Definition

Hot Air Solder Leveling (HASL) is a traditional surface finish where PCBs are dipped in molten solder (traditionally tin-lead, now often lead-free SAC alloys) and excess solder is blown off with hot air knives. HASL provides excellent solderability and is cost-effective, but the resulting surface is not perfectly flat, making it unsuitable for fine-pitch components (<0.5mm). Lead-free HASL requires higher temperatures that can stress the laminate.