Gerber Files Required for PCB Assembly: A Complete Guide

Gerber files are the standard manufacturing data used to communicate PCB layer information to fabrication facilities. However, Gerber files alone are usually not enough for complete PCB assembly (PCBA). Manufacturers also need component information, placement coordinates, and assembly instructions to build a fully functional electronic product.

This guide explains which Gerber files are required for PCB assembly, how they work with BOM and pick-and-place files, how to prepare a complete manufacturing package, and how to avoid common mistakes before submitting a PCB assembly order.

1. What Are Gerber Files in PCB Assembly?

Gerber files are digital manufacturing files that describe the physical features of a printed circuit board. They contain the graphical information required to reproduce individual PCB layers, including copper traces, solder mask openings, silkscreen markings, and board outlines.

The Gerber format is maintained by Ucamco and is widely supported by PCB design and manufacturing software. Modern Gerber formats can also carry metadata that helps manufacturing systems interpret layer functions and design features.

Each Gerber file generally represents a specific layer or manufacturing function.

For example, a four-layer PCB may require separate files for the top copper, two internal copper layers, bottom copper, solder masks, silkscreens, and board outline.

Why are Gerber files important?

Gerber files provide the geometric information needed to manufacture the bare PCB accurately. They help PCB manufacturers:

• Reproduce copper traces, pads, and plane structures.

• Define solder mask openings and exposed copper areas.

• Print component reference markings and other silkscreen information.

• Identify the board outline and certain mechanical features.

• Prepare fabrication data for CAM review and manufacturing.

For PCB assembly, Gerber files also provide valuable references for checking component pad locations, solder mask clearances, and alignment between the PCB and assembly documentation.

Important distinction: Gerber files describe the board’s physical manufacturing features. They do not normally provide a complete list of components, purchasing specifications, or machine placement instructions.

2. What Gerber Files Are Required for PCB Assembly?

The exact number of Gerber files depends on the PCB layer count, board design, and manufacturing requirements.

For a typical two-layer PCB, the following files are commonly included in the fabrication package.

Essential Gerber file checklist

File extensions are conventions rather than universal requirements. The actual layer function should be confirmed from file metadata, CAD output settings, or the fabrication drawing. NC drill files are often Excellon-format files rather than Gerber layer files.

2.1 Top and Bottom Copper Layers

Copper layer files contain the conductive patterns used to connect electronic components.

These patterns include:

• Copper traces

• Surface-mount pads

• Through-hole pads

• Copper pours and power planes

• Thermal relief connections

The top copper file commonly uses the .GTL extension, while the bottom copper file commonly uses .GBL.

For multilayer PCBs, additional internal copper files are necessary. Their correct stacking order must be clearly identified.

Missing or incorrectly ordered copper layers can cause open circuits, short circuits, and other serious manufacturing problems.

2.2 Top and Bottom Solder Mask Layers

Solder mask files define where solder mask should be opened to expose pads or other specified copper areas.

They are especially important for fine-pitch components such as QFN, BGA, and small passive devices.

Incorrect solder mask openings may contribute to:

• Solder bridging

• Insufficient solderable pad exposure

• Assembly difficulties

• Reduced manufacturing yield

Solder mask files should be reviewed together with copper and solder paste layers to ensure proper alignment.

2.3 Silkscreen Layers

Silkscreen layers contain printed markings that help identify components and provide useful assembly information.

Common markings include component reference designators such as R1, C5, and U3, along with polarity symbols, connector labels, and pin-one indicators.

Silkscreen files are helpful but not always mandatory. For example, a compact PCB may intentionally omit silkscreen markings due to limited space.

For assembly, a separate assembly drawing should still be provided when component locations or orientations cannot be clearly determined from the silkscreen.

2.4 Board Outline and Mechanical Layers

The board outline defines the final shape and dimensions of the PCB.

Depending on the CAD software, the outline may be exported as a dedicated Gerber file or included in a mechanical layer.

It should clearly identify relevant features such as board edges, cutouts, slots, and routing requirements.

Mechanical drawings may also be required for complex boards, particularly when the design includes unusual cutouts, tight dimensional tolerances, or special mounting requirements.

2.5 Drill Files

Drill files specify hole locations and sizes for plated and non-plated holes.

They are necessary for features such as:

• Through-hole component leads

• Vias

• Mounting holes

• Plated slots

• Mechanical holes

Drill files are commonly supplied in Excellon format. Plated and non-plated holes should be clearly distinguished, whether through separate files or unambiguous fabrication documentation.

Missing or incorrect drill information can result in unusable PCBs even when all copper Gerber layers are correct.

2.6 Solder Paste Layers

Solder paste files define stencil apertures used during the solder paste printing process.

