Bill of Materials for PCB: Part Numbering Systems and Organization, or Packing Tetris?

Created: January 10, 2018
Updated: September 25, 2020

Girl sitting on back bumper of car with beach gear in trunk

It would be great if spending a day at the beach didn’t require gathering towels and chairs, fixing lunch, and making sure there was enough sunscreen to go around. Swimsuit selection, packing up, and traveling are also unpleasant chores. It would be nice to just think “beach” while sitting on the couch, and suddenly be comfortably working on a tan with your toes in the sand. That’s the thing about organization though; it’s what really gets us where we want to be.

It would also be nice to just think about my design and have it made while I’m relaxing on my couch. Unfortunately, I don’t think technology has gotten that far yet. Unlike the last-minute details for what you need for a vacation, though, you should never have to last-minute detail what you need for your PCB design. By carefully planning in your approach to your Bill of Materials for PCB manufacturing you will get closer to that overdue vacation.

Common BOM Values, and Part Number Organization

There are a lot of options to consider when deciding what should be included in a BOM. Creating a template with everything that might be needed is a good place to start—it’s always easier to narrow a wide pool than it is to expand a small one. Some items are pretty much universal such as component designator, value, quantity, and price. Others such as part number assignments are less definitive but can make a big difference in terms of easily organizing important functions within the company and with its suppliers.

Depending on the size of a business, whether in-house board assembly is used, and how inventory is managed, your inclusions to a BOM will vary. Figuring out how to manage the PCB part numbering system for electronic components is one of the most important and difficult chores. If your strategy is correctly organized there will be less time wasted on unnecessarily long documentation, or worse, on confusion. This means more moments of being barefoot on a beach.

Rows of labeled drawers with cans on a countertop.
Don’t resort to organizing yours with an unclear or unoptimized system.

Understanding The Types of Part Numbers

At the end of the day, the goal of any organizational system is to make your job easier now and in the future. That’s exactly the mindset you should be thinking about while getting to know your part numbers, and choosing which organization systems are best to include in your practices. There are at least four types of part numbers that should be considered for inclusion in any Bill of Materials:

Manufacturer Part Numbers: The manufacturer part number enables engineers to determine the device’s capabilities and specifications, can help contract manufacturers find alternate suppliers, and is a good starting place for ensuring compliance. Make sure to have a plan in place to define and prioritize alternate components. Changing the manufacturer part number of a component part number in a BOM involves significant risk and should be carefully orchestrated. Do not wait until a component becomes impossible to source before you organize and test your system for dealing with alternates.

“As Ordered” Part Numbers: Another common part number is the “as ordered” or supplier part number. This is the number that a purchasing agent requires to be able to order the correct device. These sometimes include all or part of the manufacturing part number, and usually include whether or not the part requires packaging that allows for automated assembly. A contract manufacturer (CM) may not reference this number for purchasing, though it might help with error checking and allow for quick answers to questions they may have. For internal builds such as proof of concepts and early prototypes, this part number will be important.

Generic Part Numbers: Generic part numbers are definitely more useful than sand in your socks. One way these are used is when a designer is searching for a standard component for a new design. For example, they may search for LM317 to find an already defined and readily available adjustable regulator, and use whichever manufacturer’s part is convenient. Also, Technicians looking at a BOM can read “BC171” much more readily than a typical manufacturer part number, and quickly identifying that part as an NPN transistor may expedite a troubleshooting process. For many intents and purposes, generic part numbers can often be left off; though, the occasional convenience makes them nice to include if it doesn’t take too much effort.

Internal Part Numbers: The organization of a company’s physical inventory and digital part library can be greatly aided by the use of internal PCB part numbers. Companies having small inventories can sometimes supplant this requirement by using manufacturer part numbers along with a “part type” or “library reference” field associated with each BOM component part number. An internal part number strategy might be to make all jacks start with 100- and all switches with 200- and so on. Alternatively, they could be made searchable by defining a variable named “JACK” and “SWITCH” for the respective groups. Both can be useful, especially if there is a large inventory, and many types of components whose internal PCB part number prefixes may be difficult to always remember.

Hands marking document with numbers on it
Know which numbers organization will be most helpful and convenient to you and your team.

Software Setup for BOM Organization

Given the number of options available for the PCB part numbering system alone, it is obvious that having flexible software is important when it comes to organizing bills of materials for PCB design. Your bill of materials needs to be able to have comprehensive templates, clear walkthroughs for every step of the BOM production, and easy outputs. Furthermore, the best BOM software out there will give you real-time component obsolescence management, enabling you to avoid pesky manufacturing errors that will cost you time and money.

Industry leaders will go above and beyond the basic level of organization for BOMs, and Altium’s ActiveBOM delivers nothing short of real-time pricing, availability, supplier shortage alerts, and the ability to provide solutions for difficult BOM problems such as alternates and variants.

Quit fooling with that silk screen, and get ready for some sunscreen! Give Altium a try today and contact an expert at Altium to find out more.

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