1, the power supply, ground processing
Even if the wiring in the entire PCB board is completed very well, but due to the power supply, the ground line of the interference caused by the lack of consideration will make the product's performance degradation, and sometimes even affect the success rate of the product. Therefore, the power and ground wiring should be taken seriously, the power and ground lines produced by the noise interference to a minimum to ensure the quality of the product. For each engaged in the design of electronic products for engineers understand the ground and power lines between the noise generated by the reason, now only to reduce the type of noise suppression to express: It is well known in the power supply, ground plus decoupling capacitors. Try to widen the power supply, ground line width, it is best to ground line than the power line width, their relationship is: ground line & gt; power line & gt; signal line, usually signal line width: 0.2 ~ 0.3 mm, the most through the fine width of up to 0.05 ~ 0.07 mm, the power line for 1.2 ~ 2.5 mm PCB for digital circuits can be used to form a wide ground lead to form a circuit, that is, constitute a ground network to use! (Analog circuit ground can not be used in this way) with a large area of copper for the ground, in the printed circuit boards are not used on the place are connected to the ground as a ground. Or make a multilayer board, the power supply and ground each occupy a layer.
2, digital circuits and analog circuits **** ground processing
Now there are many PCB is no longer a single function of the circuit (digital or analog circuits), but by the digital and analog circuits mixed composition. Therefore, it is necessary to consider the problem of mutual interference between them when wiring, especially noise interference on the ground. Digital circuits of high frequency, analog circuits, the sensitivity of the strong signal lines, high-frequency signal lines as far away as possible from sensitive analog circuit devices, the ground, the whole PCB to the outside world is only a junction, so it must be handled inside the PCB digital, analog **** ground, and inside the board digital ground and analog ground is actually separate from each other between them are not connected to each other, but only in the PCB and outside the connection interfaces (such as plugs). Connected to the PCB and the outside world at the interface (such as plugs, etc.). There is a small short between digital and analog ground, note that there is only one connection point. There is also no **** ground on the PCB, this is determined by the system design.
3, the signal line cloth in the electric (ground) layer
In the multilayer printed circuit board wiring, due to the signal line layer did not finish the rest of the line has been not much, and then more layers will cause waste will also add a certain amount of workload to the production, the cost also increased accordingly, in order to solve this contradiction, can be considered in the electric (ground) layer of wiring. The power layer should be considered first, followed by the ground layer. Because it is best to retain the integrity of the ground layer.
4, large-area conductors in the processing of connecting legs
In the large-area grounding (electricity), commonly used components of the leg and its connection, the processing of connecting legs need to be considered comprehensively, as far as the electrical performance, the component legs of the pad and the copper surface of the full connection as well, but the components of the soldering assembly there are a number of undesirable pitfalls, such as: ① Welding requires a high-powered heater. ② easy to cause false solder joints. So take into account the electrical performance and process needs to be made into a cruciferous pad, called thermal isolation (heat shield) commonly known as thermal pad (Thermal), so that the possibility of welding due to excessive heat dissipation in the cross-section of the possibility of generating false solder joints is greatly reduced. Multilayer board of the power (ground) layer legs of the same treatment.
5, cabling in the role of the network system
In many CAD systems, cabling is based on the network system decision. Grid is too dense, although the pathway has increased, but the step is too small, the amount of data in the map field is too large, which will inevitably have a higher demand for storage space for the equipment, but also the object of the computer class of electronic products have a great impact on the speed of computing. And some of the path is ineffective, such as by the component leg of the pad occupied or by the mounting holes, set the hole occupied by the hole, etc.. Grid is too sparse, too few paths on the cloth through the rate of the great impact. Therefore, there should be a sparse and reasonable grid system to support the wiring. The distance between the two legs of the standard components for 0.1 inches (2.54 mm), so the basis of the grid system is generally set at 0.1 inches (2.54 mm) or less than 0.1 inches in multiples, such as: 0.05 inches, 0.025 inches, 0.02 inches and so on.
