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What a Bill of Materials is Not

A Bill of Materials (BOM) identifies the materials, subcomponents, components, and subassemblies that have been merged to form an end product. The BOM is not a document that is put together to show an end user what a product consists of. It is not to be confused with a parts list. It is much more complex and important than that.

A Bill of Materials is Like a Recipe

A BOM is created at the same time the product it describes is being designed, built or assembled, and tested. It serves as a means of communication among manufacturing partners, whether those partners represent second sources, or are departments within a single manufacturing plant.

A BOM is somewhat akin to a recipe. As the design/build process proceeds, ingredients (parts)are added. Some parts are not a good fit, and may require modification. Some may be deleted and replaced with different parts. Just as a recipe can require a specific type and amount of each ingredient to meet the exacting standards imposed by the master chef, each of the parts that make up an end product, must satisfy exacting quality and performance standards before they can be incorporated into the BOM.

A modular, configurable power supply is a classic example of an end product that has been designed and built in accordance with, and defined by, a BOM. Each assembly has been tested to exacting standards. The same is true for each subassembly, component, subcomponent, or part. These tests may be carried out in house or by the original manufacturer. Just as ingredients are checked for freshness and taste tested before they can be included in a recipe, parts and components, especially from a second source, must past rigorous tests before they can be added to a BOM.

The Key Relationship Between a BOM and Testing

How parts and components need to be tested will depend to some extent on how the end product will be used. There will be times when a given part has not been subjected to the right types of testing to qualify it for a place in the BOM and additional testing may be needed? whether it is done by the original manufacturer or in-house.

For example, one of the critical quality factors for a power supply, whether it is a single unit or a more complex, modular assembly, is reliability. In this case, virtually every part must satisfy MTBF and MTTF criteria under a variety of conditions. Designers and testers are always on the lookout for potential weak links. Weak links are not allowed in a BOM.

Back to the concept of recipes. Ingredients must play together perfectly when mixed together, just as the parts in an assembly must perform perfectly when integrated. The Chief Engineer has the role of a master chef, and is responsible to see that perfect performance is indeed the case before signing off and releasing the BOM.

Excelsys Technologies has been a leader in power supply design and manufacturing for more than 20 years, providing high power density, high efficiency power supplies for industrial, medical, lighting, commercial, and military clients.

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