EBOM vs MBOM: What's the difference?

The term bill of materials (BOM) can mean a lot of different things based on the context. An unfortunate fact for a document that’s so important to get right. Two of the most critical bills of materials to consider when building a system or launching a product are the engineering bill of materials (EBOM) and the manufacturing bill of materials (MBOM). We’ve written detailed posts about what makes a good engineering bill of materials and what makes a good manufacturing bill of materials, but here we want to summarize and expand on the key differences between these important documents.

Engineering BOM vs Manufacturing BOM, explained

Both are bills of materials that describe the parts and assembly make up of your product, but there are important differences between an engineering bill of materials (EBOM) and a manufacturing bill of materials (MBOM), and understanding these differences is crucial for efficient product development and manufacturing.

Here are the key distinctions between these bills of materials.

Purpose

The EBOM is primarily used by engineers for the design and development of a product. It includes all the materials — i.e. components and sub-assemblies — that are required to create a product as designed. On the other hand, the MBOM is used in the manufacturing process and has to include everything that is in the EBOM along with: manufacturing supplies like glue or solder, any spare parts, packaging materials, and/or labels that will be included with the finished product. The MBOM will also include taxes, tariffs, manufacturers costs like manufacturer value add (MVA), and other similar charges. The EBOM is the “final word” from engineering, but the MBOM has to be “the final word” up until the product is delivered.

Detail Level

The EBOM is should be only as detailed as required to build the product to meet engineering specifications. If the EBOM is not detailed enough, parts used in manufacturing might not meet the correct tolerances or values needed to perform correctly. If the EBOM is too detailed, it may remove opportunities for cost savings or risk mitigation by locking in a very specific vendor or part. The MBOM, however, is more detailed and specific and should represent exactly how a product will be manufactured. It provides a comprehensive list of all the items, parts, components, and materials required for the manufacturing process, organized in the order of assembly.

Lifecycle

The EBOM is more likely to change and develop in the early stages of the product life cycle, such as during the design or prototyping stages. Once the product design is finalized the EBOM is often "frozen" to maintain design integrity. By contrast, the MBOM is typically built only after a design has been frozen and the EBOM is finalized and is developed up as a product is transitioned into manufacturing. Once manufacturing is ready to begin (i.e. a contract has been signed with a manufacturer), the MBOM is also frozen to ensure the agreed-upon product is made consistently.

As a side note, changes can happen after the BOM is frozen in both cases but it is important to record changes via a formal Change Order (CO) process. This helps maintain a record of the what and why of each change to a product’s design or manufacturing.

Stakeholders

The EBOM is mainly used by the product design and engineering teams during design, and then by procurement, operations, quality assurance, and project management once a product’s design has been finished. The MBOM is used during contract negotiations, when setting up a factory line, and during financial discussions about the product’s performance and profitability. Both BOMs need to be closely coordinated to ensure the product can be manufactured cost-effectively and to the product specifications.

How can Bommer help?

Bommer is an indispensable tool for managing your BOM data fast and accurately. It allows engineers to work seamlessly with the most current design data by integrating BOM management with your design tools. Bommer's customization and export capabilities make it a critical tool for streamlining your design and manufacturing process.