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82 FLEX007 MAGAZINE I JANUARY 2019 via increasing the number of stations and ter- minal antennas. The wireless communication industry has advanced from the first and second generation of voice and text message transport, through the third generation of email and internet transport, to the fourth generation of imaging, online games, and cloud data transport. The current fifth generation is not only capable of the services of previous generations, but also provides data sharing, telemedicine, intellec- tual family applications, and public safety ser- vices in cities, achieving a real communication internet of things (IoT). Ericsson predicts that in 2020, 90% of the population older than age six will use mobile devices, and the forecasted bandwidth will be ten times of that in 2014. Therefore, it is concluded that both the num- ber of users and the needed bandwidth will increase. As the basis for development, the wireless point-to-point digital communication warrants an efficient method for increasing the bandwidth. According to data from ITU-R and ARIB indi- cate, 5G will start being used in 2020. To estab- lish a universal frequency standard for millime- ter wave, ITU announced after a recent WRC conference that a range of 24-GHz to 86-GHz frequencies could available to the world (Table 1). Shortly after, FCC announced 2015 NPRM on October 21, providing service rules for fre- quencies at 28, 37, 39, and 64-71 GHz. As a result, the proper frequency choices for 5G becomes clearer: 28, 39, and 60 GHz. Although 5G technology is not perfect, it is certain that millimeter wave is one of its key technologies, and will be implemented very quickly. The new 5G stations and the latest consumer electronics demand large volumes of high-fre- quency circuit boards. These circuit boards have stricter technical thresholds and higher profit margins than traditional ones in various products such as smartphones, automobiles, the internet, and artificial intelligence. PCBs are primarily used as substrates for mounting and connecting various electronic devices. As opposed to a traditional rigid circuit board, FPCs have advantages in their capabili- ties such as, enhanced trace and space density, flexibility, design freedom, 3D layout configu- ration, potential for a continuous automation process, the absence of wire connectors, and ease of soldering. Because these advantages help to make lighter, thinner, shorter, and smaller electronic products, the market for FPC is steadily increasing. The applications are increasing in the future with potential FPC applications such as enhanced mobile broadband (eMBB), VR and AR (virtual and augmented reality), smart cit- ies, automobile usage, smart manufacturing, drones, wearable devices, medication, whole- sale, and energy. Basically, these applications can be categorized into three classes: 1. Enhanced mobile wide-band communica- tion including wider coverage and hotspot transport. For the former, seamless cover- age and higher mobility are the prerequi- sites. For the latter, the major application is in densely populated areas. It is antici- pated that the transport speed increases to 20 Gbit/s from 10 Gbit/s. 2. Large-scale mechanical communication is characterized by a large number of con- nected devices (approximately one million devices/(km) 2 ), a smaller amount of data transport, and a higher tolerance of data delay. 3. High dependability and low delay com- munication; the transport requirements of data amount, delay (<1 millisecond) and dependability (error <10 -5 ) are stringent. The high frequency of data transport often increases the signal decay in the copper con- Table 1: Possible frequencies for 5G.