In PCB design, wiring is an important step to complete the product design, it can be said that the previous preparatory work is done for it, in the entire PCB, the design process of wiring to the highest qualification, the most detailed skills, the greatest workload.
PCB wiring has single-sided wiring, double-sided wiring and multi-layer wiring. Wiring also has two ways: automatic wiring and interactive wiring, before the automatic wiring, you can use the interactive pre-wiring of the more stringent requirements of the line, the input and output side lines should be avoided adjacent to parallel, so as not to produce reflected interference. If necessary, ground isolation should be added, and the wiring of two adjacent layers should be perpendicular to each other, and parallel is prone to parasitic coupling.
Even if the wiring in the entire PCB board is completed very well, but the interference caused by poorly considered power and ground lines will degrade the performance of the product, and sometimes even affect the success of the product. Therefore, the wiring of electric and ground lines should be treated seriously to minimize the noise interference generated by electric and ground lines to ensure the quality of the product.
For each of the engineers engaged in the design of electronic products understand the ground and power lines between the noise generated by the reasons, now only to reduce the type of noise suppression to express.
a. it is well known in the power supply, between the ground line plus decoupling capacitors.
b. try to widen the power supply, ground line width, preferably wider than the power line, their relationship is: ground line > power line > signal line, usually the signal line width: 0.2 ~ 0.3mm, the most by the thin width of up to 0.05 ~ 0.07mm, power line for 1.2 ~ 2.5 mm
The PCB of the digital circuit can be used to form a wide ground wire loop, that is, to form a ground network to use (analog circuit ground can not be used in this way)
c. with a large area of copper layer for the ground, in the printed circuit board is not used on the place are connected to the ground as the ground. Or make a multilayer board, power supply, ground each occupies a layer.
Now there are many PCB is no longer a single function circuit (digital or analog circuit), but a mixture of digital and analog circuits. Therefore, in the wiring will need to consider the problem of mutual interference between them, especially noise interference on the ground.
Digital circuits are high frequency, analog circuits are sensitive, for signal lines, high-frequency signal lines as far away as possible from sensitive analog circuit devices, for ground, the whole PCB to the outside world only a junction, so the PCB must be processed inside the digital and analog common ground, and the board is actually separated from the digital and analog ground they are not connected to each other, only in the PCB and the outside world connection The interface (such as plugs, etc.). Digital ground and analog ground have a short connection, please note that there is only one connection point. There is also no common ground on the PCB, which is determined by the system design.
In the multilayer printed board wiring, due to the signal line layer is not finished cloth line left has not much, and then add more layers will cause waste will also add a certain amount of work to the production, the cost has increased accordingly, in order to solve this contradiction, you can consider wiring on the electrical (ground) layer. The first consideration should be to use the power layer, followed by the ground layer. Because it is best to retain the integrity of the ground layer.
In the large-area ground (electrical), commonly used components of the leg and its connection, the processing of the connection leg requires comprehensive consideration, in terms of electrical performance, the pad of the component leg and copper surface full connection is good, but the welding assembly of the components there are some undesirable pitfalls such as: ① welding requires high-power heaters. ② easy to cause false solder points. So taking into account the electrical performance and process needs, made of cross flower pads, called thermal isolation (heat shield) commonly known as thermal pads (Thermal), so that the possibility of false solder points due to excessive heat dissipation in the cross-section when welding is greatly reduced. Multi-layer board of the electrical connection (ground) layer leg of the same treatment.
