TABLE OF CONTENTS
Before building any new product, you need to know what materials and components are required, how many you need, and whether they’re available. A printed circuit board (PCB) bill of materials (BOM) captures that information, connecting your design to what your team needs to fabricate, source, and assemble. For printed circuit boards (PCBs), that planning also affects cost. PCB prices rose by as much as 40% in April 2026 compared with March, according to Goldman Sachs analysts cited by Reuters. When prices change that quickly, an accurate BOM helps procurement teams update quotes, budgets, and sourcing decisions before orders are placed.
A bill of materials (BOM) provides that shared reference, connecting design requirements to the materials your team needs to purchase. For PCBs and printed circuit board assemblies (PCBAs), it helps engineering, procurement, and manufacturing coordinate what to fabricate, source, and assemble.
In this article, we’ll explore why effective BOM management matters in PCB design and how splitting a PCB BOM into two parts can make it easier to manage.
Key Takeaways
- A PCB BOM connects design requirements with purchasing and assembly by identifying the required parts, quantities, and reference designators. Inaccurate entries can lead to incorrect orders, assembly delays, and rework.
- Separating the bare PCB record from the electrical component BOM allows teams to track layout changes and component substitutions independently while keeping both connected under the parent PCBA.
- Reviewing BOM costs and component availability during design helps teams identify budget overruns, long lead times, and obsolete parts before committing to production.
- Controlled BOM revisions and variant records define which components belong in each build, including approved alternatives and unpopulated positions. Keeping these records aligned with manufacturing files reduces assembly errors.
What Is a Bill of Materials?
A bill of materials is a comprehensive list of all the components needed to build a product. It includes part names, descriptions, and specs so the procurement team knows exactly what to source. Depending on the product’s size and complexity, its BOM could list just a few parts or hundreds.
How Does a Bill of Materials Relate to PCB Design?
When organizing your PCB design data, it helps to distinguish the bare PCB from the printed circuit board assembly (PCBA). The PCB is the unpopulated board, while the PCBA includes the board and its mounted electronic components. A BOM can organize these under a parent assembly, with additional levels for modules or subassemblies as needed.
Many electronic products use PCBAs to support and connect their components. The board’s copper traces, pads, and vias provide electrical connections between components such as resistors, capacitors, and integrated circuits. The BOM defines which parts are required and in what quantities, while PCB design files and assembly documentation define where those parts go and how they connect.
An incomplete or inaccurate BOM can lead to missing or incorrect parts, resulting in assembly delays, rework, or a board that does not function as intended.
The example below shows a PCBA in a PLM system, with the bare PCB and electrical bill of materials (EBOM) nested beneath the parent PCBA record.
Why Are BOMs Important in PCB Design?
A PCB design can be ready for fabrication while the parts needed to assemble it are unavailable, incorrectly specified, or over budget. Keeping the BOM accurate throughout design helps your team catch these problems before they disrupt purchasing and production.
Controlling Cost of Goods Sold (COGS) Early
Your component choices affect production costs long before the first board reaches the assembly line. A costed BOM combines part quantities with supplier pricing so you can estimate material costs at your planned production volume.
With that information, you can identify expensive components and evaluate alternatives while the design is still flexible. BOM tools can check pricing and availability against build quantities, helping you account for volume discounts and purchasing requirements.
Material costs are only part of COGS, so your estimate also needs assembly labor, testing, and applicable manufacturing overhead. The BOM provides the material cost baseline for that broader cost model.
Bridging the Gap Between CAD Design and Manufacturing
A component in your CAD design needs to correspond to a specific purchasable part. The BOM makes that connection through manufacturer part numbers, quantities, and reference designators that identify components in the design.
Your manufacturing partner uses this information alongside fabrication files, placement data, and assembly drawings. Keeping these documents aligned with the same released revision reduces clarification requests and the risk of assembling boards with outdated parts.
Mitigating Component Shortages and Lead-Time Delays
A design that depends on an unavailable component can leave production waiting for a single part. Reviewing your BOM against current stock, lead times, and lifecycle information helps you identify supply risk before release.
Supply delays can also affect the bare board itself. In April 2026, a Daeduck Electronics executive told Reuters that lead times for chemicals such as epoxy resin had increased from three weeks to 15 weeks.
Your BOM gives procurement a defined list to review with component suppliers and the board fabricator. Documenting engineering-approved alternatives gives buyers options when preferred parts become unavailable without shifting compatibility decisions to purchasing.
Ensuring Single-Source-of-Truth Variant Management
Different versions of a product may share a bare PCB but use different component values, optional features, or unpopulated positions. A controlled BOM records the approved configuration for each variant, including positions marked “do not populate” (DNP).
For example, one product variant might include a sensor that another leaves unpopulated. Variant-specific manufacturing outputs keep the BOM, placement data, and assembly drawings consistent with that choice.
