PCB Technical - The PCB Common Tolerance

1. PCB tolerance definition

1. The PCB tolerance is the allowable variation of the actual parameter value. Parameters include not only geometric parameters in mechanical processing, but also parameters in disciplines such as physics, chemistry, and electricity.

2. For machinery manufacturing, the purpose of formulating PCB tolerances is to determine the geometric parameters of the product, so that the amount of variation is within a certain range, so as to meet the requirements of interchange or coordination.

3. In mathematics, the tolerance is for the special series of arithmetic series. It refers to the difference between the latter term and the previous term in the arithmetic series (that is, the difference between the nth term and the n-1th term). difference).

Two, PCB tolerance classification

The tolerances of geometric parameters include PCB size tolerance, PCB shape tolerance, PCB position tolerance and so on.

1. PCB size tolerance. Refers to the allowable size variation, which is equal to the absolute value of the algebraic difference between the maximum limit size and the minimum limit size.

2. PCB shape tolerance. Refers to the full amount of change allowed for the shape of a single actual element, including six items of straightness, flatness, roundness, cylindricity, line profile and surface profile.

3. PCB position tolerance. Refers to the total amount of change allowed by the position of the associated actual element to the datum. It limits the mutual positional relationship between two or more points, lines, and surfaces of the part, including parallelism, perpendicularity, inclination, and coaxiality, Symmetry, position, circular runout and full runout 8 items.

The PCB Thickness Tolerances as Following Parts:

Thickness Thickness Deviation Precision Deviation

0.5 / +/-0.07

0.7 +/-0.15 +/-0.09

0.8 +/-0.15 +/-0.09

1.0 +/-0.17 +/-0.11

1.2 +/-0.18 +/-0.12

1.5 +/-0.20 +/-0.14

1.6 +/-0.20 +/-0.14

2.0 +/-0.23 +/-0.15

2.4 +/-0.25 +/-0.18

3.2 +/-0.30 +/-0.20

6.4 +/-0.55 +/-0.30

The Warpage Tolerances as following Parts:

Tolerance of board thickness(mm): >0.2-1.2mm >1.5mm

Tolerance of double-layer board: ≤1%≤0.7%

Tolerance of multilayer board: ≤1%≤0.7%

Tolerance of PCB Board Thickness: (the plate thickness as customers requirments)

The Max Tolerences of Rigid Finished Double-layer Multilayer PCB Thickness as Following Parts:

Tolerences of board thickness(mm) Tolerance of double-layer boardmm(mm) Tolerance of multilayer board(mm)

0.2-1.0 ±0.1 ±0.1

1.2-1.6 ±0.13 ±0.15

2.0-2.6 ±0.18 ±0.18

>3.0 ±0.18 ±0.2

The Aperture as Customers Requirments, Tolerance Range is as Following Parts:

Hole(mm) Hole tolerance(mm) NPTH Hole tolerance(mm)

<1.6mm ±0.08 ±0.05

>1.6mm ±0.1 ±0.05

Note: Hole position drawing should meet the requirements of drawing.

The national standard for copper clad laminates: GB4723~4725 "copper clad laminates for printed circuits". Due to the revision over the years, the requirements for the nominal thickness and single-point deviation of the copper clad laminates are relatively loose in the standard. With the advancement of electronic technology, users have higher and higher requirements for the thickness deviation of copper clad laminates. Many CCL factories adopt the thickness and deviation specifications in IPC-4101A "General Specification for Substrates for Rigid and Multilayer Printed Circuit Boards" . This specification divides the thickness and deviation of the substrate into A/K level (commonly known as level 1), B/L level (commonly known as level 2), C/M level (commonly known as level 3), and D level. The thickness of grades A, B, and C is the thickness of the laminate without metal foil, the thickness of grade K, L, and M is the thickness of the laminate with metal foil, and grade D is used to measure the minimum thickness of the substrate by the microsection method. .

The geometrical dimensions and tolerances in PCB design, also known as GD&T or GDAT, are a language used in the communication of engineering drawings between engineering, production and quality management departments. GD&T is not only the national standard of the United States, but also an international standard. Reasonable marking of dimensions and tolerances plays an important role in reducing product costs.

PCB has strict requirements on size. Generally, the size of the hole, the distance between the holes, the distance between the light spots, and the size of the PCB are all required. The overall size is generally 0.1mm (some may be written as 4mil). If the pcs is larger, the tolerance will be appropriate. enlarge

If the shape of the PCB is too long, the difference should be about 0.2, but it is this kind of tolerance, and the accuracy inside it is relatively high. IPC requires a tolerance of +/-20%. Because the pads need to be mounted, the pads are generally accepted at the top.

The V-CUT cutting accuracy of the PCB board is usually between +/-0.1mm, that is, the difference of 0.2mm after the size of the unit small board is broken is acceptable! Exceeding too much is a processing error.

The PCB registration tolerance of the PCB board is the meaning of the position tolerance. The alignment tolerances of the inner and outer layers of the PCB respectively refer to the position tolerance of the hole center from the designated point of the inner and outer layers, which can be measured with a position measuring instrument.