As we saw in the previous design examples, keeping track of the necessary details to use negative Plane layers can be a bit of a task (making flash symbols, modifying padstacks, etc.). Negative planes are used because they have been used historically and are recommended in the OrCAD user's manuals. One of the reported advantages of using negative planes is that the artwork files are smaller than for positive artwork files. With the current PC speed and memory capacity, file size is less of an issue. Another argument for negative planes is a shorter processing time for negative planes at the manufacturer's end. That certainly was true when vector plotting with the flash lamps, but for current photoplotting equipment, that has also become less of an issue. Yet another argument for negative planes is that, during the board design, the planes can be distracting and result in slow drawing regeneration. But PCB Editor displays the negative planes in the positive view (WYSIWYG mode) anyway, and you can easily turn off the Plane layers. Additionally the author is aware of some designers who use positive planes for most of their work. That being the case and for the sake of completeness, we look at a very simple design to demonstrate how to use positive planes and take care of the corresponding details.

The circuit for this example is shown in Figure 9-184. As shown, the circuit consists of only two resistors. We focus on the Plane layers that will...