Electrochemical Corrosion Kinetics at Dissimilar Conductor Interfaces
Dissimilar conductor interface kinetics demand barrier electroplating and perimeter seals to restrict moisture ingress and prevent joint resistance growth.
ENIG Plating
Meaning
Electroless nickel immersion gold plating provides a metallic finish for printed circuit boards to ensure solderability and oxidation resistance. The process of enig plating creates a protective layer through a chemical deposition method that coats copper circuitry with a thin nickel barrier and a final gold surface. This configuration prevents copper corrosion while providing a reliable interface for soldering or wire bonding operations.
Deposition Mechanism
Chemical reduction forms the basis for the nickel layer as it deposits uniformly across exposed copper regions in an autocatalytic bath. Displacement then replaces a portion of the nickel surface with gold atoms upon immersion. These specific actions allow the coating to fill fine pitches and dense component pads without the thickness variations often seen with electrolytic alternatives.
High uniformity protects small features during assembly cycles.
Application Constraint
Thermal stress during component attachment occasionally produces a brittleness phenomenon known as black pad when the gold deposition rate fluctuates. Proper monitoring of bath chemistry maintains the nickel phosphorus balance required to avoid brittle fracture points at the intermetallic junction. Strict adherence to immersion timing prevents excessive copper leaching or phosphorus accumulation in the nickel barrier.
Performance Characteristic
Gold prevents oxidation of the underlying nickel during extended shelf life periods. Reliable connectivity occurs because the noble metal finish maintains a pristine surface for standard reflow soldering profiles. Superior contact resistance makes this finish suitable for high frequency boards and surface mount technology components that undergo repeated thermal or mechanical loads.