Circuit board design: explain the wiring design of the main board in detail
The design of printed circuit board is based on the circuit schematic diagram to realize the functions required by the circuit designer. The design of printed circuit board mainly refers to layout design, which needs to consider the layout of external connections. The optimal layout of internal electronic components, the optimal layout of metal wiring and through-hole, electromagnetic protection, heat dissipation and other factors. Excellent layout design can save production costs and achieve good circuit performance and heat dissipation. Simple layout design can be realized by hand, while complex layout design needs to be realized by computer aided design (CAD)
1. Mistakes in snake routing
Serpentine is a common form of cabling on the computer motherboard (it should be familiar to those who have played the Nokia mobile phone game Snake). The wiring design on the motherboard is a professional knowledge. Some people think that the more snaking lines, the higher the design level. This view is wrong.
In fact, there are two reasons for using serpentine wires on a motherboard:
One is to ensure the equal length of the route. Because like the clock line from the CPU to the Beiqiao chip, it is different from the circuit board lines of ordinary household appliances. The signals running at a high speed with a frequency of about 100MHz on these lines are very sensitive to the length of the line. Unequal length clock lines will cause the signal to be out of sync, and then cause the system to be unstable. Therefore, some lines must be routed in a curved way to adjust the length.
Another common reason for using serpentine wire is to minimize the impact of electromagnetic radiation (EMI) on other parts of the motherboard and the human body. Because the high-speed and monotonous digital signal will interfere with the normal work of various parts in the motherboard. Generally, a simple way for motherboard manufacturers to suppress EMI is to design serpentine lines to absorb as much radiation as possible.
However, we should also see that although the use of serpentine cables has the above advantages, it does not mean that the more serpentine cables used in the design of motherboard cabling, the better. Because too many and too dense motherboard cabling will cause uneven motherboard layout, which will have a certain impact on the quality of the motherboard. A good cabling should make the density of all parts of the motherboard slightly different, and should be evenly distributed as far as possible, otherwise it is easy to cause instability of the motherboard.
2. Clock line equal length
On a motherboard, the distance from the Beiqiao chip to the CPU, memory, and AGP slots should be equal. The basic requirement for motherboard design is the so-called "equal length of clock lines" concept. As a bridge between CPU and memory, the Beiqiao chip is very particular in layout. For example, some motherboard manufacturers with development strength have adopted the ingenious design of rotating 45 degrees in the arrangement and layout of Beiqiao chips, which not only shortens the routing length between Beiqiao chips and CPU, memory slots and AGP slots, but also makes the clock lines equal in length. The circuit board assembly and circuit board processing manufacturers explain the routing design of the computer motherboard pcb design.