PCB Assembly Files: Gerber, BOM, and Centroid Requirements

You'll need three essential file types for PCB assembly: Gerber files that define your copper layers, trace patterns, and design specifications; a Bill of Materials listing every component with part numbers and quantities; and a centroid file that pinpoints exact component placement for pick-and-place machines.

Each file type serves a distinct purpose in ensuring accurate manufacturing. You're likely wondering how to organize and format these files correctly to avoid costly manufacturing delays.

Improve product reliability through PCB assembly built for precision, traceability, and dependable performance.

Brief Overview

Gerber files define electrical connections and layer specifications using industry-standard RS-274X format for accurate PCB reproduction. Bill of Materials must include reference designators, part numbers, quantities, manufacturer details, and voltage/current specifications for assembly. Centroid files map component placement coordinates ensuring accurate automated assembly and reducing installation errors during manufacturing. Organize submission files with clear naming conventions, including Gerber layers, BOM, centroid data, and comprehensive README documentation. Verify file integrity using dedicated viewers and confirm consistent coordinate systems and units across all submission documents.

Understanding Gerber Files and Layer Information

Gerber files are the blueprint for your PCB assembly—they're the standardized format that communicates your design to manufacturers. You'll need to include multiple layers: copper layers for traces and pads, solder mask layers for protection, and silkscreen layers for component identification. Each layer serves a critical safety function. The copper layers define your electrical connections, while solder mask layers prevent unintended shorts and corrosion. Silkscreen layers help you and technicians identify components correctly, reducing assembly errors. You must export these files with proper naming conventions and specifications. Ensure your gerber files include accurate trace widths, clearances, and via information. Manufacturers use these files to verify your design meets safety standards before production begins.

The Role of Gerber File Formats in PCB Fabrication

Since manufacturers depend on standardized file formats to translate your design into physical boards, understanding how these formats function is essential to successful fabrication. Gerber files serve as the primary communication tool between your design software and the fabrication facility's manufacturing equipment. They contain precise layer information, trace widths, spacing, and copper patterns that directly control the PCB's electrical integrity and safety performance. Each Gerber file represents a specific layer—copper, solder mask, silkscreen, or drill data. By adhering to industry standards like RS-274X, you ensure accurate reproduction of your design specifications. Manufacturers use these files to program CNC machines, laser systems, and chemical etching processes. Providing complete, correctly formatted Gerber files eliminates ambiguity, reduces errors, and prevents manufacturing delays that could compromise your board's reliability and safety.

Creating a Comprehensive Bill of Materials

While Gerber files communicate your design's physical structure to manufacturers, you'll also need to provide detailed information about every component that goes into your board. Your Bill of Materials (BOM) lists each component's reference designator, part number, quantity, and manufacturer specifications. Accuracy here is critical—incorrect component values can cause circuit failures or safety hazards.

Organize your BOM in a clear, standardized format that manufacturers can easily parse. Include manufacturer names and part numbers to ensure suppliers source identical components. Specify component tolerances, voltage ratings, and temperature specifications where relevant for safe operation.

Remove obsolete parts and verify availability before submitting. Cross-reference your BOM against your schematic to catch discrepancies. A well-constructed BOM prevents costly errors during assembly and ensures your final product meets safety and performance standards.

BOM Organization and Component Specifications

A well-organized BOM serves as the bridge between your design and the assembly floor, so you'll want to structure it with both clarity and precision. Include essential columns: reference designators, part numbers, quantities, and manufacturer details. You'll minimize assembly errors and safety risks by specifying exact components rather than generic substitutes.

Organize your BOM logically—group components by type or placement area. This arrangement helps assemblers locate parts efficiently and reduces the chance of incorrect installations that could compromise circuit safety.

Include voltage and current ratings for critical components. You'll prevent dangerous mismatches that cause failures or fire hazards. List lead-free specifications if required by your standards. Add notes about polarized components or special handling requirements.

Your precision here directly impacts manufacturing safety and product reliability.

