PCB布线时地线的处理法

PCB布线时地线的处理法
2. in placement, attention should be paid to the height of the parts.
3. pay attention to each function distinction, do not cross.
4. if you have a high speed line, you should consider the moat problem.
The following is a copy of the professional documents in the information.
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In the PCB design, wiring is an important step of product design, it can be said in front of the preparatory work is done for it, in the whole PCB, wiring design process maximum limit, the maximum workload, fine skills. PCB wiring has one side wiring, double sided wiring and multilayer wiring. There are two kinds of methods: automatic wiring wiring and interactive wiring, in the automatic wiring before, to more stringent requirements for interactive pre wiring line, input and output lines should be avoided so as to avoid the interference of adjacent parallel. If necessary, the ground wire shall be isolated, and the wiring of the two adjacent layers shall be perpendicular to each other and parallel to each other, so that parasitic coupling is easy to occur.
Automatic routing rate, depends on good layout, wiring rules can be set in advance, including the number of bends, wire guide
hole number, step number etc.. In general, an exploratory fabric warp is used to quickly connect the short lines, and then to do the maze routing. First, the wiring of the cloth is optimized by global routing, and it can be disconnected as required. And try rewiring to improve the overall effect. The PCB design of high density has been felt through holes do not adapt, it wasted a lot of valuable routing channel, in order to solve this problem, the blind and buried hole technology, it not only completed the conduction hole, but also many province wiring channel makes the wiring process more convenient. More smooth, more perfect, the design process of PCB plate is a complex and simple process, want to have a good grasp of it, also need a large number of electronic engineering design personnel to their own experience, in order to get the true meaning.
1 power and ground handling
Even though the wiring in the whole PCB board is well done, the interference caused by the power and ground wire is not considerate, and the performance of the product will be reduced, and sometimes even the product's success rate will be affected. So for electricity,
The wiring of ground wire should be treated seriously, and the noise interference caused by electric wire and ground wire will be reduced to the minimum to ensure the quality of the product. For each engaged in electronic product design engineers can understand the reasons between the ground wire and power line noise generated, only to reduce with the expression of suppression of noise is in power: as everyone knows, the ground
between the decoupling capacitor. Try to widen the power and ground wire width, is better than the power supply line, the relationship between them is: ground, power line, signal line, usually signal line width: 0.2 ~ 0.3mm, the fine width can reach 0.05 ~ 0.07mm, 1.2 ~ 2.5 mm power line of digital circuit PCB can be used to wire form a wide a loop, which constitute a network to use (analog circuit to not used) by a large area of copper layer with the ground, was not the place to use as a ground wire is connected with the printed board. Or made of multilayer board, power, ground wire each occupy a layer.
2 、 digital circuit and Analog Circuit CO processing
Many PCB is no longer a single function circuit (digital or analog circuit), but is made up of digital circuits and analog circuits. Therefore, in wiring, it is necessary to consider the interference between them, especially the noise interference on the ground. The high frequency digital circuit, analog circuit is more sensitive to the signal lines, signal lines, high-frequency circuit device simulation as far as sensitive, to the ground, the entire PCB to the outside world only one node, so we must address the problem of total number, die within PCB, but in the internal digital and analog ground are actually separate them between each other, only in the PCB to connect with the outside interface (such as plug etc.). Please note that there is only one connection point. There are also PCB on the ground, which is determined by system design.
3 、 the signal line is distributed on the electric (ground) layer
In the multilayer wiring printed board, the signal line layer does not end the remaining cloth line is not much, more layers will be wasted will increase some work for the production cost also increases accordingly, in order to solve this contradiction, can be considered in the electrical wiring layer (ground). First, the power layer should be considered, followed by the formation. Because it is better to preserve the integrity of the formation.
4. Handling of connecting leg in large area conductor
On the ground of large area (electric), common components of the legs are connected, to connect legs need comprehensive consideration, electrical properties, and the copper pad surface element leg full connected as well, but for the assembly of welded elements there are some bad risks such as: welding needs large power heater. It is easy to cause the weld point. So both the electrical properties and process requirements, made of cruciferous pads, called heat isolation (heat shield) commonly known as thermal pad (Thermal), it can make the possibility of resulting weld point due to excessive heat in the welding section is greatly reduced. The multilayer panel has the same electrical (ground) layer legs.
