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This TechWatch will show you how to define your PCB design rules from within your schematic source files using parameters and PCB Layout directives.

To start with we will look at the PCB Layout directives, these objects can be placed on nets (wires or buses) to assign net specific design rules in PCB.

To place PCB Layout directives we use the command Place » Directives » PCB Layout.  Before placing the PCB Layout object onto the schematic press the TAB key to enter its properties.

Within the Parameters dialog box we have a predefined parameter with the Name: Rule and Value: Undefined.  To define a value click the edit button to the bottom of the Parameters dialog box and they click the Edit Rule Values button from the resulting Parameter Properties dialog box.

We can now select the type of PCB design rule you wish to apply to your nets, this dialog box allows us to chose from any of the design rules available in PCB, although many would not be applicable to nets we can use the same process for other objects, which we will look at shortly.

Select Width Constraint from the Chose Design Rule Type dialog box and click OK.

We can now assign width values to the with in the Edit PCB Rule dialog box

Once you have assigned values click OK to exit all of the open dialog boxes and back to the placement of the PCB Layout directive.

To place the directive join the electrical point at the end of the object to the wire or bus on your schematic.

It is also possible to add these PCB design rule parameters to other objects with the schematic environment.  We can add design rule parameters, for example, to components, pins and the schematic sheet.  Within the properties for these objects you will find the option to add and parameter as a rule.

For example within the pin properties, under the parameter tab we can use the Add as Rule button, assigning a rule to a pin would affect a pad in the PCB.