Centroid Files: Placement Precision and Accuracy

Once you've finalized your BOM, you'll need centroid files to guide the pick-and-place machine's precise positioning of each component on the PCB. These files contain X and Y coordinates for every component, ensuring accurate placement that prevents electrical failures and safety hazards.

You must provide centroid data in formats your assembler accepts, typically ASCII or CSV files. Verify that coordinates reference your PCB's origin point consistently—usually the bottom-left corner. Include rotation angles for polarized components to avoid dangerous misorientation.

Double-check all measurements for accuracy; even minor discrepancies cause shorts, opens, or component failures. Work with your assembler to confirm file format compatibility https://pastelink.net/ghprkl5m and coordinate systems before production. Precise centroid files protect both your design's integrity and end-user safety.

Preparing Your Files for Manufacturer Submission

Before you submit your assembly package to the manufacturer, you'll need to consolidate all your design files into an organized, clearly labeled submission that meets their specifications. Create a dedicated folder containing your Gerber files, BOM, and centroid file, naming each document according to industry standards. Include a README file documenting file formats, PCB dimensions, and any special assembly notes. Verify that all files use consistent coordinate systems and units to prevent misalignment hazards during production.

Double-check file integrity by opening them in dedicated viewers. Confirm your manufacturer's specific requirements regarding file formats, naming conventions, and acceptable tolerances. Submit files in their recommended format—typically compressed archives—to ensure nothing gets corrupted during transfer. This systematic approach minimizes production errors and accelerates your assembly timeline.

Common Mistakes and How to Avoid Them

Even with careful preparation, manufacturers frequently encounter preventable errors that delay production and increase costs. You'll want to avoid these common pitfalls to protect your assembly quality and safety.

First, don't submit mismatched file versions—your Gerber, BOM, and centroid files must coordinate perfectly. Verify component designators are identical across all documents. Second, neglecting to specify critical safety parameters creates hazards. Always include solder mask clearances, trace widths, and voltage isolation requirements on your drawings.

Third, you shouldn't omit manufacturer part numbers or use generic descriptions in your BOM. This ambiguity causes substitutions that compromise reliability. Fourth, failing to validate centroid coordinates results in misplaced components and shorts.

Finally, don't skip the final review. Cross-check file integrity, verify units consistency, and confirm your manufacturer can fulfill all specifications before submission.

Frequently Asked Questions

What File Format Should I Use if My Manufacturer Requests Gerber Files in Odb++ Instead?

You should use ODB++ format when your manufacturer requests it. It's a comprehensive, single-file format that contains all PCB design data—gerber information, drill files, and assembly details—in one package, making it safer and more efficient for production.

How Do I Handle Multiple Component Variations or Alternatives in My BOM?

You'll want to create separate BOM columns for each component option, clearly marking approved alternatives with part numbers and specifications. Use notes or revision fields to document why you're approving substitutes, ensuring your manufacturer can safely select compliant replacements.

Can I Use Centroid Files From My PCB Design Software Directly Without Modification?

You shouldn't use centroid files directly without verification. Always check your software's output format against your assembler's specifications, validate component placement coordinates, and confirm rotation values match your board's orientation to prevent assembly errors.

What's the Typical Turnaround Time for PCB Assembly After Submitting All Required Files?

You'll typically receive your assembled PCB within 5-10 business days after submitting all required files. However, you should confirm the exact timeline with your manufacturer, as expedited options and safety certifications can extend or reduce your turnaround time.

How Should I Communicate Last-Minute Design Changes to My PCB Assembly Manufacturer?

You'll want to contact your manufacturer immediately by phone or email before they begin production. You should clearly document all changes in writing, verify they've received your modifications, and confirm they won't compromise safety or timeline.

Summarizing

You've now got everything you need to submit assembly-ready PCB files. By organizing your Gerber layers, creating a detailed BOM, and preparing accurate centroid files, you'll streamline the manufacturing process. Double-check your documentation before submission to catch any errors early. When you follow these guidelines carefully, you'll minimize delays and ensure your boards assemble correctly on the first try. Improve product reliability through PCB assembly built for precision, traceability, and dependable performance.