This process allows us to apply solder to the circuit
boards after they have been screened. Thus allowing them to be wave
soldered without the lifting of the solder masks. The boards are fluxed
then dipped into a large vertical solder tank. After which the excess
solder is blown off with high temperature compressed air knives. This
process produces a flat solder finish suitable for surface mount
components.
Hot Air Solder Leveling produces one of the most stable end finishes
with very good long term solder-ability. With time the base track copper
migrates into the solder layer, hand soldering is almost unaffected but
machine soldering becomes unreliable.
With a thin pure tin finish might might expect a solder-ability
of weeks, with pure silver its a few months, but with HASL its more usually
a few years.
