Hot Air Solder Levelling

During this process, which today still represents the most common method of solderable surface finishing, the printed circuit board, after the soldermask step, is immersed in a molten Tin-Lead alloy and, during the subsequent extraction step it is hit by jets of hot air at high pressure which have the task of “leveling” the deposit, removing the excess of alloy from the holes and the pads.

Despite the considerable experience aquired, given that it is a historical finish, the flatness of the HASL finishing is strictly dependent on the circuit lay-out, with thicknesses that can be very variable.

On the other hand it is an easily inspectable finishing and maintains good characteristics of solderability over time, even with multiple soldering cycles; the solder joint is formed between tin and copper.

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