Is your printed circuit board (PCB) ready for production? This step-by-step checklist will help determine whether you’ve completed everything necessary to move your design to prototyping and production.
Before Submitting Your Board for PCB Design Review
- Look for unrouted nets
- Repour polygons
- Check that the board has a complete silkscreen, including:
- Warning and hazard labels and appropriate icons
- Company and product logos
- Copyright information
- Make sure connectors are labeled and pinouts are called out as needed
- QA/test block with barcode, along with blank areas for a serial number and dates
- QA/test checkmarks
- Review board name, print date, and revision number
- See if there are designators on the silkscreen, then check that:
- Every designator is close to — and identifies — the related component
- All designators are in one or two orientations
- Text size and font will be readable after the fabrication process is complete
- ICs have pin one marked
- The pin one marker should not be placed below another component
- Update the PCB from its schematics to make sure the schematic and board are synched
- Check that the design rule report is error-free
- Check that there is a design rule to catch nets with only one pin
- Check that the board outline appears on a mechanical layer that will go to the fabricator
- Ensure fiducials are present for the assembly. They must meet the following criteria:
- A minimum of three board-level fiducials are included
- Two fiducials diagonally oppose each other across all fine-pitch components
- Mounting points have adequate clearance for the designated washer and screw head
- If an enclosure model is available, check that it’s been tested against the board to make sure there will be no interference between the enclosure and components
- Ensure all components, including mechanical items, have the correct 3D models
Your board must be fully production-ready before sending it to colleagues for a design review check to avoid useless effort.
Submitting a PCB Design for Review
PCB Design Review: Layers
- Ensure that the layer stack and substrate heights meet your fabricator’s specifications or that they can meet yours
- Review the copper thickness on all layers to make sure it matches the target fabricator’s specifications or that there is a callout for the required copper thickness
- Check that there is at least one continuous, unbroken ground plane
- If the PCB has controlled impedance nets, check that they’re correctly set up on the layer stack and in the design rules
- Ensure the keep-out track matches the shape of the board
- Check any board cutouts or slots used for a keep-out barrier to prevent nets from crossing milled areas
A PCB stackup table developed as part of your front-end engineering specifications can be helpful. It provides a visual comparison against the data in your PCB editor. A table provided by a fabrication house or manufacturer is the best resource.
PCB Design Review: Signal Path
- Check that the ground plane has adequate current-carrying vias near connectors and voltage/return sinks
- If needed, review voltage planes and areas to ensure they have sufficient connection vias for current requirements
- Check tracks to reference planes to make sure they are wide enough to meet current requirements
- Ensure that there are an adequate number of vias for the current-carrying capacity of traces
- Check the minimum track widths for current-carrying nets and ensure they’re adequate
• Consider whether a design rule is necessary - Ensure all ground pins have a via to the ground plane
- Make sure there is a continuous ground plane within one signal layer of any signal trace
- Check that controlled impedance traces have the proper net rules and impedance profile
- Ensure that differential pair tracks are as close together as possible
- Check that differential pair track lengths match
- Make certain high-speed signals are length-matched, including:
• DDR
• Ethernet
• HDMI
• LVDS
• MIPI
• PCIe
• USB3+ - Ensure each signal trace has a constant impedance along its length
If the trace changes layers, its impedance should remain the same - Check that traces longer than 1/6th of the rise or fall time of the signal have been simulated:
• Ensure termination resistors — or another form of termination — are present to prevent ringing or overshoots
• Ensure termination resistors are in proper locations - Make certain long traces that hug other traces have been simulated for crosstalk
- Review all high-speed traces that run over a continuous ground pour
- Make sure that sensitive nets don’t run below noisy components
- Ensure that vias for decoupling capacitors aren’t shared
- Check that every decoupling capacitor has its own via for VCC and GND direct to reference planes
- Ensure the xSignals package includes features that can help automate checks after the PCB layout is complete but before a more rigorous engineering team manual review.
