PCB Advanced Spacing Rules on Altium Designer

 

Understanding PCB Spacing Rules Fundamentals

Proper spacing rules in PCB design are crucial for ensuring manufacturability, electrical performance, and reliability. Altium Designer provides a comprehensive set of advanced spacing rules that allow designers to maintain precise control over their PCB layouts. This detailed guide explores the various aspects of spacing rules and their implementation in Altium Designer.

Core Spacing Rule Categories

Electrical Clearance Rules

Electrical clearance rules are fundamental to preventing short circuits and maintaining signal integrity. These rules define the minimum spacing between different electrical objects on the PCB.

Rule Type
Typical Minimum Spacing
High Voltage Applications
Notes
Copper to Copper
0.2mm
0.5mm - 3.0mm
Varies with voltage
Pad to Pad
0.254mm
1.0mm - 5.0mm
Component dependent
Track to Track
0.2mm
0.5mm - 3.0mm
Signal type dependent
Via to Via
0.5mm
1.0mm - 3.0mm
Based on via size
Component to Component
0.5mm
1.0mm - 5.0mm
Height dependent

Manufacturing Rules

Rule Category
Standard Value
High-Density
Ultra High-Density
Minimum Trace Width
0.2mm
0.15mm
0.1mm
Minimum Via Diameter
0.6mm
0.4mm
0.3mm
Minimum Drill Size
0.3mm
0.2mm
0.15mm
Edge Clearance
0.3mm
0.25mm
0.2mm

Advanced Rule Configuration

Rule Priority System

Altium Designer implements a sophisticated rule priority system:

Priority Level
Rule Type
Application
1
Object-specific
Individual components/nets
2
Class-to-class
Net classes/component classes
3
Layer-specific
Layer constraints
4
Design-wide
General rules

Rule Scoping

Net-Based Scoping

Scope Type
Application
Example
Single Net
Individual net rules
Power nets
Net Class
Group of related nets
Differential pairs
Net Category
Functional groups
High-speed signals
Multiple Nets
Custom combinations
Mixed signal groups

Layer-Based Scoping

Layer Type
Special Considerations
Typical Spacing
Top Layer
Component clearance
0.254mm
Inner Layer
Power plane clearance
0.305mm
Bottom Layer
Component clearance
0.254mm
Mixed Layers
Inter-layer rules
0.4mm

Implementation Strategies

High-Speed Design Rules

Signal Type
Minimum Spacing
Preferred Spacing
Max Length
Differential Pairs
0.2mm
0.25mm
Design dependent
Clock Signals
0.3mm
0.5mm
Match length
Memory Interface
0.25mm
0.4mm
Length matched
Generic Digital
0.2mm
0.3mm
Not critical

Power Distribution Rules

Voltage Level
Minimum Spacing
Plane Spacing
Via Spacing
3.3V
0.2mm
0.4mm
0.5mm
5V
0.25mm
0.5mm
0.6mm
12V
0.4mm
0.8mm
0.8mm
24V+
0.8mm
1.2mm
1.0mm

Rule Verification and Analysis

Design Rule Check (DRC) Configuration

Check Type
Severity
Resolution Time
Clearance Violations
Error
Immediate
Width Violations
Error
Immediate
Power Plane Violations
Warning
Project dependent
Manufacturing Violations
Error
Immediate

Common Verification Scenarios

Scenario
Check Parameters
Resolution Approach
High-Density Areas
Component spacing
Component repositioning
Power Distribution
Copper width
Width adjustment
Signal Integrity
Parallel tracks
Rerouting
Thermal Management
Component clusters
Spacing adjustment

Advanced Rule Application Examples

Mixed Signal Designs

Signal Type
Spacing Rule
Guard Band
Notes
Analog
0.3mm
0.5mm
From digital
Digital
0.2mm
0.4mm
From analog
RF
0.4mm
0.8mm
From all others
Power
0.3mm
0.6mm
From sensitive signals

High-Voltage Applications

Voltage Range
Creepage
Clearance
Safety Margin
50-150V
0.8mm
0.6mm
+0.2mm
151-300V
1.5mm
1.2mm
+0.3mm
301-600V
3.0mm
2.5mm
+0.5mm
>600V
5.0mm
4.0mm
+1.0mm

Optimization Techniques

Rule Performance Impact

Rule Complexity
Processing Time
Memory Usage
Recommended Use
Simple
Fast
Low
General design
Moderate
Medium
Medium
Mixed signals
Complex
Slow
High
Critical systems
Custom
Variable
Variable
Special cases

Rule Management Strategies

Strategy
Benefits
Limitations
Best For
Global Rules
Simple setup
Less flexible
Basic designs
Layer Rules
Better control
More complex
Multi-layer
Net Rules
Precise control
Setup intensive
Critical nets
Combined
Maximum control
Complex setup
Advanced designs

Frequently Asked Questions

Q1: How do I prioritize conflicting spacing rules in Altium Designer?

A: Altium Designer follows a strict priority system where more specific rules override general rules. The order of priority is: object-specific rules → class-to-class rules → layer-specific rules → design-wide rules. You can view and modify rule priorities in the PCB Rules and Constraints Editor.

Q2: What are the recommended spacing rules for high-speed designs?

A: For high-speed designs, implement the following minimum spacings:

• Differential pairs: 0.2mm between pairs, 0.25mm to other signals
• Clock traces: 0.3mm from other signals
• Length-matched traces: Follow manufacturer specifications
• Guard bands around high-speed groups: 0.5mm minimum

Q3: How can I set up different spacing rules for different voltage levels?

A: Create separate rules for each voltage level using net classes. Define clearance rules based on voltage levels and use the "Rule Priority" system to ensure proper application. Include both clearance and creepage considerations for higher voltages.

Q4: What are the best practices for setting up spacing rules in dense areas?

A: For dense areas:

• Use room definitions to apply specific rules
• Create component classes for similar components
• Define rules based on signal types
• Consider manufacturing limitations
• Implement different rules for critical nets

Q5: How do I verify that all spacing rules are being followed correctly?

A: Use multiple verification methods:

• Run comprehensive Design Rule Check (DRC)
• Use the Online DRC feature during routing
• Review clearance matrices in the Rules Summary
• Generate rule violation reports
• Perform manual visual inspection of critical areas

Conclusion

Advanced spacing rules in Altium Designer are essential for creating reliable and manufacturable PCB designs. Understanding and properly implementing these rules ensures optimal performance while maintaining necessary safety and manufacturing requirements. The sophisticated rule system allows designers to create complex rule sets that can accommodate various design requirements while maintaining proper electrical and physical clearances.