The top solder paste layer is commonly named .GTP, and the bottom solder paste layer .GBP.

These files are particularly useful for SMT assembly because they help determine where solder paste is deposited before component placement.

However, the final stencil design may require adjustments based on component package, solder paste characteristics, PCB finish, and assembly process.

For example, the thermal pad of a QFN package may require segmented paste apertures rather than one large opening.

Practical recommendation: Include solder paste layers whenever SMT assembly is required, but allow the assembly manufacturer to review and approve the final stencil aperture design.

3. Are Gerber Files Enough for PCB Assembly?

No. For most conventional PCB assembly projects, Gerber files alone are insufficient.

Gerber files primarily describe the bare PCB geometry. To purchase components and assemble them correctly, the manufacturer needs additional documentation.

A typical turnkey PCB assembly package contains the following files.

Alternative integrated data packages such as ODB++ or IPC-2581 may replace some conventional fabrication outputs when supported by the manufacturer. Altium’s manufacturing documentation identifies these as established fabrication output options alongside Gerber and NC drill data.

3.1 Bill of Materials (BOM)

The Bill of Materials identifies the electronic components required for the PCB assembly.

A well-prepared BOM should include:

The manufacturer part number is particularly important because similar components can have different electrical characteristics, footprints, or operating limits.

For turnkey assembly, the BOM should also specify acceptable alternatives, do-not-populate (DNP) components, and any customer-supplied materials.

3.2 Pick-and-Place File (Centroid File)

A pick-and-place file provides the component placement information used to prepare automated SMT assembly equipment.

It normally includes the component reference designator, X/Y coordinates, rotation, and board side.

Example:

Designator,Footprint,Center-X(mm),Center-Y(mm),Rotation,Layer
R1,0603,12.50,18.20,90,Top
C1,0402,20.30,15.60,0,Top
U1,QFN-32,35.00,25.00,180,Top
J1,USB-C,42.80,12.40,0,Bottom

These coordinates and rotations are illustrative only.

A pick-and-place file is not the same as a Gerber file. It provides placement information rather than PCB copper or mask geometry.

The assembly engineer must verify the placement file against the assembly drawing and CAD footprint conventions, especially for polarized components and packages with ambiguous orientation.

3.3 PCB Assembly Drawings

Assembly drawings show the intended placement and orientation of electronic components.

They are especially important for:

• Polarized capacitors

• Diodes and LEDs

• IC pin-one orientation

• Connectors

• Mechanical assemblies

• Through-hole components

• Special assembly instructions

A clear assembly drawing reduces interpretation errors and helps technicians verify first-article assemblies.

3.4 Programming and Testing Files

For PCB assemblies that require firmware programming or functional testing, additional information may be necessary.

Examples include firmware binaries, programming interfaces, test procedures, acceptance criteria, calibration instructions, and test-point documentation.

These files are not necessarily required to fabricate the PCB, but they may be essential to deliver a fully tested electronic assembly.

4. Gerber Files vs. BOM vs. Pick-and-Place Files

Although these files are often submitted together, they serve different purposes.

The simplest way to understand their relationship is:

• Gerber: What does the PCB physically look like?

• BOM: Which components must be installed?

• Pick-and-Place: Where and how should the components be positioned?

• Assembly Drawing: How should the assembled board look?

• Test Documentation: How should the finished assembly be verified?

A reliable PCBA process depends on the consistency of all these documents.

5. How to Generate Gerber Files for PCB Assembly

Most professional PCB design tools can export Gerber and drill files.

The exact export procedure depends on the CAD software, but the underlying process is similar.

5.1 Exporting Gerber Files from Altium Designer

In Altium Designer, fabrication outputs can be generated through the PCB editor or an Output Job configuration.

A typical workflow is:

1. Complete PCB layout and run the Design Rule Check (DRC).

2. Open the fabrication output configuration.

3. Select Gerber RS-274X or Gerber X2.

4. Enable all required copper, solder mask, silkscreen, paste, and outline layers.

5. Confirm the coordinate format, units, and layer assignments.

6. Generate NC drill data.

7. Export the BOM, component placement files, and assembly drawings separately.

8. Review the output package before submission.

Gerber X2 supports additional attributes that can identify manufacturing features and layer functions, helping reduce ambiguity during CAM processing.

5.2 Exporting Gerber Files from KiCad

KiCad provides dedicated fabrication output functions for Gerber, drill, and component placement files.

