With today’s designs becoming more complex and compact, spacing between copper elements on the PCB is crucial. Inadequate copper spacing between lines, traces, component pins, vias, and more can directly impact the electrical functionality, reliability, and manufacturability of the PCB. Spacing rules can be defined and applied in the PCB to:
- Ensure adherence to manufacturer’s capabilities
- Prevent shorts
- Reduce coupling and crosstalk
- Ensure proper voltage isolation
OrCAD X enables you to quickly and easily define spacing requirements to ensure first-pass success with your design with the Constraint Manager.
This quick how-to will provide step-by-step instructions on how to define spacing rules with the Constraint Manager in OrCAD X.
This how-to covers functionality that is available across multiple products and/or releases. Please select your product below for specific steps.
To follow along, download the provided files above the table of contents.
Configuring Spacing Constraints in OrCAD X
Step 1: Open the provided design in OrCAD X Presto. OrCAD X includes a constraints panel, allowing designers to define and assign constraint sets directly on the PCB canvas.
Step 2: Select View > Panels > Constraints to open the Constraints panel if it is not already open.
Step 3: The Constraints panel opens on the right side of the canvas. This provides an efficient method for defining and assigning electrical, physical, and spacing constraints with the aid of a visual graphic. Scroll down to Spacing to assign spacing constraints. Select Advanced to define all spacing constraints available in OrCAD X.
Defining Spacing Rules in OrCAD X
Step 4: Select the plus sign for Create Spacing CSet to create a new constraint set.
Step 5: The Create Spacing CSet window opens. Enter 8_MIL_SPACE for the name.
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Step 6: Click OK. The constraint set is automatically selected in the Rule Set dropdown.
Step 7: Enter 8 into each text field in the pictorial in the Constraints panel except for Min BB Via Gap. This will set the desired spacing for each parameter to 8mil.
Note:Â Use Tab on the keyboard to quickly advance to the next text field.
Assigning Spacing Rules to Nets in OrCAD X
Step 8: The constraint set must be assigned to the appropriate nets before they can be checked. Disable All Objects in the Selection Filter subpanel and enable Nets to allow nets to be selected.
Step 9: Select a pin or trace on the V+12 net in the PCB canvas. The Constraints panel is populated with constraints assigned to this net.
Step 10: Select 8_MIL_SPACE from the Rule Set dropdown to assign the constraint set. Click anywhere in the canvas to deselect the net.
Step 11: Select a pin or trace on net V12N. Select 8_MIL_SPACE from the Rule Set dropdown to assign the constraint set. Click anywhere in the canvas to deselect the net.
Defining Same Net Spacing Rules in OrCAD X
Same net spacing constraints are constraints that govern spacing between objects on the same nets. Same net spacing is used to control spacing between two elements on the same net to prevent shorting or potential self-net shorting during fabrication, or to prevent a trace coupling to itself if there is a loop of trace running parallel to it.
Constraints can also be defined and assigned in the Constraint Manager.
Step 12: Select Electrical Analysis > Constraint Manager from the menu to activate the Constraint Manager.
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Step 13: The Constraint Manager window opens, showing a directory of constraint domains and worksheets. Select the Same Net Spacing domain and the Same Net Spacing Constraint Set > All Layers worksheet.
Step 14: Right-click Default and select Create > Same Net Spacing CSet.
Step 15: Enter 8_MIL_SPACE for the name and click OK. The constraint set is added to the table.
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Step 16: Click and drag the cells in the 8_MIL_SPACE row. Enter 8 for the value. Click outside the table to set the value of all selected constraints to 8mils.
Assigning Same Net Spacing Rules in OrCAD X
Step 17: Select the Net > All Layers worksheet in the Same Net Spacing domain.
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Step 18: Scroll to the V+12 net. Select 8_MIL_SPACE from the Referenced Same Net Spacing CSet dropdown. The same-net-spacing values for the net are adjusted to 8mils.
Step 19: Select the cell under Referenced Same Net Spacing CSet for net V12N. Select 8_MIL_SPACE from the resulting dropdown.
