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Manufacturers rely on the information that is included in the bill of materials (BOM) to build a product. The bill of materials typically includes part names, part numbers, part revisions and the quantities required to build an assembly. Thorough BOMs can include more descriptive information too, for example, the unit of measure or procurement type. BOMs that have printed circuit board assemblies (PCBAs) contain a column for listing reference designators.
To manage what can be a tremendous amount of information, companies often use either Excel spreadsheets or a dedicated BOM management system like Arena. Below are examples of how a bill of materials for a GPS navigation product would look in each system.
The great thing about using spreadsheets for your bill of materials is that they are flexible and can be formatted however you like. The bad thing about using spreadsheets for BOMS is that they are flexible and ANYONE can format them however they like, often resulting in inconsistencies across a company’s BOMs.
The screenshots below illustrate three ways of formatting an Excel spreadsheet bill of materials for a GPS navigation unit: the first is very basic, the second includes a header to make it more readable and the third uses a graphical element to show parts’ relative positions within the BOM.
The basic BOM format separates information into columns. It contains BOM level, part number, part name, revision, quantity and reference designators.
It is helpful to have unit of measure and BOM notes on a bill of materials as well. The first line, with a BOM level of zero, is the top-level product or assembly to which everything else in the bill of materials reports.
A header provides a clear overview of what your BOM contains. When your top-level product or assembly information (level zero) is included in the header, it should not be repeated below. The items in your BOM should now start with level one.
Users can quickly scan bills of materials and understand where particular parts are located when each level is denoted with a marker (e.g. a star).
The numerical BOM level is included too. With the correct Excel formula, this number can automate the placement of the visual marker in the correct column.
As you’ll see below, dedicated BOM management software like Arena differs from Excel in some significant ways. BOM management software uses a database, which allows quick reconfiguration of information and an unlimited number of one-to-many and many-to-many relationships. It also allows for complementary information, like drawings, part specifications and supplier options, to be included in a BOM without additional overhead. Here are some examples of how the same GPS navigation bill of materials can look in Arena.
An indented BOM in Arena contains all the same information as an Excel BOM: part name, part number and quantity information. However, the Arena BOM can be exploded or collapsed at each assembly level in order to see more or less depth as needed. It also includes links to more detail on individual subassemblies, parts and files.
In Arena, part data and sourcing information are linked together so users can quickly view the manufacturing information for each item on a BOM.
The redline BOM view in Arena offers a clear visual comparison of two revisions of a bill of materials. Additions and deletions are shown in red. The revisions being compared can be adjusted through the revision drop-down menu.
The BOM comparisons view in Arena has built-in capabilities that allow the differences between two similar BOMs to be easily compared. Item lines with differences are marked with red arrows on the left and those differences are marked in red on the right.
The screen shot to the right shows modifications in quantity, but differences can be shown for any attribute.
Some parts are used in more than one product or assembly. When a change is made to one of those parts, the information must be updated in EVERY location the part is used. For Excel spreadsheet users, this task may involve lots of searching through folders or working with fragile cross-linked formulas to find and update every occurrence of the part. In Arena, where the connections are built in, the update propagates automatically to every location of the part and can be easily reviewed.
The “Where Used” view for any part in Arena lists all the assemblies that include the part and that would be impacted by modifications to it. Top-level assemblies that contain the part are also noted.
Regardless of whether you use Excel spreadsheets or a dedicated BOM management system, your BOMs must contain complete and accurate information in order to be useful in building quality products. The BOM spreadsheet examples above and the Arena article on managing your bills of materials in Excel provide valuable information to help keep your BOMs in control.
See common problems with managing your BOMs in Excel and compare Excel with a modern BOM management system
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