Can someone provide a realistic  range of electoless nickel thickness to
be used in conjunction with immersion Au.  Many customers define
thickness as 150 uinches min.  Is this a carry-over from tip plating
technology for lack of a better requirement?    IPC 6012 has reference to
nickel as a barrier to prevent formation of copper-tin oxides but nothing
regarding Au etc.

We have seen product with nickel thicknesses upwards to 300 uinches, and
suspect there is some correlation (along with other factors) that
excessive nickel thickness will contribute to  "background" or "shadow"
plating.

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