In PCB design and manufacturing, the PCB Bill of materials plays a significant role. Manufacturers need several parts to design a printed circuit board. These parts need to be well-documented to avoid errors. Therefore, In the manufacturing world, the bill of material is a very common list.
As a PCB manufacturer, it is very important to understand what a PCB BOM is and its importance. In this article, we will look further into PCB BOM.
What is a PCB BOM?
A PCB BOM comprises the list of all the components a manufacturer needs to design a circuit board. BOM is an acronym that means Bill of materials. The PCB bill of materials is important for manufacturing a circuit board.
For instance, if you are making a sandwich, you need some ingredients. Similarly, you will need some parts to build a circuit board. The manufacturing of a board requires serious attention and carefulness.
PCB bill of materials consists of various components like chips, and resistors. Therefore, you can consider a BOM as a recipe for a PCB design. All of the materials needed for the design of a PCB are compiled into a list. You need a PCB BOM before commencing PCB assembly. The BOM contains the parts of a circuit board and their placement. This document should provide information such as;
- Manufacturer’s part number
- Item number
- Part type
- Manufacturer’s name
- Part description
- Package
- Reference designator
Creating an accurate PCB BOM is very important. If you miss any parts in this document, it could cause delays. This is because of the time needed to locate these parts or find alternative sources. The PCB BOM must also specify where to place each of the components. If otherwise, you can swap components with something else.
A BOM consists of raw materials, assemblies, and components for PCB manufacturing. Manufacturers are often provided this document by their clients. The information provided by the BOM guided the manufacturer in creating a circuit board.
Therefore, a BOM should be well detailed and accurate. Customers explain why they want in their PCB assembly through a BOM. The assembler then builds the circuit board according to the customer’s demands.
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What does a PCB BOM Format Include?
Since a PCB BOM is a list of parts of a circuit board, it will include some items. BOM formats are created for different purposes. A PCB manufacturer must adhere strictly to the BOM format during manufacturing. The format includes the following;
Component value
This is the specified value for some components. For instance, capacitance is the component value for capacitors. For resistors, it is resistance while inductance is the component value for inductors. The component value can help you to identify alternative components during sourcing. With this information, a manufacturer can also identify parts easily without the MPN. The MPN is a letter or number on the component package.
Quantity
This is important information on a PCB BOM format. It specifies the number of a certain component you need to order. Sometimes, the number indicates the quantity of a component on a one piece PCBA.
Manufacturer’s name
The name of the manufacturer must be included in a bill of material. This is the manufacturer that will supply you the parts of the circuit board. Sometimes, the same MPN might have different manufacturers. This may help to prevent having the cheaper copy. Therefore, it is very important to include the name of the manufacturer. Also, ensure you confirm that the manufacturer can supply you with the part.
Designators
These are labels printed in silkscreen on the circuit board. A designator tells you where to place components. You use standard letters for various types of components. For instance R1, R2 are the labels for resistors. U1, U2, U3… represent integrated circuits. C1, C2… are labels for capacitors.
With these labels, you can easily identify each of the components during soldering.
Placement method
The placement method tells your manufacturer how to assemble the part on the board. You can just indicate by writing top and bottom. The placement method should have a column on the BOM file. There are different placement methods in PCB assembly. Surface mount, through-hole, or a combination of the two are the placement methods available.
Description
This gives further details. It is not compulsory you include it in the BOM. However, if you will be giving the BOM to a purchaser, it is necessary. This is because this information can help them find alternative parts if the specified part is not available. Your assembly house will be able to save time and get a substitute for your parts.
Furthermore, when there are ambiguous or non-existent MPNs, this information can help you confirm the truth.
Package Type
This refers to the type of body the component is being housed in. The package provides information on the shape and size of the part. It can be very useful during PCB layout. You will be able to know the type of footprint to use.
The package type column is not compulsory for the assembly house. However, you can still include it in your BOM. It can be very helpful during the programming and operation of the pick and place machine.
Manufacturer’s part number (MPN)
This is a part number that helps to identify individual products. The MPN is a number provided by manufacturers and it is usually a series of letters and numbers. This number is unique to a specific product. It can be recognized by multiple manufacturers. When you provide the MPN, you are informing the vendor of the specific part you want.
Creating the PCB Bill of Materials Format
You can use a spreadsheet to create a BOM. The Excel sheet is a good example of a spreadsheet to use. After opening a spreadsheet, you can then input the list of the required parts in the sheet. However, this method is time-consuming and complicated. With the development in technology, there are now better ways of creating PCB BOMs. PCB designers now use different software tools to create a good BOM. The ECAD tool is helpful in creating a PCB bill of material.
Designers can draw a schematic with these ECAD tools. The tools provide information as regards the part numbers in the library. ECAD tools use similar information for creating the BOM for the particular schematic.