Managing these configurations in one controlled system helps prevent teams from mixing instructions across product versions. Each build should reference the approved BOM revision and variant so your assembly partner knows exactly what to install.
Reducing Prototype Iterations and Board Re-Spins
Checking the BOM before ordering prototypes can uncover incorrect part numbers, unsuitable component ratings, or package mismatches. Catching these errors early helps you avoid using a prototype build to diagnose preventable sourcing or documentation issues.
The consequences depend on the error. An incorrect component may be replaceable through rework, while a package mismatch that requires a different footprint can force a board redesign and another fabrication run.
BOM reviews work alongside schematic checks, layout reviews, and prototype testing to reduce avoidable iterations. Together, these checks help ensure the parts ordered match both the electrical design and the physical board.
Needed Fields in a Bill of Materials for PCB Design
In PCB manufacturing, you’ll need to include a few required fields to build a complete and thorough bill of materials:
1) Item Name
The first field that needs to be included in your BOM is the item name. This is where you’ll include both the printed circuit board and each of its attached individual components. Examples of these components include:
- Circuit board
- Capacitors
- Passers
- Resistors
- Diodes
- Connectors
2) Quantity Per Board
The quantity per board is a specification in the BOM that indicates the quantity of each part needed to create a single board assembly.
3) Manufacturer Part Number
The Manufacturer Part number (MPN) is a unique, specific identifier given to individual parts, typically appearing as a string of numbers and letters. This number tells your procurement team and vendors exactly which parts you need and is what you’d use to track materials through the manufacturing process.
It’s important to note that the MPN is a unique, internationally-used number and is not the same as the stock-keeping unit (or SKU), which is a vendor-assigned identifier for internal use and not relevant to board production.
4) Do Not Populate/Do Not Install (DNP/DNI)
This field indicates that a certain component is not needed for a particular version of the product. Marking items as DNP in the BOM prevents unnecessary procurement and tells Surface Mount Technology (SMT) machines to skip those footprints.
5) Reference Designator of Components
A reference designator is an identifier used in the BOM to help identify where each component is referenced in the electrical schematic. The reference designator helps to eliminate any confusion regarding the location of each part on a board.
6) Size/Footprint
Each component in a PCB will have different dimensions and layouts. This field often includes a diagram that shows where the components are located, including pins and leads. This information ensures that each component is placed correctly and that all components fit within their designated space.
7) Part Description
The description of the part is how you add further information and details about each part to the BOM. You can use this field to describe the part’s function and add information about where to find it. You can also suggest alternative parts to use if the Procurement team can’t source the original component.
Optional Items
In addition to these mandatory items on a PCB BOM, there are a few other optional fields that can be used to further detail the comprehensive list of materials needed to create a printed circuit board assembly.
- Vendor name: The vendor’s name can help determine where the parts are being sourced from and who is distributing them to you.
- Vendor part number: Vendors might have their own part numbers for materials, so you may want to include that in your BOM.
- Value of the particular part: The value of the part indicates to teams the value associated with it and how it fits into the PCB.
- Part manufacturer name: This identifies where the part is produced and where you’ll get it from.
PCB Schematics and Documents
A PCB schematic is an internal pictorial representation of the final product that will be assembled. Rather than being a direct diagram of parts, the schematic is more of a functional representation of what the circuit board will look like. Here is an example of a PCB schematic in Altium CAD.
Beyond the bill of materials, there are a few other critical documents related to PCB assembly:
- GERBER files: A collection of unique files that describe how to fabricate the printed circuit board and, in some cases, how to place the parts.
- Manufacturing document: A manufacturing document defines how the printed circuit board is fabricated, including materials, the specifics of the copper, and specifics of any kind of tolerances.
- Board file: Lays out exactly how components will be placed on the final board.
- Functional diagrams for components: Each component part can have its own detailed diagram outlining its specs, functions, and connections.
What Are the Different Types of PCBs?
Not all PCBs are created equal; they can come in a variety of different layouts and serve different purposes. Here are a few of the most common PCB types and their applications.
Single-sided PCB
A single side PCB contains a single conductive layer placed above the substrate where electronic components are soldered or placed onto one side. Because they have only one conductive layer, the paths can’t overlap or take up too much space. These are great for low-density product designs like calculators and lighting boards and tend to be both cost-effective and easy to manufacture.
Double-sided PCB
A double sided PCB, as the name might suggest, has conductive material on both the bottom and top of the substrate board. This allows the parts to be placed on both sides and connected through holes in the board. These types of boards are used for products that need smaller circuit boards than a single side PCB will allow, such as cell phones. Double sided PCBs increase the flexibility of the board and make it suitable for automotive dashboards, power amplifiers, and industrial controls.
Multi-layer PCB
A multi-layer PCB will have more than two conductive layers. The substrate and conductive layers are arranged in a “sandwich” layout that stacks on top of each other. These different layers must then be laminated to avoid air gaps and ensure that components connect. These are used for advanced electronic products like heart monitors, X-ray machines, satellite systems, space probe equipment, and weather analysis. They are even more compact and offer a high level of design flexibility.
