In the ordinary PCB design, we will encounter various problems of safe spacing, such as the spacing between vias and pads, the spacing between traces, and so on, which should be considered. So today, we will divide these spacing requirements into two categories, one is: electrical safety spacing; The other type is: non-electrical safety distance.
Electrical spacing:
1. spacing between wires:
According to the production capacity of PCB manufacturers, the spacing between traces shall not be less than 4MIL. Line pitch is also the line-to-line and line-to-pad pitch. Then, from the perspective of our production, of course, the bigger the better if conditions permit. General 10MIL is quite common.
2. Pad aperture and pad width:
According to the PCB manufacturer, the pad aperture shall not be less than 0.2mm if mechanical drilling is used, and shall not be less than 4mil if laser drilling is used. However, the aperture tolerance is slightly different according to different plates. Generally can be controlled within 0.05mm Pad width shall not be lower than 0.2mm
3. Spacing between pads:
According to the processing capacity of PCB manufacturers, the spacing between pads shall not be less than 0.2MM
4. Distance between copper skin and board edge:
The distance between the charged copper skin and the PCB board edge is not less than 0.3mm If the copper is laid in a large area, it is usually necessary to have an inward distance from the board edge, which is generally set to 20mil. Generally, for the mechanical consideration of the finished circuit board, or to avoid curling or electrical short circuit caused by the exposed copper skin at the board edge, engineers often shrink the large-area copper block by 20mil relative to the board edge, instead of laying the copper skin all the way to the board edge. There are many ways to deal with this kind of copper skin shrinkage. For example, draw the keepout layer at the edge of the board, and then set the distance between the copper plating and keepout.
Non-electrical safety distance:
1. Width, height and spacing of characters:
We generally use conventional values such as 5/30 6/36 MIL for the characters of silk screen printing. Because the text is too small, it will be blurred when printed.
2. Distance from screen printing to pad:
Screen printing does not allow bonding pads. Because if the solder pad is covered on the screen printing, the tin will not be applied to the screen printing place when the tin is applied, thus affecting the mounting of components. Generally, the board factory requires a spacing of 8mil. If it is because the area of some PCB boards is very tight, it is barely acceptable for us to achieve a spacing of 4MIL. Then, if the silk screen accidentally covers the pad during the design, the board factory will automatically eliminate the silk screen part left on the pad to ensure the tin on the pad. So we need to pay attention.
3. 3D height and horizontal spacing on mechanical structure:
When mounting PCB devices, it should be considered whether there will be any conflict with other mechanical structures in the horizontal direction and space height. Therefore, in the design, we should fully consider the adaptability of space structure between components, as well as between the finished PCB and the product shell, and reserve a safe distance for each target object.