Activating Design Rule Checks
Note: Design rule checks must be activated for Same Net Spacing constraints before any violations are reported.
Step 20: Select Analyze > Analysis Mode from the Constraint Manager menu.
Step 21: The Analysis Modes window opens. Here you can enable all design rule checks available in OrCAD X. Select Spacing from the list on the left.
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Step 22: Select On under Mark All Constraints to enable all spacing rule checks.
Step 23: Select Same Net Spacing from the list on the left. Select On under Mark All Constraints to enable same-net-spacing rule checks.
Step 24: Click OK to save the settings and close the window.
Verifying Adherence to Spacing Rules in OrCAD X
Step 25: The DRC cache must be refreshed before any new spacing errors are shown. Close the Constraint Manager.
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Step 26: Select the Properties tab to open the Properties panel. Select the Refresh button in the Properties panel to refresh the DRC cache.
Step 27: The DRC pie chart is shown in the Properties panel, showing the types of errors present. In this example, most errors are spacing errors. Select the spacing portion of the pie chart to view a list of errors.
Step 28: The Search panel opens at the bottom of the canvas, listing all errors found in the design. Each error listed is a violation of the new constraint set.
Double-click an error to be brought to its location.
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Step 29: A marker is shown at the location of the error. Hover over the marker to view a tooltip, showing the type of violation, the required constraint value, and the actual value.
Correcting Spacing Constraint Violations
Step 30: Spacing violations can be corrected by sliding or adjusting the affected traces. To activate the slide mode, select Slide from the toolbar.
Step 31: In the Slide widget, select Assisted to ensure the adjustments do not create any new DRC errors.
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Step 32: Click a trace to attach it to your cursor. Move the mouse to adjust the trace position and click again to place the trace.
Note: The Assistance mode is set to Hug, so the bends will be added to the trace as required if its new position violates any constraints. This mode can be set to Shove as well. Slide Mode is set to Manual and the trace turns white, the current position will result in additional DRC errors.
Step 33: Repeat steps 28 and 32 to correct the remaining spacing errors on the board. When finished, choose the Select mode from the toolbar and click to deselect any highlighted traces.
Note: Click Search at the bottom of the window to open the Search panel if it closes. Select the pushpin icon to disable Auto Hide mode to keep the window on screen.
Step 34: View the Properties panel. The DRC error count is zero and the pie chart is no longer drawn, indicating that all errors have been cleared.
Configuring Spacing Constraints in OrCAD X
Step 1: Open the provided design in OrCAD X PCB Designer. OrCAD X includes a constraints panel, allowing designers to define and assign constraint sets directly on the PCB canvas.
Step 2: Select Display > Windows > Constraints to open the Constraints panel if it is not already open.
Step 3: The Constraints panel opens on the right side of the canvas. Scroll down to Spacing to assign spacing constraints. Select Advanced to define all spacing constraints available in OrCAD X.
Defining Spacing Rules in OrCAD X
Step 4: Select the plus sign for Create Spacing CSet to create a new constraint set.
Step 5: The Create Spacing CSet window opens. Enter 8_MIL_SPACE for the name.
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Step 6: Click OK. The constraint set is automatically selected in the Rule Set dropdown.
Step 7: Enter 8 into each text field in the pictorial in the Constraints panel except for Min BB Via Gap. This will set the desired spacing for each parameter to 8mil.
Note: Use Tab on the keyboard to quickly advance to the next text field.
Assigning Spacing Rules to Nets in OrCAD X
Step 8: The constraint set must be assigned to the appropriate nets before they can be checked. Click All Off in the Find panel and check Nets to allow nets to be selected.
Step 9: Select a pin or trace on the V+12 net in the PCB canvas. The Constraints panel is populated with constraints assigned to this net.
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Step 10: Select 8_MIL_SPACE from the Rule Set dropdown to assign the constraint set. Click anywhere in the canvas to deselect the net.
Step 11: Select a pin or trace on net V12N. Select 8_MIL_SPACE from the Rule Set dropdown to assign the constraint set. Click anywhere in the canvas to deselect the net.
