The surface finish covers bare copper pads after soldermask, preserving solderability until assembly. The main choices are HASL and lead-free HASL, ENIG, immersion silver, immersion tin, OSP and ENEPIG, each trading flatness, shelf life, cost, wire bondability and contact reliability. Fine-pitch and BGA boards usually move away from HASL toward flat finishes, and edge connectors take hard gold.
Fine-pitch BGA and a 12-month shelf life, so the surface finish is ENIG, not HASL.
Also heard as
- final finish
- PCB finish
Related terms
ENIG
Electroless nickel immersion gold: flat surface finish of nickel topped with a very thin layer of gold.
HASL
Hot air solder leveling: finish made by dipping a board in molten solder and blowing off the excess.
Gold fingers
Hard-gold-plated contacts along a board edge that plug into a slot, as on a memory module.
Black pad
ENIG defect where corroded nickel under the gold produces dark, brittle solder joints that crack off.