What is a BOM List?
A Bill of Materials (BOM) is a comprehensive list of raw materials, components, and parts required to manufacture a final product. In PCB assembly, the BOM outlines all components necessary for a printed circuit board, including part numbers, names, and quantities. It may also include the manufacturer or supplier details, functional specifications, and additional comments. The BOM serves as a critical bridge between the customer and the manufacturer during the PCB assembly process.
Get a free quote now!
BOM List Composition
In PCB assembly, the BOM must detail each component used, including descriptions and quantities. Common elements of a BOM include:
- Serial Number: Indicates the number of components on the PCB.
- Part Number: Typically the manufacturer’s part number (MPN).
- Part Name: Identifies the component.
- Specification/Description: Includes details such as component values, sizes, or colors.
- Package/Footprint: Defines the packaging type (DIP, SMD, etc.).
- Brand/Manufacturer: Some components require specific brands or manufacturers.
- Quantity: Specifies how many of each part is needed per PCB.
Component identifiers include:
- R (Resistor)
- C (Capacitor)
- D (Diode)
- U (IC Chip)
- SW (Switch)
- F (Fuse)
- JP/CN (Connector)
- Substitutable Parts: Lists possible replacement components.
- Comments/Notes: Includes special instructions or requirements.
Importance of BOM in PCB Assembly
The BOM is crucial for ensuring smooth PCB production. It helps determine material needs and ensures all required components are accounted for. The BOM provides essential details such as brands, quantities, and sizes. Here are some key reasons why the BOM is vital for PCB assembly:
Provides a Clear Overview
The BOM shows all necessary parts, including quantities and part numbers.
Aids in Workforce Estimation
It helps determine the manpower needed based on the assembly complexity.
Facilitates Accurate Purchasing
The BOM enables efficient planning and stable production operations.
Tracks Inventory
It assists in tracking purchased components and available stock before production begins.
Ensures Correct Components
The BOM helps verify that the right parts from the right manufacturers are used.
Allows for Substitutions
If a component is unavailable, the BOM provides alternatives.
Requirements for a Quality PCB BOM
A well-prepared BOM is critical to the success of PCB assembly. Here are the main requirements:
A BOM should cover over 99% of the components used in the assembly.
The BOM must be completed before the MRP (Material Requirements Planning) phase, and any engineering changes should be reflected immediately.
A BOM should be at least 98% accurate, ideally 100%.
The quality of the BOM directly impacts the effectiveness of the ERP (Enterprise Resource Planning) system used during production.
Factors to Consider When Creating a BOM List
When creating a BOM for a PCB assembly order, it’s essential to break down the process into manageable parts. Instead of focusing on the total quantity of items, handle one PCB assembly item at a time. Work with your engineering team to determine all necessary components, then send the BOM to the customer for verification. Ensure the BOM answers the key questions of “when,” “what,” and “how” for the project to avoid delays or errors.
Steps in PCB BOM Reverse Engineering
For customers with PCB samples but no Gerber file or BOM, manufacturers can reverse-engineer the BOM by following these steps:
Check for damaged components or polished chips and analyze the PCB layout.
Test the value of each component using an electric bridge.
Copy component information from the silkscreen and research the part numbers.
Compile the components into an Excel sheet for production.
Tips for Handling BOM Lists
The difficulty of a PCB assembly project can often be gauged by the number of materials listed in the BOM. When reviewing a BOM, ensure it includes all essential details like part numbers, brands, quantities, and tags. Missing information can lead to errors in production.
Connect with us
Get an Instant Online Quote Today
Looking for reliable SMD assembly services? At ESPCBA, we’re your trusted partner for PCB fabrication, component sourcing, and electronic manufacturing. With over 16 years of experience, we’ve provided high-quality PCBs at competitive prices to over 1,000 customers worldwide. Our company is ISO9001:2015 certified and UL listed, and every product we deliver is 100% E-tested and inspected using AOI and X-ray to meet the highest standards. Get an instant quote from our sales team today, and let us handle the rest for you.