This post is part of a series on bill of materials (BOM) basics. This talks about the common consequences of having an incorrect BOM in engineering and manufacturing. For an introduction to bill of materials, the BOM acronym in manufacturing or BOM meaning in manufacturing, please see our blog post "What is a BOM".

The BOM drives manufacturing

The devices we love or enjoy using every day, like the cars we drive, are all made up of parts. To build these devices, engineers and other members of a product development and manufacturing team need to figure out where those parts are coming from. This information may be represented in the engineering bill of materials (EBOM) or as part of the manufacturing bill of materials (MBOM); the most important thing is to make sure the information is correct. If your BOM is incorrect, there are many things that can go wrong when ordering parts or assembling the final product.

Where do BOM errors come from?

Overwhelmingly, we see that BOM errors come from manually building a bill of materials document from the users' "source of truth," e.g., their CAD, PDM, or ERP, into a spreadsheet that then gets used to order parts or drive a manufacturing line. This can include manually counting parts (to populate a quantity field) or copying and pasting properties from CAD into cells in a spreadsheet. There are other sources of BOM errors, including revision control failures (i.e., using the wrong revision of a document) or design errors (i.e., inputting the wrong data into the design system), but we'll focus largely on the manual BOM building errors in this post because we see them as the most preventable given the correct tools.

What are the consequences of having an incorrect BOM?

The consequences of an incorrect BOM can vary depending on the stage of a product’s design and manufacturing, ranging from manufacturing errors that cause severe risk to your company or brand to a little additional engineering work to fix a typo. Let's work backwards from product launch to design and engineering and talk about the consequences at each step.

Product Launch: Quality and reliability failure

There is an error in your BOM related to the color, materials, finish (also referred to as CMF), the tolerances, the heat or electrical rating, or similar. After the product is launched and offered for sale, a customer buys the product and it fails to work. In some cases, it may fail in a way you didn’t expect. There are some electronic components that will catch fire if they fail. If you accidentally specify such a component in your BOM — or your manufacturer uses them because you didn’t tell them not to — and you didn’t expect or want your product to catch fire, you’re in trouble. This is the absolute worst time to find a manufacturing error in your product. Your brand or company now has to deal with the fallout of this error, and the costs to recover are going to be very high.

Manufacturing: Increased production costs and inventory waste

Same error as above, but it is caught before the product leaves the factory. Now you might have a bunch of parts sitting in a factory warehouse that you’re financially responsible for, but you can’t use those because they’re not applicable to your design. You might have a tool that you’ve paid hundreds of thousands of dollars to build that won’t produce the part that you need. To fix this, it will require you to spend money that is out of your budget, which can kill your product line or your company, depending on the severity of the problem.

Supply Chain: Inventory and supply chain disruption

You have a breakdown in your supply chain. Maybe you’ve contracted with a manufacturer for 10,000 units, but the BOM you sent to your supplier said 5000. Now you have an idle factory line, you have to deal with a manufacturer asking where you’re going to get those parts, and you can’t ship to meet your demand.

Purchasing: Bidding process delay

Your purchasing department ships a bid packet you prepared to your contract manufacturer, and the BOM doesn’t match the CAD or drawings. If you or your manufacturer’s engineers catch the BOM error in the bidding process, you could fairly easily fix it, though they’ll charge you money and you’ll waste time.

Engineering: Inaccurate design or documentation

Your engineer (or you) catches an error before or during the design process, before it even leaves their desk. It quite literally takes a couple clicks to fix: they just have to spend a few minutes to make corrections and away you go.

How can I ensure the BOM is correct?

As you can probably see, it’s relatively cheap to fix these design and manufacturing errors when caught in the engineering or purchasing stage and horrendously expensive to fix them after a product has begun mass manufacturing or has launched into the market. In an ideal world, you would avoid introducing errors when data is generated, and you would ensure that your BOM is well specified at each step of the manufacturing process.

The best way to achieve this is to start with a good foundation: automate the process of building your engineering BOM from your engineering data and ensure it includes all necessary critical-to-quality attributes. You can use an automation tool like Bommer ( to generate your bill of materials with any properties you like, from CAD, with just a few clicks and no manual counting or data entry. Starting off with accurate and complete data will set you up to avoid nearly every consequence outlined in this post.

Spend less time on your BOM with Bommer

Our products plug into CAD to make it easy to populate and export your BOM from CAD, saving engineering time and reducing potential for common errors like miscounting, omitting parts, or mistyping a critical-to-quality property. See for more info, or contact us for a demo!