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80 FLEX007 MAGAZINE I JANUARY 2019 Article by Yi-Chun Liu UNIFLEX TECHNOLOGY INC. Abstract The advance of wireless communication necessitates a higher speed and a wider fre- quency band. Because the majority of the band uses are tightly packed in frequencies at <6 GHz, the application of millimeter wave at >30 GHz has become a key technol- ogy for future development. Poten- tial applications include next generation Wi-Fi 802.11ad/ WiGig and 5G technology. With the request of high frequency and high speed, a better flexible substrate than the one commonly used in 3C electronics is needed. The common substrate adopts polyimide as the dielectric middle layer material, and its high dielectric constant and moisture absorption often cause signal loss under high- frequency and high-speed condi- tions. Therefore, flexible copper foil suppliers attempt to either modify the poly- imide or replace it with a liquid crystal poly- mer (LCP). Nevertheless, a standard testing method and wire layout have yet to be established for vari- ous materials under high-frequency and high- speed conditions. Considering numerous fac- tors affecting the material performance, we have designed a standard test wire layout and a fabrication procedure to facilitate depend- able and precise testing. Testing data in this article indicates that flexible copper foil using LCP as a dielectric substrate has the best high- frequency and high-speed performance, and this performance could even be further elevated by a thicker dielectric layer and a smoother conduc- tor surface. Introduction Because of the appli- cation requirements for connection speed, time delay, connec- tion density, cover area and power con- sumption, 5G is used at multiple bandwidths. Thus, a millimeter wave at >30 GHz with a wider frequency and bandwidth are needed for communica- tion. To solve the problem of short transport distance, traditional macro- station disposal tends to combine macro, small, and family station to form a multilayer and the densest pattern for a change. Large- scale antenna technology (Massive MIMO) enhances efficiency and decreases the delay Method for Testing FPC Materials at High Frequency

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