Hot Air Solder Leveling (HASL) is a time-tested process where the exposed copper circuitry of a PCB is coated with a molten solder (typically a tin-lead or lead-free alloy) and then passed through hot air knives溶接表面を平らにし,均質な厚さを確保し,非常に溶接可能な保護層を作り出します.