PCB positioning hole is a very important link in PCB design process to determine the specific location of PCB through hole. The role of the positioning hole is printed circuit board manufacturing processing benchmark. PCB positioning hole positioning methods are various, mainly according to different positioning accuracy requirements. Positioning holes on printed circuit boards shall be represented by special graphic symbols. When the requirements are not high, the larger assembly hole in the printed circuit board can be used instead.

In order to facilitate the printed circuit board drilling and milling shape fixed board, as well as convenient online testing, many circuit board manufacturers hope users to design three nonmetallic holes on the PCB, positioning holes are usually designed into nonmetallic holes, drilling diameter of mm or mm. Smmo if the board is tight, at least two positioning holes should be put, and placed diagonally. If you make a jigsaw board, you can also think of the jigsaw board as a PCB, the whole jigsaw board as long as there are three positioning holes. If the user does not place, the circuit board manufacturer will automatically add on the basis of not affecting the line, or use the existing nonmetallic holes in the board as positioning holes.

Location hole location method

Device hole Interface devices and connectors are mostly plug-in components. The through hole diameter of the insertion device is larger than the pin diameter of 8 ~ 20mil, and the tin penetration is good during welding. It should be noted that there is an error in the aperture of the circuit board factory, and the approximate error is ±0.05mm. 0.05mm is a kind of drill at each interval, and 0.lmm is a kind of drill at each interval if the diameter is above 3.20mm. Therefore, when designing the aperture of the device, the unit should be converted into millimeters, and the aperture should be designed as an integer multiple of 0.05. The plate factory sets the drilling tool size according to the drilling data provided by the user. The drilling tool size is usually 0.1 ~ 0.15 larger than the forming hole required by the user. The diameter of the mmo design should be large rather than small, and the tolerance requirement should also be large rather than small. If it is a crimping device, the aperture should not be increased, according to the data recommended design, and in the instructions to explain what is crimping device, so that the circuit board manufacturer can try to control the error in the process of making the board, to avoid some unnecessary trouble.

Drilling types are divided into metalized holes and nonmetalized holes. There is precipitated copper in the wall of the metallized hole, which can play a conductive role and is represented by PTH. There is no copper in the hole wall of the nonmetallic hole, so it cannot conduct electricity. It is indicated by NPTH. The difference between the outer diameter and the inner diameter of the metallized hole diameter should be greater than 20mil, otherwise the welding ring of the pad is too small for processing and not conducive to welding. If conditions permit, the aperture can be designed to be the radius of the pad. The maximum hole diameter of metalized hole is 6.35mm, and the maximum hole diameter of nonmetal hole is 6.5mm. The metallized hole should not be designed on the contour line. The hole edge should be more than 1mm away from the contour line. Cobalt hole heavy hole easily damage the drill, so should be avoided as much as possible. Without welding and no electrical non-metallic hole, hole can be designed into the characteristic of nonmetallic welding plate hole does not need to design, line or copper foil at least 1 mmo drilling hole edge distance according to the shape can be divided into circular hole and rectangular hole, ordinary drilling for the round hole, rectangular hole is bit according to the procedures prescribed by many times of drilling, thus rectangle hole design best growth is twice the width, And the width is not less than 0.8mm, as little as possible to design rectangular holes.

PCB positioning hole requirements:

The development of PCB design industry has become mature, so the requirements for PCB positioning holes are also very perfect. The positioning holes must meet the following requirements.

1. Install at least two positioning holes on the diagonal of the board.

2. The standard aperture of the positioning hole is 3.2mm _+0.05mm.

3, for different products of the enterprise veneer can also use the following preferred aperture: 2.8mm ±0.05mm, 3.0mm±0.5mm, 3.5mm±0.5mm and 4.5mm±05mm. For different boards of the same product (such as DT board and PP board of ZXJlO), if the PCB has the same dimensions, the positioning holes must be the same.

4. The positioning hole is a light hole, that is, a nonmetallic through hole (except rf board).

5. If the existing mounting holes (except the buckle mounting holes) meet the above requirements, there is no need to set another positioning hole.

Some common specifications and precision requirements for positioning holes:

1. The diameter error range of the positioning hole is generally within 0.01mm. If the error is large in PCB manufacturing room, it will cause poor contact of the probe and inaccurate alignment of the interface connector to the inserting automatic mechanism.

2, the diameter of the positioning hole requirements: try to be below 3mm, so that the positioning column will not be deformed, too large and inconvenient to operate.

3, positioning hole PCB network distance: more than 1MM, so that the installation operation is not easy to short circuit, also will not cause damage to the product route.

4, the type of positioning hole: positioning hole is generally the need for mechanical control of unsinkable copper, so that it can not be connected with the circuit on the board and higher accuracy.

5, positioning bladder layout: need to be in the PCBA four corners or diagonal, so as to form a multi-point plane positioning, positioning accuracy, the farther the better.

6, the distance between the positioning hole and the test point should be at least 2mm, to prevent the wrong short circuit in the test.

7. The distance between the positioning hole and the edge of the plate is at least 2mm, which is not easy to crack while ensuring the strength of PCBA.