI requires a very complex shielding structure and thermal insulating material (TIM). Typically, the processor is enclosed in an EMI shield, which has a TIM layer on both sides. However, this leads to multiple layers which increase the thermal resistance. Herein, we report on a new structure based on a composite material that can both suppress EMI noise and provide good heat transfer characteristics. The structure consists of a single TIM placed in an opening in the EMI shield. However, in order to maintain the EMI shielding ability, it is necessary to develop a material that exhibits both high thermal conductivity and high electrical conductivity, in order to block electromagnetic waves. The material used is a composite of carbon fibers and a FeSi alloy type magnetic material. The carbon fibers are aligned in the thickness direction, providing a high thermal conductivity of 15 W/mK, which is about six times higher than that for conventional noise suppressing heat-transfer sheets. In addition, the combination of both resistive and magnetic losses in the composite material leads to strong electromagnetic suppression. The performance of the proposed structure was evaluated using a commercial smartphone, and was found to be superior to that for a conventional structure. In the present paper, we describe the fabrication and arrangement of the proposed composite sheet.
Hiroyuki Ryoson, Seinor Manager
SHimotsuke-shi, Tochigi

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