A typical process is:

1. Open the PCB design in KiCad PCB Editor.

2. Select File → Fabrication Outputs → Gerbers (.gbr).

3. Choose the required PCB layers.

4. Generate the Gerber files.

5. Open the drill file generation dialog and export the required drill data.

6. Generate component placement files.

7. Export the BOM using the appropriate project workflow.

8. Inspect the generated files in a Gerber viewer.

KiCad also supports component placement outputs with assembly-variant handling, allowing different product configurations to produce different placement data.

5.3 Exporting from Other PCB Design Tools

Other tools, including Autodesk EAGLE, Fusion Electronics, EasyEDA, and OrCAD, also provide manufacturing output features.

Regardless of the software, the key requirement is that all exported files correspond to the same approved PCB revision.

Do not combine Gerber files from one revision with BOM or placement files from another.

6. Gerber X2 vs. RS-274X: Which Format Is Better?

Gerber RS-274X, often referred to as Extended Gerber, has long been used for PCB fabrication.

Gerber X2 builds on this format by introducing standardized attributes that describe manufacturing information more explicitly.

Ucamco continues to maintain the Gerber standard, including the 2026.05 layer format specification.

Recommendation: Use Gerber X2 when both the design software and PCB manufacturer support it. However, Gerber X2 does not eliminate the need for a BOM, assembly instructions, and other required PCBA documentation.

Gerber X3 can additionally represent component-related assembly information, but its practical use depends on CAD and manufacturing software support.

7. How Many Gerber Files Are Needed for a 2-Layer, 4-Layer, or 6-Layer PCB?

The number of Gerber files is not fixed because it depends on the board structure and which manufacturing features are used.

The following table illustrates typical requirements.

These totals are examples, not mandatory counts. They exclude separate drill files and optional fabrication documentation.

A board without bottom-side SMT components may not need a bottom solder paste layer. Likewise, some boards have no bottom silkscreen.

The important factor is not the number of files but whether all required manufacturing information is present and correctly identified.

8. Common Gerber File Errors That Cause PCB Assembly Problems

Even when a PCB design passes electrical rule checks, its manufacturing package may still contain errors.

8.1 Missing Solder Mask Layers

Without complete solder mask information, the manufacturer may not be able to determine the intended exposed copper areas reliably.

This can cause incorrect mask openings or delays while the design intent is clarified.

8.2 Incorrect Board Outline

An inaccurate board outline may result in boards that do not fit their intended enclosure or assembly fixtures.

Always verify board dimensions, cutouts, and mechanical tolerances.

8.3 Missing or Incorrect Drill Files

Incorrect drill coordinates, hole diameters, or plating information can make the PCB impossible to assemble.

The drill data should match the copper layers and fabrication drawing.

8.4 Mismatched BOM and Pick-and-Place Files

If a component is listed in the BOM but missing from the placement file, the manufacturer must determine whether it is a manual-placement component, a DNP item, or an export error.

This often requires clarification before assembly can proceed.

8.5 Incorrect Component Rotation

Rotation conventions vary across CAD libraries and manufacturing equipment.

A component marked as 0° in one workflow may require a different machine orientation depending on its footprint origin and package standard.

Diodes, LEDs, connectors, and integrated circuits deserve particular attention.

8.6 Inconsistent PCB Revisions

Submitting Rev A Gerber files with a Rev B BOM can cause component-to-footprint mismatches.

All files should use consistent project names, revision identifiers, and release dates.

8.7 Missing Special Manufacturing Instructions

Some design requirements cannot be safely inferred from Gerber images alone.

Examples include controlled impedance, via filling, special copper thickness, blind and buried vias, selective surface finishes, and tight mechanical tolerances.

These requirements should be explicitly documented and approved.

9. How to Check Gerber Files Before Sending Them to a PCB Assembly Manufacturer

Before submitting production data, engineers should perform a structured file review.

A Gerber viewer should be used to inspect the layers visually. The review should include the board outline, copper-to-mask alignment, drill locations, and overall layer registration.

For higher-complexity projects, additional CAM, DFM, and DFA reviews are recommended.

10. Example: Preparing Manufacturing Files for a Four-Layer SMT PCB

Consider a four-layer industrial controller PCB with the following design characteristics.

For this project, the manufacturing package might be organized as follows:

Industrial_Controller_RevB/
|
|-- 01_Gerber/
|   |-- Top_Copper.GTL
|   |-- Inner_Layer_2.G2
|   |-- Inner_Layer_3.G3
|   |-- Bottom_Copper.GBL
|   |-- Top_Mask.GTS
|   |-- Bottom_Mask.GBS
|   |-- Top_Silkscreen.GTO
|   |-- Bottom_Silkscreen.GBO
|   |-- Top_Paste.GTP
|   |-- Bottom_Paste.GBP
|   |-- Board_Outline.GKO
|
|-- 02_Drill/
|   |-- PTH.DRL
|   |-- NPTH.DRL
|
|-- 03_BOM/
|   |-- BOM_RevB.xlsx
|
|-- 04_Pick_and_Place/
|   |-- Placement_RevB.csv
|
|-- 05_Drawings/
|   |-- Assembly_Top.pdf
|   |-- Assembly_Bottom.pdf
|   |-- Fabrication_Drawing.pdf
|   |-- Stackup.pdf
|
|-- 06_Test/
|   |-- Test_Procedure.pdf
|   |-- Firmware.bin
|
|-- README_RevB.txt

This is an illustrative package structure. Actual file names and requirements should be confirmed with the manufacturer.

