Define the Reference for PCB Hole Position Measurements

A board can satisfy a hole-to-hole spacing requirement while failing to fit an enclosure because the entire hole pattern is displaced relative to the profile. Position is a relationship between features. Identify the relationship that controls assembly before assigning a tolerance or requesting an inspection report.

Start with the mating assembly

List the features that locate the PCB: mounting holes, board edges, connector faces or slots. Determine which are actual locating features and which provide clearance. A floating screw hole and a precision locating pin serve different purposes even if they have the same nominal diameter.

Draw the relevant dimensions from a consistent reference system. Avoid a chain of redundant dimensions that implies incompatible requirements. If geometric tolerancing is used, have the drawing reviewed by someone competent in the selected convention and identify that convention clearly.

Separate manufacturing relationships

Würth Elektronik’s technical delivery specification distinguishes several mechanical relationships, including holes to one another, holes to edges and conductor patterns to holes. Those distinctions explain why a single phrase such as ‘position tolerance’ is incomplete. The supplier’s standard values are not automatically the requirements of another manufacturing process or product.

Record which relationship each critical tolerance controls. For a connector aligned to an enclosure opening, the useful check may involve both its locating holes and a finished board edge. Copper registration alone does not verify that mechanical fit.

Choose an inspection approach that sees the reference

Specify how the board is supported and which features establish the measurement coordinates. Include the finished state of the board, particularly when tabs, burrs or an unseparated panel could affect the chosen edge. Measurement should not rely on a temporary production feature unless that is intentional.

For example, measuring the distance between two holes can miss a common shift of both holes relative to an enclosure datum. Conversely, measuring each from an irregular broken edge can add uncertainty unrelated to their mutual spacing. Select the check that matches the functional requirement.

Review tolerance accumulation

Combine PCB variation with mating-part, connector and assembly variation using a justified method. A tight PCB tolerance cannot compensate for an uncontrolled enclosure feature. Identify the few dimensions that control fit instead of tightening every dimension by default.

Keep the mating model, reference definition and inspection results together. When a profile or connector position changes, review the reference relationships again. The acceptance report should make clear what was measured from what, allowing a reviewer to connect the result to actual assembly fit without reconstructing an undocumented coordinate system.