5 、 the role of network system in wiring
In many CAD systems, routing is determined by the network system. The grid is too dense, although the pathway has increased, but the step is too small, the amount of data field is too large, which is bound to the equipment storage space have higher requirements, but also have a great impact on the object
computer electronics operation speed. Some of the channels are ineffective, such as those that are occupied by the pads on the leg of the components, or are installed, holes, holes, etc.. The grid is too sparse, too little pathway has a great influence on the efficiency of the. Therefore, a grid system with reasonable density is needed to support the routing.
The distance between the legs of a standard component is 0.1 inches (2.54mm), so the base of the grid system is usually 0.1 inches (2.54 mm) or less than 0.1 inches, such as 0.05 inches, 0.025 inches, 0.02 inches, etc..
6, design rules check (DRC)
The wiring design is completed, need to carefully check the wiring design meets the set designer rules also need to confirm compliance with the rules in the production process of printed demand, general examination are as follows: the line and line, line and line element pad, and a through hole,
Whether the distance between the component pad and the through hole, the through hole and the through hole is reasonable, and whether the production requirement is met or not. Is the width of the power line and ground wire appropriate, and is the coupling (low impedance) between the power and ground? Is there any place in the PCB that can widen the earth's ground?. For the key signal line, the best input, such as the shortest length, plus the protective line, the input line and the output line are clearly separated. Do analog circuits and digital circuits have separate ground lines?. Does the pattern (such as icons or labels) added to the PCB cause a signal to be shorted?. Modify
some undesirable alignment. Is there a process line on the PCB? Does the solder resist conform to the requirements of the manufacturing process and is the size of the solder joint appropriate and whether the character mark is pressed on the pad of the device so as to avoid affecting the quality of the Denso?. The outer edge of the power layer in the multilayer plate is reduced, such as the copper foil of the power stratum is exposed outside the plate, and the short circuit is easy to be caused. Summary
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The purpose of this document is to explain the PCB design software PowerPCB using PADS printing process design board and some matters needing attention, provide the design specification for the design staff of a working group, to carry on the exchange and mutual check between the convenience of design personnel.
2, design process
The design flow of PCB is divided into six steps: netlist input, rule setting, component layout, wiring, check, review and output
2.1 netlist input
There are two ways of network input, one is to use the PowerLogic OLE PowerPCB Connection Send Netlist, application function, OLE function, can keep the principle diagram and PCB diagram,
to minimize the possibility of error. Another approach is to load the netlist directly in PowerPCB, select File->Import, and enter the netlist generated by the schematic.
2.2 rule settings
If the design rules of PCB have been set up at the stage of schematic design, there will be no need to set up any more
These rules, because when you enter the netlist, the design rules have been entered into the PowerPCB with the netlist. If the design rules are modified, the schematic diagram must be synchronized to ensure that the schematic diagram is consistent with the PCB. In addition to the design rules and layer definitions, there are some rules that need to be set, such as Pad Stacks, which need to modify the size of the standard vias. If the designer creates a new pad or through hole, add Layer 25.
Be careful：
PCB design rules, layer definition, hole setting, CAM output settings have made the default boot file name for the Default.stp, after the netlist input in, in accordance with the actual situation of the design, the power supply network and distribution for power and ground planes, and other advanced rules. After all the rules are set up, in PowerLogic, use the Rules PowerPCB Connection function of the OLE From PCB to update the rule settings in the schematic diagram to ensure that the schematic and PCB diagrams are consistent.
2.3 component layout
After the netlist is input, all the components will be placed at the zero of the work area and overlap. The next step is to separate the components,
According to some rules put neatly, that is, components layout. PowerPCB provides two methods, manual layout and automatic layout. 2.3.1
Manual layout
1. tool printed board structure size, draw plate edge (Board Outline).
2. Disperse Components components, components will be arranged around the edge of the plate.
3. move the components one by one, and place them inside the edge of the board, and put them in order according to certain rules.
