With the versatility and miniaturization of electronic products, the assembly density of surface mount panels (SMA) is becoming higher and higher, and the wiring difficulty is increasing. The main contents of the wiring design include the inner and outer wire width、spacing and design, the routing method.
Pcb board layout must not only meet the electrical performance requirements of the product, but also consider factors such as safety, reliability, processability, and cost.
(1) Wire width. The design of the wire width is determined by four factors, namely load current, allowable temperature rise, plate adhesion and complexity of production and processing. The design principle is to not only meet the electrical performance requirements, but also to facilitate processing, but also to consider adhesion. The ministerial standards stipulate that the adhesion of FR-4 is 14N/cm.
In general, the ground line width > power line width > signal line width, usually the signal line width is 0.2~0.3mm, the finest width is 0.05~0.07mm, the power line width is 1.2~1.5mm, and the common ground line is used 2~3mm line width as much as possible. If there is a large area of ground wire and power line area on the printed circuit board (area over 500mm²), the window should be partially opened, the width and spacing of the opening should be no more than 15mm, or using grid-like wiring.
(2) Wire spacing. It is determined by the insulation resistance, withstand voltage of the substrate and the processing technology of the wire. As the voltage rises, the wire spacing should increase. Generally, the insulation resistance of FR-4 substrate is greater than 10 to the 10meters/mm, the insulation resistance of good substrate is greater than 10 to the 12meters/mm; the withstand voltage is greater than 1000V/mm, which can actually reach 1300V/mm. Since the wire is burred, the maximum width of the burr must not exceed 20% of the wire spacing.
(3) Way of routing. When the signal line of the same layer changes direction, the diagonal line should be taken, and the acute angle should be avoided at the corner, and the acute angle will be warped due to the stress.
(4) The inner ground wire is designed as a mesh to increase the bonding force between the layers. A grid structure must be used for line widths above 5 mm.
The above is a reasonable operation method for wiring when setting up the circuit board.
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