Trying to assemble a printed circuit board (PCB) or electronics assembly without a quality bill of material (BOM) is like trying to put together a puzzle without a picture to reference. Critical to the quality of an electronics manufacturing project is a complete and accurate BOM.
The BOM is more than just what parts and pieces are included to build your product. The BOM provides:
- quantities
- part names
- part numbers
- descriptions
- reference designators
- manufacturer
- relevant notes
Creating a BOM is easier when you have a parts library. This parts library consists of a list of overarching part numbers that contain an approved vendor list (AVL) for that part. For instance, a part number for a 10.0k ohm, 1%, 1206 resistor might be RS62-1002-RC, which references the following for a AVL:
Building a BOM from an established parts library allows you to select a component without have to re-specify on every BOM. It also creates standardization so that multiple projects are using common components, eliminating multiple purchases of like components that can increase on-hand inventory and costs. When the BOM is created, it’s important to get as many details as possible as this is the text version of your blueprint. The context required for the build is just as important as the components.
Leave No BOM Detail Behind
If you are working with a design team who needs to put together a BOM, we recommend instructing them to provide as much detail as possible. Even the seemingly obvious items.
Consider this: If you are a model airplane builder, it’s a given you will need glue or a solvent to build your model. But if you’ve never attempted to build a model before, you might assume the pieces just click or snap together. Not knowing you need glue, means you might not have or use glue, and while your finished model might superficially look okay, as soon as you touch it, will fall to pieces.
Keep the BOM an Evolving Document
As the product lifecycle progresses, be prepared to update, edit, and revise the BOM. And all parties involved need to have processes in place and be ready for ongoing change. Suppliers may not be able to provide components, regulations shift which may affect what parts you can use, or technology may change and better options may become available. The world moves pretty fast—the BOM has to keep up. Using a parts library allows you to add equivalent or replacement parts to an AVL without having to revise the BOM. As long as the parts are a form, fit and function replacements, they can be added without risk.
Which BOM Works Best?
Because every design firm, manufacturing company, and product is different, there are no standard, one-size-fits-all templates for a BOM. Everyone is partial to their own methodology of delivery—whether they use spreadsheets and shared drives, a product lifecycle management system, or proprietary software or programs. Further, within each system of delivery, everyone is partial to their own organization structure—whether they use a hierarchy of priority or a flat system, giving everything the same importance. Whatever method for delivery and organization is used, the most important part is to ensure it is understandable, clear, and detailed enough for the manufacturers to get everything they need.
Practicing the BOM Makes Perfect
Going through the BOM—and sharing it with additional parties to ensure it is “dummy proof” is one great way to make sure the level of detail has captured what is needed to build the product.
Consider the airplane model again. If you have built a model before, glue is such a given that you might not notice the omission of it in the instructions. Show the directions to someone who has never built a model airplane and see if they can follow each step with no previous experience or context (note: in BOM scenarios, building isn’t necessary—just have someone review the components to see if they make sense). Capture their questions, concerns, and feedback to add further details or comments to the BOM.
“How does this airplane stay together if there is no glue involved?”
Note: Add glue to the supplies list. Update directions to include glue use.
Once this person can build the airplane, your BOM is probably sufficient.
Need a BOM Head Start?
We’ve created a simplified BOM template that, while it won’t work for every project and company, is an excellent start with the minimum of requirements. BOM-TEMPLATE