Bill of materials
A bill of materials (sometimes bill of material or BOM) is a list of the raw materials, sub-assemblies, intermediate assemblies, sub-components, parts and the quantities of each needed to manufacture an end product. No physical dimension is described in a BOM, however the rough outline should include:
Creating a Bill of Materials should include:
- BOM Level
- Part Number
- Part Name
- Unit of Measure
- Procurement Type
- Reference Designators
- BOM Notes
When creating or using a BOM, who will be using it should be considered. It may be used for communication between manufacturing partners, or confined to a single manufacturing plant.
A BOM can define products as they are designed (engineering bill of materials), as they are ordered (sales bill of materials), as they are built (manufacturing bill of materials), or as they are maintained (service bill of materials). The different types of BOMs depend on the business need and use for which they are intended. In process industries, the BOM is also known as the formula, recipe, or ingredients list. In electronics, the BOM represents the list of components used on the printed wiring board or printed circuit board. Once the design of the circuit is completed, the BOM list is passed on to the PCB layout engineer as well as component engineer who will procure the components required for the design.
Modular BOMs 
In many cases, BOMs are hierarchical in nature with the top level representing the finished product which may be a sub-assembly or a completed item. BOMs that describe the sub-assemblies are referred to as modular BOMs. An example of this is the NAAMS BOM that is used in the automotive industry to list all the components in an assembly line. The structure of the NAAMS BOM is System, Line, Tool, Unit and Detail.
The first hierarchical databases were developed for automating bills of materials for manufacturing organizations in the early 1960s. At present this BOM is used as a data base to identify the many parts and their codes in automobile manufacturing companies.
A bill of materials "implosion" links component pieces to a major assembly, while a bill of materials "explosion" breaks apart each assembly or sub-assembly into its component parts.
A modular BOM can be displayed in the following formats:
- A single-level BOM that displays the assembly or sub-assembly with only one level of children. Thus it displays the components directly needed to make the assembly or sub-assembly.
- An indented BOM that displays the highest-level item closest to the left margin and the components used in that item indented more to the right.
- Modular (planning) BOM
A BOM can also be visually represented by a product structure tree, although they are rarely used in the workplace.
Configurable BOM 
A configurable bill of materials (CBOM) is a form of BOM used by industries that have multiple options and highly configurable products (e.g. telecom systems, data-center hardware (SANS, servers, etc.), PCs, autos).
The CBOM is used to dynamically create "end-items" that a company sells. The benefit of using CBOM structure is it reduces the work-effort needed to maintain product structures. The configurable BOM is most frequently driven by "configurator" software, however it can be enabled manually (manual maintenance is infrequent because it is unwieldy to manage the number of permutations and combinations of possible configurations). The development of the CBOM is dependent on having a modular BOM structure in place. The modular BOM structure provides the assemblies/sub-systems that can be selected to "configure" an end-item.
While most configurators utilize top-down hierarchical rules syntax to find appropriate modular BOMs, maintenance of very similar BOMs (i.e., only one component is different for various voltages) becomes highly excessive. A newer approach, (Bottom-Up/Rules-Based Structuring) utilizing a proprietary search engine scheme transversing through selectable componentry at high speeds eliminates the Planning Modular BOM duplications. The search engine is also used for all combinatorial feature constraints and GUI representations to support specification selections.
To decide which variant of the parts or components are to be chosen, they are attributed by the product options which are the characteristic features of the product (business). If the options of the product build an ideal boolean algebra, it is possible to describe the connection between parts and product variants with an boolean expression, which refers to a subset of the set of products.
|Wikimedia Commons has media related to: Bill of materials|
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- BOM template used for PCB assembly – Bill of materials template used for printed circuit board assembly service.