印刷电路板设计大全 Complete PCB Design Using OrCad Capture and Layout_Part5

Figure 9-15 Final BOM listing with all footprints assigned.ou can also use the Find tool to automatically select a part or parts of a certain type. To useFigure 9-16 Using the Find tool to locate parts.Grouping related componentsFigure 9-17 Using the Property Editor to assign components to groups.To view group information for the entire design go to the Project Manager and select Design icon. Right click and select Part Manager from the pop-up (or select Part Figure 9-18 Using the Part Manager to view all groups.Figure 9-19 The Confi gure Part Property Display dialog box.ou can also add the COMPGROUP property to the bill of materials listing by adding “\tCOMPGROUP” to the Header: list and “\t{COMPGROUP}” to the Combined PropertyFigure 9-20 Performing a design annotation.Warning!■ Do not perform another annotation after you have generated a Layout netlist or performed a back annotation from Layout (especially if you had Layout renumber the parts), because the project can become unsynchronized and produce verypeculiar, irreversible results! To read more about the annotation function, searchFigure 9-21 The Capture Design Rules Check dialog box.Figure 9-22 Creating a circuit netlist for Layout from Capture.Defi ning the board requirementsOne of the fi rst steps in setting up a new board in Layout is to select a technology fi le, which requires deciding on a couple of design requirements up front. Choosing a technology fi le requires knowing what types of parts will be used in the design (packaging and assem-bly requirements), the number and type of layers required, and the trace width and spacing requirements. These considerations for the analog design example are discussed in the follow-Figure 9-23 Layer stack-up for Example 1.Figure 9-24 Using the AutoECO to begin a new PCB design in layout.rst view you have of your new board will probably be a black background and part of a red square. Click the Zoom All button, so that you can see the entire design. Y ou should see something similar to Fig. 9-27.Setting up the boardMaking a board outlinerst step in laying out the board is to make the board outline and add mounting holes so that the boundaries of the board are known. First turn off the DRC box by toggling theFigure 9-25 Example of the AutoECO Link Footprint error. Figure 9-26 Adding a footprint library to the AutoECO tool’s library list.Figure 9-27 Initial view of the analog design.Online DRC button, located on the toolbar. Then, draw a board outline: select the Obstacle tool, . Right click in the work space and select New from the pop-up, right click again, and select Properties to invoke the Edit Obstacle dialog box. Make sure the obstacle Board outline on the Global layer. Click OK.Left click at point 0,0 to place the fi rst vertex. Left click to place each vertex of the board outline. Make the board outline about 2.0 ϫ 2.5 in. (2000 ϫ 2500 mils). Right click and select Finish from the pop-up after you have placed the fourth vertex.Next, place mounting holes on the board. This should be done before moving any parts intoselect the Component tool, right click, anddialog box shown in Fig.Figure 9-28 Using Edit Component dialog box to add mounting holes.Figure 9-29 Adding a mounting hole to a net.The mounting holes supplied with Layout are plated by default. To make mounting holes , toggle the Pin tool and select the mounting hole’s padstack (useFigure 9-30 Use the Edit Padstack dialog box to make a padstack nonplated. connectors, etc. Dimensions can be placed on assembly or comment layers (e.g., the layer). Once you are satisfi ed with the board layout, you can turn off documentation layers and/or delete temporary dimension lines.Adding dimensions and measurements is a three-step process. Each step is accomplished Tools →Dimension menu (see Fig. 9-31) and is used to (1) specify the snap settings, (2) specify the type of dimension, and fi nally (3) place the dimension.Figure 9-32 shows examples of relative and absolute dimensions. Relative dimensionsFigure 9-31 Setting up and placing dimension lines.5002000There are two ways to turn off the rat’s nest. This just makes the nets look invisible and does not actually affect their connectivity. The second way is to actually disable the nets (which affects bothFigure 9-33 Using the Find function to select parts for placement.To select certain parts without having to actually fi nd them in the pile, you can have a partFigure 9-34 Using Component Selection Criteria to select parts for placement.Placing parts in the queueAn elegant way to place parts is to make a placement list to queue parts for placement. Then all you need to do is hit N on your keyboard to cycle through the list. Y ou can add parts to the placement queue using the Tool →Component →Queue For Placement... optionFigure 9-35 Selecting parts from the placement matrix.as a minipile. To place the parts, left click inside the board outline in the location where the parts should go. The parts within the group will be stacked on top of each other like football To enable and disable netsbutton, and selectFig. 