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Design and Thermal Management of a Miniaturized 3D Radio in Package
Keywords: thermal management, miniaturization, 3D packaging
The system consists of memory chips, transceivers, power amplifiers (PA), baseband processor, LNA, and power management module. Typically, the footprint of the RF components in a cell phone is 10 cm2. The objective of this new system, is to reduce the footprint to approximately 12mm x 12mm, the size of a microSD card. The system consists of seven radio bands, including a quad GSM and a tri-WCDMA. The envisioned functionalities include multiple network compatibility, smart power management, and sufficient computing power capable of voice command and control. The module consists of three layers and measures 12 mm x 12 mm x 1.6 mm. Each layer is 0.5 mm thick with the interconnect in between being 0.05 mm thick, and electromagnetic shielding on each layer. A model of the package is created using Flotherm 7.1, a CFD software that solves the conjugate heat transfer problem using finite volume method. The ambient temperature is set at 20 oC. The package is put in still air, and the heat is dissipated through natural convection. Due to the small footprint, and the low heat transfer rate of natural convection, the peak temperature is as high as 900oC under GSM mode, and over 400oC under WCDMA mode. Therefore, good heat spreading material is required to reduce the operating temperature of the package. In a mobile phone application, the package is placed on a thin motherboard with typical dimension of 90 x 45 x 1.0 mm. Various thermal management designs were investigated to reduce the maximum temperature, including: a magnesium case, natural graphite heat spreaders on the package, and advanced thermal interface materials. Peak temperature on the power amplifiers were reduced to below 120 oC. Further system design optimization will be presented in the full paper.
Hongyu Ran, Sr. Thermal Engineer
Tessera Technologies, Inc.
San Jose, CA

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