Massive Wireless Broadband with 5G mmWave Systems

Mobile applications are demanding ever-increasing bandwidths and consumer expectations are for high-throughput connectivity even in crowded environments. Ultra-high Gb/s capacity can only be achieved with small cell infrastructure using mmWave bands. However, such high frequencies drive the radio frequency (RF) front ends towards highly integrated hardware:

• Shorter wavelengths require smaller structures for analog signal manipulation, such as with filtering and antennas.

• Losses per unit length generally climb with frequency, forcing short interconnects.

As a result, RF system-on-chip (SoC) is required, with the antenna integrated into the packaging and even the inclusion of mixed (analog and digital) processing.  Power amplifier die will be implemented with dedicated high-speed III-V materials such as InP and GaN.  They can then be embedded into substrates for shorter connections to the rest of the RF front end, while maintaining bottom-side contact with heat-spreaders via thermal interface materials.  Substrates themselves will also increase in complexity, with multi-layer stack-ups of ultra-low-loss materials such as glass sandwiched between other, more easily machined dielectrics. 

Essentially, the packaging stack-up becomes an integral part of the design to achieve core functionality for, in this case, wireless connectivity in the mmWave and terahertz ranges.  This level of integration, however, comes with additional challenges in manufacturing (who has the right range of capabilities needed to complete the entire stack?), in testing (test interfaces are now deeply embedded in the packaging) and in quality control (sophisticated cleaning strategies to minimize impact of contaminants).

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References

1. 5G/6G MAESTRO, “Materials Development and Electrical Test Roadmap,” https://thor.inemi.org/webdownload//5G-6G-MAESTRO/2023/WP2-Roadmap_MatlsCharacter.pdf, September 2023.