Preparing for 6G
While the 5G era continues to take hold, materials science must advance for us to move to the next stage.
It’s part of the human condition to never be satisfied. We are always looking forward to what comes next, and this tendency is starkly evident in our attitudes toward technology. As our daily lives have become substantially enabled, empowered, and – many would probably agree – enhanced by the technology in our pockets, in our cars, and in our homes and offices, we have become increasingly demanding of more and better. More features and functions, more sophistication, faster responses, less waiting.
Our attitudes toward mobile services illustrate the point. No sooner had 5G networks started rolling out than the focus shifted to 6G and the exciting new opportunities it could bring. But is this a harsh truth about our nature, or simply the reality of a massive scientific and engineering challenge? The mobile industry has established a rhythm that introduces a new generation about once every 10 years: 3G arrived around 2000, 4G-LTE in 2010, and 5G rollouts based on Release 15 of the 3GPP specification began around 2020. 5G evolution has continued, with non-standalone deployments giving way to standalone 5G core and further enhancements in 3GPP Release 16 and 17 to support industrial IoT (IIoT) applications. Release 18 now paves the way for 5G Advanced, which will offer energy savings and greater spectral efficiency, leverage AI to improve network performance, and, of course, enable additional new services and enhanced capabilities.
To ensure 6G – taking performance, reliability, efficiency, and service advancement even further – can be ready for deployment by 2030, work needs to begin now to determine performance targets and start drafting specifications. Where 5G has brought advanced services such as cloud gaming, augmented/virtual reality (AR/VR), and 4K video to our mobiles, 6G will raise the peak data rate from 5G’s 20Gbps to 1Tbps and maximum bandwidth from 1GHz to 100GHz. Latency is expected to reduce from 1ms in 5G to just 100µs, while mobility will double from 500km/h to 1000km/h. Connection density is also expected to rise significantly, to 10 million devices per square kilometer from 1 million today. We can expect these improvements to be manifested in more immersive extended reality (XR) experiences and new capabilities in wireless positioning and remote sensing.
It’s exciting to imagine all this happening, particularly as many of us will have a direct role in bringing it to life. Our wishes are constrained by the laws of physics, however: so often this is the issue that divides the possible and the impossible.
Materials science is one of the defining disciplines in the PCB industry. Substrate properties such as dissipation factor and dielectric constant are a limiting factor governing maximum data speed, signal power and transmission distance, and thermal management, while CTE and high-temperature performance heavily influence circuit integrity and reliability. We depend on the work of materials scientists and the properties of advanced synthetic materials such as the PPE (poly-phenylene ether) resins that allow us to engineer high-performing prepregs and laminates to handle multi-gigahertz signal frequencies and multi-gigabit data rates.
Currently, PTFE-based materials offer exciting opportunities to raise substrate performance to new heights. Its molecular structure has a very low dipole moment that ensures minimal absorption of energy from signals carried in the adjacent conductive foil. This extremely low energy loss enhances signal integrity at extremely high frequencies and demands less power at the transmitter in relation to signal-path length. Heating of the substrate is also reduced. Adjusting the PTFE resin/filler blend allows control over the dielectric constant of materials, permitting a range of Dk from a little over two to around 10 while the dissipation factor (Df) can be engineered to be extremely low, in the region of 0.002 or even 0.001. There are some challenges, however. From a technical standpoint, the low surface energy makes PTFE difficult to use for building multilayer substrates.
Despite this, the industry sees PTFE as an essential tool enabling the evolution of 5G networks and the transition to 6G in the future. However, PTFE – polytetrafluoroethylene – faces legislative challenges as a member of the group of synthetic chemicals known as PFAS, or per- and polyfluoroalkyl substances.
There are about 10,000 of these in existence, products of the global chemicals industry. They have become known as “forever chemicals,” or persistent organic pollutants (POP), because they decompose extremely slowly, if at all, and hence remain in the environment. They are widely used in a huge variety of products and processes, including liquid-resistant coatings, clothing, food packaging, even fuel-production processes. They are easily absorbed in the body – including ourselves and the animals we farm and eat – and can adversely affect the endocrine system.
There are moves to restrict the production and use of PFAS. Earlier this year, the European Chemicals Agency (ECHA) published proposals as an update to the EU’s REACH legislation. Clearly, restrictions would have major implications for many industries, including our own. CEFIC, the European Chemical Industry Council, have set up a dedicated sector group, FPP4EU, whose remit is to represent the views of producers, importers, and users of fluorinated products and PFAS and other parties with an interest in the fluorinated products and PFAS sector group activities in Europe. Its aim is to ensure that any eventual regulatory measures are science-informed, implementable and enforceable.
New materials suitable for substrate applications capable of delivering performance comparable to PTFE will be difficult to formulate: those strong molecular bonds that prevent degradation and earn their “forever” nickname are the same characteristics that ensure the high-frequency performance we need to build future mobile infrastructures, including 5G Advanced and 6G.
While the industry seeks exemptions, it’s equally important to begin work to engineer suitable alternatives. Quantum computing may help, having already shown its ability to accelerate materials science simulations. We need a solution, and fast. We also need to have faith in technology’s ability to deliver.