The Best Way to Review Your PCB Designs

 

Introduction

Printed circuit board (PCB) design review is a critical step before manufacturing your boards. A thorough review can catch errors in the schematic, footprints, placement, and routing that could lead to expensive re-spins. While there are many ways to review a design, having a standardized process using automated design rule checking and manual inspection will ensure you don't miss any major issues. This guide covers the best practices for reviewing your PCB designs to avoid costly mistakes before sending gerber files out for fabrication.

Schematic Review

The first step in any PCB review process should be verifying the schematic design. Schematics show the logical connections between components and are the basis for PCB layout. Here are some key things to check in your schematic review:

Component Choice

• Are all components appropriate for their application based on electrical specs, form factor, cost, etc?
• Do any components need to be consolidated or replaced with equivalents?
• Are any components obsolete or at risk of becoming unavailable?

Pin Connections

• Do pin connections match component datasheets? Pay special attention to power, enable, and polarity pins.
• Are all device pins connected properly? Look for floating/disconnected pins.
• Do buses have the correct connections to multiple pins?

Power

• Is supply voltage clearly defined for all components?
• Are there any missing connections to power or ground?
• Are decoupling capacitors placed near each IC?

Interface Signals

• Are all input and output signals labeled clearly?
• Do signals match external system interfaces and test points?

Thoroughly verifying these aspects of your schematic will minimize errors propagating to PCB layout. Use design reviews and comparisons to datasheets to catch mistakes at this stage.

Footprint Review

Once the schematic is finalized, the next step is reviewing PCB footprints. Footprints define the physical pads and lands for component mounting and soldering. Mistakes in footprints can mean components won't fit or won't solder properly during assembly. Here are key areas to focus on:

Dimensional Accuracy

• Do footprint land patterns and pad sizes match component datasheets?
• Are pad spacings and positions correct?
• Do footprints meet manufacturer recommended solder mask and paste design rules?

Pin Mapping

• Is the footprint pin 1 orientation consistent with schematic symbol and datasheet?
• Are pad numbers mapped properly to schematic pins?

Variations

• Are there multiple footprint variations defined for pad or lead config differences?
• Do all component variants in BOM have a matching PCB footprint?

Standards

• Are company footprint standards followed for naming, land patterns, and markings?
• Are any footprint exceptions properly noted and approved?

Doing cross-checks between datasheets, schematics, and footprints at this stage reduces the chance of assembly errors, short circuits, or soldering problems later on.

Placement Review

With schematics and footprints completed, placement review involves verifying component locations and rotations on the PCB. Good component placement is crucial for designing a compact, manufacturable, and testable board. Focus on these areas during placement inspection:

Component Density

• Are components placed as tightly as possible without violations?
• Is space utilized efficiently without excessive unused areas?

Placement Rules

• Are company placement standards and guidelines followed?
• Are any exceptions properly noted and approved?

Component Orientation

• Are polarized components facing the right direction?
• Are component markings readable and accessible?
• Are component lead pitches matched to adjoining footprints?

Thermal Management

• Are any hot components properly spaced from heat sources?
• Is there sufficient copper and air flow for cooling requirements?

Manufacturing

• Can picker and place heads access all components during assembly?
• Is there sufficient clearance for rework and soldering?

Doing comprehensive placement review from both circuit design and manufacturing perspectives helps minimize problems during assembly and testing.

Routing Review

Verifying PCB routing is the final critical stage of design review before manufacturing. Routing inspection focuses on trace design, layout, and quality to avoid signal or power integrity problems. Key routing aspects to review include:

Trace Width and Spacing

• Do track widths and clearances meet impedance matching and current requirements?
• Are spacing and clearance rules followed, especially around high voltage traces?

Routing Paths

• Do critical nets have optimized direct routing paths?
• Is routing done symmetrically for differential pairs?
• Are high frequency traces kept short with minimal vias?

Plane Connections

• Do traces connect properly to power and ground planes?
• Are stitching vias used appropriately for plane connections?

Component Connections

• Are all component pins correctly routed to pads?
• Is routing direct without unnecessary meandering?

Manufacturability

• Can fabrication shop manufacturing capabilities support minimum trace/space rules?
• Are acute trace angles and spline connections acceptable for fabrication?

Doing thorough routing inspection and cross-checking against constraints helps avoid signal issues, excessive EMI, and fabrication problems.

Design Rule Checking

In addition to manual inspection, running automated design rule checks is essential for thorough PCB review. Design rule checking tools like Allegro's APD and Cadence's Assura can validate your design against a set set of geometric constraints and electrical rules. Key checks include:

• Short circuits
• Trace width violations
• Clearance violations
• Spacing violations
• Acute trace angles
• Annular ring violations
• Plane entry spacing
• Via placement
• Pad errors

Design rule checking will systematically identify any oversight in routing that could lead to electrical or fabrication issues. Modern PCB tools can run these checks incrementally during layout or as a final validation step. Proactively addressing any reported violations should be part of review prior to release.

