Checklists play a crucial role in various aspects of life, serving as reliable tools for ensuring tasks are completed successfully. Airline pilots employ them to verify landing gear deployment, while shoppers utilize checklists to prevent overlooking essential items like eggs. Checklists are integral to our routines, providing a structured approach to tasks.
In the realm of PCB design, checklists also prove invaluable in preventing oversights. Although components and nets placement is typically straightforward, and tools automate the creation of silkscreen part outlines and reference designators, there's a potential area of oversight when it comes to the diverse labeling requirements of a PCB.
Ensuring comprehensive labeling on your design involves two key aspects: identification labels and markers facilitating PCB manufacturing. Having personally encountered the ease with which these elements can be overlooked during board design, it becomes essential to conduct a thorough "design complete" checklist before sending it for manufacturing. Let's explore the various labels and markers that should be included in this checklist.
The initial category of labels and markers imperative for your design includes identification labels. These labels are crucial for accurate board identification and alignment with the bill of materials. The omission of these labels can lead to confusion and errors. Consider incorporating the following types of identification labels:
1. PCB name
2. Serial number
3. Model number
4. Fabrication number
5. Assembly number
6. Revision number or letter
7. Any additional identifiers, such as FCC numbers, etc.
8. Clearly designated areas for manufacturing stamps
Typically, these labels are etched onto the top or bottom layers of the board. Some companies may mandate covering the labels with identical text in silkscreen to enhance visibility. The specific labels required can vary between companies due to different standards. It is essential to include the labels mandated by your company, and employing a checklist can assist in ensuring their inclusion.
In addition to identification labels, it is crucial to incorporate markers and labels essential for the manufacturing process into your design. Failure to include these markers might result in the design being rejected by the manufacturing process – a lesson learned from personal experience. Here are key markers and labels commonly utilized in manufacturing:
1. Layer Number Markers: These small blocks, situated within the board outline, feature sequentially placed numbers for each layer of the board. They serve as a rapid verification method to ensure all board layers are correctly stacked.
2. Global Fiducials: These small metal pads, positioned on the top and bottom layers within the board outline, act as reference points for automatic pick and place machines during manufacturing.
3. Targets: Placed on the outer edges of the board outline, targets are utilized for layer registration. While not as critical as in the era when PCB layers were manually aligned during manufacturing, targets still provide a valuable check for the final layer-to-layer registration.
Here's an additional tip that could prove beneficial for your design process. Incorporate essential labels and markings at the outset of your design, or ensure there's adequate space reserved for them from the beginning. Discovering at the end of the design phase that there's insufficient room for a crucial element like the serial number can be disheartening. While others may not be affected by the need for redesigning to accommodate overlooked details, it can be personally frustrating.
Another important consideration is when making revisions to a design. It's imperative to revisit the checklist and update identification numbers accordingly. Revisions may alter some or all of the identification numbers on the board, and neglecting this detail can lead to significant consequences. For instance, if a revised design introduces new functionality without changing part numbers, it becomes challenging to differentiate the new board from the previous version. This can result in manufacturing and testing errors, potentially causing product failures and substantial costs for repairs and replacements. Ultimately, any inaccuracies may be traced back to you.
Having a checklist to ensure the inclusion of labels and markings is immensely helpful. Personal experience has taught me the challenges that arise when these details are overlooked. These labels play a crucial role in aligning your board with the bill of materials and other PCB documentation. Accuracy in labeling is paramount, and it is your responsibility to ensure their correctness to avoid a myriad of potential problems.
