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Manufacturing Tolerances

PCB Manufacturing
PCB Assembly
PCB Design and Layout
PCB Basics
Vias, Drilling & Throughplating
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What are the manufacturing tolerances for PCBs?

Tolerance is the allowed diversion/variation from a specific dimension. It defines the acceptable variation between the maximum and minimum limits. For example, if an ideal part is to be 10mm with a tolerance of ± 1mm, any part that falls between 9 and 11 mm will be acceptable. PCB manufacturing tolerances with respect to material thickness, copper thickness, drilling, plating, and solder masks play an important role in the fabrication process. Maintaining these tolerances will ensure that your circuit boards are manufactured precisely.

Circuit board dimensional tolerances

Bow and twist tolerances

Bow and twist are flatness-based criteria that determine alignment problems in a circuit board.

Bow observed on a PCB surface

Bow is the deviation from flatness of a circuit board. It is a cylindrical/spherical curve on a rectangular plane surface as shown in the image above.

Twist seen on a PCB surface

Twist is the deformation of a rectangular circuit board causing one of the sheets’ corners to be off the plane containing the other three corners.

For non-rectangular boards, bow and twist can be measured by placing a rectangle over the PCB that is being tested. The imaginary rectangle’s dimensions should be the minimum that completely encloses the specimen.

Adhering to design for manufacturing guidelines can help you prevent bow and twist. To learn the DFM rules and best practices download the DFM Handbook.


Design for Manufacturing Handbook - Cover Image

Design for Manufacturing Handbook

10 Chapters - 40 Pages - 45 Minute Read
What's Inside:
  • Annular rings: avoid drill breakouts
  • Vias: optimize your design
  • Trace width and space: follow the best practices
  • Solder mask and silkscreen: get the must-knows


IPC 2422-1 and 2422-2 define the maximum bow and twist on circuit boards as:

Maximum bow and twist for boards with SMD0.75%
Maximum bow and twist for boards without SMD1.5%

Circuit board thickness

The thickness primarily depends on factors such as copper thickness, materials used, number of layers, and the operating environment. The standard PCB thicknesses are 31 mils, 62 mils, 93 mils, and 125 mils.

Acceptable tolerances for board thickness

Boards with thickness 31 mils and above± 10%
Boards with thickness less than 31 mils± 0.003”

Drilling tolerances

The drilling process is the basis for vias and layer interconnections. A design engineer must always look into the board manufacturers’ capabilities and tolerances before placing an order.

The below table summarizes the drilling tolerances followed at Sierra Circuits

Drill diameter tolerance for PTH and NPTH drills±3 mils (0.003”)
Drill to copperMinimum 8 mils (0.008”)
Tolerance in location/registration of the drilled hole1 mil (0.001")
Drill (hole) to drill (hole)6 mils (0.006")
Drill (hole) to board edge6 mils (0.006")
Annular ring tolerancesWill be specified by the designer
Laser hole location tolerances5 mils (0.005”)

Routing tolerances

Product featuresRouted part size tolerance
Standard5 mils (0.005”)
Advanced3 mils (0.003”)
Micro3 mils (0.003”)
Product featuresLaser routed part size tolerance ( can only be done with panels < .032” thick)
Standard2 mils (0.002”)
Advanced2 mils (0.002”)
Micro2 mils (0.002”)

Controlled impedance tolerances

To achieve undistorted signal propagation through traces, a uniform controlled impedance is a must to minimize signal reflections, hence distortion.

Controlled impedance tolerances at Sierra Circuits:

Product featuresControlled impedance tolerance

Solder mask feature tolerances

Product features
Solder mask feature tolerance
Standard1.5 mils (0.0015”)
Advanced1 mil (0.001”)
Micro1 mil (0.001”)
PCB Manufacturing
PCB Assembly
PCB Design and Layout
PCB Basics
Vias, Drilling & Throughplating
PCB Fabrication
PCB Ordering

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