Final Output Verification

As a final step before generating gerbers, carefully inspect all manufacturing outputs including:

Layer Views

• Do layer colors and contents match board requirements?
• Are there any unintended or missing copper areas?

Drawings

• Is board outline in fabrication drawing correct?
• Do assembly/drill drawings accurately reflect design?

Bill of Materials

• Does BOM contain all required components?
• Are component designators and footprints correct?

Gerber Files

• Do gerber layers align correctly when overlaid?
• Are any required layers missing in gerber set?
• Are file names, units, and polarity configured properly?

Verifying all outputs that will be sent for fabrication and assembly avoids hard-to-diagnose errors slipping through to manufacturing. Having a second person double check final design files is recommended.

Review Iterations

Design reviews should be iterative, not a one-time activity. As the schematic, footprint, placement, and routing progress, repeated reviews at each step ensures errors don't compound across the entire design. Schedule reviews with sufficient time to fix issues found and verify fixes prior to board fabrication and assembly stages.

Review Tools

Having the right tools can streamline the PCB review process:

• Comparison Tools: Automatically compare footprints, BOM, gerbers, etc. to CAD data to identify discrepancies.
• Annotation Tools: Allows adding review notes, markers, dimensions, and comments to call out issues.
• Real-time DRC: Design rule checks that run in real-time during routing to prevent rule violations.
• Review Checklists: Checklist of key review items to systematically inspect during each review.
• Revision Control: Track all review comments and subsequent design changes.

Leveraging these tools helps perform more thorough reviews in less time and provides audit trail of the review process.

Team Reviews

In addition to engineering doing self-reviews of their work, formal design reviews should include a broader team to catch issues that others may spot:

• Peer Designers: Fresh eyes from another designer will spot things overlooked.
• Layout Engineers: Can validate manufacturability and identify any fabrication issues.
• Test Engineers: Ensure the design is testable and supports required test points.
• Manufacturing Engineers: Provide guidance on design for manufacturing and assembly.
• Project Managers: Track review action items and issues to resolution.

Getting constructively critical feedback from others prevents designers from being blinded to their own errors and oversight. Formal design reviews should be scheduled milestones with mandatory participation to ensure quality.

Review Meetings

Regular PCB review meetings provide structured time to discuss designs as a team. Some best practices for review meetings include:

• Review on large format displays to easily spot issues.
• Annotate designs in real-time to illustrate issues.
• Have designers walkthrough designs highlighting risk areas.
• Assign action items for fixes with owners and timelines.
• Leverage checklists to guide discussion systematically.
• Keep minutes of issues raised, decisions, and actions.
• Schedule follow-up reviews to verify issues corrected.

Proactively identifying issues and addressing them early avoids wasted effort from late design changes. Reviews are most effective when recommendations are actionable and lead to measurable improvements.

Design Review Checklist

Having a comprehensive design review checklist is key to methodically inspect all aspects of a PCB design. Here is an example checklist covering major review items:

Schematic Review

•  Verify component selection
•  Confirm pin connections
•  Check power connections
•  Review interface signals
•  Simulation/analysis results reviewed

Footprint Review

•  Check footprint dimensions against datasheet
•  Verify pin mapping to schematic
•  Confirm footprint variations defined
•  Standards followed or exceptions approved

Placement Review

•  Check component density optimization
•  Confirm placement rule compliance
•  Verify component orientation
•  Review thermal design
•  Check manufacturing clearances

Routing Review

•  Confirm trace width and spacing rules
•  Check critical net routing
•  Verify plane connections
•  Validate component pad connections
•  Review manufacturing tolerances

Output Review

•  Verify layer stackup
•  Confirm drawings/BOM match design
•  Inspect gerber overlaids
•  Check file naming and formats

Overall

•  Design rule check passed
•  Peer review completed
•  Review punchlist addressed
•  Changes approved and versioned

Formalizing checklist items helps drive a consistent, high quality review process across all designs. The checklist should be tailored for company-specific standards and requirements.

Design Review Guidelines

Some overall guidelines to follow for effective design reviews:

• Schedule reviews for maximum impact at each design phase milestone. Don't wait until the end.
• Come prepared with areas of concern highlighted. Avoid surprise issues.
• Bring solutions, not just problems. Offer options to resolve issues.
• Focus discussions on critical issues and risks. Don't get bogged down in minutiae.
• Capture clear action items and owners for follow-up.
• Iterate reviews until all major issues fully resolved.
• Leave time to validate fixes and re-check.
• Maintain an open, constructive tone focused on improvements.
• Leverage lessons learned for future designs and reviews.

