PCB Layout Review Checklist

Key Takeaways

• The PCB layout should be reviewed by the team working on the project to confirm its manufacturability. 

• In component placement, check the clearance for IC extraction tools, socketed ICs, and electrical isolation of mounting holes.

• In routing, check whether the analog and digital signal commons are interconnected only at a single point.

Completing the PCB layout review checklist is necessary to ensure money and time isn’t wasted on printing faulty boards

As the number of pieces on a circuit board increases, printing becomes cheaper. However, contrary to what you might think, this affordability can cause trouble in the PCB design process. Imagine you are printing 25 pieces of a 6-layer PCB board and, later, you find mistakes in the circuit. If it's up for product development, then the board will need to be discarded. This is why a PCB layout review checklist is so essential. Once the PCB design is ready, engineers must ensure each step of the layout review checklist is complete before sending it to the manufacturer. 

PCB Layout Reviews Catch Unexpected Errors

PCBs may consist of several circuits, and each of these individual circuits contain passive and active components. In the worst-case scenario, if one of these components is missed in the layout design, the circuit board will not function as intended and must be discarded.

Another scenario that engineers sometimes encounter is when all the components are in the circuit board but a few are misplaced. This kind of component misplacement can lead to unexpected errors. This scenario requires a PCB respin. 

Interdepartmental Reviews

The manufacturability of the PCB design needs to be inspected before sending it for printing. The PCB layout should be reviewed by the team working on the project to confirm its manufacturability. A review should be conducted not only by the electrical engineering team but also by any other departments involved in the workflow.

In certain cases, mechanical roadblocks can be identified through interdepartmental review meetings. For instance, mechanical engineers who guestimate the board area or the outer packaging of the product are not involved with the schematic or bill of materials. They just put together the mechanical design and interface components and define the PCB layout area equal to the remaining area. Sharing the completed layout design with the mechanical engineer can help detect any component height mismatch with respect to the outer covering. They can also help modify the design to more easily harness wires.

Irrespective of the complexity or size of the board, it is good to have a PCB layout review checklist so that the review process can be streamlined in an organization.

Before PCB Layout Review

PCB Layout Review Checklist

The PCB layout review checklist has five steps: 

Component placement

•  Check SMD component orientation consistency, polarized components, the orientation of connectors, component body spacing, bypass capacitors near IC power pins, series terminators near the source, I/O drivers where the signal leaves the board, the label of test points, and SMD pad shapes.

•  Check the clearance for IC extraction tools, socketed ICs, and electrical isolation of mounting holes.

•  Check whether the through-hole components are placed on a 50-mil grid. 

•  Check whether the EMI filters are located closer to the entry and exit points in the shielded areas. 

Routing 

•  Check whether the analog and digital signal commons are interconnected at a single point.

•  Check for traces running under sensitive or noisy components, susceptibility to solder bridging, and dead-ends. 

•  Avoid vias under poorly insulated parts.

•  Provide multiple vias for low impedance or high current traces. 

•  Observe the component and trace keep-out areas.

Dimensions

•  Check whether the hole diameter on the drawing indicates finished sizes after plating.

•  Ensure the trace width is sufficient for the current to be carried.

•  Ensure sufficient clearance for traces handling high voltage.

•  Note through-hole drill tolerance, through-hole solder mask tolerance, through-hole route tolerance, and through-hole silkscreen legend tolerance.

•  Make sure finished holes sizes are 10 mils larger than lead, silkscreen legend text weight is greater than 10 mils, pads are at least 15 mils greater than finished hole sizes, components are placed at least 0.2″ from the board edge, and traces are routed at least 20 mils from the board edge. 

Silkscreen

•  Verify the silkscreen to ensure the revision number, blank space, and date are updated.

•  Check component labels for connector pins, ICs, LEDs, mounting holes, etc. 

•  Make sure the fuse wire details are included.

Mechanicals

•  Verify the connector arrangements and placement. 

•  Check whether there are any unwanted layers; if so, remove them. 

•  Examine the position and arrangement of various components on the board by the 360-degree rotation of the 3D file. 

Ensuring the PCB layout review checklist is complete is essential to ensuring the design process doesn’t waste money or time. Cadence’s PCB Design software offers 3D tools, an interconnect floor planner, and a host of other calculators, routers, design rules, and constraints to support designers in working through the steps of the PCB layout review checklist process.

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