Immersion gold and gold plating are two methods of metal coating on PCB circuit boards that can enhance electrical performance and mechanical strength. Immersion gold involves chemical deposition of thick gold layers through oxidation-reduction reactions, while gold plating uses electroplating to create a thinner gold layer. The metal thickness, color, surface flatness, and crystal structure differ between the two processes. Immersion gold creates a thicker metal layer with a golden yellow color, smooth surface, and softer crystal structure, making it easier to weld. In contrast, gold plating produces a thinner, light yellow colored layer with a rougher surface and denser crystal structure, providing stronger wear resistance. Both processes offer benefits for improving conductivity, corrosion resistance, and reliability of circuit boards, protecting them from oxidation and increasing their service life.