Electrical safety distance
1. Spacing between wires
As far as the processing capabilities of mainstream PCB manufacturers are concerned, the minimum distance between wires should not be less than 0.075mm. The minimum line spacing refers to the minimum distance from the board line to the line and from the line to the pad. From a production point of view, the larger the line spacing, the better, and the more common one is 0.25mm.
2. Pad aperture and pad width
As far as the processing capabilities of mainstream PCB manufacturers are concerned, if the pad is mechanically drilled, the minimum aperture shall not be less than 0.2mm; if it is laser drilled, the minimum aperture shall not be less than 0.1mm.
The hole diameter tolerance is slightly different according to the different board materials, and it can generally be controlled within 0.05mm, and the minimum pad width should not be less than 0.2mm.
3. The distance between pad and pad
As far as the processing capabilities of mainstream PCB manufacturers are concerned, the spacing between pads should not be less than 0.2mm.
4. The distance between the copper skin and the edge of the board
The distance between the charged copper skin and the edge of the PCB is preferably not less than 0.3mm. This spacing rule can be set on the Design-Rules-Board outline page.
If it is a large area of copper laying, usually there needs to be a shrinkage distance from the edge of the board, which is generally set to 0.5mm. In the PCB design and manufacturing industry, under normal circumstances, due to the mechanical considerations of the finished circuit board, or to avoid the possibility of curling or electrical short circuit caused by the exposed copper skin on the edge of the board, engineers often lay a large area of copper The block is set back 20mil relative to the edge of the board, instead of spreading the copper all the way to the edge of the board.
There are many ways to deal with the shrinkage of the copper skin, such as drawing the keepout layer on the edge of the board, and then setting the distance between the copper laying and the keepout. A simple method is introduced here, which is to set different safety distances for copper laying objects. For example, the safety distance of the entire board is set to 0.25mm, and the copper laying is set to 0.5mm, which can achieve the effect of shrinking the board edge by 0.5mm , while also removing dead copper that may occur within the device.
Non-electrical related safety distance
1. Character width, height and spacing
The text film cannot be changed in any way, but the character line width of D-CODE less than 0.22mm (8.66mil) is thickened to 0.22mm, that is, the character line width L=0.22mm (8.66mil).
The width of the entire character is W=1.0mm, the height of the entire character is H=1.2mm, and the distance between characters is D=0.2mm. When the text is smaller than the above standard, the processing and printing will be blurred.
2. Via-to-via spacing
Via (VIA) to via spacing (hole edge to hole edge) is preferably greater than 8mil.
3. The distance from silk screen to pad
Silkscreen is not allowed to cover the pads. Because if the silk screen covers the pad, the silk screen will not be tinned when tinning, which will affect the component mounting. Generally, the board factory requires to reserve a spacing of 8mil. If the PCB board is really limited in area, it is barely acceptable to achieve a 4mil spacing. If the silk screen accidentally covers the pad during design, the board factory will automatically eliminate the part of the silk screen left on the pad during manufacturing to ensure that the pad is tinned.
Of course, the specific situation should be analyzed in detail when designing. Sometimes the silk screen is deliberately placed close to the pad, because when the two pads are very close, the silk screen in the middle can effectively prevent the short circuit of the solder connection during soldering, which is another matter.
4. Mechanical 3D height and horizontal spacing
When mounting components on the PCB, it is necessary to consider whether there will be conflicts with other mechanical structures in the horizontal direction and in the height of the space. Therefore, when designing, it is necessary to fully consider the adaptability between components, between the finished PCB and the product shell, and the space structure, and reserve a safe distance for each target object to ensure that there is no conflict in space.