Rigid PCB
A rigid PCB has a firm circuit board that cannot be manipulated. It gives added strength to the board and is composed of multiple layers tightly adhered together. These boards are both compact and lightweight but cannot be modified once made. Rigid PCBs are often used in robotics and automotive production, and due to their ability to withstand vibrations and extreme temperatures, they are also used in aerospace and large, complex medical technology (MR systems and EKG machines).
Flex PCB
A flex PCB is the opposite of a rigid PCB. This flexible board is made out of movable materials like polyamide. The board is designed to move and bend without destroying the components attached to the board. It’s used for products like flex solar cells, cameras, and some automotive devices. They can save space in a design and help provide thermal management for products.
Rigid Flex PCB
A rigid flex PCB is a hybrid board that is made of both flex and rigid components. This creates an end product that can both be folded and manipulated while still maintaining a high level of strength. Their flexibility and strength make them more complicated to create, but ideal for medical applications like cochlear implants and pacemakers, and aerospace technology like radar equipment and radio communications systems.
Why Split a PCBA BOM into Two Parts?
We recommend splitting your PCBA BOM into two different parts: the PCB itself and the eBOM, or electrical bill of materials for all the component parts. In addition to simplifying the process from your computer-aided design (CAD) software, there are some other key reasons why we consider this a best practice:
Simplifies Independent Revisioning
When your PCB and its components are laid out on two separate levels, it becomes much easier to make revisions to each level independently. For example, you might decide that a chip in your board is too close to where a mechanical enclosure comes together and decide to nudge the chip a millimeter to the left. In this instance, you would only need to revise the PCB itself — not the entire eBOM — because you’re only adjusting the location of one of the components.
Sometimes the Assembly House and the Fab House Are Not the Same
Having a separate PCB and eBOM also makes it simpler to communicate information. For example, you might send the entire PCB assembly structure to one vendor to have it fabricated for you. However, they might split it up because it’s not always the case that the assembly house is also the fabrication house. If the PCB and eBOM are already separate, you can easily separate information and send it to the right party.
How PLM Centralizes a PCB and eBOM
Businesses often face challenges centralizing PCB and eBOM data. Transferring the information from CAD into an Excel spreadsheet and then into a product lifecycle management (PLM) tool can be time-consuming. The tools aren’t set up the same way, and it can involve renaming and creating new columns. This can lead to confusion, input errors, and miscommunication between teams.
However, Duro PLM can recognize columns from an Excel sheet and understand their context in the eBOM. Additionally, Duro can integrate with ECAD tools (like Altium), allowing you to transfer BOM information directly from your CAD tool. This skips the step of manually transferring data, resulting in fewer errors, as all part information is centralized in the PLM system.
A PLM like Duro can automate this process, greatly reducing manual data entry and leading to cleaner, more accurate (and complete) eBOMs.
Build Better PCBs With Accurate BOM Management
An accurate bill of materials for PCB design connects the parts your engineers specify with what procurement orders and manufacturing assembles. Keeping it current helps your team estimate material costs, identify supply risks, and prevent component errors before production.
Separating the bare PCB record from the electrical component BOM lets you track board changes and component substitutions independently. Managing both under the parent PCBA keeps the assembly definition connected, while approved revisions and variant records tell your manufacturer exactly what to build.
Duro brings BOMs, product records, and engineering changes into one PLM system, helping your team coordinate updates across design and manufacturing.
Request a demo to see how Duro can support your PCB BOM management workflow.
Bill of Materials for PCB Design FAQs
What are the benefits of using a bill of materials?
A bill of materials gives engineering, procurement, and manufacturing a shared list of the parts and quantities needed to build a product. It helps your team estimate costs, check availability, and order the correct components. Keeping the BOM aligned with approved design revisions also reduces purchasing errors, assembly mistakes, and avoidable rework.
What is the 3W rule in PCB layout?
The 3W rule is a guideline for reducing crosstalk between parallel PCB traces. In its common center-to-center definition, adjacent traces of equal width should have their centers at least three times the trace width apart. For 0.2 mm traces, that means 0.6 mm between centers, leaving a 0.4 mm gap between their edges.
Some guidance uses a three-width edge-to-edge gap instead, so check which convention your design rules follow. Required spacing also depends on the board stackup, signal edge rates, and parallel routing length; trace-spacing guidance is a starting point, not a guarantee of signal integrity.
Which materials are used for PCBs?
Most rigid PCBs use FR-4, a glass-reinforced epoxy laminate, with copper forming the conductive traces, pads, and planes. Solder mask protects the copper, while a surface finish protects exposed pads and supports soldering.
Other constructions use polyimide for flexible circuits, specialized low-loss laminates for high-frequency designs, or metal cores for heat dissipation. Your material choice depends on the board’s electrical, thermal, and mechanical requirements.