From Shack to Shed: What is a Bill of Materials and How Does it Help

Altium Designer
|  Created: January 22, 2018  |  Updated: December 11, 2020

Picture of small utility shed being constructed

I’m planning on building a new utility shed in my backyard; the original shed was old and worn out when I first bought the house 20 years ago and it absolutely has to be replaced now. In fact, if it wasn’t for the thick coating of rust that seems to be protecting it, I’m not sure that it would even be standing anymore.

I haven’t used a hammer and nails in my PCB designs before, so I ordered some plans on how to build this “Deluxe Backyard Storage Shed.” The plans include safety tips, drawings, cutting lists, step-by-step instructions, and a list of materials. But what an intimidating list of materials it is: 2 X 4’s, 2 X 6’s, shingles, hinges, a window, and the list goes on and on.

The fact is that I wouldn’t have a clue as to how to proceed with this project if it didn’t include a list of materials, and I’ll really be in trouble if the materials list has any mistakes in it. In the world of PCB manufacturing, it’s the same thing. Without a correct materials list or a Bill of Materials (), we couldn’t build a circuit board either. If you’re not familiar with a PCB, here’s a brief description of it and why a good and accurate is so important.

A Bill of Materials, What is it?

Like the list of materials needed for building my new shed, the PCB will contain every component needed to build the printed circuit board. Not only will this include the electrical components of the PCB, but it will also include non-electrical items such as brackets, bolts, labels, and stickers. The majority of these items will come from the PCB CAD system where the board was designed. Additionally, other items can be added in manually as well, although as we will see, that can be a problem if the manual edits do not synchronize with the CAD database.

Each item in the PCB will be listed by its part number and will contain a description of that part as well as a unique designator so that the part can be found on the board. Additional information can also be added depending on the requirements of the board. This information can include extra fields for items such as suppliers and costs, or whether or not a specific part is to be fitted on different versions of the same board.

Picture of a  report
An example of a PCB report

A Bad can be Catastrophic

When a PCB bill of materials is incorrect, it can cause serious problems on the manufacturing assembly line. The wrong will be queued up for the automatic pick and place machines, and the correct may not be available. You may be incorrect for the following reasons:

Incorrect PCB: If the PCB are incorrect, it could result in the wrong part numbers being reported on the bill of materials.

PCB database was not updated correctly: Schematic updates during the design cycle are a normal part of PCB design. If those changes are not updated correctly though, the wrong part numbers could find their way into the bill of materials.

Incorrect design version used to create the bill of materials: Sometimes a is generated from an incorrect version of the PCB database, or an older is used but not updated correctly.

Incorrect manual additions or changes made to the bill of materials: Often non-electrical will get added or changed in a PCB manually with a text editor. If there is a data input error here, the will be incorrect.

These kinds of problems can cause lost time and money in manufacturing. At best it will take time to sort through the to make the corrections and re-set the assembly line. At worst it could cause significant delays while waiting for the correct to be ordered, or even the expense of scrapping bad boards.

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Using management software like Altium’s will help you to create an error-free PCB

Tips for Creating a Correct and Dependable

The key is to get an accurate PCB into the hands of your manufacturer in order to avoid costly manufacturing errors and delays. To accomplish this, consider the following:

Follow a documented design process. By doing this you can ensure that your BOMs are created consistently. This will avoid BOMs that are created in a panic at the last moment, as well as providing a procedure for everyone to follow.

Create your manufacturing data in a unified design environment: When all of your CAD tools are working together in the same environment, you can tie the different portions of the PCB design process together. For instance, when your part data is tied together with your PCB design tools, you can work with that you know will be available for manufacturing.

Avoid manual changes to the bill of materials the with text editors: Manual edits are an open invitation to introduce human error into your bill of materials. A better solution is to use generation software that allows you to enter miscellaneous within the context of your PCB design environment. This will allow you to select the correct from your sources without the worry of human error.

These suggestions can help you to deliver a correct and reliable PCB to your manufacturer every time. With the automation of a clean bill of materials, your engineering team can focus its efforts on design instead of documentation.

For advanced creation utilities that will make your tracking more efficient and less prone to error, strong PCB design software like Altium will incorporate the into a living, active creation environment. With tools such as altium, the entire unified design platform will tie your schematic, layout, and PCB together.

If you are interested in learning how to make your more reliable, find out more information by talking to an expert at Altium.

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About Author

PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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