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64 PCB007 MAGAZINE I AUGUST 2018 the phos-palladium thickness was as high as 7.7 µin (0.19 µm). No signs of nickel corrosion were found at any level of palladium thickness (Figure 11). Mitigation of Nickel Corrosion The data clearly indicates that increasing the thickness of the palladium layer in the range of 6-8 µin would go a long way towards minimiz- ing nickel corrosion in ENEPIG. Presently, the IPC-4556 specification for ENEPIG specifies for 2–12 µin (0.05–0.3 µm) for the EP layer and 1.2-2.8 µin (0.03–0.07) µm for IG. The authors of this paper recommend increasing the lower limit of EP thickness to 7 µin (0.18 µm). The increased dwell time in the immersion gold bath, to achieve higher thickness of the IG, will create a level of nickel corrosion, par- Table 5: Phos-Pd with reduction-assisted immersion gold. Figure 10: Chart of phos palladium with reduction-assisted immersion gold vs. time in the palladium bath.

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