What it is
A thin silver layer deposited by chemical displacement over bare copper. It protects the copper until soldering and dissolves into the joint during reflow, so the finished connection is copper-tin, not silver.
Where it wins
- Solderability — excellent wetting on both SAC and leaded alloys.
- Flatness — no meniscus, so fine-pitch printing is predictable.
- Cost — below ENIG, with no nickel step.
- High frequency — the thin layer has little effect on insertion loss compared with thicker finishes.
Where it needs care
Silver tarnishes. Boards should be sealed, stored dry and handled with gloves; tarnish is cosmetic until it affects wetting, but it makes visual inspection ambiguous. If the assembly line cannot control storage, ENIG is the safer specification.
