The Electronics Designers' Optimum PCB Design Flow – Right First Time

The Electronics Designers' Optimum PCB Design Flow – Right First Time

Achieving an optimum PCB (printed circuit board) design flow that results in correct-first-time board layouts the first time is a goal for many electronics designers. With increasing time pressures and the need to avoid costly mistakes, having an efficient and error-free design process is critical. This article looks at key elements of an optimum PCB design flow and how to implement them.

Why First Time Right Matters

Getting the PCB layout right first time has multiple benefits:

  • Reduces costly design iterations and board spins
  • Avoids deadline pressures from having to rework the design
  • Minimizes risk of faulty PCBs going into production
  • Saves time and cost compared to fixing issues post-manufacture
  • Results in a quality board that meets the product requirements

The price of getting the design wrong can be high. Multiple design spins to fix issues are time-consuming and expensive. Faulty boards that go into production can mean field failures, costly product recalls and damage to a company's reputation.

Elements of an Optimal PCB Design Flow

An optimum PCB design flow that facilitates first-time-right layouts depends on several key elements:

1. Define Design Requirements Upfront

Clearly defining all the design requirements at the start of the project is essential. This includes:

  • The product specifications
  • Target components to be used
  • PCB parameters e.g. board size, number of layers
  • Applicable standards to be met e.g. safety, EMC
  • Environmental operating conditions
  • Manufacturing requirements e.g. tolerances
  • Test and inspection requirements
  • Timelines and budget

Documenting all requirements in a specification helps ensure the PCB design meets expectations. It also helps manage sign-off by all stakeholders.

2. Simulation Early in the Design Process

Performing simulation and analysis of the PCB layout earlier rather than later can avoid many issues. Important analyses include:

  • Signal integrity - ensures high-speed signals maintain integrity
  • Power integrity - verifies clean power delivery to components
  • Thermal analysis - checks components operate within temperature limits
  • EMI/EMC - confirms the design meets EMI/EMC requirements
  • DFM (design for manufacturing) - verifies the design is manufacturable

Doing these analyses during the design process flags any problems early when changes are easier. This avoids late-stage issues after layout is complete.

3. Design Reuse Where Possible

Reusing proven schematics, circuit blocks and layout elements from previous designs saves significant time. It also leverages previous design expertise and avoids reinventing the wheel.

Common approaches for design reuse include:

  • Creating reusable schematic macros for common subsystems
  • Maintaining libraries of generic layout cells e.g. power, high-speed routing
  • Storing common circuit schematic fragments in a database

Reuse works best when standardized, modular design is employed within a product family. This facilitates combining common design building blocks across multiple products.

4. Rules-Driven Layout

A rules-driven approach to PCB layout embeds designer knowledge into design rules and constraints. This automates many routine design tasks while still meeting layout requirements.

Typical design rules cover:

  • Component placement constraints e.g. grouping by type
  • Routing widths and clearances
  • High-speed topological constraints e.g. length matching
  • Plane connections and splits
  • Manufacturing allowances and tolerances

This automation simplifies layout tasks for the board designer while adhering to sound design practices. Violations of the rules during layout are immediately flagged.

5. Cross-Discipline Design Reviews

Reviews of the PCB layout at multiple stages by other engineering disciplines can identify potential issues early. Important cross-reviews include:

  • EE design review - verifies schematics, placement, routing
  • Mechanical review - checks 3D clearances, connector mounting
  • Manufacturing review - confirms design is manufacturable
  • Test review - validates test points, fixture design

By representing all stakeholders during design reviews, problems can be found and addressed before board fabrication. This avoids costly change orders after design release.

6. Prototype Boards Prior to Production

Building and evaluating prototype PCBs prior to committing to full production can derisk the design. Prototyping helps confirm:

  • The design meets the product requirements
  • All components are correct and integrated successfully
  • Manufacturing processes produce quality boards
  • Testing procedures are adequate

Prototypes also provide an opportunity to tweak the design prior to release. This useful feedback then improves the production design.

