Best Practices for Gerber File Output Settings: PCB Engineer’s Complete Guide

Getting Gerber file output settings wrong is one of the fastest ways to delay a PCB project. I’ve seen boards come back with misaligned drill holes, inverted solder masks, and features scaled to the wrong size—all because of incorrect export settings. The frustrating part is that these errors are entirely preventable. This guide covers the best practices for Gerber file output settings that ensure your designs translate correctly from CAD to fabrication every single time.

Why Gerber File Output Settings Matter

Your Gerber files are the manufacturing blueprint for your PCB. Every setting you choose during export—coordinate format, units, zero suppression, aperture handling—directly affects how the manufacturer interprets your design. Get these settings wrong, and features end up in the wrong locations, traces appear at incorrect widths, or layers simply don’t align.

Impact of Incorrect Output Settings

Setting Error	Consequence	Typical Symptom
Wrong coordinate format	Features scaled incorrectly	Board appears 10x larger or smaller
Mismatched zero suppression	Coordinate misinterpretation	Drill holes offset from pads
Incorrect units	Dimensional errors	25.4x scaling (inch vs mm confusion)
Missing aperture definitions	Unknown feature shapes	Pads and traces render incorrectly
Wrong layer polarity	Inverted masks	Solder mask covers pads instead of openings

The good news is that once you understand these settings and configure them correctly, you can save your export configuration and reuse it for every project.

Choosing the Right Gerber Format Version

Before adjusting any other settings, select the appropriate Gerber format version. This fundamental choice affects compatibility and data completeness.

Gerber Format Comparison

Format	Released	Apertures	Attributes	Recommendation
RS-274D	1960s	External file required	None	Avoid—obsolete
RS-274X	1990s	Embedded in file	Limited	Industry standard—use this
Gerber X2	2014	Embedded in file	Full layer/function data	Use if manufacturer supports
Gerber X3	2019	Embedded in file	Extended attributes	Limited adoption

Best practice: Export in RS-274X format unless your manufacturer specifically requests Gerber X2. RS-274X is self-contained (no separate aperture files needed) and universally supported. If your CAD tool supports X2, you can export in both formats to maximize compatibility.

RS-274X vs RS-274D: Why It Matters

RS-274D required a separate aperture list file that defined all pad shapes and sizes. If this file was missing, mismatched, or corrupted, the Gerber data became unreadable—the manufacturer had no way to know what shapes to draw. RS-274X solved this by embedding aperture definitions directly in each Gerber file. Always verify your export uses “Embedded apertures (RS-274X)” rather than external aperture files.

Coordinate Format Settings

The coordinate format defines how numerical precision is expressed in your Gerber files. This setting must match between Gerber files and drill files to ensure proper alignment.

Understanding Coordinate Format Notation

Coordinate format is expressed as X:Y where X is integer digits and Y is decimal digits.

Format	Total Digits	Resolution (inches)	Resolution (mm)	Common Use
2:3	5	0.001″ (1 mil)	0.001mm	Legacy, low precision
2:4	6	0.0001″ (0.1 mil)	0.0001mm	Standard imperial
2:5	7	0.00001″ (0.01 mil)	0.00001mm	High precision imperial
3:3	6	N/A	0.001mm	Standard metric
4:5	9	N/A	0.00001mm	High precision metric

Best practice: Use 2:5 format for metric units or 2:4 format for imperial units. These provide sufficient precision for modern manufacturing tolerances including fine-pitch components and HDI designs. Always confirm your manufacturer supports your chosen format before exporting.

Matching Format Across All Files

A critical requirement: Gerber files and NC drill files must use the same coordinate format. If your Gerbers use 2:5 and your drill files use 2:4, drill holes will appear offset from their intended positions.

File Type	Recommended Format (Metric)	Recommended Format (Imperial)
Copper layers	2:5 or 4:5	2:4 or 2:5
Solder mask	2:5 or 4:5	2:4 or 2:5
Silkscreen	2:5 or 4:5	2:4 or 2:5
Board outline	2:5 or 4:5	2:4 or 2:5
NC drill files	Same as Gerbers	Same as Gerbers

Unit Settings: Inches vs Millimeters

Choose either inches or millimeters and use that unit consistently across all output files. Mixing units is a common source of manufacturing errors.

Unit Selection Guidelines

Scenario	Recommended Unit	Reason
Designs in metric CAD	Millimeters	Maintains native precision
Designs in imperial CAD	Inches	Maintains native precision
Working with Asian manufacturers	Millimeters	Preferred by most Asian fabs
Legacy designs from US sources	Inches	Matches original design intent
High-precision RF/microwave	Millimeters	Finer resolution available

Best practice: If your PCB design was created in millimeters, export Gerbers in millimeters. Converting units during export can introduce rounding errors, especially for features on non-standard grids.

Verifying Unit Consistency

Before sending files to manufacturing, verify unit consistency:

1. Open each Gerber file in a text editor
2. Look for the format statement (e.g., %MOIN*% for inches or %MOMM*% for millimeters)
3. Confirm all files use the same unit declaration
4. Verify drill files use matching units

Zero Suppression Settings

Zero suppression determines how coordinate numbers are formatted by removing unnecessary zeros. This setting must be interpreted correctly by the receiving CAM software.

