A protective buffer that prevents gold chemistry from corroding the nickel layer.
"All exposed copper pads shall have ENIG per IPC-4556A: Ni 3-6µ, Au 0.05-0.23µ, P% 7-11."
The foundational structural circuit trace. ipc4556 pdf
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) standard deviations from the process mean , typically evaluated on a reference test pad. A protective buffer that prevents gold chemistry from
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Per the standard, layer dimensions must be statistically verified on a nominal pad area of 1.5 mm × 1.5 mm (or equivalent) using specific process standard deviation limits ( Plating Layer Minimum Thickness Limit Maximum Thickness Limit Key Engineering Function Diffusion barrier; prevents copper dissolution Electroless Palladium (Pd) Mitigates nickel oxidation; stabilizes wire bonds Immersion Gold (Au) Preserves shelf life; prevents air contamination Evolution of the Standard: From Base to Revision A