What is BOM File in PCB Assembly

Posted on 2022-03-24


A BOM is a comprehensive list of raw materials, assemblies and sub-assemblies, components, and other crucial items for product manufacturing. PCBA manufacturers must depend on the information included in their BOM to run the PCB assembly, so it has to be highly accurate and sufficiently detailed. Customers use BOMs to explain to PCB assemblers what exactly will get populated on a printed circuit board when they place an order. As a professional PCBA manufacturer, PS will get started with PCB assembly by creating a bill of materials (BOM).

A BOM file serves as the foundation for building the product. It’s a fundamental set of data, used throughout the process. A well-constructed BOM file clearly communicates all of the technical ingredients required to build the product.

From this information, it’s possible to determine:

Lead-time to procure the materials
Cost of Goods Sold (COGS)
Manufacturing processes
Quality of the Design for Assembly
Supply chain robustness
Cash flow requirements

What You Need to Know Before Creating a BOM file?

What are you building?

Before you move on to the BOM step, you should have at least begun the design phase of your project. If you don’t, you won’t know how to prepare your BOM file. You might start compiling information about the parts you need as you design, but you can’t start creating a BOM in earnest until you have your design ready. You should have made sure your plan worked as expected and produced a Gerber file, which explains the design information for a PCB to the manufacturer. This step will help you determine what parts to include in your BOM file.

How will you manage your BOM?

As you create your BOM, it’ll likely go through multiple iterations, numerous people may handle it. Before you get started, you should establish a system for managing it and ensuring the latest version is in use. Track changes and create identifiers for different versions. Allow as few people as possible to edit the document, and decide ahead of time who will be responsible for what tasks to avoid confusion.

Who will use it?

Because of the range of information, this document includes, it’s likely multiple departments, including design, engineering, purchasing, and manufacturing, will use it during the PCB production process. Having an idea of who will need your BOM will help you include the correct information.

What information will you include?

You don’t need to know the specifics at this point, but you should know what categories you want to include in your document. Every BOM should consist of some basics, such as part name and quantity, but other items are optional. You need to decide if you’ll include consumables — for example, glue and bolts. Do you have a preference for suppliers to buy parts from? Keep in mind, though, the best practice is to make your BOM as detailed and complete as possible.

How will you organize it?

It can be helpful to decide on basic organization strategies before you begin. Consider how many levels and sub-assemblies — items you will assemble separately and then attach to the main assembly — your file will have, how you’ll group items, and any special designations you plan to have. If you create your BOM list format ahead of time, you’ll be able to plug data in more efficiently once you start writing your BOM.

What program will you use to create it?

Before you can make your bill of materials, you have to know what software you will use to create it. A BOM is essentially a spreadsheet, and many companies use Excel. As your business grows and your projects get more complicated, you may find you need a more advanced program expressly designed for BOMs, of which there are many.