Final finish is all about connectivity. It is the starting point to connecting a component to the board, or the board to a device. Connections are primarily made by three methods; soldering, wire bonding or, mechanical contact. In the 1980s and early 1990s, products used simple through holes coated with tin-lead based HASL (Hot Air Solder Leveling) as the dominant finish. Electrolytic nickel followed by hard gold was the coating for insertion tabs and other mechanical contacts. The introduction of technology advances has forced the industry to seek alternatives to HASL. HASL could not meet the co-planarity requirements to today's product.
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