What is the Importance of BOM in PCB Assembly

Apr 23,2019 A PCB production involves several raw materials, which need to be assembled before the actual production begins. How to determine the raw material requirements of a PCB? A Bill of Materials (BOM) is the answer. A proper bill of materials for a PCB assembly enables you to know the exact components and materials required along with their brand, quantity, dimensions, and other details. Typically, in case of a PCB assembly, the BOM comprises the list of wires, boards, surface mount components, and circuitry requirements among others. This post discusses the significance of BOM for a PCB assembly and other related factors.

What is a Bill of Materials (BOM)? 

A bill of materials (BOM) is a list of raw materials, components, and parts required to manufacture a particular end product. It primarily comprises part numbers and names, and quantity. It may also have the manufacturer or supplier name, a column for additional features and a comments section. It is a key link between the customer and the manufacturer that gives details about procured items. It can also be given to an in-house department if the product is to be made within the organization.

Why is a BOM Important for a PCB Assembly?

Designing a PCB and then assembling a number of PCBs is quite complex. Hence, it is essential that you fill the information in it accurately. Here are some reasons by BOM is important:

• This list comes handy, so you exactly know the materials you have, the quantity, and the remaining parts you require.
• It also gives an estimate of how many employees you would need for a particular assembly, based upon the parts procured.
• BOM helps in proper planning and smooth functioning.
• BOM is required when audits are to be carried out, and it helps keep track of the parts bought and the ones available in the inventory.
• It is crucial to getting exactly the part you want or made by a particular manufacturer.
• In case, it is unavailable, other options can be discussed and provided immediately.

  Factors to Consider When Making a BOM

  If you receive an order for 50 PCB assemblies from a consumer electronics manufacturer, here are some points to consider when making a BOM:
  • It is not a good idea to consider the entire quantity, that is 50 PCB assemblies at once, based on what you think would be required.
  • Instead consider one PCB assembly, find out the type of PCB and the components required and enlist the part details for just one assembly.
  • Let your team of engineers figure out all the parts required.
  • Send the list to your client for verification.
  • Almost always, you may require more than one BOM.
  • Finalize the BOM after final discussion with your team and the client.
  • It is crucial that your BOM can answer “when”, “what”, and “how” questions pertaining to the project.

  Format of BOM for a PCB Assembly

  Here is how a sample BOM for a PCB assembly with arbitrary values looks like:

  Date	Customer
  Date of BOM generation	Customer name	Code

  Sr. No.	Part Number	Part Description	Package
  1	P001	Red, 50V	AB-1234	50 units	XYZ Mfg.	Replacement part
  2	P002
  3	P003

  So, one should never do a BOM hastily as it is quite easy to miss out some parts or mention wrong quantities. This will lead to a lot of back and forth mails and waste of productive time. Most companies give a format for BOM, and it is convenient to fill up. But apart from the BOM, it is essential that your PCB assembly is accurate and functioning well. So, it is essential that you deal with a reliable manufacturer and service provider of PCB assemblies. Sierra Assembly is a US-based manufacturer of PCB assemblies.