Creating effective PCB layouts requires following proven design rules that ensure signal integrity, manufacturability, and reliability. Whether you’re designing a simple prototype or a complex multilayer board, understanding and implementing proper layout rules is critical for project success. Doing so will help you avoid costly redesigns and manufacturing issues.
General PCB Design Layout Rules and Recommendations
Electronic circuit boards come in various shapes and sizes, and with varying functionality and performance objectives. Yet, each requires PCB layout design decisions based on performance expectations and manufacturability requirements. For example, spacing board elements according to clearance and creepage standards is important to satisfy your contract manufacturer’s design for manufacturing (DFM) requirements. These requirements are essential to minimize the effects of electromagnetic interference (EMI) and to avoid structural damage due to unintended shorts or surface arc tracking on high-voltage boards. As shown below, there are many PCB design layout rules and recommendations that are equally important.
| PCB Design Layout Rules by Application | |||
| Rule | Minimum Value | Recommended Value | Critical Applications |
| Trace Width (Signal) | 0.1mm (4 mil) | 0.15mm (6 mil) | Digital circuits |
| Trace Width (Power) | 0.3mm (12 mil) | 0.5mm (20 mil) | Power delivery |
| Via Size (Standard) | 0.2mm (8 mil) | 0.25mm (10 mil) | Layer transitions |
| Via Size (Micro) | 0.1mm (4 mil) | 0.15mm (6 mil) | High-density designs |
| Trace Spacing | 0.1mm (4 mil) | 0.15mm (6 mil) | Adjacent signals |
| Component Spacing | 0.5mm | 1.0mm | Assembly clearance |
| Drill Size | 0.15mm (6 mil) | 0.2mm (8 mil) | Manufacturing |
| Annular Ring | 0.05mm (2 mil) | 0.1mm (4 mil) | Reliability |
| Copper Pour Clearance | 0.2mm (8 mil) | 0.3mm (12 mil) | Isolation |
| Solder Mask Opening | +0.1mm | +0.15mm | Pad coverage |
| Silkscreen Width | 0.1mm (4 mil) | 0.15mm (6 mil) | Visibility |
| Board Edge Clearance | 0.5mm | 1.0mm | Manufacturing |
| Keepout Zone | 0.3mm | 0.5mm | Component clearance |
| Differential Pair Gap | 0.1mm (4 mil) | 0.15mm (6 mil) | Impedance control |
| Layer Stack Thickness | 1.6mm standard | Custom per needs | Impedance matching |
| Hole-to-Hole Spacing | 0.1mm (4 mil) | 0.15mm (6 mil) | Drill accuracy |
NOTE: The dimensions given in the table are general and should only be used as guides. You should always verify physical dimensions with your CM to ensure your specifications align with their equipment capabilities.
The list above is not exhaustive. For example, annular ring size, which is an important parameter for plated through holes (PTHs), like vias, is not included. Yet, it is included in the prevailing PCB layout standard IPC-6011, which defines circuit board manufacturing requirements based on intended performance. However, the list does cover general layout areas, rules, and guidelines that you should know, regardless of your board type.
Trace Width and Current Capacity Guidelines
The layout guidelines for your board traces are typically determined by current capacity levels. Consequently, it is important to calculate these specifications accurately. This is done by following IPC standards that define the relationship between trace width, current capacity, and temperature rise:
Current Capacity Equations:
- External traces: I = k × (ΔT^0.44) × (W^0.725) × (TH^0.725)
- Internal traces: I = k × (ΔT^0.44) × (W^0.725) × (TH^0.725) × 0.7
Where I = current (amps), ΔT = temperature rise (°C), W = width (mils), TH = thickness (mils), k = constant (0.048 for external, 0.024 for internal)
For boards where signal integrity is prioritized, important considerations include the following:
Signal Integrity Considerations:
- High-speed signals require controlled impedance traces
- Differential pairs need matched lengths within 0.1mm
- Clock signals should be routed as short as possible
- Critical signals need ground reference planes
Component Placement and Spacing Rules
Component placement and grouping are another critical aspect of circuit board design. Strategic component placement directly impacts your PCB’s performance, manufacturability, and cost. Following proven PCB layout placement rules prevents assembly issues and optimizes signal flow.
