Lead Finish
Deposition of a crystalline, non-reflective tin layer on electronic components and printed circuit boards provides a solderable surface that is free of organic brighteners. The use of matte tin plating has become standard for lead-free electronics due to its high melting point and excellent compatibility with SAC alloy solders. This finish establishes a stable protective layer that resists oxidation during storage and subsequent assembly operations.
Deposition Process
The plating is typically applied through electrodeposition in an acid bath, producing a surface with a grain size of several micrometers. This larger grain structure compared to bright tin reduces the internal stress within the plated layer and minimizes the risk of tin whisker formation. Tin whiskers are crystalline structures that can grow spontaneously from the plating and cause short circuits on high-density circuit boards.
Adding a nickel underplate or implementing a post-plating bake cycle further mitigates this risk by limiting copper-tin intermetallic growth.
Finish Performance
Uncontrolled plating parameters can lead to uneven thickness or high internal stresses in the tin layer. Utilizing matte tin plating ensures a reliable, lead-free finish that maintains solderability through multiple reflow cycles. This plating supports the long-term reliability of solder connections in consumer and industrial applications.
