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74 PCB007 MAGAZINE I MARCH 2025 Results and Discussion Insertion Loss As shown in Figure 6, the insertion loss of the Ni-less surface finish is almost exactly identical to the insertion loss of bare copper over the 0–100 GHz frequency range. is indicates that the Ni-free surface finish is able to be used in high- frequency applications with hardly any inser- tion loss increase compared to bare copper. e graphs can also be compared to Figure 1, which shows that ENIG has a loss of around 2.75 dB/ in at 50 GHz, compared to the values shown in these graphs, about 1.25 dB/in at 50 GHz—more than a 50% decrease in insertion loss. Since the Ni-less surface finish has such a small difference in insertion loss compared to bare copper, espe- cially when contrasted with ENIG insertion loss, the Ni-less surface finish solution is a good sur- face finish for high-frequency applications. e frequency level at around 25 GHz is critical and oen termed as 5G high band or mmWave frequency. Several of the wireless applications are targeted to run at this level. e graph above shows the comparison of the insertion loss between ENIG and Ni-free surface finish. ENIG shows ~2 dB/in loss at around 25 GHz whereas the Ni-free surface fin- ish shows no loss at that frequency. Electroless palladium immersion gold (EPIG) has shown promise as the Ni-free sur- face finish where electroless palladium layer of 6–8 microinches is deposited on the cop- per surface which is followed by an immersion gold layer of 6–8 microinches deposited on palladium layer. e comparison graph (Fig- ure 8) shows EPIG showing insertion loss at higher frequencies whereas Ni-free surface fin- ish does not show insertion loss up to 100 GHz. e comparison of insertion loss was con- ducted between different Au (gold) thickness ENIG options, EPIG, and Ni-free surface fin- ish. As seen in Figure 9, the Ni-free surface fin- ish shows superior performance in terms of least insertion loss compared to other options. Also, lower Au thickness (ENIG) shows infe- Figure 7: Insertion loss comparison between ENIG and Ni-free surface finish, especially at around 25 GHz level. Figure 6: Insertion loss of the Ni-free surface finish (blue) compared to bare standard half-ounce ED Cu (orange) from 0–100 GHz on tightly coupled GCPW circuits.