How important is Electroless nickel immersion gold (ENIG) vs normal HASL or hot air solder leveling is?
I'm prototyping a board that has an Spartan 6 FTG256 BGA. I'm trying to get a 4-layer board with min 5-mil trace width, min 5-mil trace spacing board. Partly, I'm asking about ENIG vs. HASL because of cost.