KiCad, Altium Designer, and Allegro PCB editor are examples of software you can use. Typically, the bill of materials format will include rows and columns. Each part will have a row in the spreadsheet. If a part shares the same manufacturer and part number, the information will be in the same row.
Factors to consider when creating a BOM
Before you create a PCB BOM, it is important you consider certain factors.
The purpose of the BOM
You need to ask yourself why you need a BOM. This will guide you in imputing the necessary information.
Type of Program
There are several programs for creating a PCB BOM. You need to decide which of these programs you will use to create the BOM. The Excel spreadsheet is a common program for creating BOM in the PCB industry. However, you can go for other advanced programs.
Type of information
What type of information are you including in your BOM? At this point, you don’t have to know the specifics. However, it is important you know the categories you are including in your BOM. There is basic information a PCB BOM must include. You will have to decide if you will be including consumables like bolts or glue. Ensure you provide the necessary information in your BOM.
Organization
You need to decide on the strategies for organizing your BOM. This involves considering the number of subassemblies and levels on your circuit. You also have to know how to put your items in groups.
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How to Create a PCB Bill of Materials Template Excel
The Excel spreadsheet is one of the simplest ways of creating a BOM template. Most manufacturers use this software because of its simplicity. One advantage of using Excel is that it can hide or reveal specific materials. This is possible through the sort and subtotal function.
- You need to design a new workbook in Excel. After this, you will type the column headings for your BOM. The column headings must show all features of a part. For instance, the “Categories” heading categorizes a component based on its function. Other column headings are Part Name, Quantity, and Part ID.
- In the rows under the column headings, input the entry for each part. Click on the “insert” tab and select ” Header & Footer.” Input your company’s address and name. Click on “Picture” in the Header and Footer category of the Header and Footer Tools Design tab. After this, navigate to where your images are on the computer. Doing this will help you to insert your company’s logo in the sheet.
- Click on the “Page Layout” tab. Then select “Orientation” and click on “Landscape.” You will realize there are many cells on the Excel sheet. For instance, A1, B1, B2, E2, and more. Navigate to B1 and input “Product name.” Click on B2 and input “Product number.”
- In A5, type “Item number” and type “Name” in cell B5. You can type “Part No” in cell D5 and in C5, type “Description.”
- Add all other important details in the PCB bill of materials template Excel. Press “Ctrl-S” to save the file. You can also click on “Save” on the Quick Access Toolbar.
The PCB bill of materials Template Excel is very simple to create. However, ensure you pay attention to details while creating it.
Tips in Creating a PCB
Create your BOM according to your requirements
It is important you create a PCB BOM to meet your requirements. Different projects need different information and organization. Customizing your BOM according to your needs will make PCB manufacturing easy.
Add the right details
You need to include the right information in your BOM. A PCB BOM serves as a guide to your manufacturer. This document explains your PCB assembly to assemblers. Therefore, you need to make your bill of materials as accurate and detailed as possible. The information you include in your BOM shouldn’t confuse your manufacturer. You should explain in the best language your manufacturer understands.
Make use of a template
You can get a PCB BOM template from the websites of manufacturers. A template helps to prevent problems with accessing the document. Each PCB assembler has BOM templates on its website. A BOM template helps to avoid technical issues resulting from incompatible file types.
Cross-check all details
It is important you cross-check the BOM before sending it to your manufacturer. Check properly to ensure the appropriate information is included. Any mistake in your BOM can cause a delay in PCB assembly.
Consider automation
You can incorporate automation in your BOM management. This will help you identify differences among records. Also, it helps you to easily export and import details for different file formats. BOM automation helps to minimize data management overhead.
Common Errors in BOM File PCB
If a BOM file PCB doesn’t meet the quality standards, there may be problems during manufacturing. Problems like higher costs, delays in product supply, and mismatched parts could occur. Mismatched parts or wrong placement of components is one of the commonest errors. A missing component will result in more cost.
Manufacturers may switch components if a BOM file PCB doesn’t indicate where to place them. However, it is easy to change the production batch if the manufacturer detects this problem early. The common types of errors are below;
Product evaluation error
The parts in the BOM must be in line with the budget imposed for manufacturing. Otherwise, the manufacturer can abandon the project since it is unprofitable.
BOM not tracked or updated
Ensure you confirm the accuracy of the information in your BOM. Also, ensure you send your manufacturer the most recent version of the BOM.
Inventory error
It is very important that you specify the number of units for every part. Otherwise, there will be delays in your project.
Conclusion
PCB BOM is an important document in PCB assembly and manufacturing. With this document, the manufacturer gets the exact details of the parts of the circuit board. Creating an accurate BOM helps a lot. It helps to avoid errors that could ruin the entire project.
