How to consider the safety spacing in PCB design?

In PCB design, there are many places that need to consider the safety spacing. Here, it is classified into two categories for the time being: one is electrical-related safety spacing, and the other is non-electrical-related safety spacing.

Electrical related safety spacing

1. Spacing between lines

As far as the processing capacity of general PCB manufacturers is concerned, the minimum spacing between lines should not be less than 4mil, but Shenzhen professional PCB manufacturer - SysPCB can achieve 3mil. The minimum line spacing is also the spacing from line to line, line to pad. From a production point of view, the bigger the better, the more common spacing is 10mil.

2. Pad aperture and pad width

As far as the processing capacity of mainstream PCB manufacturers is concerned, if the pad aperture is mechanically drilled, the minimum should not be less than 0.2mm, while SysPCB can achieve 0.15mm. If laser drilling is used, the minimum should not be less than 4mil. The aperture tolerance is slightly different depending on the material, generally it can be controlled within 0.05mm. The minimum pad width should not be less than 0.2mm.

3. The spacing between the pads

As far as the processing capabilities of mainstream PCB manufacturers are concerned, the distance between pads should not be less than 4mil, but SysPCB can do 3mil, and FPC can do 2mil.

4. The spacing between the copper and the board edge

The distance between the copper and the edge of the PCB board is preferably not less than 0.3mm, Shenzhen PCB manufacturer - SysPCB can do 0.2mm.

If it is a large area of copper, it usually needs to be retracted from the edge of the board, generally set to 20mil. In the PCB design and manufacturing industry, under normal circumstances, due to the mechanical considerations of the finished circuit board, or to avoid curling or electrical short-circuiting due to the exposed copper on the edge of the board, engineers often shrink a large area of copper by 20mil relative to the edge of the board edge instead of spreading the copper to the edge of the board.

Non-electrically related safety spacing

1. Character width, height and spacing

The text film cannot be changed during processing, just thickened the character line width below 0.22mm to 0.22mm, that is, the character line width L=0.22mm (8.66mil) ). The width of the entire character is W = 1.0 mm, the height of the entire character is H = 1.2 mm, and the space between the characters is D = 0.2 mm, when the text is smaller than the above standard, the processing and printing will be blurred.

2. Spacing from via to via

The distance between vias is preferably greater than 8mil.

3. Spacing from silk screen to pad

The silk screen is not allowed to cover the pad. Because if the silk screen is covered with the pad, the silk screen will not be soldered when soldering, which will affect the component placement. Generally, the PCB factory requires a space of 8mil to be reserved. If the PCB board has a limited area, a 4mil pitch is barely acceptable. If the silk screen accidentally covers the pad during design, the PCB factory will automatically eliminate the part of the silk screen left on the pad during manufacturing to ensure that the pad can be soldered.

Of course, specific conditions are analyzed in design. Sometimes the silk screen is deliberately close to the pad, because when the two pads are very close, the middle silk screen can effectively prevent the solder connection from shorting during soldering. This situation is another matter.

4. Mechanical 3D height and horizontal spacing

When mounting 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, when designing, it is necessary to fully consider the adaptability between the components, the PCB board, product shell, and the space structure, reserve a safe spacing for each target object to ensure that there is no conflict in space.