Defining Same Net Spacing Rules in OrCAD X
Same net spacing constraints are constraints that govern spacing between objects on the same nets. Same net spacing is used to control spacing between two elements on the same net to prevent shorting or potential self-net shorting during fabrication, or to prevent a trace coupling to itself if there is a loop of trace running parallel to it.
Step 12: Select Setup > Constraints from the menu to activate the Constraint Manager.
Step 13: The Constraint Manager window opens, showing a directory of constraint domains and worksheets. Select the Same Net Spacing domain and the Same Net Spacing Constraint Set > All Layers worksheet.
Step 14: Right-click Default and select Create > Same Net Spacing CSet.
Step 15: Enter 8_MIL_SPACE for the name and click OK. The constraint set is added to the table.
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Step 16: Click and drag the cells in the 8_MIL_SPACE row. Enter 8 for the value. Click outside the table to set the value of all selected constraints to 8mils.
Assigning Same Net Spacing Rules in OrCAD X
Step 17: Select the Net > All Layers worksheet in the Same Net Spacing domain.
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Step 18: Scroll to the V+12 net. Select 8_MIL_SPACE from the Referenced Same Net Spacing CSet dropdown. The same-net-spacing values for the net are adjusted to 8mils.
Step 19: Select the cell under Referenced Same Net Spacing CSet for net V12N. Select 8_MIL_SPACE from the resulting dropdown.
Activating Design Rule Checks
Note: Design rule checks must be activated for Same Net Spacing constraints before any violations are reported.
Step 20: Select Analyze > Analysis Mode from the Constraint Manager menu.
Step 21: The Analysis Modes window opens. Here you can enable all design rule checks available in OrCAD X. Select Spacing from the list on the left.
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Step 22: Select On under Mark All Constraints to enable all spacing rule checks.
Step 23: Select Same Net Spacing from the list on the left. Select On under Mark All Constraints to enable same-net-spacing rule checks.
Step 24: Click OK to save the settings and close the window.
Verifying Adherence to Spacing Rules in OrCAD X
Step 25: The DRC cache must be refreshed before any new spacing errors are shown. Close the Constraint Manager.
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Step 26: Select the DRC button in the bottom-right corner of the PCB canvas and select Display Status from the resulting dropdown.
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Step 27: The Status window opens. This window shows a tally of unplaced components, unrouted nets, isolated and unassigned shapes, and DRC errors. The DRC errors button is red, indicating that the DRC cache is out of date. Select Update DRC to refresh it.
Step 28: The DRC errors button is now yellow, indicating that the cache is up to date but errors are present. Click the button to view the error report.
Note: Click OK in the Display Status window to close it.
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Step 29: The Design Rules Check Report window opens, listing all errors found in the design. Each error listed is a violation of the new constraint set.
Select the coordinates under DRC Marker Location for an error to be brought to its location.
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Step 30: A marker is shown at the location of the error. Hover over the marker to view a tooltip, showing the type of violation, the required constraint value, and the actual value.
Correcting Spacing Constraint Violations
Step 31: Spacing violations can be corrected by sliding or adjusting the affected traces. To activate the slide mode, select Route > Slide from the menu.
Step 32: Click a trace to attach it to your cursor. Move the mouse to adjust the trace position and click again to place the trace.
Note: The Bubble mode is set to Hug Only, so the bends will be added to the trace as required if its new position violates any constraints. This mode can be set to Hug Preferred or Shove Preferred, or the feature can be turned off. If the feature is off and the trace turns red, the current position will result in additional DRC errors.
Step 33: Repeat steps 29 and 32 to correct the remaining spacing errors on the board. When finished, right-click and select Done.
Step 34: Close the Design Rules Check Report window.
Step 35: Select the DRC button and Display Status again to reopen the status window.
Step 36: Select Update DRC. The DRC error button is now green, indicating no errors in the design. All spacing violations have been corrected.
Wrap Up & Next Steps
Quickly and easily define spacing rules with constraints in OrCAD X to improve signal integrity, reliability, and manufacturability. Test out this feature and more with a free trial of OrCAD X. Get more how-tos for OrCAD X at EMA Academy.
