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IN MY FIRST COLUMN, I will focus on hot-air solder (lead containing and lead-free) leveling (HASL) since this was and continues to be a widely used surface finish. This process came into its own during the early 1980s at a time when reflow solder was still predominate. The emerging HASL process offered a more automated way to protect copper through holes and surface attachment areas. When HASL became popular, surface-mount technology was not yet widely used; so solder planarity was not an absolute prerequisite for the surface finish treatment. HASL was ahead of its time.
