ENIG PCB: Immersion Gold Finish for Your Assembly

Electroless nickel forms the barrier between copper and the outer gold layer. Immersion gold protects that surface until assembly and normally dissolves into the solder during joining. The resulting connection must be evaluated as a solder system, not simply as a gold-colored pad.

The planar deposit makes ENIG a candidate for dense surface-mount layouts, but finish selection cannot correct a poor land pattern, filled-via requirement or an unsuitable solder-paste stencil. Send the smallest package geometry and any via-in-pad details for a combined fabrication review and BGA assembly review where array packages are involved.

Call out the required finish specification and revision, layer requirements and measurement locations. Nickel and gold readings are separate quantities. A supplier report should identify the actual lot, instrument method, calibration basis and sampling arrangement so a number can be interpreted correctly.

Use the workbench to convert micrometers and microinches for three readings of one layer. One microinch equals 0.0254 micrometers. A converted average is not proof that every location meets a limit, and the tool does not assess uncertainty or replace the contractual acceptance method.

ENIG process control includes the condition of the nickel deposit and its interaction with the gold deposition process. Excessive nickel corrosion, often discussed as black pad, cannot be ruled out by a visually bright gold surface or by a single thickness value.

Request the process-quality evidence required by the applicable specification and your project. If an assembly failure occurs, preserve lot identity, samples and the thermal history for investigation. Avoid declaring every dark pad a black-pad defect or promising that a particular thickness alone eliminates the mechanism.

Repeated mating, wire bonding and sensitive RF paths add requirements beyond ordinary solder lands. Hard gold may be relevant to wear contacts; ENEPIG or other qualified finishes may be considered for bonding. For high-frequency PCB manufacturing, nickel-containing finishes should be assessed against the actual RF structure rather than a general frequency threshold.

PCBSync can review the intended connection map, quantity and assembly route. Ask the quotation to identify the agreed finish, exceptions, storage instructions and requested lot records. Keep substitutions subject to the appropriate engineering approval and link the final choice to the released drawing.