Wireless

5G communication technology is round the corner with sub-6GHz deployment beginning to take place. As a follow-on it is expected that 5G mmWave communication networks will be developed and deployed in the near future as well covering the frequency band 24GHz – 86GHz. With such a broad frequency spectrum available, the data rate and latency is expected to increase beyond 4G LTE. As depicted in Figure 1, the 5G mmWave networks are for short range communication (~500m) with a large density of base stations required to provide the necessary coverage.

Figure 1: 5G mmWave spectrum & coverage [https://www.androidauthority.com/what-is-5g-mmwave-933631/] and 5G 28GHz RF Front End Module [S. Shinjo et al, IMWS-5G, 2018]

Given the path loss at mmWave frequencies the RF modules will need to support massive MIMO with a multitude of antenna array elements required to realize the necessary gain and directivity through beam steering. For such RF transceivers the use of highly integrated packaging technology becomes critical for minimizing losses in the module so as to meet the link budget. An example of an antenna RF module is shown in Figure 1 where the GaAs and Si chips along with the switches need to be packaged in a substrate containing antennas, phase shifters, filters, power dividers and other components. Thermal management solutions for such modules are critical as well with a heat flux of 20W/cm2 expected that need to be dissipated on the transmit side. Beyond 5G (6G) is an emerging application area that covers the sub-THz frequency band (0.1THz – 0.5THz) for MIMO, Imaging, Non-destructive testing, Virtual Reality etc. The key metrics for both 5G and 6G are shown in Table 1.

Table 1: 5G & Beyond (6G) State of the Art and PRC Objectives

The technical approach for wireless is to use glass based packaging using either a chip-first or chip-last approach as shown in Figure 2. In the chip-last approach, the substrate is first fabricated followed by chip assembly while in the chip-first approach the redistribution layers (RDL) layers are fabricated after embedding the die in the glass cavity. Unlike chip-last, in the chip-first approach the parasitics of the solder bumps can be eliminated with the disadvantage of having to remove the heat from the back side of the die. The PRC research focus areas are shown in Figure 2 using glass based packaging consisting of i) antennas and arrays, ii) interconnects, waveguides using conventional (microstrip, CPW) and unconventional (substrate integrated waveguide SIW, conductor backed dielectric waveguide CBDW), iii) passives such as filters, power dividers, couplers, phase shifters and butler matrix, iv) fanout panel level packaging (FOPLP) using die embedding for front end module (FEM) in glass substrates and v) thermal management. The 6G work at 140GHz is being supported by SRC JUMP (through ASCENT) and hence the outcome of this work is being leveraged here post publication.

Figure 2: PRC Research focus areas for Wireless