Hot air solder leveling (HASL), is known as the tried-and-true copper plating method. This process works by dipping a board in molten solder and then leveling it off with a hot air knife, hence its name.
HASL is known for being the least expensive type of PCB surface finish, for being widely available, and for being very economical. Other advantages of using HASL include being able to easily rework the copper finish, providing a long copper finish shelf life, and serving as an ideal option for through-hole and/or larger SMT components on your PCB. However, you might run into problems if your board uses either SOIC or small SMT components.
Some other disadvantages include having uneven surfaces, possible solder bridging, plugged or reduced plated through-holes, and, of course, HASL uses lead, so this option isn’t viable for projects requiring RoHS-compliance. If your project does indeed require RoHS-compliance, you might need to consider using lead-free HASL. Lead-free HASL is a process similar to HASL only without the lead, specifically the tin-lead solder. Materials used, in place of the lead, are tin-copper, tin-nickel, or tin-copper-nickel germanium. Although this lead-free HASL process is an economical one that offers RoHS compliance, it’s similar to the regular HASL process in the sense that it’s not ideal for smaller components.
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