PCB surface finishes are crucial to prevent the exposed copper surface from oxidation. The finishes can ensure good solderability and electrical properties of the circuit board. Based on the customer's applications and the property of the board, several surface finishes are available such as HASL, OSP, ENIG, ENEPIG, Hard Gold Plating, Immersion Tin, Immersion Silver, and also plain copper. This video gives a brief introduction to the HASL.