Even if the wiring in the whole PCB board is well done, the interference caused by poor consideration of power supply and ground wire will reduce the performance of the product and sometimes even affect the success rate of the product. Therefore, we should pay attention to the wiring of electricity and ground wire, minimize the noise interference caused by electricity and ground wire, and ensure the product quality. For every engineer engaged in electronic product design, it is obvious that the noise between the ground wire and the power wire is caused. Now, only reduced noise suppression will be described: it is well known to add decoupling capacitors between power supply and ground. Try to widen the width of power supply and ground wire, preferably the ground wire is wider than the power supply wire. Their relationship is: ground wire >; Power line > For signal lines, the width of the signal line is usually 0.2 ~ 0.3 mm, the narrowest width can reach 0.05~0.07mm, and the power line is1.2 ~ 2.5 mm. For the PCB of digital circuits, a wide grounding line can be used to form a loop, that is, a grounding network (the ground of analog circuits cannot be used in this way). A large area of copper layer is used as ground wire, and all the unused places are used on printed boards. Or make it into a multilayer board, a layer of power supply and a layer of ground wire.

2, digital circuit and analog circuit processing * * *

Nowadays, many PCBs are no longer single functional circuits (digital or analog circuits), but are composed of digital and analog circuits. Therefore, it is necessary to consider the mutual interference between them, especially the noise interference of the ground wire. The digital circuit has high frequency and the analog circuit has strong sensitivity. For signal lines, high-frequency signal lines should be as far away from sensitive analog circuit devices as possible. For the ground wire, only one node of the whole PCB leads to the outside world, so it is necessary to deal with the digital, analog and grounding problems inside the PCB. In fact, the digital ground and analog ground inside the board are separated and not connected with each other, only at the interface between PCB and the outside world (such as plug). Digital ground is slightly short-circuited to analog ground. Please note that there is only one connection point. Some of them are not on the PCB, which is determined by the system design.

3. The signal line is laid on the electrical (grounding) layer.

When wiring multi-layer printed boards, because there are not many wires left in the signal line layer, adding more layers will cause waste and correspondingly increase the production workload and cost. To solve this contradiction, we can consider wiring on the electrical (grounding) layer. First of all, we should consider the power level, and then the class. Because it is best to preserve the integrity of the formation.

4. Treatment of connecting legs in large area conductors

In a large area of grounding (electricity), the pins of common components are connected to it, so the treatment of pins needs to be considered comprehensively. As far as electrical performance is concerned, it is best for the bonding pads of the component pins to be completely connected with the copper surface, but there are some hidden dangers in the welding and assembly of components, such as: ① welding requires a high-power heater. ② It is easy to cause virtual solder joints. Therefore, considering the electrical performance and process requirements, a cross-shaped pad is made, which is called thermal shield, commonly known as thermal pad. This can greatly reduce the possibility of virtual solder joints caused by excessive heat dissipation in the cross section during welding. The grounding pin of multilayer board is treated the same.

5. The role of network system in wiring.

In many CAD systems, wiring is determined according to the network system. The grid is too dense, the paths increase, but the step size is too small, and the data in the drawing field is too large, which will inevitably require higher storage space for equipment and have a great impact on the running speed of computer electronic products. However, some paths are invalid, such as those occupied by pads of component legs or by mounting holes and fixing holes. The grid is too sparse and the paths are too few, which has a great influence on the distribution rate. Therefore, a reasonable grid system is needed to support wiring. The distance between the legs of a standard part is 0. 1 inch (2.54 mm), so the basis of a grid system is generally 0. 1 inch (2.54 mm) or an integer multiple of less than 0. 1 inch, such as 0.05 inch, 0.025 inch, 0.02 inch, etc.

6. Check the design rules

After the wiring design is completed, it is necessary to carefully check whether the wiring design conforms to the rules formulated by the designer, and at the same time confirm whether the formulated rules conform to the requirements of PCB production technology. Generally check the following aspects: wires and wires, wires and component pads, wires and through holes, component pads and through holes, and the distance between through holes and through holes is reasonable and meets the production requirements. Is the width of power line and ground line appropriate, and is there close coupling (low wave impedance) between power line and ground line? Is there any place on the PCB where the ground wire can be widened? Whether the best measures have been taken for key signal lines, such as the shortest length, the increase of protection lines, and the obvious separation of input lines and output lines. Whether analog circuits and digital circuits have their own independent grounding wires. Whether the graphics (such as icons and labels) added on PCB will cause signal short circuit. Modify some unsatisfactory line shapes. Is there a process line on PCB? Whether the solder resist meets the production process requirements, whether the solder resist size is appropriate, and whether there are characters on the device pads, so as not to affect the quality of electrical appliances. Whether the edge of the outer frame of the power supply layer in the multilayer board is narrowed, such as the copper foil of the power supply layer exposed out of the board, is easy to cause short circuit. The purpose of this document is to explain the process of PCB design using PADS PCB design software PowerPCB and some matters needing attention, to provide design specifications for designers of a working group, and to facilitate communication and mutual inspection among designers. A, wiring fault diagnosis technology

1. High-precision time-domain reflection technology

2. High-precision time domain crosstalk analysis technology

3. Compensation technology

4. Optical time domain reflection technology

Second, the wiring fault diagnosis

1. coil fault diagnosis

There are several types of circuit diagram faults, such as short circuit, reverse connection, wrong pair and series winding. The first two kinds of faults are easy to find with common test equipment, such as DSP—4300 of Fluke Company, and the test technology is also very simple.

2. Length fault diagnosis

When the cable is too long (exceeding the limit length specified by the link), the link will have great impedance change, which will cause great signal attenuation, so it can be located by HDTDR technology.

