PCB Cabling 6 Major principles

PCB Cabling 6 Major principles
1 power, ground processing not only in the entire PCB board in the wiring is done well, but due to the power, grounding the consideration of the interference caused by, will make the performance of the product decline, and sometimes even affect the success rate of the product. Therefore, the wiring of electricity, grounding wire to be taken seriously, the electricity, ground noise caused by the interference to a minimum to ensure product quality. For each engineering person engaged in electronic product design understand the ground and power line noise caused by the cause, now only to reduce the noise suppression to express: it is well known that the power supply, ground between the addition of decoupling capacitor. As far as possible to widen the power, ground width, preferably ground than power cord width, their relationship is: Ground > power line > Signal line, usually the signal line width is: 0.2~0.3mm, the most fine width up to 0.05~0.07mm, the power cord is 1.2~2.5 mm To the digital circuit of the PCB can be a wide range of ground wire to form a circuit, that is, the formation of a network to use (analog circuit can not be used in this way) with a large area of copper layer for the ground, on the printed circuit board is not used on the place is connected to the ground as ground. Or made of multilayer board, power, ground each occupy a layer.
2 co-processing of digital circuits and analog circuits there are now many PCBs that are no longer a single functional circuit (digital or analog), but are composed of digital and analog circuits. As a result, it is necessary to consider the interference between them in the wiring, especially the noise disturbance on the ground. The frequency of the digital circuit is high, the sensitivity of the analog circuit is strong, to the signal line, the high-frequency signal line as far away from the sensitive analog circuit device, to the ground, the trick PCB to the outside world only a node, so must be in the PCB internal processing number, mold common problem, And in the board of the digital and analog is actually separate between them are not connected, just in the PCB interface with the outside world (such as plug, etc.). Digitally with analog ground a little short, note that there is only one connection point. There is also a non-common on the PCB, which is determined by the system design.
3 Signal wire Cloth in the electrical (ground) layer in the multilayer printed circuit board wiring, because the signal line layer has not finished the line left is not much, and then more layers will cause waste will also increase the production of a certain amount of work, the cost is correspondingly increased, in order to resolve this contradiction, you can consider the electrical (ground) layer on the wiring. First, the power layer should be considered, followed by the formation. Because it is best to preserve the integrity of the strata.
4 large area of the conductor in the treatment of the leg in a large area of grounding (electricity), the legs of common components and connection, the treatment of connecting legs need to be considered comprehensively, in terms of electrical performance, the component leg of the pad and copper surface full connection as well, but the components of the welding assembly there are some bad hidden dangers such as: ① welding needs ② easily cause false solder joints. So take into account the electrical performance and process needs, made of cross-flower pad, known as thermal isolation (heat shield) commonly known as hot pad (Thermal), so that in the welding due to excessive heat dissipation of the cross-section of the possibility of a significant reduction in the welding point. The multi-layer board is treated the same as the ground leg.
5 The function of network system in the wiring in many CAD systems, the cabling is based on the network system. The grid is too dense, although the path has increased, but the step is too small, the data volume of the graph field is too large, this will inevitably have higher requirements for the storage space of the equipment, but also the object of computer-type electronic products computing speed has a great impact. And some of the channels are not valid, such as the pads of the component legs occupied or by the installation of holes, fixed holes occupied. The mesh is too sparse and the channel is too small to affect the pacchiosi rate greatly. Therefore, there should be a reasonable grid system to support the wiring. Standard components The distance between the legs is 0.1 inches (2.54mm), so the base of the grid system is generally set to 0.1 inches (2.54 mm) or less than 0.1 inches in full multiples, such as: 0.05 inches, 0.025 inches, 0.02 inches, etc.
6 Design Rules check (DRC) wiring design is completed, you need to carefully check the wiring design is in line with the rules set by the designer, but also to confirm that the rules are in line with the requirements of the production process, general inspection has the following aspects: line and line, wire and component pads, wire and through hole, component pad and through hole, Whether the distance between through hole and through hole is reasonable, whether meet the production requirement. Whether the width of the power and ground lines is appropriate, and whether the power and ground are tightly coupled (low wave impedance). Is there any place in the PCB where the ground can be widened? For the key signal line whether to take the best measures, such as the shortest length, add protection line, the input line and the output line is clearly separated. Analog circuit and Digital circuit section, whether there are separate ground. Whether the graphics (such as icons, labels) added to the PCB will cause short-circuit signals. Modify some of the undesirable alignments. Whether the process line is added to the PCB. Resistance welding is in line with the requirements of the production process, the size of the solder is suitable, the character mark is pressed on the device pad, so as not to affect the quality of the Denso. The outer frame edge of the power stratum in the multilayer board is reduced, such as the copper foil outside the power formation is easy to cause short circuit. The purpose of this document is to illustrate the process and considerations for the design of printed boards using pads's printed circuit board design software POWERPCB, and to provide design specifications for a team of designers to facilitate communication and mutual inspection among the design staff.