How do I choose a PCB surface finish?

We offer three finishes: HASL (tin-lead). The lowest cost, with good solderability. It contains lead, so it is not RoHS compliant, and the pad surface is not perfectly flat. Lead-free HASL. RoHS compliant. A good default for through-hole parts and larger surface-mount parts. ENIG (immersion gold). A flat surface for BGAs, QFNs and fine-pitch parts, with a longer shelf life. It costs more than HASL. If your board has fine-pitch parts or will be stored for a long time before assembly, choose ENIG or ask an engineer.