2.3.2 automatic layout
PowerPCB provides automatic layout and automatic local cluster layout, but for most designs, the effect is not ideal and is not recommended. 2.3.3 notes
The first principle is to ensure that the layout of the A. routing rate, mobile devices that connected with a fly line, the device has connections together
B. digital devices and analog devices should be separated from each other as far away as possible
C. decoupling capacitor as close as possible to the device VCC
D. devices should be considered for future welding, not too dense
E. uses the Array and Union features provided by the software to improve the efficiency of the layout
2.4 wiring
There are two ways of wiring, manual routing and automatic routing. Manual routing functionality provided by PowerPCB is very powerful, including automatic pushing, online design rule checking (DRC), automatic wiring wiring by Specctra engine, usually the two methods with the use of commonly used manual - Automatic - manual steps.
2.4.1 manual wiring
1. automatic wiring, handmade cloth first with some important network, such as the high frequency clock, the main power supply, these networks tend to walk the line distance, Xian Kuan, line spacing, shielding and other special requirements; some other special packages, such as BGA, automatic wiring difficult cloth has rules, but also with the manual wiring.
2. after the automatic wiring, but also with manual wiring to
adjust the line of PCB.
2.4.2 automatic routing
When the manual wiring is finished, the rest of the network is handed to the router, from the cloth. Select Tools->SPECCTRA, start the Specctra router interface, set the DO file, press Continue started the automatic wiring Specctra router, if after the completion rate is 100%, then you can manually adjust the wiring; if less than 100%, indicating the layout or manual wiring problems, need to adjust the layout or manual wiring, until all about so far.
2.4.3 notes
A. power cord and ground wire as bold as possible
The B. decoupling capacitor is directly connected to the VCC
When C. sets the DO file for Specctra, first, add the Protect all wires command to protect the line of hand cloth from being automatically wired
D. if you have a hybrid power layer, you should define this layer as Split/mixed Plane, split it before routing, and use Pour after the line is finished
The Manager Plane Connect is clad in copper
E. sets all of the device pins to hot pads. The method is to set the Filter to Pins, check all the pins, modify the
properties, and tick before the Thermal option
F. manual routing, open the DRC option, using dynamic routing (Dynamic Route)
Two
5 check
The items checked are High (Clearance), connectivity (Connectivity), and high-speed rules
Speed) and the power layer (Plane), these items can be selected by Tools->Verify Design. If you set high speed rules, you must check, otherwise you can skip this item. To check for errors, you must modify the layout and wiring.
Be careful：
Some errors can be ignored. For example, some of the connectors' Outline are placed outside the frame, and errors are detected when checking the space.
2.6 review
According to the review of the PCB checklist, including the design rules, definition, Xian Kuan, layer spacing, pad, hole; rationality review should focus on the layout of the device, power and ground network cabling, network cabling and
high-speed clock shielding, decoupling capacitor placement and connection etc.. If the review fails, the designer shall modify
the layout and wiring. After passing the qualification, the re sign shall be signed by the designer and the designer respectively.
2.7 design output
PCB designs can be output to printers or output light drawn documents. The printer can print PCB hierarchically, which is convenient for the designer and the supervisor to check. The light drawing file is handed over to the board maker to produce the printed board. The output of the drawn file is very important and related to the success or failure of the design. The following will focus on the notes of the output light drawing file.
The A. output layer has a wiring layer (including the top and bottom layer, middle layer wiring layer), power supply (including VCC and GND layers), screen layer (including the top and bottom of screen printing), solder layer (including the top and bottom solder solder), in addition to generate the file (NC Drill)
B. if the power layer is set to Split/Mixed, then at Add
Document Routing Document window, and each output Gerber files before, to use the Pour Manager Plane Connect PCB map for copper; if set to CAM Plane, select Plane, in the setting of Layer, the Layer25, in the Layer25 layer Pads and Viasc. settings window in the device (Device Setup), change the Aperture value to 199
Layer sets the Board Outline on each layer of the D.
E. set screen printing layer of Layer, do not choose Part Type, select the top (bottom) and screen layer of Outline, Text, Line
When the f. sets up the Layer of the solder resist, the hole is selected to indicate that there is no welding resistance on the vias, and no holes are selected to indicate the resistance to welding, as determined by the specific conditions
When g. generates a drill file, use the default settings of PowerPCB without making any changes
After all the H. drawing files are output, open and print with CAM350, checked by the designer and the supervisor according to the PCB checklist。