ENGINEERING ANSWER
ENIG offers a common solderable finish, but its nickel layer can affect high-frequency conductor behavior. The importance depends on frequency, line geometry and which portions of the RF current path receive the finish.
What to decide before release
Evaluate electrical and assembly needs together. Discuss selective finish or RF mask openings only if the supplier supports them. Compare test structures with the same geometry and clearly documented finish process.
Checks to put in your design brief
- Specify the finish process
- Identify exposed RF conductors
- Validate loss and solderability requirements
Important distinction
A gold appearance does not mean the current flows in a thick, pure-gold conductor.
Sources & basis
Material facts follow the cited source. Design checks are preliminary guidance, not supplier process instructions.