Common PCB surface treatment processesinclude: HASL(hot air solver leveling) ,OSP, electroless nickel plating / immersiongold, immersion silver, immersion tin, etc.

HASL, hot air solver leveling

Hot air leveling, also known as hot airsolder leveling, is a process of coating molten tin lead solder on the surfaceof PCB and leveling (blowing) it with heated compressed air, so as to form acoating layer which not only resists copper oxidation, but also provides goodsolderability. The thickness of copper tin metal compound is about 1-2 mil.

During hot air leveling, PCB should beimmersed in molten solder, and the air knife can blow the liquid solder beforethe solder solidifies, which can minimize the crescent shape of solder on thecopper surface and prevent solder bridging.

Hot air leveling can be divided intovertical type and horizontal type. It is generally considered that horizontaltype is better. The main reason is that horizontal hot air leveling has uniformcoating and can realize automatic production. The general process is: Microetching --- > Pre-heating --- > coating flux --- > spraying tin  --- > cleaning