Radio Frequency (RF) modules have been miniaturized to meet the demand for smaller and more enhanced handsets for wireless applications such as cellular phones. However, area for passive devices used in RF modules has made further miniaturization difficult. Passives embedded in substrates are now being studied intensively. In addition, circuit simulation technology has been developed that enables efficient designing of RF module circuits. Circuit designers, however, have limited database of organic substrates and embedded passives. Further, optimized thermal designs are required to prevent thermal resistance increase due to miniaturization of substrates. In this paper, we describe the high-frequency properties of the capacitors embedded in the organic substrates and present the equivalent circuit models of the embedded capacitors. We also present the thermal design of organic substrates applicable to RF modules. 1. Introduction Radio Frequency (RF) modules have been miniaturized to meet the demand for smaller and more enhanced handsets for wireless applications such as cellular phones. Smaller semiconductor devices and passives have been usually used for the miniaturization of modules, but it is sometimes required to embed passives into substrates for further miniaturization. Embedded passives have been studied with ceramic substrates such as LTCC (Low Temperature Co-fired Ceramic) or silicon substrates to date, and studies with organic substrates are becoming active recently because of the advantages of CTE (Coefficient of Thermal Expansion) matching to motherboards and the manufacturing cost [1–12]. For designing circuits, the simulation is becoming more important to improve the efficiency of R&D. However, the information on the electrical properties and the circuit design of organic substrates are so poor that the efficient usage of organic substrates is difficult for designers. In this paper, we describe high-frequency properties of capacitors embedded in organic substrates and present equivalent circuit model of embedded capacitors. We also present the thermal design of organic substrates applicable to RF modules. 2. Embedded Passives in an Organic Substrate 2.1. The Concept of Embedded Passives Figure 1 is a conceptual model of embedded passives with an organic substrate for RF module. It embeds a thick film capacitor, a thin film capacitor, and an inductor. The thick film capacitor is formed by assembling high-dielectric-constant material between electrodes and the thin film capacitor is formed with high-dielectric-constant film as well. The
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