How to Prepare BOM for PCB Assembly?

How to Prepare BOM for PCB Assembly?

Sep 14,2021

Printed circuit boards (PCBs) contribute to the performance and function of most electronic devices that we use today. For this reason, immense importance is given to the circuit board designing process. There are several important factors that need to be considered for quality PCB design and assembly, and the bill of materials or BOM is one among them. Let’s focus on BOM and its significance in the PCB assembly in this post.

What is Bill or Material (BOM)?

Bill of Materials is an important document for a PCB assembly. A well created BOM allows you to know the exact quantities and part numbers, brand names of raw materials, components required, and other important details. In other words, BOM includes a list of components, wires, boards, and circuitry requirements. The bill of materials also helps to set expectations with the customer, and let them know what they can expect. For instance, through BOM, PCB manufacturers can give the customers the estimated cost per part, and let them know how long it will take to source each part. This gives the maker and the customer some control during the PCB assembly process.

What Should a BOM Include?

BOM is considered as an inventory-control document that describes all the parts that go into a product. In some cases, it can also help manufacturers to manage their suppliers by itemizing exactly what is needed to create the product.

A BOM should include everything that is required to produce a final product. The information included in the BOM varies depending on the project requirement. The document must be created carefully as this saves time, cost, and last moment confusion. However, the following are some important categories of information that are common in them.

  • Reference Designators: It is of utmost importance to include reference designators, which indicate the details regarding components placement on the circuit board. The component labels printed in silkscreen on the PCB quickly help identify the particular part while soldering.
  • Manufacturer’s Name: One should include the manufacturer's name in case you are looking for a specific brand. Also, it is crucial to confirm the availability of that part before listing it. Checking the information early in the process helps avoid the extra cost and time of finding the replacement part at the time of the production process.
  • Part Name and Number: To identify the required part easily and effectively, it is essential to list the manufacturer’s part name and number in your BOM. This will help the PCB assembler to use the correct component. A part number is a unique number is assigned to every part for easy reference and effortless tracking.
  • Description: Each part in the BOM should have an appropriate description such as voltage, color, dimension, and other specifications. This detailed information ensures that the right parts get ordered and avoids unnecessary confusion. Also, mention the units of measure such as ohms, ounces, centimeters, and meters with each description.
  • Quantity: The number of parts to be produced should be specifically estimated for each PCB assembly. Keeping this information up to date helps you get discounts on bulk purchases.
  • Procurement Method: Listing the procurement type in the BOM sheet identifies whether the component is bought from external sources or manufactured internally.
  • BOM Level: A BOM has multiple levels. Each has its unique structure that specifies ranking for each component to identify all the BOM components, whether single or multi-level. BOM level also helps the user navigate through the documentation and understand the circuit board assembly.
  • Alternate Parts: It is important to list the potential alternate parts in a BOM. This is helpful in case the requested part is unavailable or another change arises.
  • Placement Method: One must list the placement method for PCBs, which defines how each part and component will be attached to the board. The placement method can be either through-hole or surface mount technology, or a combination of both.

Tips to Create an Effective BOM

If you are creating a Bill of Materials, there is a lot to think about. If you have never created a BOM before, there are some considerations to make before getting started. The following are a few tips and guidelines on how to create an effective BOM.

  • Customize Properly: BOMs are created in a variety of methods and different projects necessitate varying levels of structure, information, and other aspects. Hence, it is recommended to customize your BOM to meet the specific needs of your project.
  • Encompass all Details: Include as much useful information as possible. Remember that your BOM is critical for explaining your PCB assembly to people who are building it from the ground up. These individuals may have never met you in person and may not even speak the same language as you do. As a result, your BOM must be as clear, detailed, and precise as possible. Some forms of information aren't useful and will just cause confusion; therefore, using your best judgement is crucial while creating BOMs.
  • Automate: Businesses have traditionally created their BOMs on a spreadsheet. This necessitates human data entry, which takes time and can result in errors. Consider automating some components of your BOM management process. This will make it easier to spot anomalies in records and improve traceability. It can also make importing and exporting data for multiple file types easier.
  • Move to Cloud: BOMs are required by many stakeholders and teams in the business for various reasons. BOMs are frequently modified, yet different versions make it difficult to keep track of the changes. Someone may open an email with a BOM, but it may not be the latest version. This can waste time, lead to misunderstandings, and cause people to grow frustrated. Consider moving your BOM to the cloud, where you can track changes in real time and ensure that everyone has access to the most up-to-date version. You can track changes to component numbers, procurement prices, and inventory stock numbers using a more dynamic system, and make updates as needed easily.

Considering the importance of BOM in the PCB assembly, one should never do it rapidly as there are chances that you miss out on some parts or mention wrong quantities. Today, many companies are providing a standard BOM format, and it is absolutely convenient to fill up. But apart from an effective BOM, it is also important that your circuit board is accurate and functions as expected. Therefore, you must employ a reliable manufacturer and supplier of circuit board assemblies. With years of industry experience, Sierra Assembly provides the best PCB assembly solutions of different specifications and capabilities.