6, Design Rule Check (DRC)
Wiring design is completed, the need to carefully check the wiring design is in line with the rules developed by the designer, but also need to confirm that the rules developed to meet the needs of the production process of the printed circuit board, the general check is as follows: line and line, line and component pads, line and through-hole, component pads and through-hole, through-hole and through-hole The distance between wires and wires, wires and component pads, wires and through-holes, component pads and through-holes, and through-holes and through-holes is reasonable and meets production requirements. Is the width of the power and ground lines appropriate, and is there tight coupling (low wave impedance) between the power and ground lines? Is there any place in the PCB where the ground line can be widened? Are optimal measures taken for critical signal lines, such as minimum lengths, protective wires, and clear separation of input and output lines? Are there separate ground lines for analog and digital circuits? Whether the graphics (e.g. icons, labels) that are added to the PCB can cause short-circuiting of signals. Modify some undesirable line shapes. Are process lines added to the PCB? Whether the solder resist meets the requirements of the production process, whether the solder resist size is appropriate, whether the character mark is pressed on the device pads, so as not to affect the quality of the electrical installation. Whether the outer frame edge of the power ground layer in the multilayer board is narrowed, if the copper foil of the power ground layer is exposed outside the board, it is easy to cause a short circuit. Overview The purpose of this document is to illustrate the use of PADS printed circuit board design software PowerPCB for printed circuit board design process and some of the precautions for a working group of designers to provide design specifications to facilitate the exchange of designers and mutual checks. First, wiring troubleshooting techniques
1. high-precision time-domain reflection technology
2. high-precision time-domain crosstalk analysis technology
3. compensation technology
4. optical time-domain reflection technology
Two, wiring troubleshooting
1. coil troubleshooting
Wiremap faults are mainly short-circuited, reversed, wrong pair, string winding and several other types. General test equipment can easily find the first two kinds of faults, such as with Fluke DSP-4300, test technology is also very simple.
2. length fault diagnosis
Cable length (more than the link limit length value), the link has a large impedance change, will cause a large signal attenuation, available HDTDR technology to locate.
3. String-winding fault diagnosis
String-winding faults are difficult to detect. The main reason for the string winding error is that in the production of connecting modules or connectors do not comply with ANSI/TIA/EIA 568-B regulations, although the physical realization of the 1-1, 2-2, ..., 8-8 connection, but does not ensure that the 1-2, 3-*-5, 7-8 pairs of twisted; or in the connection of the modules or connectors when the pairs of loose stranded too long. Such errors can be detected by utilizing the tester's HDTDX technology, which accurately reports the beginning and end points of a stranded cable, even if the stranding exists in one part of the link.
4. Return Loss Troubleshooting
Return loss faults are primarily caused by link impedance mismatches. The mismatch occurs primarily at the connector, but can also occur in the cable where the characteristic impedance changes. Especially in Gigabit Ethernet, four pairs of wires in a twisted pair cable are required to transmit in both directions simultaneously (full duplex), so reflected signals can be mistaken for received signals and cause confusion leading to faults. Using HDTDR technology, return loss faults can be pinpointed. For example, for a particular link with unqualified return loss.
5. Fiber optic cable link troubleshooting
Factors affecting the fiber optic cable link include laying fiber optic cables, fiber optic cable double-ended connector termination, double-ended patch cords and network equipment connection. The termination has the greatest impact on link loss and can cause mode interference with multimode fiber optic cables.
Effective ways to reduce fiber optic cable failures in cabling projects are: ① Remember the strength factor of fiber optic cables, do not vigorously drag cables, and do not over-bend cables; ② Clean the connectors during installation according to the manufacturer's requirements; ③ Test installed fiber optic cables according to the standards using OLTS and OTDR; ④ When testing fiber optic cable links, use clean patch cords and keep them clean at all times; ⑤ All connectors are fitted with dust cover sleeves.
