What are the requirements and specifications for pwb positioning holes?
What is a PCB positioning hole?
The circuit board positioning hole refers to the specific position of the PCB via hole in the PCB design process, which is a very important link in the PCB design process. The positioning hole functions as a processing reference for the production of printed circuit boards. The positioning methods of PWB positioning holes are various, mainly based on different positioning accuracy requirements. The positioning holes on the printed circuit board should be indicated by special graphic symbols. When the requirements are not high, the larger assembly holes in the printed circuit board can also be used to replace.
In order to facilitate the board mounting and drilling of the board to fix the board, and to facilitate online testing, many circuit board manufacturers hope that users can design three non-metallized holes on the PWB. The positioning holes are usually designed as non-metallized holes, and the diameter of the holes is mm. At least two positioning holes should be placed and placed diagonally. If you make a panel, you can also regard the panel as a piece of PWB. As long as there are three positioning holes in the whole panel. If the user does not place it, the board manufacturer will automatically add it without affecting the circuit, or use the existing non-metallized holes in the board as positioning holes.
Positioning hole positioning method
Device hole interface devices and connectors are mostly plug-in components. The through-hole diameter of the interposer is 8-20 mils larger than the lead diameter, and the good tin penetration during soldering. It should be noted that there is an error in the aperture of the circuit board factory. The approximate error is ±0.05mm. Each interval 0.05mm, it is a drill. a diameter over 3.20mm, each interval 0.1mm is a kind of drill. Therefore, when designing the device aperture, the unit is converted into millimeters, and the aperture is designed to be an integral multiple of 0.05. The board factory sets the size of the drilling tool according to the drilling data provided by the user. The size of the drilling tool is usually 0.1~0.15mm larger than the forming hole required by the user. The design aperture should be larger and not smaller. The tolerance requirement should be larger and not smaller. Less aperture type is better. If it is a crimping device, the aperture should not be enlarged. It should be designed according to the data, and in the board description, which should be described as a crimping device, so that the circuit board manufacturer can control the error as much as possible during the board making process, avoiding some unnecessary trouble.
The types of drilling are divided into metallized holes and non-metalized holes. The metallized hole has immersion copper in the wall of the hole, which can conduct electricity and is represented by PTH. There is no immersion copper in the pore walls of the non-metallized holes, which cannot be electrically conductive, and is represented by NPTH. The difference between the outer diameter and the inner diameter of the metallized hole diameter should be greater than 20 mils, otherwise the solder ring of the pad is too small to be processed and is not conducive to soldering. If conditions permit, the aperture can be designed to be the radius of the pad. The maximum diameter of the metallized hole is 6.35mm, and the diameter of the non-metallized hole is 6.5mm. Metallized holes should not be designed on the outline line, and the edge of the hole should be larger than 1mm from the outline. When the cobalt hole is used, the heavy hole is easy to damage the drill bit, so it should be avoided as much as possible. Holes that do not need to be soldered and have no electrical characteristics can be designed as non-metallized holes. Non-metallized holes do not need to be designed. The edge of the hole is at least 1 mm away from the line or copper foil. The hole can be divided into a circular hole and a rectangular hole according to the shape. The drill holes are mostly round holes. The rectangular holes are drilled several times according to the specified procedure. Therefore, the rectangular holes are preferably designed to be twice as wide as the width, and the width is not less than 0.8 mm, and the rectangular holes are designed as little as possible.
PCB positioning hole requirements:
The development of the PWB design industry has matured, so the requirements for PWB positioning holes are also very perfect. The positioning holes are as follows.
1，At least two positioning holes must be setat the diagonal of the board.
2，The standard hole diameter of the positioning hole is 3.2mm _+0.05mm.
3，The following preferred apertures can be used for thesingle sided boardof different products of the enterprise: 4.
4，8mm ± 0.05mm, 3.0mm ± 0.5mm, 3.5mm ± 0.5mm and 4.5mm ± 05mm. For different single sided boards of the same product (such as ZXJlO DT board and PP board, etc.), if the PWB dimensions are the same, the position of the positioning holes must also be uniform.
5，The positioning hole is a light hole, that is, a non-metalized through hole (excluding the radio frequency board).
6，If the existing mounting holes (except the button mounting holes) meet the above requirements, it is not necessary to set the positioning holes.
Some common specifications and accuracy requirements for positioning holes:
1，The diameter error of the positioning hole is generally within 0.01mm. If the PWB manufacturing room has large error, the probe will be in poor contact, and the interface connector will not be aligned with the automatic mechanism.
2, The diameter of the positioning hole requirements: as far as possible below 3mm, so that the positioning column will not be deformed, too large and not easy to operate.
3, The distance of the positioning hole PWB network: above 1MM, so the installation operation is not easy to short circuit, and will not cause damage to the product route.
4, The type of positioning hole: positioning hole is generally required to do not immersion copper mechanical control, so that it can not be connected to the on-board circuit and higher precision.
5, Positioning hole layout: need to be on the four corners or diagonal lines of the PCBA, so that the formation of multi-point face-to-face positioning, accurate positioning, the farther the better.
6，The distance between the positioning hole and the test point should be at least 2mm to prevent short circuit in the test.
7， The distance between the positioning hole and the edge of the board is at least 2mm, which is not easy to break while ensuring the strength of the PCBA.
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