Definition of bill of materials
Content of bill of materials
Type of bill of materials
Structure of bill of materials
If you are starting a small business which manufactures or assembles electronic products, you need to create and keep bill of materials(BOM) for your products. To explain it, a cook has a recipe and list of ingredients to cook delicious food, if you are designing, selling, or servicing an electronic product, you need an instruction and a list of materials to create your unique article.
The BOM list is used to calculate the cost of a product and to order parts from suppliers. Although you may use more advanced inventory control software or a full-fledged MRP system eventually, you can get started using ALLPCB free Bill of Materials template at the bottom of this article and customize it as your request.
What is a Bill of Materials (BOM)?
A bill of materials (also known as a BOM or bill of materials) provides a comprehensive list of parts, components, items, assemblies and other materials as well as the quantity of each required item to create a product. Instructions for gathering and using the required materials are also needed. The bill of materials explains what, how, and where to buy required materials and includes instructions for how to assemble the product from the various parts ordered.
A bill of materials usually shown in a hierarchical format, with the highest level displaying the finished product and the bottom level showing individual components and materials. All manufacturers build products, regardless of their industry, getting started by creating a bill of materials (BOM).
A bill of materials is most common used in manufacturing or engineering projects to create electronic products, and it is less common in software development or intangible creative products like graphic design or written work. BOM can cover several stages of a product, from the design to the order to the build to the maintenance.
What to include in an effective Bill of material?
here is a high level list of information to include in your BOM record:
1. BOM Level
Assign each part or assembly a number to detail where it fits in the hierarchy of the BOM. This allows anyone with an understanding of the BOM structure to quick decipher the BOM.
2. Part Name
Record the unique name of each part or assembly. This will help you identify parts more easier.
3. Part Number
Assign a part number to each part or assembly in order to reference and identify parts quickly. It is common for manufacturers to choose either an intelligent or non-intelligent part numbering scheme. Whichever scheme you use, make sure you avoid creating multiple part numbers for the same part.
Record what stage each part is at in its life-cycle. For parts in production, it is common to use a term like ‘In Production’ to indicate the stage of the part. New parts that have not yet been approved can be classified as 'Unreleased' or 'In Design'. This is helpful during new product introduction (NPI) because it allows you to easily track progress and create realistic project time-lines.
Provide a detailed description of each part that will help you and others distinguish between similar parts and identify specific parts more easily.
Record the number of parts to be used in each assembly or sub-assembly to help guide purchasing and manufacturing decisions and activities.
7. Unit of Measure
Classify the measurement in which a part will be used or purchased. It is common to use ‘each’, but standard measures like inches, feet, ounces and drops are also suitable classifications. Be consistent across all similar part types because the information will help make sure the right quantities are procured and delivered to the production line.
8. Procurement Type
Document how each part is purchased or made (i.e. off-the-shelf or made-to-specification) to create efficiencies in manufacturing, planning and procurement activities.
9. Reference Designators
If your product contains printed circuit board assemblies (PCBAs), you should include reference designators that detail where the part fits on the board in your BOM. Capturing this information in the BOM can save time and help you avoid confusion down the road.
10. BOM Notes
Capture other relevant notes to keep everyone who interacts with your BOM on the same page.
What Kinds of Types of BOM?
1. EBOM(Engineering Bill of Materials)
The engineering bill of materials (EBOM) defines the finished products as they were originally designed, used in the design phase. It lists items, parts, components, sub-assemblies, and other assemblies of the product as engineer designed it. For a finished product, more than one EBOM may be created. For instance, the BOM for a printed circuit board assembly that’s been designed by an electrical engineer will list the resistors, chips, and capacitors.
A precise and accurate EBOM is essential, especially for a new product, since this is the document that ensures the correct materials and parts—in the correct quantities—are available when the item is being manufactured. The ramifications of errors in the EBOM are serious. Incorrect quantities can cause production to be stopped.
To ensure that parts are available when required, the purchasing department needs information on what vendors to purchase items from and how much lead time is required for each ordered part. The purchasing department will negotiate to obtain the best price for each part in efforts to reduce the overall cost of the finished product.
2. MBOM(Manufacturing Bill of Materials)
The manufacturing bill of materials(MBOM) is a list of a BOM which defines how a product is assembled, which includes packaging materials, usage instructions and all other items it takes to build the final product. It contains the details of all the required parts to build a product that manufacturers can ship to customers. Anything that can be found in the final packaged product as it arrives to the customer should be included on the MBOM at some level. If MBOM isn’t accurate, manufacturers risk building the product too slowly, incorrectly, or being unable to build it at all.