3. Fault diagnosis of series winding

The fault of series winding is difficult to find. The main reason for the series winding error is that the ANSI/TIA/EIA 568-B regulations were not observed when making the connection module or connector. Although the connection of 1- 1, 2-2, …, 8-8 is physically realized, the lines of 1-2, 3-*-5, 7-8 are not guaranteed. Or the wire pair is too long when connecting the module or connector. This kind of error can be found by using the HDTDX technology of the tester, which can accurately report the starting point and ending point of the series wound cable, even if the series wound exists in a certain part of the link.

4. Return loss fault diagnosis

Return loss fault is mainly caused by link impedance mismatch. Mismatch mainly occurs in connectors, but it may also occur in cables with changed characteristic impedance. Especially in Gigabit Ethernet, four pairs of twisted pairs need to be transmitted in both directions at the same time (full duplex), so the reflected signal will be mistaken for the received signal, causing confusion and failure. HDTDR technology can be used to accurately locate the return loss fault. For example, for the link with unqualified return loss.

5. Fault diagnosis of optical cable link

The factors that affect the optical cable link include the laying of optical cable, the termination of optical cable double-ended connector, double-ended jumper and the connection of network equipment. However, termination has the greatest influence on link loss, which will cause mode interference to multimode optical cables.

The effective methods to reduce the failure of optical cable in wiring engineering are as follows: ① Remember the strength coefficient of optical cable, don't drag the optical cable hard and don't bend the optical cable excessively; (2) according to the requirements of the manufacturer, clean the connector during installation; ③ According to the standard, OLTS and OTDR are used to test the installed optical cable; ④ When testing optical cable links, use clean jumpers and always keep them clean; ⑤ All connectors shall be equipped with dust covers.

Third, the wiring troubleshooting

1. Troubleshooting of line damage

2. Troubleshooting of network wiring open circuit fault

3. Troubleshooting of excessive return loss

4. Troubleshooting of impedance discontinuity fault

5. Troubleshooting of long links

6. Troubleshooting of slow speed of the whole network caused by optical fiber link

7. Eliminate the chain effect of chrysanthemum.

Fourthly, network health maintenance technology.

1. What is network health maintenance?

The so-called mission-critical network refers to the complete trust of the network owner in the network application. Once the network is shut down due to failure or poor performance, the efficiency will be reduced, which will lead to huge losses for the owner company. Such as air traffic control network, financial securities trading network, national defense and military command network and hospital medical network are typical mission-critical networks.

Minimize the frequency and impact of network failures. Specifically, it includes the following measures:

① Management should participate in the network decision-making;

(2) Make emergency preparations and plans when the failure occurs;

③ Implement preventive measures for possible problems;

④ Monitor the network in an all-round way, and try to find network faults as early as possible;

⑤ Quickly isolate faults and eliminate them;

⑥ Adopt advanced network monitoring equipment, train managers and improve the quality of network management and maintenance.

Among them, "comprehensive network monitoring" and "rapid fault isolation and elimination" are the essence of "network health maintenance strategy", while "adopting advanced network monitoring equipment and well-qualified network managers" is the means and method to realize "network health maintenance strategy". The ultimate goal is to realize the network running zero failure.

2. Realization of network health maintenance

The implementation of network health maintenance is mainly to use advanced network test equipment to test and monitor the network system regularly, and report the network operation in time, and then quickly troubleshoot the network fault according to the report results.

Network health maintenance requires that the used test instruments have the ability to identify bad frames without frame start identifier (SFD), to monitor "short frames" and to automatically test related network performance. 1, cable bending radius is too large.

In wiring construction, due to the limited space of trunking, such bending radius is easy to occur, and there are strict requirements for the bending degree of twisted pair. The bending radius of the cable shall not exceed 8 times the diameter of the steel wire of the cable itself. Obviously, the construction on the drawings is not standardized. Therefore, the performance of the cable will be degraded. Over time, excessive bending for a long time will destroy the electrical performance of the cable. For the outer sheath of the protective cable, although the appearance cannot be reflected in a short time, the life of the outer sheath will be greatly shortened due to the changes of objective phenomena such as climate and temperature, which will affect the service life of the cable.

2, strong and weak cable laying together

I have seen it in many reference rooms or wiring occasions. I believe that many experienced cabling engineers will ask whether such cable laying meets the relevant standards. There are detailed provisions in the national standard GB/T503 1 1-2000.

Communication cables are different from power cables. When the power cable generates electromagnetic waves, it will affect the communication performance of the communication cable and lead to data confusion. So that normal communication cannot be realized.

3. There are too many redundant cables under the cabinet.

In the wiring management room, the cabinet after wiring is very neat, and the cables are littered. But when you open the floor under the cabinet, you can see that there are too many cables that have not been cut, and the bottom is reserved. Excessive redundant accumulation of cables not only affects the beauty of wiring, but also greatly reduces the communication performance of cables due to the influence of temperature. The most effective way to avoid this kind of construction phenomenon is:

(1) In the early stage of computer room design, determine the location of the cabinet at the survey site to ensure that the cabinet will not be changed in future use, and make a good plan.

(2) When laying cables, do not leave too long cables to meet the actual needs.

(3) When installing the equipment, cut off the redundant cables, so there is no need to keep too long redundancy.

Bundles of cables are tied too tightly.

Regular cable laying increases the aesthetic feeling of the whole computer room and horizontal area, making the whole system look beautiful. However, the core wire of communication cable is generally very thin. When multiple cables are laid together, if they are tied together too tightly, it is easy to produce crosstalk, which is not worth the loss for the cables themselves. In addition, if the wire is tied too tightly for a long time, it is very easy to break the outer sheath of the cable.