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34 DESIGN007 MAGAZINE I FEBRUARY 2024 Article by Frank Xu, PhD, Martin Bunce, and John Coonrod e introduction of 5G/6G has created a growing demand for faster rates of data transfer and operation at higher frequencies, pushing signals to travel toward the outer edges of con- ductors. As a result, the surface finish applied over the copper circuitry is now gaining more attention. It has previously been shown that the low conductivity and magnetic properties of the electroless nickel (EN) layer negatively affect electrical signals as they travel along the con- ductor's outer surfaces, leading to insertion losses. Subsequent studies show that reduc- ing the EN thickness can offset some inser- tion losses observed. In more recent times, nickel-free finishes, such as EPIG (electroless Reassessing Surface Finish Performance for Next Generation Technology, Part 2 palladium, immersion gold, no EN), thin EN ENEPIG, silver-gold (immersion silver fol- lowed by immersion gold), have been pro- moted as solutions for improving signal integ- rity at higher frequencies. In Part 1 of this article 1 , we reported the signal loss properties of the new nickel-free surface finishes, along with immersion silver, organic solderability preservative (OSP), and ENIG/ENEPIG surface finishes. As expected, ENIG and ENEPIG are challenged by sig- nal losses at higher frequency, with OSP and immersion silver demonstrating no contribu- tion to the signal losses. e new generation surface finishes (silver-gold, thin EN ENEPIG, and EPIG) perform similarly—outperforming

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