Baby, it’s the BOM

The importance of the Bill of Material (BOM) can’t be stressed enough in the electronic contract manufacturing (ECM) world. The BOM needs to be thought of as the “bible” of product manufacturing, with authority over all people and other documents, lesser documents bow in presence of the BOM.

Having been in the contract manufacturing business since Intel’s leading edge product was the 16 pin DIP Eprom, I’ve seen BOMs in every imaginable format. From the many hundreds of customers that I’ve have manufactured products for, most get that the BOM is driving force behind the entire process. Surprisingly though, there are a higher than expected number of companies having work done by electronic manufacturing services (EMS) companies that need a little guidance. For the multitude of companies getting it right, good job, your ECM, or EMS thanks you, there still may be some useful info in this post for you too.

This is really for the folks that are driving their suppliers crazy and don’t know it. In my opinion, probably the most important thing for customers to remember is that they should never relinquish total BOM control to their supplier. Sure, your ECM will need to alert you to BOM changes for many reasons like obsolete and changing manufacturer part numbers, errors, typos, etc. A good supplier should also be providing specs & samples and requesting approval from you for component substitutions for cost reduction and availability reasons. The point is, even if your supplier has well organized and well documented substitution approval procedures; make sure that BOMs in your possession are always accurate. Believe me, your supplier wants you to be in control of the BOM and will be glad to help maintain accuracy of your documents. A good supplier would never want to risk a BOM discrepancy dispute later, take advantage of it.

BOM File Format The most common format to share BOMs between supplier and customer is MS Excel. Not only is Excel a universally common application but most MRP systems are able to import and export to that format. Providing the BOM in a digital format like Excel is important to help keep typos and data entry errors to a minimum. Digital file formats and file sharing techniques between supplier and customer can vary greatly; discuss it with your supplier early in the program.

BOM Rev Control Yes, you should use revision control on your BOM. Suppliers are accustomed to working within many different customer rev control systems, the important thing is to use one and maintain it well. I have observed customers using rev letters, numbers, combination letter/number, and even a date to identify and successfully control BOM revisions. I personally don’t have a strong preference as to the method, just keep it current. To close the loop on quoting and building the correct product version, it’s a smart idea to include the BOM rev on the RFQ, quote, PO, and assembly.

Indented and Multilevel BOMs There are so many different opinions about Indented BOMs that I was not planning on going into too much detail about it. Indented and Multilevel BOMs generally refer to material required to assemble subassemblies that are assigned their own part numbers. The process can get complicated with components changing part numbers as work is completed. To further complicate matters, various MRP programs manage the process differently, coordinating between customer and supplier documentation systems can be a chore. I can’t offer “one size fits all” solutions here, all I can do is raise awareness and recommend that customers and suppliers have the conversation early in the program.

Next time we’ll talk about BOM content, really fun stuff. See part 2 “You Can’t Say BOM on an Airplane” Thanks for checking out the blog, I encourage and welcome any questions, comments, or input.