10. The design of PCB (multiple layer board)--Basic requirement of designing multiple layer PCB VOL2

The requirements of wire cloth and wiring
 Juvtmall ( a company supply PCB PrototypingPCBA service and sell kinds of components, modules and so on) 

In general, PCB multilayer board wiring is performed according to circuit function. In outer wiring, it is required to have a lot of wiring in the welding surface, and the components are less wiring, which is beneficial to the maintenance and platoon of printing plate.
Thin, tight conductor and easily disturbed signal lines, usually arranged in the inner layer.
The large area of copper foil should be evenly distributed in the outer layer, which will help to reduce the warping of the plate and make the plating more uniform on the surface.
In order to prevent the short circuit between the surface and the printed wire and the mechanical processing, the distance of the conductive graph in the inner and outer layers should be greater than 50mil.



Wire direction and line width requirements


The PCB multilayer strake is to separate the power layer, the stratum and the signal layer, and reduce the interference between the power supply, the earth and the signal.
The lines of the adjacent two-layer printing plates should be as vertical or oblique as possible, curves, and not parallel lines, to reduce the interlayer coupling and interference between the substrate.
And the wire should be as short as possible, especially for small signal circuits. The shorter the line, the smaller the resistance and the smaller the interference.
Signal lines at the same level should avoid sharp corners when changing direction.
The width of the wire should be determined according to the circuit's requirements for current and impedance. The power input line should be larger and the signal line can be relatively small.
For the general digital board, the width of the power input line can be 50 ~ 80mil, and the width of the signal line can be 6 ~ 10mil.


The line should also pay attention to the width of the line should be as consistent as possible, avoiding the sudden change of the lead and the sudden thickness of the line, which is conducive to the impedance matching.


The hole size and the requirements of the welding disk


The hole size of the components in the PCB multilayer board is related to the size of the selected components, and the holes are too small to affect the device's loading and tin.
The hole is too large and the solder is not full.
Generally speaking, the calculation method of the size of the hole pore diameter and welding disk is:

Aperture of component hole = element pin diameter (or diagonal) + (10 ~ 30mil)

The diameter of the element welding disc is greater than the diameter of the element


As for the hole aperture, it is mainly determined by the thickness of the finished plate, which is generally controlled in the thickness of the plate: the aperture is less than 5:1.
The calculation method of overhole welding disk is:

The diameter of the VIA PAD (VIA PAD) is greater than the hole diameter + 12mil.

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