Surface Treatment Processes for PCBs

• Electroless Nickel/Immersion Gold

  The electroless nickel/immersion gold process provides a robust protection for PCBs, enhancing their electrical properties over time. By coating the copper surface with a nickel-gold alloy, the PCB is shielded for an extended period. This process also offers environmental tolerance not found in other methods, preventing diffusion between gold and copper and limiting expansion at high temperatures.

• Immersion Silver

  Immersion silver, simpler than electroless nickel/immersion gold, offers good electrical performance and solderability even under harsh conditions. While lacking the physical strength of nickel, it ensures minimal assembly issues after years of use. The process involves a displacement reaction resulting in a pure silver coating, sometimes including organic matter to prevent corrosion and migration.

• Immersion Tin

  Immersion tin, compatible with various solders, forms a flat copper-tin compound for excellent solderability. Additives in the solution enhance thermal stability and bonding between copper and tin. However, tin whisker formation and migration issues limit its application, requiring prompt assembly post-treatment.

• Other Surface Treatment Processes

  Nickel-gold electroplating and electroless palladium plating are common in the industry. Electroplated nickel gold involves nickel plating followed by a gold layer to prevent diffusion. Two types of gold—soft and hard—are used for different applications, with selective plating reducing gold usage. Electroless palladium plating, similar to nickel plating, enhances welding reliability and surface smoothness.