3.6 Starting layout in orcad  (Page 4/9)

You can now see all of the connections to the ground plane. You can do the same thing for the power plane. Press ‘ F5 ’ or the Refresh All button to make the whole design visible again.

We still have one voltage net to route, and that is the input voltage from an external power supply. This net only touches a few components, so we could just put a trace to connect all the components. However, we can also draw a solid piece of copper and associate it with that net. This is especially useful for high-current traces or small voltage planes. We do this using the Obstacle Tool just like when drawing obstacles for footprints. Turn the Obstacle Tool on and then right-click anywhere in your design. Select New… and then right-click again and select Properties… to bring up the Edit Obstacle dialog. Name this obstacle VCC_IN, leave the Width at 10 mils. Set the Clearance to 15 mils Change the Obstacle Type to Copper pour. Finally, set the Net Attachment to the name of the net, which should be V_IN . Click OK and you are ready to draw your copper pour. Draw a rectangle around the power connector and other components that are attached to this net. When you are done, click Refresh All to redraw the ratsnests.

You have now routed all the power and ground connections. That was easy, right? Let’s look a little bit at some of the tools that OrCAD gives you to check on the progress of your design. Click the View Spreadsheets icon and choose Statistics . The statistics spreadsheet gives you information on time in layout, percent of components placed, percent of traces routed, and some other information.

100% of your components should be placed, and you can also see that a majority of your traces have been routed (power and ground make up the majority of connections in most designs). You are well on your way to completing your design.

Routing other nets

You are now prepared to route the other connections on your board. Open the nets spreadsheet and highlight all the nets in the design. Right-click and select Enable<->Disable to make the ratsnets visible for the remaining nets. Refresh the display to clean things up a bit.

Before beginning routing in earnest, it is helpful to change a few settings. Open the System Settings and make the following changes: Visible Grid = 10, Routing Grid = 5, and Via Grid = 0. Next, select Options-->User Preferences and check Allow DRC Errors under Global Preferences . You may have to check the box labeled Activate Online DRC . The box with the dashed line will reappear. While DRC is on, you will only be able to place routes inside this box, but Layout will inform you if any spacing errors occur while you are routing. This will help you limit the number of errors that you will have to clean up later. You can resize the DRC box by pressing ‘ B ’ and drawing a new rectangle.

Let’s route a connection. Turn on the Edit Segment Mode or Add/Edit Route Mode .