What is Hot Air Solder Level (HASL)
Hot Air Solder Level (HASL) is a surface finish process involving the application of a thin layer of solder onto the exposed copper pads of a printed circuit board. HASL begins by applying a solder mask to the board, which is then immersed into a bath of molten solder. The molten solder adheres to the available copper surfaces on the board. After removing the board from the solder bath, any excess solder is removed by blasts of hot air knives, resulting in a thin, uniform layer of solder bonded to the unmasked copper areas.
Traditionally, HASL utilized a solder mixture consisting of approximately 63% Tin and 37% Lead. However, with the introduction of regulations such as RoHS and REACH, there has been a shift towards lead-free processes. This has led to the development of “Lead Free HASL,” which employs solder alloys that do not contain lead.
HASL is a cost-effective surface treatment option and is commonly used as the default application in many PCB fabrication facilities. The resulting surface from HASL is relatively rough compared to immersion finishes like Electroless Nickel Immersion Gold (ENIG). Additionally, there is a risk of contamination as the hot air blast may not completely clean the solder mask or fully remove excess solder from smaller plated through hole footprints, exposed vias, or Ball Grid Arrays (BGAs).
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