Recently, we replaced the dishwasher in our house. We’ve had it for many years, and it was starting to leak water all over the kitchen floor. Part of the purchasing process included a list of questions for us to answer. Some, like the dimensions of the old dishwasher, were expected. Others, such as the slope of my driveway, surprised me. The appliance store simply wanted to make sure that the delivery and installation of this new dishwasher wouldn’t have any problems.
Do you know that when you send your PCB design fabrication and assembly data to a contract manufacturer, it goes through a list of questions, too? The CM is obviously not looking at the slope of your driveway, but they do want to make sure that your circuit board can be built without problems according to the data that you have provided. This is called the PCB design review process, and your CM will be looking at several different aspects of your design to make sure that it is completely manufacturable. Here are some of the details your CM will be looking for when your board goes through its design review.
Why Does Your Project Need a PCB Design Review?
You probably have already designed many PCBs in your career, and this current design you are about to have built is very similar to those that you’ve done before. With your final checks and sign-offs complete, the design is ready to go and the fabrication and assembly data has been submitted to your PCB contract manufacturer. Since you have been working ahead with your CM, you already know that the design circuitry has been vetted in the project kick-off meeting they hosted. So why do they still need to do another design review?
To put it simply, the pre-manufacturing design review is to check for those things that a customer may not realize they’ve missed. Once the manufacturing process has begun, there could be a lot of wasted time and resources due to mistakes that could have been discovered during a review. Sometimes, the errors can be dealt with, such as vias in pads that cause soldering problems or isolated traces that won’t etch correctly.
The CM can use their experience to correct those during manufacturing if necessary. However, larger problems, such as non-optimal layer stackups or obsolete parts, could derail the manufacturing process completely. To guard against problems that could slow or even stop production of your board, here is what the CM will be looking for in their design review.
What Is the PCB Design Review Process?
To ensure there aren’t any problems during fabrication and assembly, your CM will conduct a final design review that will look at the following areas:
- Bill of materials (BOM): This is to verify the availability and lead times of all components to be used in the design and identify any components with minimum order quantity (MOQ) issues. Components that are found to be classified as not recommended for new design or obsolete will need approval before proceeding.
- Fabrication: This will confirm that the requested materials and board layer stackup will work as expected together with the plating requirements and component footprints. Other mechanical considerations, such as the drill diameter versus the board thickness, will be checked for compatibility, as well.
- Schematic: As the circuitry functionality has already been vetted during the kick-off meeting, the schematic is now checked against the test specifications provided by the customer. Any adjustments to the layout that are discovered during this review will be examined closely and sent back to the customer for their approval.
- Layout: Next, the component footprints are validated for accuracy, as well as their PCB placement for assembly challenges. Trace routing and power planes are examined for manufacturability issues, such as isolated traces and copper balancing of the planes. Finally, a complete design for manufacturability (DFM) analysis is done to confirm that the board is ready for assembly.
- Assembly: At this point, the critical assembly requirements of the board, such as unique hardware mounting steps, are identified. The panelization requirements are also defined, which includes looking at any panel and component conflicts, and the PCB design is incorporated into a production panel design.
- Netlist comparison: A final comparison between the schematic and the layout will be recommended if the reviews have turned up issues that weren’t expected.
These steps are generalized and will vary from board to board and between different customers depending on the types and formats of the manufacturing data that is received. Contract manufacturers typically have a lot of experience with multiple styles of design data, giving them the flexibility to work with a wide range of customers.
Once Your Design Is Reviewed, Here Is What You Can Expect
A design that doesn’t have any problems show up during its pre-manufacturing design review is ready to go into production. If the design review does turn up some issues, however, a quality contract manufacturer will work with you to resolve them.
If your production volumes aren’t high, and you are trying to maintain a tight schedule, your CM will likely use their manufacturing expertise to resolve as many issues as possible to achieve your schedule goals. If the design is expected to move toward higher volumes, however, you can expect your CM will urge you to go through a corrective action cycle to clean up the problems. By engaging with you early, many of these types of problems can be caught and corrected before your design ever gets to this final review.