9-36) by selecting (highlighting) a net (or nets). Right click and toggle theFigure 9-36 Enabling and disabling nets.10 R11Figure 9-39 Default layer stack-up.Converting a routing layer to a plane layerThere are two ways to add plane layers. The fi rst method is to convert a routing layer into a plane layer. The second method is to add a new plane layer based on the properties of anFigure 9-40 Converting a routing layer to a plane layer.Note■ Do NOT change the Layer NickName. The layer nickname is associated with aFigure 9-41 Layer setup that defi nes the six-layer stack-up.Assigning nets to layersThe next step is to assign the power and ground nets to their respective plane layers. To assign ground and power nets to plane layers click the View Spreadsheet button and select Nets from the pop-up to open the Nets spreadsheet. Select the GND net and then right click and select Properties from the pop-up. In the Edit Net dialog box (Fig. 9-42), click the Net Layers... button in the lower left corner. In the Layers Enabled for RoutingFigure 9-42 Assigning power/ground nets to plane layers.Repeat the procedure and assign the Vϩ and VϪ nets to the Vϩ and VϪ plane layers, respec-tively, and include the TOP and BOTTOM layers. Y ou should now see YES* in the Routing Enabled column of the spreadsheet for each of the plane layers (at least before performing aFigure 9-43 Assigning alternate vias to a net.ou can select more than one via for the autorouter to use, but you also need to let Layout know it is allowed to use other vias than the default via. Go to Options →Route Settings to display the Route Settings dialog box (Fig. 9-44). Check the Use All Via Types option.Figure 9-44 Route Settings dialog box to specify via usage.Open the Nets spreadsheet and drag a box across all of the nonpower and nonground nets (cells) to select them. Right click and select Enable Ͻ-ϾDisable from the pop-up to toggle off the selected nets. Close the spreadsheet.On your board layout you should notice that some of the rat’s nest lines (nets) have disap-peared. The only lines you should see are the power and ground lines. To identify which lines are which, enable one of the routing tool buttons (Add/Edit Route Mode, forleft click and select one of the nets. In the bottom left corner of your. More lines will disappear. The lines that disappear are ones that are connected to through-hole pins that are connected to their respective plane layersFigure 9-45 Specifying fanout settings.through the layer list. Each pin that is connected to a plane layer will have a thermal relief around it as that layer is made active as shown in Fig. 9-46. The lines that did not disappear are not connected to a plane yet because the surface-mount devices do not have a way toget to the plane(s). So the next step is to provide paths (called fanouts or stringers) for the surface-mount devices to become connected to their planes.Fanning out power and groundNormally it is recommended that power and ground are fanned out separately and that ground rst. Ground can usually be fanned out using the automatic fanout feature butbutton. The DRC should report about 19 errors. The errors are marked on the board by circledFigure 9-51 Viewing Error Markers.The list of errors may look formidable, but as you will soon see, one problem often causes several errors. By looking for patterns between the comments on the error spreadsheet and the layers on which the errors have occurred, you should be able to get an idea of the problems.activate the Pin tool,PadstacksFigure 9-52 Errors caused by padstack settings on a defi ned plane layer.Changing padstack propertiesTo change pad dimensions manually double click the cell for the VϪ layer, right click, and select Properties to display the Edit Padstack Layer dialog box. Change the Pad WidthFigure 9-53 Copying plane-type padstack layers.If the second ground plane had been generated by converting another routing layer (INNER2, for example) into a plane layer it would have had the same errors and the same process could x the errors (i.e., copy all GND padstack layers into the GND2 padstackbutton, . Once the DRC box (the dotted rectangle) is displayed you can change the size and starting box being drawn, the view will also be zoomed to the size of the new DRC box. To zoom outbutton, or hit thezoomed back out, but the size of the DRC box will be unchanged.Figure 9-55 Board statistics spreadsheet. Figure 9-56 Clearing Route Pass fl ags to redo autoroute.Figure 9-57 Setting up back annotation settings in Capture.On the schematic in Capture double click on the part that you looked at before you did the back annotation and see how the spreadsheet has changed. The locations and orientation of the parts on the board (and any new footprints, etc.) will be listed in Capture. If you want (or need) to start a new board layout, all of this information will be included with the .MNLFigure 9-58 Forward annotation warning.Figure 9-60 Connection of the analog and digital grounds.leave the board separately and be connected at the power supply, or they may be connected at a pin (or pins) and leave the board together as one common ground. In this example the two grounds are connected at pin 5.To place the analog and digital ground symbols use the Place Ground tool, and select the desired ground symbols. To change the symbol’s name select the ground symbolFigure 9-61 (a) Change a ground/power symbol’s name and (b) display it.Figure 9-62 Select ground net name (analog or digital).It appears on the schematic that the analog and digital grounds are separate ground systemsBusses are placed on the schematic using the Place Bus tool, . After you have placed the ne (name) it with an alias using the Place Net Alias tool, . Busses are namedis the alias (a name you give it) that make up the members are placed on the schematic using the Place Wire tool, members are placed on the schematic as you would place any other wire, but they are addedbutton, , from the toolbar and place no-connect symbols on the unused pins.。