PCB Materials and Design Requirements for 5G Systems

May 24, 2019 Cadence PCB Solutions

Future 5G systems will run on the back on high speed and high frequency PCBs

 

Although it might raise some eyebrows, I’ll admit it: I still have a flip phone. I know what you’re thinking: why would a PCB design engineer still have a flip phone? For me, it’s the easiest way to disconnect from the hustle and bustle of modern life. Seeing 3G appear in the top corner of my phone screen is comforting when I’m on an outing with family. It means I can really focus on what’s important while screening out interruptions from work and social media.

I also have a smartphone that runs at 4G, which I use for work (I’m not a total dinosaur). Compared to 4G, the imminent rollout to 5G is forcing designers to rethink PCB design for mobile and IoT devices. These 5G systems are pushing the speed limit available to most consumers to new heights. When you bring in the communication requirements in these boards, you’ll have a lot of material considerations to account for.

5G Systems Requirements

If you start searching for a comparison between 3G, 4G, and 5G networking requirements, you’ll find information is scattered in a number of locations, some which appears to be conflicting. With the 3 billion additional mobile and IoT devices expected to come online by 2021, the goal with 5G systems is to provide 10-20x faster data rates (up to 1 Gbps), about 1000x more traffic, and 10x as many connections per square km compared to 4G. 5G also aims to provide as low as 1 ms latency, which is 10x faster than the latency in 4G networks.

5G wireless networks will also operate at a range of higher frequencies compared to 4G and 3G. PCBs for mobile devices and networking equipment will need to accommodate higher digital data rates and higher frequency simultaneously, pushing mixed signal design to its limits. 4G networks operate at frequencies ranging from 600 MHz to 5.925 GHz, while 5G networks push the upper frequency limit firmly into mm-Wave frequencies.

The bandwidth per channel is also important when designing wireless communication capabilities in your PCBs for 5G systems. The channel bandwidth in 4G is set at 20 MHz (200 kHz for IoT devices), while the channel bandwidth in 5G is set to 100 MHz below 6 GHz carrier frequencies and 400 MHz above 6 GHz carrier frequency. The high speeds and high frequencies in these devices can be accommodated by current ICs, yet PCB materials will play an important role in ensuring the performance of 5G systems.

 

Cell tower with antennas for 5G systems

This cell tower may look very different on a 5G network

Material Selection for 5G Systems

Designing 5G systems is all about high speed/high frequency mixed signal design. In addition to standard high speed design rules and high frequency layout rules, material selection is an important part of preventing signal losses and ensuring signal integrity. As these systems are inherently mixed signal, designers must prevent EMI between analog and digital board sections, as well as design their boards to meet FCC EMC requirements.

In anticipation of the coming 5G revolution, PCB materials companies are already developing substrate materials with lower dielectric constant (around 3) than that of standard FR4. Despite the higher frequency, these newer materials have less loss at 5G wireless frequencies compared to PTFE laminates.

PCBs for 5G systems will require processors and power amplifiers that operate at high speed and high frequency, and variations in the output from these components can be minimized with effective thermal management. Two material properties that are of interest in 5G systems are the thermal conductivity and thermal coefficient of, which measures changes in the dielectric constant of the substrate with temperature. The heat generated by circuit operation or by ICs can lead to temperature rise which would cause the loss of dielectric performance gradually.

The importance of the first parameter should be obvious: a substrate with higher thermal conductivity easily dissipates heat away from an active device, and a substrate with higher thermal conductivity is a better choice when working at higher speed and higher frequency. The importance of the second parameter may not be so obvious. Variations in the dielectric constant can induce dispersion along an interconnect, and severe dispersion will stretch digital pulses, change the propagation speed along an interconnect, and lead to signal reflections along a transmission line in extreme cases.

 

Smartphone schematic and PCB for 5G systems

Your next 5G system design shouldn’t be an impossible task

 

No matter which substrate material you opt to use in your 5G system, you’ll need to follow best PCB design practices to ensure consistent impedance throughout interconnects. With RF signal lines, traces should be routed using the shortest possible path. Conductor widths and spacing also require tight control in order to maintain consistent impedance throughout interconnects.

Ultimately, 5G will drive broader adoption of AR/VR, networking among autonomous vehicles, new smart devices, and other applications we can only dream of. The right PCB design and analysis software from Cadence includes a full suite of design and simulation tools to help you design 5G systems. The Allegro PCB Designer software package includes a multitude of design tools that engineers need to build 5G systems, including RF design features and interconnect planning tools.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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