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The Importance of the Electrical BOM in PCB Design

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • An electrical BOM is the centralized source that lists out the raw materials, components, assemblies, and other related items that are needed to build a PCB.

  • An electrical BOM opens a communication channel between the different departments regarding the components used in a design.

  • PCB fabrication machines are configured and programmed based on the electrical BOM.  Illustration of BOM

Electrical BOMs are usually systems-generated lists using computer-aided design (CAD) software or similar software systems

A bill of materials (BOM) is critical for engineering designs. The engineering BOM is the source that provides comprehensive information regarding the raw materials or items required to make a finished product. While constructing a printed circuit board or electronic product, engineers prepare electrical BOMs. Electrical BOMs are usually systems-generated lists using computer-aided design (CAD) software or similar software systems. Let’s explore the electrical BOM and its importance.

The Electrical BOM

Printed circuit board design is an overwhelming process. There are a lot of complexities and challenges associated with each stage of PCB design. Even the sourcing of components for a circuit board can bring complications or disagreements between the design and engineering teams. Documenting the details of the circuit board components or raw materials can be helpful in such cases, which is why electrical BOMs are created by designers. Electrical BOMs can alleviate the complications involving raw materials, components, and assemblies.

The electrical BOM is the centralized source that lists out all the raw materials, components, assemblies, and other related items that are needed for building the PCB. The electrical BOM consolidates the details about components, such as the designator, quantity, value, part number, manufacturer, and package style. 

Who Uses Electrical BOMs?

In PCB design and assembly, electrical BOMs are vital for manufacturers, customers, and assemblers. The electrical BOM opens a communication channel between the different departments regarding the components used in a design.

Imagine you are designing your hardware project and are outsourcing the PCB fabrication and assembly to a PCB service bureau. As a customer, you can use the electrical BOM generated from the CAD software to effectively explain to the PCB fabrication and assembly service what exact service you are looking for.

Every stage of PCB development relies on the electrical BOM in some way. The sourcing of the components is performed according to the electrical BOM. The PCB fabrication and assembly services refer to the electrical BOM as the base for preparing the quotation of their work as well. The PCB assembly service utilizes the BOM to build the board as per the customer specification. PCB fabrication machines are also configured and programmed based on the electrical BOM. Finally, the PCB manufacturer relies on the electrical BOM to fabricate and assemble the board.

Common Details Included in an Electrical BOM

The electrical BOM is generated as a spreadsheet. The columns in the electrical BOM specify the fields or captions that give you complete and accurate information regarding a part or components, and each row corresponds to a part present in the design. The following are some of the column captions that describe a somewhat decent electrical BOM.

Item: The first column caption of an electrical BOM is usually the item that is used as an index for all the specifications on the list.

Reference or designator: The reference or designator refers to the alphanumeric name of the component as per the PCB schematic design. It aids in the positioning of the component on the board.

Quantity: The quantity is the number of units of each component required in the board design. 

Value: The value of the particular component can be given in the electrical BOM. However, this is optional when the electrical BOM provides the part number. 

Part number: The part number, otherwise called the manufacturer part number (MPN), is the unique number given by the manufacturer to identify each part. 

Manufacturer: When the manufacturer’s name is provided in the electrical BOM, it is easy to navigate to the manufacturer's catalog or website and identify the part. 

Description: The part is described under this caption by providing details such as color, size, weight, and electrical parameters like voltage, current, power, etc. 

Package reference: The packaging reference specifies the package used by the part, such as QFN16 or 20-SSOP, or it gives the footprint information of the part such as 0603, 0805, etc. 

More fields can be included in the electrical BOM such as the mounting type or alternative part number. You can use different electrical BOM formats by compiling them by hand or automatically generating them using PCB design software.

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