Influence of Full-filled Polymer Molding on High-frequency Circuits
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0969-W01-05
Influence of Full-Filled Polymer Molding on High-Frequency Circuits
Kiyoshi Nakanishi1 and Masayuki Fujimoto2 1
Shizuoka University, Hamamatsu, 432-8561, Japan
2
Shizuoka University, 3-5-1 Jyouhoku, Hamamatsu, 432-8561, Japan
ABSTRACT The influence of full-filled polymer molding on high-frequency circuits in cellular phones is evaluated using computer simulations and high-frequency measurements. Polymer-molded high-frequency circuits of cellular phones increase radiation harmonics and line and antenna phase errors. High-frequency properties are degraded due to a decrease in line impedance and an increase in stray capacitance of land electrodes that are used in the assembly of components. Degradation problems caused by full-filled polymer molding can be alleviated by appropriate circuit design, such as by adjusting the distance of components and creating more effective electromagnetic shielding. Better circuit design must satisfy the specifications of several different types of cellular phones, including global systems mobile telecommunications and digital cellular systems. INTRODUCTION The cellular phone, a common mobile consumer electronic device, has become indispensable
in modern life. Subscribers to cellular phone service number almost 1.5 billion people worldwide. The first generation of cellular phones, the analog cellular system, has disappeared, and the second generation, the digital cellular system (global systems mobile telecommunications, GSM), is now used all over the world. Furthermore, the third generation (international mobile telecommunications–2000, IMT), which can connect to and download rich quality content from the Internet, has already been introduced in many countries. The fourth generation (IMT-advanced) is scheduled to begin service in Japan in 2010 [1]. Camera phones, which include photographic and audio and visual (AV) functions, were introduced in the third generation of cellular phones. Such functions require not only multi-radio frequency (RF) band circuit blocks, but also extremely large memories in increasingly small phones [2–4]. To obtain a higher density of surface mounting of components, three-dimensional mounting and printed circuit boards (PCB) with buried components have already been adopted (Fig. 1). The only remaining spaces for effective mounting of components or functions are the gaps between components. The knowledge of RF circuit design has already been condensed as much as possible to fit the circuit patterns. A “black-box” covering, which is preferable, makes the design difficult to see and protects the intellectual properties. Therefore, we used the gaps between components for functions, such as shielding, noise suppression, heat sinks, and stress dispersion, as well as for functional mold materials.
Fig. 1. Schematic of components in buried multilayer polymer substrate.
EXPERIMENTAL Given that the major multilayer substrate of cellular circuits is a multilayer FR-4 with an inner via, we developed an epoxy dispenser that includes an SiO2-based cer
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