Want to Build a Killer PCBA BOM? Here's Your Step-by-Step Guide

Posted:05:45 PM October 26, 2022 writer: NexTPCB - LL

Stuck wondering what a BOM file for PCB assembly actually does and how to create one properly? Your bill of materials acts as the crucial ingredient list guiding every step of PCB fabrication and assembly. Getting it right saves headaches, costs, and ensures your boards build correctly. Let's break down how to build an effective PCB bill of materials step-by-step. > Is PCB manufacturing different from PCB fabrication?

What is a BOM?

BOM stands for the bill of material. A BOM is a list of materials used in PCB manufacturing and assembling. The function of a BOM is to provide the engineer with all he needs to produce a circuit board. In most random cases, the bill of material is the first thing in PCB manufacturing that gets finalised and proceeded.

As stated above, a Bill of material has all the necessary information, such as the size, manufacturer and packaging type. It is efficient to do it at first as later it helps the PCB designer to design the footprints of components and also helps to check whether the required element is available in the market in the desired packaging, size and manufacture.

Engineer reviewing PCB bill of materials spreadsheet on desktop computer for electronics manufacturing planning

> Recommend reading: PCB Assembly Drawings: Boost PCBA Manufacturing Efficiency & Reliability

What's the Heartbeat of your PCB Project? The BOM!

Think of your bill of materials (BOM) as the master shopping list and build blueprint. This essential document lists every single physical component needed to manufacture and assemble your printed circuit board. Locking down a comprehensive PCB bill of materials early lets your design team:

Plan component footprints accurately from the start.
Verify part availability (size, packaging, manufacturer specs) before committing to the design.
Set the stage for smooth manufacturing and assembly later.

Why Your PCBA Life Depends on a Solid BOM File for PCB Assembly

During PCB assembly (PCBA), technicians place and solder components precisely. Your PCB assembly bill of materials provides the unified reference containing all the nitty-gritty details about every part. A well-crafted BOM file powers the assembler by:

Enabling easy cross-checking of component values against design specs before soldering, catching potential errors early.
A well-prepared PCB bill of materials is essential for preventing assembly errors, especially when sourcing components from non-authorized channels where specifications like packaging or electrical values might differ.
During pre-assembly verification, technicians group components by type before placement. Using the BOM as their definitive reference, they actively check critical specifications: measuring resistor resistance, capacitor capacitance, and confirming transistor package types (like SOT-23 or SOT-89) against the values listed. This BOM-driven verification process catches mismatched or substandard parts early, ensuring every component meets the required quality criteria before it hits the board.

Close-up of a populated printed circuit board showing components listed in a PCB bill of materials for electronics assembly

Essential Elemetns for Your PCB BOM Checklist

Don't let your bill of material for PCB leave out mission-critical details! Every field tells part of the component's story:

1. Item Number: The unique row identifier. Keeps track of every line item. Simplicity wins!
2. Quantity Per Board: How many of this component do you need per PCB? Add buffer components for test/repair! Smart planning reduces cost surprises later.
3. Description: The detail zone. Add color code, tolerance, wattage - whatever clarifies the part beyond basic designation.
4. Manufacturer Part Number (MPN): The gold standard ID. This unique code ensures everyone orders the exact component from the intended source. Vital for any PCB bill of materials report.
5. Reference Designator (RefDes): Think R1, C5, U3. These match the silkscreen labels on the physical PCB, guiding precise placement. Mandatory!
6. Populate Status: Clearly mark any Do-Not-Populate (DNP) or Do-Not-Install (DNI) locations. Saves confusion during assembly.
7. Component Value: Electrical heart. Resistance (Ω), Capacitance (F), Inductance (H), chip-specific IC codes, etc.
8. Component Size/Ftprint: Crucial for design feasibility. Does its footprint match your board layout? Define physical dimensions clearly.
9. Package Type: SOIC-8, 0805, SOT-23? Describes physical pins/legs/pads and overall shape.
10. Manufacturer Name: While sometimes optional, naming the preferred source (e.g., Texas Instruments, Murata) helps prevent knock-offs. Strongly recommended.
11. Alternate Part Number: Backup heroes! List acceptable substitutes if the primary part faces shortages, saving massive delays. Mark clearly (e.g., in another column or with color-coding).
12. Vendor Info (Optional but Recommended): Vendor Name & Vendor Part Number (VPN) speed up procurement. Where can we actually buy this?

BOM Example

The NextPCB recommends a BOM that has as many details of the parts mentioned as possible to ensure an error-free buying and assembling of the components. To aid your learning NextPCB is incorporating an example of a Bill Of Material BOM.

Bom Template Example

Beyond the List: Role of BOM in Cost Estimation of the Project

Your finalized bill of material for PCB becomes a powerful cost estimation tool. It allows buyers to:

Check local/global component availability instantly.
Compare prices across multiple vendors efficiently.
Spot expensive or long-lead items driving up costs/delays.
Calculate total project Material Costs (BoM × Qty).
Pro Tip: Modern BOM management software can auto-update pricing and availability, revolutionizing your quote process!

A BOM is a list mentioning all the materials required to produce a PCB. Thus it helps estimate the cost in terms of several factors, such as if all the components are locally available or not, helps compare the prices of the parts and materials from the different vendors etc. However, if designers use modern software to create BOM, it can make their lives easier. Because BOM software usually provides automatic price comparison and automatically updates the prices if they fluctuate.

Building Your BOM File: Tools & Tactics

Spreadsheets (Excel/Sheets): The battle-tested standard. Flexible, accessible, but requires manual upkeep. (Excellent free templates exist! Download Free Excel BOM Template from NextPCB).
Dedicated BOM Software: Offers automation (cost updates, stock checks, vendor links), revision control, and integration with design tools. Ideal for complex products or teams.
Your EDA Tool: Altium, KiCad, Eagle – most export basic BOMs. Supplement with critical fields like Vendor info and DNP status.
Or, you can contact us for a personalized BOM Service.

Skip the Part-Hunting Hassle: NextPCB Component Sourcing Services

Perfecting your BOM file for PCB assembly is step one. Finding all those parts reliably is step two. NextPCB offers full component sourcing services alongside our 15+ years of expert PCB manufacturing, assembly (PCBA), and testing.

For Component Sourcing: Visit HQ Online | NextPCB, one of China's largest distributors of electronic components.

We build:

Diverse boards (FR-4, Metal/Aluminum, LED, Ceramic, Hi-Freq PCB)

Source globally at scale

Pre-test components rigorously before shipping or assembly

Prioritize quality and your satisfaction above all

Ready for a smoother PCB journey?

Get a personalized PCBA quote based on your BOM today!

Or, you may want to know about our PCB Assembly Services.

Contact your dedicatedNextPCB sales rep.

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Tag: BOM