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34 I-CONNECT007 MAGAZINE I JUNE 2026 Rather than eliminating nickel entirely from the solderable finish stack, a more practical alternative is to use a thinner electroless nickel deposit with a smoother topography. Electroless Nickel-Immersion Gold (modified) If one follows the IPC-4552 ENIG standard, the electroless nickel plating thickness is specified as 118.1–236.2 µin (3–6 microns). There is a proven alternative to ENIG, with several commercially available final finish combinations designed to reduce signal loss. These include Direct Immersion Gold (DIG) over copper, Electro- less Palladium-Autocatalytic Gold (EPAG), and Elec- troless Palladium-Immersion Gold (EPIG). It's notable that these processes eliminate the nickel deposit from the stack. Electroless nickel is often considered a significant contributor to signal loss. Other considerations include the nickel thick- ness as required by IPC-4552 and the overall topography of the nickel deposit. However, the various processes described above have process complexity and cost issues. So, simply eliminating the nickel deposit is not the answer. Nickel, plated from a specially formu- lated process, will provide a thinner deposit (which Figure 1: Smooth EN finish (left) vs. rougher topography EN, cauliflower (right). is non-magnetic), a higher phosphorous content, and a near smooth topography. These three attri- butes improve conductivity and reduce skin effect signal loss due to the smooth topography. Figure 1 shows the comparison of the grain boundaries of the modified nickel formulation as compared to the conventional process. Note the roughness (often called cauliflower) of the conventional nickel. As others have pointed out, nickel metal contrib- utes to conductor signal loss due to its lower conductivity as compared to copper. However, the research hypothesis stated that if the nickel deposit morphology could be minimized and the magnetic effect eliminated, skin-effect signal loss at higher frequencies would be reduced. A second hypothesis considered the overall plating thickness of the electroless nickel deposit. Previous experiments showed that a lower nickel thickness would improve the deposit's conduc- tivity. Nickel plating uniformity across the circuit is also improved with a lower metal thickness. This adds further improvement in signal integrity, 2 and, in turn, reduces lossy characteristics to a manage- able level. Signal integrity testing showed that the modified electroless nickel deposit reduces signal attenua- tion loss. Figure 2 compares the signal loss of the T RO U B L E I N YO U R TA N K