PCB Design Checklist Before Fabrication

PCB routing and layout

After designing your PCB layout, you want to review and approve its details before sending it for fabrication. At this time, you need a complete checklist. Your PCB design checklist should contain all the board specifics and requirements, or some defects might go unidentified.

This article aims to provide a list of essential checks every designer must carry out and why you must do so.

Why Perform PCB Design Review?

Checking your circuit board design is an essential part of its production process. You’ve spent hours upon hours of work, so you want it error-free. That’s why you must check it as the final step before production–using a comprehensive checklist.

Without one, unseen (but avoidable) defects may proceed to the fabrication stage, causing costly reworks and other issues. The details to check for depend on the type of PCB and the required components or features.

For example, if you’re designing a high-frequency board, you want to ensure the traces are well-spaced or confirm EMI shields and heat dissipaters correctly sited. In other words, the aim is to identify and correct design mistakes before production.

Designing a printed circuit board
Designing a printed circuit board
Resource: https://youtu.be/yVINGOkStcY?

PCB Design Checklist

A PCB design checklist has all its details, from component placement and drill holes to routing and other specifications. And while the exact details are board-specific, the checks apply to all design procedures. The following is a list of the things to verify when reviewing your circuit board design.

1. Mechanical Checks

Mechanical checks include everything physical about your board. Start by reviewing and confirming its dimensions. Ensure mounting holes are correct sizes (over 3.3 mm), appropriately spaced, and at the required position from the board edges. Check to see if they have anti-pads, too.

For trace-to-edge clearance, ensure a minimum of 10 mils. Confirm the position of connectors and other components. Examine the layers for height and other specifications. If there are unwanted layers, remove them. Remove unwanted stubs, too.

2. Component Placement

Component placement is a critical check of any checklist for PCB design verification. They should be adequately spaced and aligned. Use 3D images to check component placement, including their orientation and positions.

Their clearance from the board edges should exceed 125 mils. Ensure that there are no traces under sensitive parts and that your bypass capacitors sit near power pins. Confirm small components are a distance from large, heat-producing parts like transformers.

Your PCB layout checklist should also include ensuring the separation of analog and digital circuits, the correct sizing and position of connectors, and the proper design of the board’s power system.

3. Drill Holes

Ensure different drill holes have their proper symbols: + signs for via, squares for plated holes, and triangles for the non-plated types.

Ensure their correct tolerances: 2 mils for vias and non-plated holes and three mils for non-plated holes. Ensure your PCB’s drill chart shows the values for every hole type.

4. Routing Checks

Review your routing topography to confirm its correctness based on the board requirements. Ensure proper trace spacing and length for controlled impedance and crosstalk avoidance.

Your PCB review checklist, when validating routing, should also include an inspection of the different traces. Confirm that sensitive lines do not sit close to other traces to prevent crosstalk.

Check if the number of vias matches your preference to prevent reflections and other signal-related problems. Inspect your design for stubs that may require back drilling.

5. Testing Checks

If your PCB requires test pins, check to see if they do not come in the way of the board’s circuit to interfere with signals. They should not create stubs, or their presence will degrade signals.

Ensure they are in the right places to facilitate testing procedures, such as fixture installation. Place them on one side. Their location will depend on the testing method.

Place them on the top for manual tests and the bottom if using a bed-of-nails fixture. When carrying out your checks, ensure the test points are easily accessible and marked.

6. Soldermask and Solder Paste

Solder mask and solder paste errors can lead to assembly and reliability problems. Confirm that thru-hole components have solder masks and that surface mount types have solder mask and solderpaste areas.

7. Silkscreen Layer

Your PCB layout design checklist should check the silkscreen. Review its markings for correctness, especially if your board has high-density components. Ensure the following markings:

  • The correct names of the components, their polarity, and ICs pin one.
  • Board information specifics such as its name and print date.
  • Product information like hazard labels, company logo, etc.
  • Identical sizes for the legend text.

8. BOM Checks

A PCB review checklist must have verification details for the bill of materials file. Include a check of the DNI/DNP components to ensure all information is correct per your specific board’s requirements.

Mark these on the design and layout files. If some parts need to be updated or are no longer available, identify and replace them with their alternatives.

Checking a completed circuit board design
Checking a completed circuit board design
Resource: https://forum.kicad.info

Updating PCB Design after Review

Fabrication files are the final details before producing your PCB and should be without design errors. After successfully reviewing your circuit board, it’s time to update the fabrication files with the modifications. Check to see everything is in order and validate all files, including the following:

  • Board drawings file
  • The BOM file
  • Drill files for CNC-drilled holes
  • The netlist file
  • The solder mask and silkscreen layer files

Be sure to include modification details such as their time and date. Documenting your PCB design review process makes tracing the changes more accessible in the future.

Conclusion

A PCB design checklist is an essential part of its finalization process. It ensures the design is without errors and validates the PCB for fabrication. And while checks are different for specific boards, a general guide should get you started. This article details these checks so you can efficiently perform your final inspection.

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