| PCB Design Layout Rules for Component Placement | |||
| Component Type | Placement Priority | Spacing Requirement | Special Considerations |
| Power regulators | High | 5mm minimum | Heat dissipation |
| Crystal oscillators | Critical | 2mm from switching | EMI isolation |
| Decoupling capacitors | Critical | <5mm from IC | Power delivery |
| Connectors | Medium | 3mm board edge clearance | Mechanical stress |
| Test points | Low | 1mm spacing | Probe access |
| LEDs | Low | 2mm spacing | Light pipes |
The placement of your components is important for manufacturing, operation, and safety, and this is critical when designing flex boards, too. Placing high-power components inappropriately can create many problems. For example, inadequate heat dissipation can lead to component failure and/or PCB damage. Here are some important thermal considerations to keep in mind:
Thermal Management Rules:
- Place heat-generating components away from temperature-sensitive parts
- Use thermal vias under power components (0.3mm diameter, 0.8mm spacing)
- Maintain 3mm clearance around high-power components
- Consider component height restrictions for enclosures
Via Design and Layer Transition Best Practices
Today, many boards are multilayer due to board size restrictions and performance requirements, and require the use of vias. It is important to understand the various via types and their impact on your layout design.
| Via Selection Guide | ||||
| Via Type | Diameter | Drill Size | Best Applications | Cost Impact |
| Through-hole | 0.6mm | 0.3mm | Low-speed signals | Low |
| Blind | 0.4mm | 0.2mm | High-density routing | Medium |
| Buried | 0.3mm | 0.15mm | Inner layer connections | High |
| Micro | 0.2mm | 0.1mm | BGA breakout | High |
| Filled | 0.4mm | 0.2mm | Thermal/power | Medium |
Where to place vias is as important as when to use them. Consider the following via placement guidelines in your PCB layout.
Guidelines for via placement to follow are:
- Maintain 0.3mm spacing between via edges
- Use via stitching for layer transitions every 5mm on power planes
- Avoid vias in differential pair routing unless necessary
- Place vias on a 0.5mm grid for manufacturing efficiency
Guidelines for Grounding and EMI Control
Proper ground plane design forms the foundation of good PCB performance. A well-designed ground system reduces noise, improves signal integrity, and ensures electromagnetic compatibility (EMC).
Ground Plane Strategies:
| PCB Design Layout Recommendations for Grounding | |||
| Strategy | Application | Benefits | Implementation |
| Solid ground plane | Digital circuits | Low impedance return | Full copper pour |
| Split ground planes | Mixed-signal designs | Isolation | Separate analog and digital circuitry |
| Ground grid | RF applications | Controlled impedance | Mesh pattern |
| Local grounds | Sensitive circuits | Noise isolation | Island approach |
Effective grounding helps reduce opportunities for unwanted EMI, such as from inductive loops. Additional specific actions can be taken to minimize EMI.
EMI Reduction Techniques:
- Use continuous ground planes under high-speed traces
- Implement guard traces around sensitive signals
- Place bypass capacitors every 2cm on power rails
- Route clock signals over solid ground planes
- Minimize loop areas in critical circuits
Manufacturing Constraints and DFM Guidelines
Understanding manufacturing limitations prevents costly redesigns and ensures your PCB can be reliably produced. DFM and DFA (DFMA) rules vary by CM, but follow common industry standards based on IPC class performance standard requirements and board complexity. Some good general PCB design layout rules and recommendations to know and implement include the following for efficiency and reliability.
DFM Cost Optimization Tips:
- Use standard board thicknesses (1.6mm is the most economical)
- Minimize layer count where possible
- Avoid unnecessary via types (stick to through-hole when sufficient)
- Use standard drill sizes to reduce tooling costs
- Keep board dimensions within panel constraints
DFM Quality Assurance Checklist:
- Run DRC (Design Rule Check) before finalizing layout
- Verify impedance calculations for high-speed signals
- Check component orientation and polarity markers
- Ensure adequate solder mask openings
Following proper PCB design layout rules and guidelines is essential for creating reliable, manufacturable circuit boards that meet the design intent and operate reliably over their projected lifetime. Knowing the rules and recommendations is the first step in achieving this goal. Having the best PCB design software and/or simulation tools to verify your design is also required. The best option to ensure your capabilities meet these thresholds is to partner with the industry leader in supplying engineers with the software tools needed to optimize their workflow and meet quality standards.
EMA Design Automation is a leading provider of the resources that engineers rely on to accelerate innovation. We provide solutions that include PCB design and analysis packages, custom integration software, engineering expertise, and a comprehensive academy of learning and training materials, which enable you to create more efficiently. For more information on pcb design layout rules and recommendations and how we can help you or your team innovate faster, contact us.
