Understanding Bill of Materials (BOM) and the Importance of Justifying Components

Introduction

In engineering and technology development, every successful project is built on careful planning and structured documentation. One of the most crucial tools in this process is the Bill of Materials (BOM). A BOM is essentially a detailed list of all the components, materials, and parts required to bring a project to life. From robotics and electronics to large-scale industrial production, BOMs serve as the backbone for procurement, assembly, and quality assurance.

What is a BOM and Why is it Important?

A BOM outlines all the items needed to build a system. It usually contains part names, part numbers, specifications, quantities, and sourcing details. For instance, when building a robotic system, the BOM may list microcontrollers, motors, sensors, connectors, and even screws.

In industries such as electronics, automotive, or manufacturing, the BOM plays a vital role in:

• Ensuring consistency and standardization during production.

• Making procurement easier by clearly specifying what is needed.

• Preventing mistakes or mismatched parts during assembly.

• Allowing cost estimation and project budgeting.

Without a proper BOM, projects can face delays, unnecessary costs, or even failure due to poor part selection.

Types of BOM

BOMs are not one-size-fits-all. Different industries and applications require different types of BOMs depending on their purpose and structure. The most common types include:

1. Engineering BOM (EBOM)

   • Prepared by engineers during the design phase.

   • Contains the technical representation of components, such as microcontrollers, resistors, or sensors in a robotic project.

   • Used for design verification and engineering documentation.

2. Manufacturing BOM (MBOM)

   • Defines all the parts and assemblies required for manufacturing.

   • Includes raw materials, subassemblies, and packaging information.

   • Used by production teams to plan and execute the manufacturing process.

3. Sales BOM (SBOM)

   • Used in sales and distribution processes.

   • Defines the product as it is sold to the customer, including options or configurations.

   • Example: A robotic kit may have variations (with or without additional sensors) listed under SBOM.

4. Service BOM

   • Used in after-sales and service industries.

   • Lists parts required for servicing, repairing, or maintaining a product.

   • Example: Replacement of motors or batteries in robotics.

5. Configurable BOM (CBOM)

   • Applied when products can be customized or configured by customers.

   • Useful in industries like automotive or modular robotics where customers select features.

Structures of BOM

BOMs can also be represented in different structures depending on how information is organized:

1. Single-Level BOM

   • A flat list of all parts and materials required.

   • Best suited for simple projects, like a small electronic circuit.

     

2. Multi-Level BOM

   • Hierarchical structure showing parent-child relationships between assemblies and subassemblies.

   • Example: In a robot, the parent assembly is the chassis, and child assemblies are motors, wheels, and sensors.

   

3. Indented BOM

   • A visual, indented format that clearly shows the hierarchy and relationships of parts.

4. Flattened BOM

   • Consolidates parts from all levels into a single list, useful for procurement.

     

Key Components in a BOM

A complete BOM typically contains the following details:

• Part Number: Unique identifier for each component.

• Part Name/Description: What the part is.

• Quantity: Number of units required.

• Unit of Measure: For clarity (e.g., pieces, meters).

• Procurement Type: Whether it is bought or custom-made.

• Supplier/Manufacturer: Where to source the part.

• Reference Designators: For electronics, which circuit location the part belongs to.

• Notes/Comments: Any additional remarks, such as alternative parts.

Here is sample of a BOM

BOM Displays

BOMs can be displayed in different formats:

• Tabular Display – The most common, showing parts in a table format with columns for each attribute.

• Graphical Display – Often used for multi-level BOMs, showing assemblies and subassemblies in tree structures.

• Software-Based Displays – Using tools like ERP systems, PLM software, or spreadsheets for real-time updates and easier management.

Why Justify Components?

Creating a BOM is not just about listing parts—it is about making informed decisions. Every component included in a BOM must be justified. This means answering the question: Why this component and not another?

Justification is essential because:

1. Suitability for Application – Different components may perform the same task but with varying efficiency. For example, an Arduino Uno or an Arduino Mega can both control wheel ticks, but the Mega has more digital pins and higher memory, making it better suited for projects requiring multiple sensors or extended functionalities.

2. Cost Efficiency – Choosing the right component balances performance with budget. Sometimes, a cheaper component might do the job without over-engineering the system.

3. Reliability and Compatibility – Components must integrate seamlessly. Using parts that match the voltage, resistance, communication protocol, or current ratings ensures reliability.

4. Future Scalability – Justifying parts also considers whether the system may need expansion in the future.

Examples of Justifying Component Choices

• Arduino Uno vs. Arduino Mega: If your project only needs a few sensors and actuators, the Uno may be sufficient. However, if the project requires multiple PWM pins, larger memory for code, or more serial communication ports, the Mega is the justified choice.

• DC Motor vs. Stepper Motor: A DC motor may be fine for simple rotational tasks, but if precise control of angle and position is needed (e.g., in robotic arms), a stepper motor is better justified.

• Li-ion Battery vs. Lead Acid Battery: While lead-acid batteries are cheaper, Li-ion batteries are lighter, rechargeable, and have higher energy density, making them ideal for portable robotic applications.

Advantages of Creating a BOM

• Promotes clarity and avoids confusion during production.

• Saves time in procurement and assembly.

• Reduces costs by avoiding duplication and wrong purchases.

• Ensures quality and consistency across builds.

• Facilitates project management and collaboration.

• Enables easy troubleshooting and servicing in the future.

Steps to Creating a Good BOM

1. Define the Project Requirements – Understand the functions and scope of the project.

2. List All Components – Include every part, from microcontrollers and motors to wires and screws.

3. Document Justification – For each component, provide:

   • Why it was chosen.

   • Alternative options available.

   • Key specifications (voltage, resistance, memory size, etc.).

   • Photos or datasheets for reference.

4. Organize in a Structure – Decide if you need a single-level or multi-level BOM.

5. Assign Part Numbers and Quantities – To avoid confusion.

6. Validate with the Team – Review to ensure accuracy and feasibility.

7. Update Regularly – A BOM is a living document and should be updated as the project evolves.

How Does This Help in the Industry?

The process of justifying components builds a culture of critical thinking, efficiency, and accountability. In industries:

• It reduces waste and unnecessary costs.

• It ensures systems are robust and well-engineered.

• It improves collaboration, as everyone in the team understands why certain parts were chosen.

• It supports documentation for certifications and compliance.

Conclusion

Through my internship with Dojo Robotics, I have experienced firsthand how essential a BOM and its justification are in real-world projects. Every time a BOM is created, careful thought must go into each part. This practice not only ensures the success of current projects but also strengthens problem-solving and decision-making skills. Ultimately, learning how to justify components equips engineers and innovators with the ability to design smarter, more efficient, and reliable systems. By understanding BOM types, structures, and best practices, engineers are better prepared to transition from classroom projects to impactful industrial applications.

References

1. https://www.appknox.com/blog/bill-of-materials

2. https://www.optiproerp.com/blog/10-types-boms-explained/