Engineering resources
ENIG versus electrolytic hard gold: intended use
A drawing that calls for “gold finish” leaves a major functional choice unresolved. Solderable component pads and repeated-mating edge contacts are different interfaces. The finish decision should begin with the interface and its required performance, then specify the coating system and acceptance criteria.
Separate solder joints from wear contacts
Eurocircuits’ edge-connector guidance distinguishes ENIG as a board surface finish from hard plated gold over nickel for connector fingers. That distinction is more useful than comparing the visible color of two samples. A finish appropriate for a soldering process is not automatically qualified for repeated sliding contact.
ENIG names an electroless-nickel/immersion-gold system. Electrolytic hard gold involves a different deposition route and is often considered for contact surfaces. Selection still requires the actual product drawing and qualification requirements. Do not infer a universal mating-cycle rating or a required thickness from the process name alone.
Example: a board with two kinds of exposed copper
Hypothetical design review. Consider a controller board containing fine-pitch component pads and an edge connector. The initial note says “all exposed pads gold.” A reviewer should split the requirement into two defined coverage regions: solderable pads and connector contact areas. The connector drawing supplies contact geometry and durability requirements; the assembly process supplies solderability needs.
| Region | Design question | Required evidence |
|---|---|---|
| Component pads | Which finish supports the agreed assembly process? | Finish specification and solderability acceptance |
| Edge fingers | What contact conditions and mating history must be tolerated? | Connector requirements and qualification plan |
| Boundary between finishes | Where does each coating start and stop? | Dimensioned coverage artwork |
| Beveled board edge | How do bevel and contact dimensions interact? | Mechanical drawing reviewed with fabrication |
Specify the coating, not just its thickness
Record the governing standard or project specification, relevant revision, thickness acceptance ranges, measurement locations and any required composition or hardness criteria. Define the underlying layer as well as gold. If quoting a thickness in microinches, check the units before comparing proposals: 50 microinches equals 1.27 micrometres. This is a conversion example, not a recommended coating thickness.
Request a review of selective plating and panel constraints before final layout release. A contact that looks correctly drawn on the finished outline may still need manufacturing provisions. Keep those provisions separate from the functional finished-board geometry.
Use the gold unit converter to reconcile drawing units and the fabrication review to resolve finish coverage and inspection. A more expensive or thicker finish is not automatically a better match for every surface on the board.
Discuss your fabrication package
Submit project requirements and fabrication files for review. Material suitability, availability and commercial terms require project-specific confirmation.
Sources and scope
Manufacturer references checked 9 October 2026. Examples and review worksheets are original editorial guidance, not approved process instructions. Historical reference documents are used for fundamentals, not current product availability.