Some areas will need processing before they are ready to be assembled into the final product – such as programming or painting. The altered part is the only one that makes into the final product, but the pre-processed base, and the finished part must both be represented on the MBOM. This way, your manufacturing team can decide which steps should be taken care of in-house and which steps can be outsourced to another vendor. Over the life of the product, processing locations can be changed to improve quality, increase flexibility, or if necessary, reduce costs.
3. SBOM(Sales Bill of Materials)
The sales bill of material (SBOM) defines a product in the sales stage, illustrating details of the product prior to assembly stage. An MBOM usually lists every material that goes into manufacturing products. Here, the finished product is regarded as a sales item instead of an inventory item.
4. CBOM(Configurable BOM )
A configurable bill of material(CBOM) relies on a modular BOM structure, and it is used for meeting an individual customer's specifications. The CBOM contains all the components that are required to manufacture the material to that customer's detailed requirements. Because users may need to re-organize parts combinations for each variation, most organizations use “configurator” software for CBOM, but you can also manage them manually.
5. EBOM(Equipment BOM)
The equipment is another BOM variation which uses the modular structure. EBOM lists all of the components of an asset, including its assemblies and subassemblies. Opposed to a traditional BOM, an EBOM provides all the tools and equipment needed to finish a product, rather than the basic materials.
This video explains the definition and type of BOM.
What Kinds of BOM Structure?
Typically, there are two kinds of structure for BOM:
1. Single-level bill of materials, which is a relatively simple list for a product. For this type, each assembly or subassembly is displayed only once, with the corresponding quantity required of each part to make the products. Though easy to develop, this type of BOM is unsuitable for complex products because it does not specify the relationship between assemblies and subassemblies. If the product fails, a single-level BOM makes it difficult to determine which part needs to be replaced or repaired.
2. Multilevel bill of materials, which takes more work to make but offers greater details and differences on the parent and child parts in the product. In a multilevel BOM, the total material required is shown. Additionally, the product structure is indented to show the relationship between the parent and child product, as well as assemblies and subassemblies.
Excel spreadsheet example of Bill of Materials
The biggest advantage of using spreadsheets for your bill of materials is that they are flexible and can be formatted however you like. However, the bad thing about using spreadsheets for BOMS is that they are so flexible that anyone can format them however they like.
Example of a basic Excel Bill of Materials
The basic BOM format separates information into columns. It contains BOM level, part number, part name, revision, quantity and reference designators.
It is helpful to have unit of measure and BOM notes on a bill of materials as well. The first line, with a BOM level of zero, is the top-level product or assembly to which everything else in the bill of materials reports.
Example of an Excel Bill of Materials with a Header
A header provides a clear overview of what your BOM contains. When your top-level product or assembly information (level zero) is included in the header, it should not be repeated below. The items in your BOM should now start with level one.
Example of an Excel Bill of Materials with Graphic Representation of Assembly Level
Users can quickly scan bills of materials and understand where particular parts are located when each level is denoted with a marker (e.g. a star).
The numerical BOM level is included too. With the correct Excel formula, this number can automate the placement of the visual marker in the correct column.
Creating a BOM in SAP
Step one: Create BOM
1) Enter T-code CS01 in the command field.
2) Enter Material / Plant / BOM usage .
Step two: Enter Item Code, Material component and Quantity.
Step three: Click on save button. Below screenshot will displayed.
4 Key tips
1. The different types of BOM depend on the project usage and business needs of the individual project.
2. A BOM is a centralized source of information used to manufacture a product.
3. A BOM is often shown in a hierarchical way, from the finished product all the way down to individual components and materials.
4. Some parts are used in more than one product or assembly. When a change is made to one of those parts, the information must be updated in every place the part is used.
4 related questions
1. Will you document consumables in your BOM record?
Many manufacturers second-guess the decision to include glue, wires, fasteners and other non-modeled parts like labels and boxes
in their BOM record. But if the part does not make it into your BOM, it might not make it into your product. So take the time to document these parts.
2. How will you attach files to your BOM record?
As you create your BOM, keep records of supporting documentation like CAD drawings, part data sheets and work instructions. It is best to also associate these files with their specific BOM level items.
3. Who is going to use the BOM record?
It is important to include as many details as possible in your BOM. You may never interact face-to-face with some of the people utilizing your BOM, so it should convey all the information they might need throughout the product’s lifecycle.
4. How will you reconcile your BOM record?
Your BOM record may go through several iterations during the design phase, so you should have a way to distinguish between multiple BOM record versions. That way, when it is time for production, you can be sure each person who uses your BOM is consulting the correct version.