Measuring the Minimum Clear Opening of a Finished Plated Slot

A rectangular terminal may not enter a plated slot even when a top-view image shows the specified width. The mating part must pass through the complete opening. Local copper buildup, corner geometry and through-thickness variation can make the usable clearance smaller than the visible entrance.

Define the functional width

Eurocircuits identifies tooling, cleaning, plating and finish as contributors to finished-slot variation. The requested dimension should describe the finished feature. A router diameter or a preplating slot measurement does not establish final fit.

For a rectangular terminal, consider its maximum width, thickness, corner radius and insertion alignment. A circular pin gauge can check part of a slot but cannot represent every rectangular mating envelope. Select a gauge shape or dimensional method that answers the actual fit question without damaging the plated wall.

Inspect several locations and both ends

Measure near the center and rounded ends where appropriate, and inspect both board faces. If optical and functional results disagree, determine whether the entrance is flared, the slot is tapered or a local obstruction exists. A section through the suspected region can help, but it destroys the original fit condition and should follow nondestructive observations. Record any cleaning before gauging, because removing lodged material can change the result without changing the underlying plated geometry.

• Identify the minimum usable width and the required overall length.
• Record final surface finish and any post-fabrication coating.
• Define insertion force and prohibit forcing a gauge through a marginal opening.
• Retain the terminal drawing used to establish the fit envelope.

Correct the right contributor

For example, a slot with excessive local plating may pass after its nominal width is enlarged, but that change may reduce the surrounding annular copper or create loose fit elsewhere. Compare plating distribution and machining evidence before widening the design. The acceptance condition should retain both mechanical fit and the required conductive barrel.

Coordinate this review with plated-slot fabrication data and panel copper-thickness mapping. Keep gauge results tied to slot coordinates so a production trend can be compared with panel position. A single passing insertion demonstrates one sample and one orientation; the released control should address the permitted variation across the manufactured slot.