We will encounter various safety spacing issues in ordinary PCB design, such as the spacing between vias and pads, and the spacing between traces and traces, which are all things we should consider.

We divide these spacings into two categories:
Electrical safety clearance
Non-electrical safety clearance

1. Electrical safety distance

1. Spacing between wires
This spacing needs to consider the production capacity of the PCB manufacturer. It is recommended that the spacing between traces is not less than 4mil. The minimum line spacing is also the line-to-line and line-to-pad spacing. So, from the perspective of our production, of course, the bigger the better if possible. Generally, the conventional 10mil is more common.

2. Pad aperture and pad width
According to the PCB manufacturer, if the pad aperture is mechanically drilled, the minimum should not be less than 0.2mm. If laser drilling is used, it is recommended that the minimum is not less than 4mil. The aperture tolerance is slightly different depending on the plate, generally can be controlled within 0.05mm, and the minimum pad width must not be lower than 0.2mm.

3. The spacing between the pad and the pad
According to the processing capability of the PCB manufacturer, it is recommended that the distance between the pad and the pad is not 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 PCB board edge is preferably not less than 0.3mm. If it is a large area of ​​copper, it usually needs to be retracted from the board edge, generally set to 20mil.

Under normal circumstances, due to mechanical considerations of the finished circuit board, or to avoid curling or electrical shorts caused by exposed copper on the edge of the board, engineers often shrink large-area copper blocks by 20 mils relative to the edge of the board. The copper skin is not always spread to the edge of the board. There are many ways to deal with this kind of copper shrinkage. For example, draw a keepout layer on the edge of the board, and then set the distance between the copper paving and the keepout.

2. Non-electrical safety distance

1. Character width and height and spacing
Regarding silk screen characters, we generally use conventional values ​​such as 5/30 6/36 mil and so on. Because when the text is too small, the processed printing will be blurred.

2. The distance from the silk screen to the pad
The silk screen is not allowed to put on the pad, because if the silk screen is covered with the pad, the silk screen will not be tinned during the tinning, which will affect the component mounting.

Generally, the board factory requires a space of 8mil to be reserved. If it is because some PCB boards are really tight, we can barely accept the 4mil pitch. Then, 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. So we need to pay attention.

3. 3D height and horizontal spacing on the mechanical structure
When mounting the components on the PCB, consider whether there will be conflicts with other mechanical structures in the horizontal direction and the height of the space. Therefore, in the design, it is necessary to fully consider the adaptability of the space structure between the components, and between the finished PCB and the product shell, and reserve a safe distance for each target object.