For this example, the production workflow would include:

1. Engineering review: Check Gerber data, stackup, BOM, and placement information.

2. PCB fabrication: Manufacture the four-layer bare boards according to approved specifications.

3. Component sourcing: Procure and verify the required electronic components.

4. Stencil preparation: Review solder paste apertures for the SMT process.

5. SMT assembly: Print solder paste, place components, and perform reflow soldering.

6. Inspection: Use appropriate inspection methods, including AOI and X-ray where needed.

7. Functional testing: Verify the assembled controller against the agreed test procedure.

The purpose of the complete data package is to reduce engineering clarification, prevent revision mismatches, and support a repeatable production process.

11. Gerber Files vs. ODB++ vs. IPC-2581

Gerber is not the only format available for transferring PCB manufacturing data.

ODB++ and IPC-2581 are structured data formats that can consolidate multiple aspects of PCB design and manufacturing information.

For standard PCB and PCBA projects, Gerber files combined with a BOM, placement file, and assembly drawings remain a practical and widely accepted approach.

For complex multilayer, HDI, or high-volume production projects, integrated formats may simplify some aspects of CAD-to-CAM data exchange.

However, no file format automatically guarantees manufacturing readiness. Design verification and engineering review remain essential.

12. Best Practices for Preparing PCB Assembly Files

A reliable PCB assembly package should be accurate, complete, and easy for the manufacturer to interpret.

Use consistent file naming

Use the same project identifier and revision across all manufacturing documents.

For example:

Industrial_Controller_RevB_Gerber.zip

Avoid ambiguous file names such as final_v2_new_latest.zip.

Provide manufacturer part numbers

Do not rely only on generic component descriptions.

Include exact manufacturer part numbers and approved alternatives wherever possible.

Clearly identify DNP components

Components marked Do Not Populate should be clearly identified in the BOM and assembly documentation.

The pick-and-place output should reflect the intended assembly variant.

Define the layer stackup

For multilayer boards, provide the intended stackup, material requirements, copper weights, and controlled impedance requirements when applicable.

Verify component orientation

Check polarized and orientation-sensitive components against assembly drawings.

Include test requirements early

Functional test coverage, programming procedures, and acceptance criteria should be discussed before production begins.

Use a controlled release package

Store all approved manufacturing files in one revision-controlled package.

Any later change should trigger a review of affected Gerber, BOM, placement, drawing, and testing documents.

13. How Leadsintec Supports PCB Manufacturing and Assembly

Preparing complete manufacturing files is an important part of a successful PCB assembly project, but it is only the beginning.

At Leadsintec, we provide PCB manufacturing and assembly services covering prototype development, component sourcing, SMT assembly, through-hole assembly, and production testing.

Our one-stop PCBA workflow can support customers through:

• PCB fabrication data review and manufacturability evaluation.

• BOM verification and electronic component sourcing.

• Prototype and small-batch PCB assembly.

• SMT and through-hole component assembly.

• AOI, X-ray inspection, and functional testing according to project requirements.

• Production coordination from prototype validation to volume manufacturing.

Whether you are developing an industrial controller, IoT device, medical electronics product, or custom embedded system, a complete manufacturing data package helps improve communication between your design team and the production facility.

Need a PCB Assembly Quote?

Send your Gerber files, BOM, pick-and-place file, and assembly requirements to the Leadsintec engineering team for review.

If your manufacturing package is incomplete, identify the available documents and the missing information so the necessary engineering clarifications can be addressed before production.

Website: Leadsintec PCB Manufacturing & Assembly

Conclusion

Gerber files are fundamental to PCB fabrication, but successful PCB assembly requires more than PCB layer data.

A complete PCBA manufacturing package should combine Gerber files, drill data, a verified BOM, pick-and-place coordinates, assembly drawings, and relevant testing requirements.

The most important step is ensuring that all documents are accurate, consistent, and based on the same approved design revision.

By preparing a complete manufacturing package and reviewing it before submission, engineers can reduce production delays, avoid assembly errors, and improve the transition from PCB prototype to reliable volume manufacturing.