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48 PCB007 MAGAZINE I OCTOBER 2022 electroless palladium/immersion gold) was shown to provide a more reliable solder joint. Still another option was to also eliminate the palladium and immerse gold directly on cop- per, immersion gold (DIG). A new develop- ment in DIG is reduction-assisted immersion gold. RAIG deposits a thicker gold layer (6-8 µins) that prevents the diffusion of copper into the gold wire bonding surface. Newer and advanced surface finishes are constantly being researched, tested, and imple- mented. It is important to keep in mind that all the SFs mentioned above are presently used in board fabrication. More advanced finishes are beginning to make headway as the higher tech- nology boards continue to use high RF signals in their designs. Stay tuned. PCB007 George Milad is the national accounts manager for technol- ogy at Uyemura. To read past columns, click here. diffusion of nickel into the thin immersion gold layer. A diffusion barrier was needed to pre- vent the nickel from reaching the surface. Elec- troless palladium was the answer and ENEPIG (electroless nickel/electroless palladium/ immersion gold) was the right finish when the desired attributes included Au wire bonding. As military and aerospace boards continued to advance into RF signal propagation, there was a need for a new class of finishes that did not include electroless nickel. RF signals travel along the surface of the trace and the presence of electroless nickel would interfere with high frequency (RF) signal propagation. One way to achieve this was to dramati- cally reduce the thickness of the nickel layer in ENEPIG to below 0.1 micron. Other fin- ishes, including EPIG or EPAG (electroless palladium/immersion gold or electroless pal- ladium/autocatalytic gold), eliminated the nickel completely. ese finishes relied on cat- alyzing the copper surface with immersion pal- ladium; a more advanced system to achieve the same goal is using immersion gold to catalyze the copper surface. IGEPIG (immersion gold/ With the explosive growth of the spectrum demand of the Internet of Things (IoT), Non-orthog- onal Multiple Access (NOMA) and spectrum sens- ing are considered as key candidate technologies to improve spectrum utilization in next generation wireless communications technology. However, this brings new challenges on how to ensure the perfor- mance of spectrum utilization and system through- put in large-scale IoT scenarios when using both technologies at the same time. A joint research team from the Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences, VTT Technical Research Cen- tre of Finland and University of Windsor of Canada, proposed a novel spectrum sensing technique for 6G-oriented intelligent IoT communications, seek- ing a feasible way to provide underlying support for perceptual interference and intelligent identifica- tion between large-scale coexistence and aliasing IoT users in future 6G scenarios. Results were pub- lished in the latest issue of IEEE Internet of Things Journal. Focused on inter-system orthogonal/non-orthog- onal aliasing coexistence scenarios, the research- ers designed a multilayer spectrum sensing tech- nology based on feature detection in NOMA sce- narios with multi-users. The corresponding rational workflows and transceiver structures according to different scenarios were presented, and the thresh- old expressions were deduced accordingly. This work will promote the theory of signal per- ception and recognition for 6G-oriented intelligent IoT communications, and provide technical support and development potentials for the promotion of global 6G strategy. (Source: Chinese Academy of Sciences) Researchers Develop Novel Spectrum Sensing Technique for 6G IoT Comms

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