Issue link: https://iconnect007.uberflip.com/i/1472851
60 DESIGN007 MAGAZINE I JULY 2022 should be part of any decision to choose a final finish: • Lead tolerant or lead-free (LF) process • Shelf life • Flatness • Lead or ball pitch • Wire bondability • Lead insertion • Solder joint integrity • Corrosion resistance • Potential problems • Cost Lead-free finishes are considered "RoHS" compliant (< 0.1% BW of finish, for Pb, Hg or Cd) with the single exception of tin/lead HASL. e RoHS compliant finishes include the following: • ENIG • ENIPIG • ENEPIG • ImmAg • ImmSn • Electrolytic nickel/gold • LF HASL • OSP Lead-free PCBs require that the standard HASL surface finish cannot be used. ere is still a significant amount of discussion on what the long-term surface finishes will be. Cur- rently, the immersion silver and OSP surface finishes are the most prevalently specified sur- face finishes for solderable PCBs. Immersion tin is the prevalent surface finish for press-fit backplanes. Please contact your PCB fabrica- tor for current information on where industry specifications are heading. I will discuss just two of them here. Two Final Finishes ENIG (Electroless Nickel, Immersion Gold) ENIG is a two-layer metallic coating of 1.97 µin [0.05 µm] minimum, 2-5 µin [0.05 to 0.012 µm] typical, immersion deposited Au over 118.1-236.2 µin [3 to 6 µm] electroless depos- ited nickel, per IPC-4552 nominal pad size of 0.060" x 0.060" (1.5 mm x 1.5 mm). ENIG is typically used for flat surface/fine pitch devices. e benefits of ENIG are a long shelf-life and environmental resistance, as well as low contact resistance. Figure 1: Lead-free finishes.