Substrates for Advanced PCB Technologies: What Will the Future Hold?

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Frequencies between 30 GHz and 300 Ghz were classed as millimetre-wave, and it became increasingly critical to use low-loss materials with stable dielectric constant in applications such as 77-GHz automotive radar and V-band and E-band telecommunications—which could use PCB technology on PTFE and LCP substrates although the choice and thickness of substrates and positional accuracy of PCB features would be critical considerations. Microstrip, stripline, and coplanar waveguide transmission line technologies were all employed in millimetre-wave PCB design, and substrate-integrated waveguide principles were becoming popular for power dividers, signal couplers, filters, and antennae with the benefits of low-radiation leakage and low interference compared with microstrip and coplanar waveguides.

Francey used the example of a beam-switching Rotman Lens antenna to illustrate typical millimetre-wave PCB structures and discussed the defining features and critical tolerances that had to be satisfied within the PCB manufacturing technology. To summarise, he quoted the words of a microwave engineer: “When the frequency increases, everything has got to shrink. Manufacturing tolerances start to become a problem at about 20-30 GHz. Below that, you can pretty much design anything you want; the production will not fail. Above that, it is no exaggeration to say that everything is about manufacturing tolerances and producibility. Being a microwave designer is a completely different job at 77 GHz compared to one GHz.”

In his concluding comments, Francey observed that the laminate industry was meeting the needs for system miniaturisation, signal integrity, assembly, and reliability with thinner cores and engineered polymer composites to satisfy dielectric and thermomechanical requirements. Moreover, the PCB industry was reacting to the needs for higher packaging densities, signal integrity, and the use of PCB technology in IC packaging. However, he stressed that the convergence of future needs for circuit miniaturisation, feature tolerances, and feature-to-feature positional could only be achieved with additive technology, which would require a step change in PCB manufacturing capability and know-how.

I found this webinar enlightening and extremely interesting. I learned a lot from it, and I am grateful to IMAPS-UK for giving me the opportunity to attend. Piers Tremlett and Jim Francey should be congratulated for the quality and content of their presentations and thanked for generously sharing their knowledge and experience. Thanks also to Martin Wickham for acting as the anchorman, and to the ubiquitous Bob Willis for his professional management of the event.



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