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5 Tips for BOM Structure

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A bill of materials (BOM) is an important component to product manufacture and design. Without an effective BOM, your product will suffer through countless unnecessary revisions, build problems, and delays. To help you experience a smooth manufacture and product design process, we've compiled 5 quick tips for structuring your BOM:

1) Decide what you need from the BOM.

It may be tempting to simply draw up a BOM around how the product is structured, but a BOM is only as good as its functionality. Ask yourself:

  • Who will be working with the BOM: engineers, designers, or a third-party manufacturer?
  • Is the product configurable?
  • What is the risk of parts involved - is one part expensive or does it have a single-source vendor?
  • Will multiple products use the same sub-assemblies?

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2) Know what type of BOM you're making.

The next step is to choose a type of BOM based on your needs. If your BOM is largely for product design purposes, you'll want an engineering BOM (eBOM). If your BOM needs to explain exactly how a product is built, you'll use a manufacturing BOM (mBOM). 

Each type of BOM involves a different structure and level of detail. For example, an eBOM may only list parts related to a specific function of the product, like listing resistors, capacitors, and chips for a circuit board. An mBOM, on the other hand, must list absolutely every material needed to create the product.

3) Decide how many levels your BOM includes.

After choosing the type of BOM you need, you'll need to decide on a single-level or multi-level BOM. Single-level BOMs are good in cases where:

  • The goal of the BOM is to give a broad overview of the product.
  • Those using the BOMs do not need to see the overall structure of the product's design; electrical engineers, for example, may only need to see the wiring schematic.
  • You need your BOM to provide an overall part summary in one location.
  • Lean or pull based manufacturing often favors a flat single-level BOM.

Multi-level BOMs require more work and may require ERP software to use efficiently, but they come with the following advantages:

  • Sub-assemblies can be copied to other products.
  • You can share only a portion of your BOM with manufacturers or other partners.
  • Products can be changed quickly, which is particularly good for configurable products or products that need a part substitution.

For multi-level BOMs, you'll need to decide how detailed they will be. Do you drill all the way down to raw materials, or do you only include known off-the-shelf components? Deciding this will help you figure out how many levels to include in your BOM.

4) Build in support for explosions and implosions.

Unless your product only consists of a few parts, you will likely need to include support for explosions and implosions. Explosions are simply taking an assembly and viewing its necessary components. Even if you have a single-level BOM, you may need to make explosion BOMs to help engineers or your manufacturers.

Implosions, on the other hand, allow an engineer or manufacturer to see what components or assemblies a specific part is used in. This can also help you determine what components are linked to at-risk parts.

5) Include only the information you need.

The most important thing to keep in mind when structuring your BOM is that it should only be as complex as you need it to be. It may seem smart to build a multi-level BOM that drills down to raw materials and includes every piece of information you can fathom, but this level of detail could actually make things more difficult for you. Carefully evaluate your needs and build your BOM around those.