PCB News - Detailed explanation of motherboard routing and layout design

For a motherboard, in addition to the parts materials (such as the use of high-quality capacitors,three-phase power lines, etc.),the wiring and layout design of the motherboard is also very important. Since there are many forms of motherboard routing and layout design and very technical,this is also a major difference between high-quality motherboards and low-quality motherboards. But how can we tell whether a motherboard is designed well or not?Now,let’s analyze it briefly.

Interpret the wiring design of the motherboard

The concept of equal length of clock line

On a motherboard, the distance from the Northbridge chip to the CPU,memory,and AGP slots should be equal. This is a basic requirement of the motherboard design, which is called the concept of equal length of clock line. As a bridge between the CPU and memory,the Northbridge chip is very picky about its layout. For example, some motherboard makers with development capabilities have adopted a clever design that rotates the Northbridge chip by 45 degrees in the layout, which not only shortens the length of the cable between the Northbridge chip and the CPU,memory slots, and AGP slots,but also allows more clock lines to be of the same length.

Misunderstating and ingesting of snake walking line

Snake line is a common form of wiring on computer motherboards. It should not be unfamiliar to anyone who has played the Nokia mobile game “Snake”. Snake line is a common form of wiring on computer motherboards. Some people think that the curvier the line, the better the design. This view is wrong.

In fact,there are two reasons for adopting a snake line on a motherboard

One is to ensure the equal length of the wiring lines. Because the clock lines from the CPU to the Northbridge chip are different from the circuit board circuits of ordinary household appliances, the signals running at high speeds of about 100MHz on these circuits are very sensitive to the length of the circuits. Clock lines of varying lengths will cause the signals to become desynchronized, leading to system instability.For this reason,some circuits must be routed in curved tubes to adjust the length.

Another common reason for using snake wire is to minimize the influence of electromagnetic radiation (EMI) on the rest of the motherboard and the human body.Because of the high speed, monotonous digital signals,it interferes with the normal operation of various components in the motherboard.Often,a simple way for motherboard manufacturers to suppress electromagnetic interference is to design a serpentine to absorb as much radiation as possible.However,we should also note that despite the advantages of using a serpentine cable, it does not mean that it is better to use more serpentine cables when designing motherboard cabling.This is because too many and dense motherboard traces will result in an uneven motherboard layout, which will have an impact on the quality of the motherboard. Good traces should have little difference in wire density between motherboard parts and should be distributed as evenly as possible, otherwise the motherboard will become unstable easily.

Avoid using “flying wire” motherboards

To judge the quality of a motherboard's wiring,look at the corners of the wiring.A good motherboard's wiring should be more even and neat, and the corner of the wiring should not be less than 135 degrees. The reason is that traces with too small an angle are equivalent to inductive components in a high-frequency circuit, and they will interfere with other devices.

Some pcb plate manufacturers with poor design standards often cause defects in the final product due to their technical strength when designing the wiring. At this time, manual maintenance is used to solve the problem. This kind of wire that appears due to unreasonable design is called “flying wire” (Figure 2).If there are flying wires on the motherboard, this proves that there is something wrong with the layout design of the motherboard.

Interpreting the layout design of the motherboard

The layout of the motherboard is mainly embodied from the position arrangement of the various components on the board (such as integrated circuit chips, resistors, capacitors, etc.). The layout of the motherboard is mainly embodied from the position arrangement of the various components on the board (such as integrated circuit chips, resistors, capacitors, slots, etc...) , and wiring,and wiring. In the eyes of experts, a good motherboard is like a piece of fine art.

Usually,chipset manufacturers will provide chipset design guides (CHIPSET DESIGN GUIDE) when supplying motherboard manufacturers. At the same time, there are usually standards-based templates, the so-called “engineering committees”,which are often used in the design of motherboards. “engineering committees“, public boards. Major motherboard manufacturers usually follow standard board designs and produce motherboards that meet the technical standards provided by the official chipset. The quality of these products is guaranteed, but the price is higher. On the contrary,some small and medium-sized manufacturers often make drastic changes to the motherboard structure in order to balance cost and functionality. The quality of these products can be said to be mixed.

The motherboard routing and PCB layout design is described in detail above. Ipcb also provides information for PCB manufacturers and PCB manufacturing technology.