PCB Manufacturing Tolerances
Make the important dimensions clear, and we will help match them to the manufacturing process. FLJ reviews thickness, holes, routed profiles, slots and impedance around the way your board will fit and function.
What does a PCB tolerance describe?
A PCB tolerance is the permitted variation around a specified dimension or electrical target. It should identify both the feature being measured and the condition used to accept it.
A finished hole diameter is different from the drill-tool diameter because plating changes the opening. Likewise, a routed slot and a drilled slot use different processes. Describing the finished feature helps us quote the right route and helps your receiving team inspect the same thing.
Send your current drawing even if every tolerance has not been assigned. We review the features that matter to connectors, enclosures, press-fit parts or controlled-impedance signals, then discuss any details needed to agree the production specification.
Published general-process reference values
The following values come from FLJ’s existing general-process capability table. They are reference points for engineering review, with the final drawing and inspection conditions agreed for the order.
Material-specific capability tables can use different values. Aluminum, ceramic, HDI, flexible and rigid-flex boards should be reviewed against their own construction and process. A special-process value is not a default tolerance for every PCB.
| Feature | Published reference | Measurement or construction condition |
|---|---|---|
| Board thickness up to 1.0 mm | ±0.1 mm | General-process table; measured finished board thickness |
| Board thickness above 1.0 mm | ±10% | General-process finished thickness; critical fits reviewed with the drawing |
| Hole position | ±2 mil (about ±0.051 mm) | Compared with CAD data; datum arrangement reviewed |
| Non-plated hole diameter | ±2 mil (about ±0.051 mm) | General drilling capability; finished opening |
| Routed outline | ±8 mil (about ±0.203 mm) | Edge-to-edge profile dimension |
| Non-plated milled slot | ±0.10 mm | Slot width and length |
| Plated milled slot | ±0.15 mm | Slot width and length |
| Controlled impedance below 50 Ω | ±5 Ω | Target type and test conditions agreed |
| Controlled impedance at or above 50 Ω | ±10% | ±8% published as a review option |
Tell us which dimensions control the fit
For mounting holes, the relationship between holes can be as important as their individual diameters. For an enclosure, the outline and connector locations may be the critical features. For a press-fit connector, finished hole size, plating and the connector manufacturer’s application guidance need to be considered together.
You can mark these features on a PDF or send a mechanical drawing with the PCB files. If a mating part or housing controls the fit, its relevant dimensions help us understand the requirement. Our team can then discuss practical tolerances and the measurement reference before production.
Routed profiles, internal corners, V-scored edges and plated slots need different treatment. We explain the manufacturing options so the drawing describes a feature the inspection method can actually verify.
Copper geometry and impedance need different checks
A dimensional tolerance describes a physical feature. An impedance tolerance describes the electrical response of the specified structure.
The FLJ general-process table lists trace-width variation of ±1 mil for widths up to 10 mil. The relationship between trace width, copper thickness and etching should still be reviewed for the selected construction; minimum line width and line-width tolerance are different specifications.
Impedance depends on the stackup as well as trace width and spacing. We review the target, dielectric spacing, copper construction and test approach together. Coupons can provide a practical measurement structure when included in the agreed panel and test plan.
A target of 50 Ω with ±10% corresponds to 45–55 Ω. This arithmetic example explains the tolerance band; it does not define a universal acceptable value for every circuit.
Copper, drilling and depth-control tolerances
Tell us which dimensions control connector fit, press-fit assembly or enclosure mounting. We will review the relevant finished-board measurements with you.
| Feature | Process reference | How it applies |
|---|---|---|
| Line width at ≤10 mil | ±1.0 mil (±0.0254 mm) | Line-width tolerance, separate from minimum clearance |
| Line width above 10 mil | ±1.5 mil (±0.0381 mm) | General-process reference |
| PTH finished diameter | Project-specific finished-hole tolerance | Identify press-fit or tight connector fits on the drawing; we will review the plated opening |
| Countersink depth / opening diameter | ±0.15 mm | Published tapered-hole reference; angle and fit reviewed separately |
| Depth-controlled NPTH milled slot | ±0.10 mm | Depth accuracy for the published milling process |
| Drilled PTH slot width | ±0.075 mm | Slot-length tolerance: ±0.10 mm below 2:1 length/width; ±0.075 mm at ≥2:1 |
| Drilled NPTH slot width | ±0.05 mm | Slot-length tolerance: ±0.075 mm below 2:1 length/width; ±0.05 mm at ≥2:1 |
| Bow and twist | Review flatness with board size, stackup and assembly | Share the assembly or mechanical-fit concern so the agreed limit matches the product |
V-scoring and gold-finger beveling
Panel preparation supports assembly and separation. Share the intended outline or connector drawing, and we will help select the scoring or beveling arrangement.
| Feature | Process reference | How it applies |
|---|---|---|
| V-score angles | 20°, 30°, 45° | Select with board thickness and depanelization |
| V-score angle tolerance | ±5° | Published angle tolerance |
| V-score symmetry | ±4 mil (±0.102 mm) | Top/bottom score alignment reference |
| Gold-finger bevel angles | 20°, 30°, 45° | Reviewed with connector drawing and contact area |
| Gold-finger bevel angle tolerance | ±5° | Published beveling reference |
| Uninterrupted tab beside gold fingers | 6 mm minimum | Discuss panel breakaway and handling |
| Gold-finger side to profile edge | 8 mil (0.203 mm) | Keep contact geometry connected to the finished outline |
Copper clearance beside a V-score
The published distances below are from the V-score centre line to the copper pattern, for 20° / 30° / 45° respectively. H is board thickness.
| Board thickness H | Copper distance at 20° / 30° / 45° |
|---|---|
| H ≤1.0 mm | 0.30 / 0.33 / 0.37 mm |
| 1.0 < H ≤1.6 mm | 0.36 / 0.40 / 0.50 mm |
| 1.6 < H ≤2.4 mm | 0.42 / 0.51 / 0.64 mm |
| 2.4 < H ≤3.2 mm | 0.47 / 0.59 / 0.77 mm |
The drawing and final panel arrangement are reviewed together. These references help preserve copper during scoring.
Agree the inspection record around your critical features
For first articles or qualified production, discuss the dimensions and electrical targets you would like recorded. We can define the inspection scope around the features that matter, rather than adding the same measurement list to every order.
The production drawing, revision, agreed tolerances and inspection method should remain aligned. If a design change affects the mechanical fit or stackup, we review that change before a repeat build. Send the information you already have, and we will help close the remaining questions.
Frequently asked questions
Are all published tolerances available together on one board?
The combination depends on material, thickness, copper and the selected process. Send the design so we can review the complete construction and agree the values that matter.
Should I specify a drill size or finished hole size?
For component fit, the finished hole size is usually the useful dimension. Send your current notes and connector information, and we can clarify how they should be represented.
Can you review a tighter outline tolerance?
Yes. Mark the critical edge and explain the mating requirement. We will review machining and inspection options for that specific feature.
What if my drawing has no tolerance notes?
Send it as it is. Our team can discuss the critical features and suitable general conditions before the production specification is agreed.
Explore related capabilities
Let’s review your next build
Send your available board files, drawings or project questions. Our team will review the information and follow up with you about the next step.