Proceedings of the 40th European Microwave Conference
Advanced Polymers for Advanced RF Packaging Applications Madhavan Swaminathan, Nevin Altunyurt, and Seunghyun Hwang School of Electrical and Computer Engineering, Georgia Institute of Technology 266 Ferst Drive Atlanta, Georgia, USA
[email protected] Abstract— This paper presents advanced polymers for RF packaging applications including filters and antennas. First, micro-scaled LCP technology for front-end modules is presented. Next, nano-scaled ultra-thin RXP technology is introduced with its integration capability and embedded passive performances. Simulated results of bandpass filter, and antennas for 60 GHz are also presented in this paper. RXP technology provides low cost and promising high performance solution for wireless applications operating around microwave and millimeter frequencies. Magneto-dielectric substrates are proposed for effective miniaturization of antennas.
I. INTRODUCTION As a rapidly increasing segment of communications industry, wireless communications have been a major aspect of everyday life. From hundreds of MHz to millimeter wave frequency, the evolution of wireless communications includes several indispensible technologies such as cellular communications, wireless local area networks (WLANs), ultra wide band (UWB) and wireless personal area networks (WPANs). The consumer demand for accessing these radio technologies in compact devices has been pushing RF engineers for low-cost, effective integration and miniaturization of RF components. There has been a considerable amount of effort in the past years to find and implement novel packaging technologies to achieve this goal. Recently, an advanced technology operating around 60GHz (V-band) has been emerging for high-speed short-range wireless communications and WPANs. The high-speed communication and miniaturization factors that can be achieved at 60GHz are especially attractive compared to those that can be achieved at WLAN/WiMAX frequencies (< 10GHz). However, this emerging technology brings new challenges regarding the performance and the maturity of the available integration techniques to support 60GHz wireless communications. System-on-package (SoP) technology has been proved to provide low-cost highly-integrated modules for the aforementioned wireless applications. SoP architecture is based on integrating high-speed digital, RF and passive components in a compact multilayer substrate. Therefore, in an SoP architecture, the substrate not only provides the mechanical support but also becomes the medium for the electromagnetic wave propagation between the embedded components. This makes the selection of the substrate material
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critical since the characteristics of wave propagation and capabilities of the technology are determined by the substrate parameters. Hence, advanced packaging technologies require using advanced packaging substrates. Low temperature co-fired ceramic (LTCC) technology has been a popular solution for applying SoP in both microwave and V bands to integrate RF components and the antenna in a multilayer substrate. Although, high dielectric constant and the low loss tangent of the LTCC substrate have been advantageous for the miniaturization and the integration of RF components, LTCC may not provide a long-term effective packaging solution because of higher processing temperature (> 900°C), larger manufacturing variation, difficulty of embedding actives, bulkier substrate, and higher cost as compared to multilayer organic technologies (MLO) [1]. Liquid crystalline polymer (LCP) has been shown to be a promising organic material with superior electrical properties up to millimeter-wave frequencies [2]. LCP-based MLO substrates have been reported to achieve highly-integrated RF systems [1]. Recently, another organic dielectric material, called RXP, has been proposed to eliminate the limitations of LCP by expanding micro-scale SoP to nano-scale SoP [3]. Another type of novel materials called magneto-dielectrics, materials with εr>1 and μr>1, has been proposed to overcome the limitations of dielectric substrates for effective antenna miniaturization. It has been reported in [4] that magnetodielectrics can be used to miniaturize the antenna while improving the bandwidth and the radiation properties, which cannot be achieved with high-permittivity dielectrics. In this paper, therefore, these novel packaging materials are presented with their advantages and limitations. II. LIQUID CRYSTALLINE POLYMER (LCP) LCP (Ultralam 3850) is a laminate-type organic dielectric material that can be stacked to form multilayer substrates with the use of adhesive bondply layers (Ultralam 3908) in between stacked LCP layers. In addition to being a low-cost dielectric for a large panel area fabrication process, LCP has a combination of good electrical and mechanical properties. LCP has a low dielectric constant of εr=2.95 and a low losstangent of 0.002 up to millimeter wave frequencies. LCP also has favorable mechanical properties such as mechanical flexibility, a low coefficient of thermal expansion, and low
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moisture absorption. Furthermore, LCP has the mechanical strength to be the final printed wiring board (PWB), making it an excellent packaging substrate for SOP applications [2]. As shown in Fig. 1, previous work on RF SoP has shown that high performance front-end modules with significant size reduction can be designed by 3-D integration of RF front-end functional blocks into LCP-based MLO substrates. Fullsystem integration along with the antenna can be achieved using conformal antenna configuration exploiting the mechanical flexibility of LCP [4]. Applications using multilayer LCP technology have been commercialized by Jacket Micro Devices, a spin-off company from Georgia Tech [6].
110GHz. The dielectric constant and the loss tangent of the build-up RXP4 was characterized to be εr=2.98±0.05 and tanδ