Three, cabling troubleshooting
1. line breakage troubleshooting
2. network cabling open-circuit troubleshooting
3. return loss exceeds the standard troubleshooting
4. impedance discontinuity troubleshooting
5. link length fault troubleshooting
6. fiber-optic links lead to slowdowns in the entire network troubleshooting
7. the fiber optic links to slow down the whole network. Slow down the entire network due to fiber-optic link troubleshooting
7. regurgitation daisy-chain effect excluded
Four, network health maintenance technology
1. What is network health maintenance
The so-called mission-critical network refers to the network owners rely entirely on the network applications, once the network failure or poor performance caused by network shutdown and efficiency will lead to the owners of the company's huge losses. Networks such as air traffic control networks, financial securities exchange networks, defense and military command networks, and hospital medical networks are typical mission-critical networks.
Minimize the frequency and impact of network failures. Specifically, the following measures are included:
①Management should be involved in network decision-making;
②Prepare and plan for emergency response in the event of a failure;
③Implement preventive measures for possible problems;
④Comprehensively monitor the network, and try to achieve early detection of network failures;
⑤Quickly isolate failures and troubleshooting;
⑥Adopt a comprehensive monitoring of the network, and try to achieve early detection of network failures. p>
⑥Adopt advanced network monitoring equipment and train managers to improve the quality of network management and maintenance.
Wherein, "comprehensive monitoring of the network" and "rapid isolation of faults and troubleshooting" are the essence of the "network health maintenance strategy", and the "use of advanced network monitoring equipment and training of managers to improve the quality of network management and maintenance. The "use of advanced network monitoring equipment and good quality network management personnel" is to realize the "network health maintenance strategy" means and methods. The ultimate goal is to achieve zero network failure.
2. Implementation of Network Health Maintenance
The implementation of Network Health Maintenance mainly involves using advanced network testing equipment to test and monitor the network system on a regular basis and report the network operation in a timely manner, and then, based on the results of the report to quickly eliminate network faults.
Network health maintenance requires the use of test equipment with the ability to identify bad frames without the start of frame identifier (SFD), "short frame" monitoring capabilities, and related automatic network performance testing capabilities. 1, excessive cable bending radius
In wiring construction, due to the limited space over the wire channel, such a bending radius is very easy to occur, the twisted pair of bending degree is a strict requirement. The bending radius of the cable shall not exceed 8 times the bending radius of the wire diameter of the cable itself. Obviously, the construction in the figure is not standardized. The result is a decline in the performance of the cable, and over time, excessive bending for a long time will destroy the electrical properties of the cable. For the protection of the outer sheath layer of the cable, although the appearance in the short term does not reflect, but due to climate, temperature and other objective phenomena change, will make the life of the outer sheath is greatly shortened, and the impact of the cable's service life and so on.
2, strong and weak power cables are laid together
I have seen in many of the data room or cabling occasions, such cable laying is in line with the relevant standards, I believe that many experienced cabling engineers will raise questions. In the national standard GB/T50311-2000 standard, there are detailed provisions described.
Communication cables are different from power cables, when power cables produce electromagnetic waves will affect the communication performance of communication cables, resulting in data confusion and other phenomena. Thus can not be normal communication.
3, leaving too many cables under the cabinet spare redundancy
In the wiring management room, after playing the line of the cabinet is very neat, the cable is also horizontal and vertical, but open the cabinet under the floor, see there are too many cables are not cut, all reserved in the bottom, too many cables spare redundancy piled up, not only affects the aesthetics of the cabling, affected by the temperature, the cable communication performance will be greatly reduced. The most effective way to avoid the occurrence of this construction phenomenon is:
① In the early stage of the design of the server room, survey the site to determine the location of the cabinet, to ensure that the cabinet is not changed in the future use of good planning.
② construction, in the laying of cables do not leave too long cable to meet the actual demand.
③ equipment installation, cut the excess cable, do not have to reserve too long redundancy.
4, bundles of cables too tightly tied together
Specification of neat cable laying to increase the entire room and horizontal area of the beautiful, so that the whole system looks beautiful, but the communication cable core is generally thin, multi-stranded cable laying together, if too tightly tied together, prone to crosstalk, which is the cable itself, is more than worth the loss. In addition, a long time too tight tie line, it is very easy to cause the rupture of the outer sheath of the cable.