PCB Technical - How to design the different spacing in the circuit board

How to design the different spacing in the circuit board

1. Spacing between wires

As far as the processing capabilities of mainstream Shenzhen PCB manufacturers are concerned, the minimum spacing between wires should not be less than 4mil. The minimum line distance is also the distance from line to line and line to pad. From a production point of view, the bigger the better if possible, the more common is 10mil.

2. Pad aperture and pad width

As far as the processing capabilities of mainstream Shenzhen PCB manufacturers are concerned, if the pad aperture is mechanically drilled, the minimum should not be less than 0.2mm, and if laser drilling is used, the minimum should not be less than 4mil. The aperture tolerance is slightly different depending on the plate, generally it can be controlled within 0.05mm, and the minimum pad width should not be less than 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 skin on the edge of the board, engineers often spread copper on a large area The block is shrunk by 20 mils relative to the edge of the board, instead of spreading the copper to the edge of the board.

There are many ways to deal with this kind of copper shrinkage, such as drawing a keepout layer on the edge of the board, and then setting the distance between the copper paving and the keepout. Here is a simple method to set different safety distances for copper paving objects. For example, the safety distance of the whole board is set to 10mil, and the copper paving is set to 20mil, and the effect of 20mil shrinkage of the board edge can be achieved. The dead copper that may appear in the device is removed.

Non-electrically related safety clearance

The text film cannot be changed during processing, 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 spacing between the characters is D=0.2mm. When the text is smaller than the above standard, the processing and printing will be blurred.

Via-to-via spacing

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 tinned during the tinning, which will affect the component mounting. Generally, the circuit board factory requires a space of 8mil to be reserved. If the area of the circuit board is limited, the 4mil pitch is barely acceptable. If the silk screen accidentally covers the pad during design, the circuit board factory will automatically eliminate the part of the silk screen left on the pad during manufacturing to ensure that the pad is tinned.