Interconnection technologies for up to 80 GHz
Leoben, 6 July 2017 – The automotive industry is focusing its efforts on developing solutions for autonomous driving and car-to-car communication. At the same time, the communications industry is moving towards 5G, and broadband networks are becoming ever faster. Large and complex volumes of data need to be transmitted securely in fractions of a second. Demanding applications such as these require specially developed printed circuit board (PCB) and interconnection technologies. They not only serve as an interconnecting platform for the electronic components, but also provide functions such as antennas and filters. AT&S is a world leader in this field, and has developed PCBs that deliver the required performance in the frequency range up to 80 GHz. For example, these technologies form the basis for high-performance radar components (long-range radar at 77/79 GHz) in driver assistance systems – an essential building block for autonomous driving.
High-frequency (RF) laminates are expected to see accelerating growth in the next few years, especially in vehicle radar applications and micro base stations. AT&S has evaluated materials and processes that are specifically suited to these high-speed applications, primarily with the goal of minimizing performance losses. RF signals reflect off the PCB depending on various parameters, which means that the signal impedance changes. To prevent capacitive effects of this kind, all parameters have to be precisely defined, and implemented with maximum process reliability. Critical factors for the signal impedance of high-frequency PCBs include the conductor path (trace) geometry, but particularly the layer structure and material used.
To achieve frequencies of up to 90 GHz, the dielectric constants (Dk) need to be brought below 3.0, and the loss factor (Df) to less than 0.001. For comparison, the corresponding values for standard FR4 are > 4 and > 0.015. Hence materials such as LCP, PTFE, polyamide or organic materials with special fiberglass and resin mixes are required. Losses at high frequencies can be further minimized during manufacture by applying very thin copper foils with low roughness to the PCBs. AT&S is able to offer asymmetric hybrid and sandwich structures (FR4 for the digital layer and PTFE for the high-speed layer) for PCB technologies up to frequencies of 80 GHz, for all kinds of different applications. For even higher frequencies, the company uses a homogeneous PTFE structure. In addition, optimized processes are available for filters / via shielding, controlled precision drilling, and precise, level and flat conductor paths with reduced skin effects. Shielding can be implemented with stacked or filled vias.
Based on high-speed/RF technologies from AT&S, driver assistance and radar systems for automobiles (77 GHz) and 60 GHz telecommunication systems have now been implemented. To further enhance performance, AT&S is working on hybrid solutions that combine RF layers with AT&S 2.5D technology. With 2.5D technology, defined cavities in the PCB can be used to position electronic components “deeper”, thereby giving the assembled PCB a thinner overall structure. Finally, in another process, embedded components are combined with the RF design.