PCB engineers in doing PCB design, often encounter a variety of safety spacing problems, usually these spacing requirements are divided into two categories, one is the electrical safety spacing, the other is: non-electrical safety spacing. So, what are the spacing requirements for designing PCB circuit boards?
First, the electrical safety spacing
1 the spacing between the wires: the minimum line spacing, also line-to-line, line-to-pad spacing shall not be less than 4 MIL. from the production point of view, the greater the better, of course, when available. The general routine 10MIL is more common.
2 pad aperture and pad width: according to PCB manufacturers, pad aperture if the mechanical drilling method, the minimum shall not be less than 0.2mm; if the laser drilling method, the minimum shall not be less than 4mil. and aperture tolerance according to different plates slightly different, generally can be controlled within 0.05mm; pad width of the minimum shall not be less than 0.2mm.
3 the spacing between the pads and pads: according to PCB manufacturers processing capabilities, the spacing shall not be less than 0.2MM.
4 the spacing between the copper skin and the board edge: preferably not less than 0.3mm. If it is a large area of copper laying, usually with the edge of the board has an inward shrinkage distance, generally set to 20mil.
Second, non-electrical safety spacing
1 the width and height of the characters and spacing: on the screen printing characters generally use conventional values such as: 5/30, 6/36 MIL, etc.. Because when the text is too small, processing printing out will be blurred.
2 screen printing to the pad distance: screen printing is not allowed on the pad. Because if the silk screen on the pad, the silk screen will not be able to tin at the time of tin, thus affecting the components mounted. General PCB manufacturers require 8mil spacing. If some PCB board area is very tight, to do 4MIL spacing is also acceptable. If the screen printing in the design accidentally cover the pad, PCB manufacturers in the manufacturing will automatically eliminate the part of the screen printing on the pad to ensure that the pad on the tin.
3 the 3D height and horizontal spacing on the mechanical structure: PCB devices in the installation and paste, to take into account the horizontal direction and space height will not have conflicts with other mechanical structures. Therefore, the design should be fully considered between the components, as well as between the finished PCB and the product shell, the adaptability of the spatial structure, to reserve a safe spacing for each target object.
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