bill of materials in circuit board assembly
A good analogy to describe the importance of a bill of materials in circuit board assembly is that it’s like a recipe for baking – you can’t bake a cake without having all of the necessary ingredients listed. For PCB assembly, this includes everything from solder paste and a stencil to the proper tools and equipment for the job. A well-structured and complete BOM can greatly expedite the procurement process by clearly communicating all of the necessary parts needed to assemble a product.
Creating a BOM can be done manually through spreadsheets, but the easiest and most efficient way is to use an integrated design tool that provides a built-in component library for your specific platform of choice. Several of the leading CAD/EDA platforms include this functionality, including Altium Designer, KiCad, and Cadence Allegro. The software will automatically generate the bill of materials, and all you have to do is review it for accuracy before sending it off for purchase.
Once the components are purchased, they’re shipped to a circuit board assembly fab shop. A jiggling component, a dangling coil, or even a loose screw can lead to malfunction or failure during manufacturing, which is why having a thorough BOM is so important. This ensures that the right components are brought to the assembly line and that each piece of the puzzle is in its proper place to function properly as intended.
What is a bill of materials in circuit board assembly?
Aside from providing an accurate list of the necessary pieces for a specific project, a BOM also contains other pertinent information that can help the team manage its inventory and production process effectively. The most essential components to include in a BOM are the part name, part number, reference designator, and value. These details are critical to ensuring that the correct component is assembled onto the board and that it will be functional when it’s ready for testing.
The manufacturer part number is a unique identifier that distinguishes a component in the manufacturer’s catalog. It’s a required field in the BOM because it makes it easier for the assembler to identify which version of the part is being used. The reference designator is another essential field to have because it specifies where a particular part will be placed in the electrical schematic.
In addition to identifying the correct components, a BOM will also contain a field that describes its phase of use. This can be as simple as a “Do Not Install” or as detailed as a description of the component’s size and specifications. The inclusion of this detail is helpful to reduce confusion during the assembly process, especially when there are multiple versions of a design that require different components.
Other optional fields to consider in a BOM are package type, pin count, and through-holes. Having this information available in the BOM can help to speed up the quoting process by making it easier for assemblers to determine the correct assembly price based on part type.