Implementing the Optimal Design Flow

Hire Skilled PCB Designers

Having skilled designers who understand the entire electronics development process is key. Look for expertise in:

  • Schematic capture and PCB layout tools
  • Simulation, DFM, library management
  • Working cross-functionally across disciplines
  • Managing constraints and design complexity

Provide ongoing training to expand designers' knowledge and skills. Mentoring less-experienced designers also improves quality.

Adopt a Modular, Hierarchical Design Style

A modular design methodology which breaks the design into reusable functional blocks aids reuse and simplifies layout. Maintaining schematic and layout hierarchy also improves designer productivity and reduces errors.

Utilize Modern Design Tools

EDA tools have advanced PCB design flows significantly. Critical capabilities include:

  • Schematic and layout constraint management
  • Real-time DRC/ERC during layout
  • Automated placement and routing
  • Interactive 3D/GD&T analysis
  • Linked simulation and analysis

Using these tools in an integrated design flow prevents errors and improves results.

Institute Design Reviews and Approvals

Build formal design reviews into the project schedule at multiple stages e.g. requirements, schematic, layout. Use checklists to verify completion of each stage prior to sign-off. This governance process ensures no steps are missed.

Develop Scalable Rules and Libraries

Create libraries of generic layout cells, schematic macros, and symbol definitions which can scale across product families. likewise, craft design rulesets to be reused across multiple designs. This aids consistency while minimizing manual work.

FAQs

What are some key ways to reduce PCB design errors?

Some key ways to reduce errors in PCB design include:

  • Comprehensively defining design requirements upfront
  • Performing simulation and analysis early to flag issues
  • Codifying designer knowledge into reusable design rules
  • Automating repetitive layout tasks as much as possible
  • Doing rigorous design reviews before release
  • Prototyping boards prior to full production

Following these practices catches more errors during design rather than after fabrication.

How can you cut down PCB design time?

Methods to help cut down overall PCB design time include:

  • Reusing proven schematics and layout from previous projects
  • Employing hierarchical, modular design approaches
  • Using powerful, automated EDA tools for placement and routing
  • Having an efficient design flow with reuse, rules and reviews
  • Working concurrently across disciplines e.g. parallel schematic/layout
  • Prototyping only critical sections vs. full board

An efficient design flow minimizes manual work and avoids late-stage changes.

What DFM checks help ensure manufacturable PCBs?

Key DFM checks that help ensure manufacturable PCB layouts include:

  • Confirming trace/space widths meet capabilities
  • Checking hole sizes and routability
  • Verifying minimum clearance requirements
  • Validating pad shapes and sizes are consistent
  • Reviewing layer stackup against fab shop rules
  • Assessing thermal heat dissipation in board and traces
  • Evaluating solder mask expansion tolerances
  • Reviewing panel utilization layouts

Running DFM analyses early and working closely with manufacturers prevents production issues.

What are some benefits of a rules-driven PCB layout?

Benefits of rules-driven PCB layout include:

  • Embeds designer knowledge into design rules
  • Automates repetitive layout tasks
  • Ensures designs adhere to company/industry standards
  • Rapidly validates changes during layout
  • Reduces manual work for designers
  • Helps new designers get up to speed quickly
  • Aids consistency across designs
  • Makes layout changes and evaluation fast

Overall, rules-driven layout boosts designer productivity while improving quality.

Why are cross-discipline design reviews valuable?

Cross-discipline design reviews are valuable because they:

  • Identify issues from different engineering perspectives
  • Ensure the design meets requirements
  • Help work through integration details early
  • Clarify uncertainties before release
  • Build consensus across stakeholders
  • Represent all viewpoints e.g. EE, ME, manufacturing
  • Improve first-time quality before build

Reviews align the full product team and drive better results.

Giuseppe Rossati

Senior HW Developer presso Coges S.p.A.

10 个月

i do not 100% agree with this flow. Component creation, in my opinion, need to be completed as a part of schematic drawing, including also attributes, and assembly drawing. If you do as a furder actions, somebody can be lost on the way.

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