Following structured design review best practices will continuously improve quality across all your PCB development efforts.

Automated Review Options

For teams designing lots of complex boards, manually reviewing every design becomes challenging. Automated review tools can help by programmatically inspecting designs:

Visual Inspection Bots

AI-based visual inspection tools like Zuken's CR8000 can automatically scan artwork on all layers, flagging potential issues for engineers to review. This acts as an initial filter to catch the most obvious errors.

Machine Learning Tools

Systems like Ucamco's Integr8tor analyze thousands of known good designs to learn layout patterns. It uses this to detect anomalies and outliers compared to statistical norms.

Design Guidance Systems

Tools like Siemens' Velocity provide real-time feedback during routing on placement, routing, and via patterns based on best practices. This allows correcting issues dynamically.

Cloud-Based Reviews

Services like Xpedition's proving ground let you submit designs to be automatically reviewed using highly adaptive rules tuned by collective learning across users.

While automated checks are not a substitute for human review, they augment engineers' abilities by systematically eliminating classes of errors. This shifts focus to higher value inspection of complex logic and tricky areas.

Third Party Design Reviews

For mission-critical or high reliability designs, having an independent third party review your design may be warranted. Some options include:

Design Review Contractors

Specialist design review firms like BQR offer detailed inspection and reporting based on your custom checklist and standards. They provide an unbiased assessment.

PCB Fabricators

Your board fabrication shop may offer design review services to catch manufacturability issues prior to acceptance. They have significant expertise from seeing thousands of customer designs.

Test Houses

Engage your test and verification partner early on to review designs for testability. This ensures the needed access and instrumentation is designed in upfront.

While adding cost, independent reviews bring specialized expertise and avoid oversight from design blindness. They are recommended for Class III medical, automotive, aerospace, and other highly compliant applications.

Review Documentation

Formal design reviews should always be documented for traceability. Some examples of useful review records include:

• Completed design review checklists.
• Annotated drawings noting issues found.
• Meeting minutes with recommendations and action items.
• Detailed reports from third party reviews.
• Tracker of punchlist issues and signoff.
• Change orders implementing design modifications.
• Release notes on changes from version to version.

Maintaining thorough review documentation provides visibility into the process. This is crucial for regulated industries requiring full audit trails of product development. The documentation also lets you continuously improve review effectiveness.

New Product Introduction Reviews

In additional to regular design reviews, formal reviews should bookend the new product introduction (NPI) cycle:

Design Validation Reviews

At design completion, validation reviews ensure the product meets all requirements before release to manufacturing. This is the final checkpoint avoiding costly late-stage changes.

Build Review

A build review is done when initial prototypes are assembled to confirm the design is manufacturable. Build issues like soldering defects or clearance problems can be corrected before full production.

First Article Inspection

A comprehensive first article inspection on a production-ready prototype verifies design, quality, performance, and functional compliance criteria are met. This is the final stop sign before full ramp-up.

Rigorous reviews at each NPI milestone improve quality and reduce risk of problems arising in volume manufacturing. Verifying designs early and at each stage is more efficient than extensive troubleshooting after-the-fact.

Continuous Improvement

Perhaps most importantly, PCB reviews should be treated as an ongoing continuous improvement process. Quantitative metrics on review effectiveness, issues found, and escape rates highlight areas needing improvement. Consistently monitoring and enhancing review processes, checklists, tools, and team interactions is key to extracting maximum value. Well-structured reviews that catch issues early accelerate innovation by enhancing design quality and time-to-market.

Frequently Asked Questions

Q: Should PCB layout engineers review their own work or have someone else do it?

A: It is always best to have a second person review any design to get a fresh perspective. Self-reviews are still valuable but subject to design blindspots from closely working on details. Independent peer reviews are recommended whenever possible.

Q: When is the optimal time to review a design?

A: Reviews should be conducted incrementally, not just once at the end. Validate schematics before layout, then do placement reviews, routing reviews, and final verification before manufacturing. This allows correcting issues earlier in the process when changes are less disruptive.

Q: What type of checklists should be used during design reviews?

A: Checklists should include all key aspects to verify in the design based on your company standards and process requirements. Organize checks by categories like schematic, placement, routing, manufacturability, SI/PI, BOM, outputs etc.

Q: How long should a thorough design review meeting take?

A: There is no fixed duration, but typically 2-4 hours is needed for an effective review. Schedule breaks every hour or two as reviews longer than that become inefficient due to fatigue. Budgeting a full morning or afternoon is reasonable for detailed reviews.

Q: When does it make sense to use an independent third party design review?

A: Third party reviews provide value for medical, aerospace, automotive, and other highly regulated products where unbiased assessment is required. They can also supplement bandwidth when many complex designs exceed internal team review