PCB Design Review: Components
- Ensure through-hole pads are set to plated if they need to be soldered
- Check there is sufficient clearance for:
• Pick and place heads in the production process
• Hand assembly in prototypes
• Soldering pen tip access if rework is needed - Ensure bypass capacitors are placed as close as possible to IC power pins
• Under 15mm - Check that termination resistors are as close as possible to the signal source
- Make sure crystal/oscillator clock sources are as close as possible to IC clock pins
- Ensure EMI/RFI filtering is as near as possible to the exit point
• Board edge, connector, or shield - Make sure that potentiometers raise signal/voltage when turned clockwise
- Check that programmable devices have programming header/pads that are accessible
- Ensure that no high thermal mass components, such as large transformers or inductors, are too close to small components
- Ensure that component placement makes short track lengths a priority for high-speed signals
- Ensure that copper areas are large enough for heat-sinking high-dissipation devices, including:
• Chargers
• High-frequency gate drivers
• High power LEDs
• High-speed microprocessors
• Linear regulators
• MOSFETs
• Motor drivers
• Power amplifiers
• Switched-mode power supplies, including LED drivers
PCB Design Review: Testing
- Make sure test pads are far enough from the board edge to allow fixturing
- Check that test pads don’t create stubs or impedance mismatch on high-speed nets
- Ensure that components do not obstruct access to test pads for manual or automated testing
- Make sure test pads are clearly labeled for prototypes
- Check any signal needed for inspection or testing, includes a test point
- Ensure test points are located on the same side of the board, ideally:
• On the bottom of the board for bed of nails fixture assets
• On the top of the board for test equipment manual access
Test points are sometimes placed in inconvenient locations, often too close to other pads or near board edges. There is a risk of shorting when probing if placed near other pads. They could interfere with the enclosure or mechanical mounting when placed too close to the board edge. Because test points don’t often have a placement spec, it’s a good idea to consider moving them and identify alternative locations during a design review.
PCB Design Review: Protection/EMI/EMC
- Ensure correct creepage and clearance rules are in place for all high-voltage nets
- See if separate earth tracks/paths are needed for ESD
- Ensure there are decoupling capacitors next to connectors and vias that require them
- Check that TVS diodes or other ESD mitigation component pads are in series with the track to the component
• The ESD event must pass through the component pad before arriving at a sensitive device - Check that no track stubs/net antennas go to test points or unused connector pins
- Check that high-speed signals are routed as directly as possible
- Make sure any track carrying more than 100mA is wide enough for the current
If the PCB will be placed in an enclosure with little or no airflow, calculate or simulate the width for an internal layer instead of an external layer - SEE if an RF shield is NEEDED anywhere on the board and if it has an adequate footprint
- If it is a two-layer board, ask yourself:
• Are there any ground loops?
• Is there an unbroken ground pour under each high-speed trace?
• Is the ground track of adequate size for the return current of the device? - If multiple grounds exist, ensure they are tied together at a single point.
PCB Design Review: Panels
- Make sure there is enough frame area to handle conveyors and clamping
- Check that the silkscreen includes:
• Blanks for QA/testing marks
• Board part number and revision
• Company name
• Machine name
• Panel barcode
• Print date - Ensure that panel fiducials are present
- Look for an origin identification mark
- Check that impedance/layer/other test areas are present if needed
- Make sure that V score, milling, and tab layers are present and aligned with the board if they aren’t included in the board file
Check the panel isn’t too large for the board thickness and any milling (i.e., low flexibility/bounce)
Conclusion
While we’ve tried to make this checklist as comprehensive as possible, we may have left some things off that could be critical to your business. There may also be review items on here that do not apply to your company or project. Feel free to tailor this checklist to meet your specific needs.
Need help designing circuits for your applications? The experienced professionals at Tramonto are always available to answer your questions. Contact us today.