What Materials to Include in Your Bill of Materials
As an electrical engineer, I am constantly impressed with the brilliant designs my colleagues come up with. I’m also constantly shocked to see how mismanaged most of their BOMs are. I’ve been on projects with a huge range of practices for handling a bill of materials. On one end of the spectrum, there was my senior design project, with no BOM at all, just a series of sticky notes my group placed on the front cover flap of our notebooks. Protip for those just starting out, this makes version control basically impossible.
On the other end of the spectrum was the first project I did when working as an engineer. My boss had a really tough time with most software tools and modern technology in general. At times, even email was questionable. When it came to BOM management, I was his digital-to-analog converter. I would print the latest version of the BOM for him and bring approximately a dozen pages to every single meeting or design review. It would get marked up with red sharpie, and then I’d stay late to update all the changes. Waiting until the next morning was not an option in case someone else got in before me and made changes that conflicted with the boss’s guidance.
As awful as it was to be the digital-to-analog converter for information reaching my boss, I did get a good look at what needs to go into a BOM to make sure it’s complete and accurate for production.
It’s obvious that when you prepare a BOM you’ll want to include all of your components. However, there may be more to that list than you think. In our final modules, we had a small tuning circuit where components could be added later if needed. During the main production run, these components were all listed as NP or “not placed.” We still needed to order them, though, so all the components on a module came from the same supplier.
The other BOM items that surprised me were consumables. Items like solder, glue, and wires needed to be included to make sure a production run had every material required for fabrication and assembly.
Even consumables like solder, wire, or glue should be included on the BOM.
When I was neurotically manually updating our BOM so my manager didn’t have to get trained on the software, we checked the accuracy of each item against several criteria.
Part numbers (PNs): Getting your part numbers night, even all the suffixes, is really important for ordering everything correctly. If you have similar components on the board, like different colored LEDs, or capacitors with the same packaging but different values, you should be sure the PNs are all present in their entirety.
Packaging: Sometimes, you’ll use the same component more than once, but with different packages or sizes. It’s important not to let an overzealous intern (*cough, cough*) combine them and unintentionally eliminate what you actually need. Many part numbers specify the packaging, but you should track it separately to be certain it’s not lost later in the process.
Tolerance: Depending on your application, tolerances might be absolutely critical for you, or a great opportunity to cut costs. Make sure to specify that in your spreadsheet, so you’re managing your money and assembly as effectively as possible.
Quantity: When you use reels, manufacturers often require extra components to compensate for losses due to loading. You want to account for those losses in your initial order, rather than be surprised when they can’t finish a manufacturing run.
There is a lot of information to manage in a spreadsheet, so you should be sure you’re keeping track effectively.
Hopefully, you’ll never have to simultaneously manage both manually and in software. It’s so much better to work with software that makes BOMs so easy, your boss can do it. Altium software has a great BOM tool. Its version control and interfaces are easy and intuitive. It even helps you source your components, so you can ensure quality controls throughout your product life cycle.
Have a question about using BOM software? Contact an expert at Altium.