PCB Design Parameters With OrCAD X

Key Takeaways

• PCB design parameters impact performance, reliability, and manufacturability.

• Key constraints include signal integrity, power integrity, and thermal management.

• Setting constraints in OrCAD X ensures compliance with electrical and physical requirements.

When you aren’t used to a new set of PCB design tools, the amount of setup that goes into the parameters can seem overwhelming. There are, however, good reasons for all of these parameters, and with the right touch on the controls, your layout tools can conform to your method and style of design. Here are some of the problems these PCB design parameters intend to solve and how you can fine-tune your design environment for maximum productivity by working with them.

Types of PCB Design Parameters  and Key Considerations

Why Do We Need All of These Parameters for PCB Layout in the Design Tools?

The PCB design process used to suffer from various shortcomings, some of which included the difficulty of manipulating individual component footprint changes, the primitive nature of area fill (copper pour) features, and many other restrictions on how you worked due to the limitations of the tools.

Now, however, advanced PCB software can efficiently deal with all of these issues. However, these new features require more setup time to run properly.

As layer counts increased, it became more difficult to identify each design element on the screen visually, and as new routing and area-fill functionalities became available, the existing grid and rule structures couldn’t control them. You would know what I mean if you’ve ever worked on a 16-layer board using a design system from 35 years ago that only offered a monochromatic display. 

EDA vendors began to include UI-related PCB design parameters that needed to be set up for layout to give users more flexibility. When using a new set of design tools, these parameter setups can be a little overwhelming, but there are very good reasons for all of them, even if they don’t get used by each user:

• Units of measurement, tolerances, fonts, text sizes, and other standards can vary from company to company.

• Some people will see colors and patterns differently than others, and the display must be able to be changed as needed.

• Display schemes that may look good for some tasks, such as library development, may be distracting or difficult to see during layout.

• Parameters such as grid settings that benefit one user may be difficult for others to use in the same tasks.

• A group may find working with an individual user's display scheme during a design review.

Next, let’s examine some of the parameters that PCB designers would most like to be able to change

CAD Layout Parameters Most Beneficial to Change

Getting a PCB design system set up for the most productive work environment means being able to change the parameters of the tools as needed. Here are some of the parameters that designers need to be able to work with the most:

Setting Design Constraints in OrCAD X to Ensure Optimal PCB Design Parameters

Setting appropriate design constraints ensures that a PCB meets electrical, physical, and manufacturing requirements when designed in OrCAD X.  The Constraint Manager allows users to edit constraint rules with the Constraint Manager, which allows designers to define trace widths, spacing via types, and differential pair settings.

PCB Design Parameters in OrCAD X In The Constraint Manager

• Open OrCAD X Layout.

• Navigate to Tools > Constraint Manager.

• The left panel contains different constraint categories, including Electrical, Physical, Spacing, and Manufacturing rules.

Defining Constraint Sets for Reusability

• Constraint sets (CSet) act like templates that can be assigned to multiple nets or regions, reducing repetitive work.

• To create a new constraint set:

• Right-click Physical Constraint Set → Create Physical CSet.

• Name the CSet appropriately (e.g., Power or Signal).

• Assign values for minimum and maximum line width, neck width, and via types.

 Setting Design Constraints for Key PCB Parameters

Electrical Constraints

Signal Integrity

• Go to Electrical Constraints > Target Impedance, Propagation Delay.

• Set trace width and spacing to control impedance.

• Enable differential pair constraints for high-speed signals:

• Select Electrical Constraint Set > Routing > Differential Pair.

• Define maximum uncoupled length (e.g., 5.08 mm).

• Set static phase tolerance (e.g., 0.508 mm).

• Ensure EMI compliance by setting proper trace clearances.

Power Integrity

• Define power plane constraints under Physical Constraint Sets.

• Assign wider traces for power nets:

• Minimum width: 0.508 mm (for power traces).

• Maximum width: 2.54 mm (converted from 100 mils).

• Apply decoupling capacitor rules for stable power distribution.

Physical Constraints

Board Dimensions

• Ensure the PCB fits within the mechanical enclosure.

• Set constraint rules for mounting hole placements.

Component Placement

• Place high-speed components close to signal paths.

• Assign power components near thermal reliefs.

• Maintain proper spacing between analog and digital components to reduce interference.

Manufacturing Constraints

Design for Manufacturability (DFM)

• Set trace width and spacing to meet fabrication requirements.

• Use standard via sizes:

• Assign Route Via type in Physical Constraint Manager.

• Avoid unnecessary blind/buried vias unless required.

Material Selection

• Choose high-frequency, low-loss materials for signal integrity.

• Set up thermal constraints by enabling via stitching for heat dissipation.

Driving Design Choices by Constraints for an Optimized Final Product

Optimized Component Placement – Place high-speed components close to their corresponding signal paths to minimize interference; power components must have proper thermal dissipation areas.

Layer Stack-Up Decisions – The number and arrangement of PCB layers include constraints such as signal integrity, power distribution, and cost considerations. A well-planned stack-up reduces EMI and improves performance.

Manufacturability Considerations – Design-for-manufacturing (DFM) principles ensure the PCB is scalable while minimizing costs. Avoiding unnecessarily small features and aligning with manufacturer capabilities results in a smooth production process.

Ensuring PCB Design Parameters Are Met in OrCAD X 

Verifying Design Rule Compliance

• Run Analyze > Analysis Mode to check enabled rules.

• Verify that constraints are applied correctly:

• Yellow headers indicate rules that are OFF.

• Right-click and select Analysis Mode to turn them ON.

• Check real-time DRC errors in the Properties Panel.

• Correct violations using slide adjustments in the PCB layout editor.

Ensuring Proper Routing Adherence

• Use Add Connect Tool to route traces.

• Flagged violations appear in white during routing.

• Adjust trace paths to comply with spacing and impedance rules.

Reviewing and Fixing Errors

• Open the DRC Summary Panel.

• Click Pie Chart Segments to see categorized DRC violations.

• Double-click an error to locate it on the PCB.

• Modify the trace or component placement to fix the issue.

• Run DRC refresh to validate corrections.

Optimizing PCB design parameters is essential for achieving high performance and manufacturability. Learn more about how OrCAD X can enhance your PCB design workflow and sign up for a free trial today.