GlobalWellPCB

PCB Manufacturing Tolerances

Specify the finished feature, its allowed variation and how it will be measured—before releasing the production files.

Name the featureFinished size, location or minimum

State the acceptanceLimits, datums and conditions

Confirm feasibilityReview the complete construction

01 / Start with the requirement

A tolerance needs a clear definition.

A nominal dimension without an acceptance range leaves room for disagreement. A tolerance without a defined feature does the same.

Separate finished dimensions from manufacturing tool sizes, and distinguish size from location, minimum requirements and electrical acceptance. Supplier capability tables are useful context, but they are tied to that supplier’s service and process.

This is a specification guide, not a GlobalWellPCB capability guarantee. All numerical examples below are illustrative arithmetic. Confirm manufacturability and acceptance in the quotation and approved drawing.

02 / What to specify

Different features need different acceptance rules.

Match the drawing requirement to the feature your product actually depends on.

On smaller screens, scroll the table horizontally.

Feature-definition checklist · no default production tolerances are implied
Feature	Define explicitly	Avoid this ambiguity
Finished board thickness	Target, limits and whether the measurement includes coatings or local build features.	Using a raw laminate thickness as the finished PCB requirement.
Plated through-hole size	Finished internal diameter after plating, tolerances and any connector fit requirement.	Confusing the drill-tool diameter with the accepted finished hole.
Non-plated holes / slots	Finished geometry, position and the drawing datum.	Assuming diameter tolerance also controls location.
Routed profile / cutouts	Finished outline, internal features, datums and corner constraints.	Measuring from an undefined origin or conflicting profile layers.
Trace width / spacing	Layer, finished conductor requirement and the agreed treatment of etch geometry.	Treating a minimum spacing as a symmetric tolerance about a nominal.
Copper and plating	Base versus finished requirement, location and verification method.	Assuming one copper-weight label completely specifies every finished layer.
Mask registration / openings	Required exposure, coverage, clearances and any critical pad geometry.	Using a visual preference where a dimensional rule is needed.
Bow / twist	Applicable acceptance requirement, board condition and measurement method.	Applying one unspecified percentage to every board construction.
Controlled impedance	Mode, target, tolerance, structure, coupon and evaluation conditions.	Equating DC continuity with transmission-line impedance verification.

03 / Translate the requirement

Turn a tolerance into visible limits.

Two common forms

Percentage: limits = nominal × (1 ± percentage / 100).

Absolute: limits = nominal ± the stated deviation, in the same unit.

ILLUSTRATIVE EXAMPLES ONLY Thickness: 1.60 mm ±10% → 1.44–1.76 mm Finished hole: 0.80 mm ±0.08 mm → 0.72–0.88 mm Profile length: 100.00 mm ±0.20 mm → 99.80–100.20 mm Impedance: 50 Ω ±10% → 45–55 Ω

Do not copy an example as a supplier promise. The figures demonstrate calculation only; they are not recommended defaults or an acceptance standard.

Tolerance range calculator

Calculate limits from a target. This tool does not determine manufacturing capability.

Nominal value

Tolerance (±)

Tolerance type

Display unit

1.44 – 1.76 mm

Example: 1.60 mm ±10%. Changing the unit label does not convert the entered number.

Units are labels, not conversion controls. 1 mil = 0.0254 mm exactly.

04 / Agree how to inspect

The measurement plan belongs with the tolerance.

Define the datum

State the coordinate origin and controlling datum features. A hole’s acceptable diameter does not resolve its acceptable position.

Define the finished condition

Record plating, coatings, temperature or other relevant conditions. Choose the condition that matches the agreed acceptance requirement.

Choose the evidence

Identify the inspection method and report. A dimensional inspection, microsection and impedance test answer different questions.

Resolve conflicting files

Reconcile drawing notes, drill data, outline layers and the stackup. State which approved document governs a feature if a conflict is discovered.

Review critical dimensions

Flag interference fits, mounting patterns and other functional limits early. Tighter limits require feasibility review; they are not automatically available.

Document disposition

Agree sampling, recording, out-of-limit handling and approval authority. Do not silently change the target to accommodate a measured result.

Practical answers

Questions before
you release the design.

Use these answers to clarify the specification, then resolve project-specific requirements with your manufacturing and assembly teams.

Is a minimum feature size the same as a tolerance?

No. A minimum requirement provides a boundary, such as “not less than.” A symmetric tolerance specifies deviation around a nominal target. Choose the form that represents the functional requirement.

Does a plated hole equal the drill-tool size?

No. A plated hole is accepted against its specified finished geometry after relevant processing. The manufacturing tool is selected to support that result.

Are tighter tolerances always better?

They may be necessary for function, but they also need an agreed manufacturing and measurement approach. Specify functional requirements rather than tightening every dimension without a reason.

Can a continuity test prove a 50 Ω impedance requirement?

No. Continuity and characteristic impedance are different quantities. Specify an appropriate impedance structure, method and acceptance plan separately.

Continue your review

Technical references

Use these references to compare materials and technical requirements. Confirm the exact grade, construction and applicable documents for your board before ordering.