Zero Suppression Options Explained

Setting	Effect	Example (coordinate 15.2500)
Suppress leading zeros	Removes zeros before significant digits	152500
Suppress trailing zeros	Removes zeros after significant digits	1525
Keep all zeros	No suppression	00152500
Explicit decimal	Uses actual decimal point	15.2500

Best practice: Use “Suppress leading zeros” for Gerber files—this is the most widely supported option. For drill files, match the zero suppression setting to your Gerber files. Some CAD tools default to trailing zero suppression, which can cause interpretation errors at the manufacturer.

Zero Suppression Format Statement

In RS-274X files, the format statement indicates zero suppression:

• %FSLAX24Y24*% = Leading zeros suppressed, absolute coordinates, 2:4 format
• %FSTAX24Y24*% = Trailing zeros suppressed, absolute coordinates, 2:4 format

Always verify this statement matches your intended setting.

Aperture Settings

Apertures define the shapes used to draw pads, traces, and other features. Proper aperture configuration ensures features render at correct sizes.

Essential Aperture Settings

Setting	Recommended Value	Purpose
Aperture format	Embedded (RS-274X)	Self-contained files
Flash apertures	Enabled	Discrete pads render correctly
Vector apertures	Avoid when possible	Can cause interpretation issues
Aperture matching tolerance	0.001mm or tighter	Prevents duplicate apertures

Best practice: Always enable “Embedded apertures (RS-274X)” in your export settings. This eliminates the need for separate aperture files and prevents aperture mismatch errors. Avoid using vector (drawn) apertures for pads—use flash apertures instead for cleaner, more reliable results.

Aperture Table Optimization

Some CAD tools generate excessive aperture definitions, creating unnecessarily large files. Configure your export to:

• Merge identical apertures
• Remove unused aperture definitions
• Use standard aperture shapes when possible

Layer-Specific Output Settings

Different layer types require specific attention during export.

Copper Layer Settings

Setting	Value	Notes
Polarity	Positive (dark)	Standard for copper layers
Include thermal reliefs	Yes	Required for proper plane connections
Include test points	Per design	Export if present in design
Plot mode	Filled	Not outline mode

Solder Mask Settings

Setting	Value	Notes
Polarity	Negative	Drawn areas = mask openings
Include via openings	Per design	Depends on tenting requirements
Expansion	As designed	Don’t modify during export

Critical: Solder mask polarity causes more manufacturing issues than almost any other setting. Verify your solder mask files show openings where pads should be exposed, not the inverse.

Silkscreen Settings

Setting	Value	Notes
Polarity	Positive (dark)	Drawn areas = ink applied
Clip to board outline	Recommended	Prevents ink outside board edge
Remove overlaps with pads	Recommended	Prevents solder issues

Board Outline Settings

Setting	Value	Notes
Line width	0.1mm or as specified	Defines routing path center
Closed contour	Required	Outline must form complete loop
Include cutouts	Yes	Internal routing paths

NC Drill File Output Settings

Drill files require their own careful configuration to match Gerber data.

Essential Drill File Settings

Setting	Recommended Value	Notes
Format	Excellon	Industry standard
Units	Same as Gerbers	Critical for alignment
Coordinate format	Same as Gerbers	Critical for alignment
Zero suppression	Same as Gerbers	Critical for alignment
Tool definitions	Embedded in header	Self-contained file

PTH and NPTH Separation

Configuration	When to Use
Separate files	Manufacturer requires separate plated/non-plated
Single merged file	Manufacturer accepts combined, reduces missing file risk
With slot file	If design includes routed slots

Best practice: Check your manufacturer’s requirements. Many modern fabs accept merged PTH/NPTH files, which reduces the risk of forgetting to include one file. If separating, clearly name files to indicate plated vs. non-plated.

CAD-Specific Output Configuration

Different CAD tools have different default settings and export workflows.

Altium Designer Settings

Setting	Location	Recommended Value
Format	General tab	2:5 (metric) or 2:4 (imperial)
Apertures	Apertures tab	Embedded apertures (RS-274X)
Zero suppression	General tab	Suppress leading zeros
Film size	Advanced tab	Match board dimensions + margin
Origin	General tab	Reference to relative origin

KiCad Settings

Setting	Location	Recommended Value
Plot format	Plot dialog	Gerber
Coordinate format	Plot dialog	4.6 (mm)
Use extended X2	Plot dialog	Enable if manufacturer supports
Subtract soldermask	Plot dialog	Enable
Drill format	Drill dialog	Excellon
Drill units	Drill dialog	Same as Gerber

Eagle Settings

Setting	Location	Recommended Value
Output format	CAM Processor	RS-274X
Wheel/apertures	CAM Processor	Embedded
Position offset	CAM Processor	0,0 or board origin
Optimize	CAM Processor	Enable

Pre-Export Checklist

Complete these checks before generating Gerber files.

Design Verification

Check	Action
Run DRC	Resolve all errors, review warnings
Verify connectivity	Check for unrouted nets
Check zone fills	Refill all copper pours
Verify board outline	Confirm closed contour exists
Review layer stackup	Confirm correct layer count and order

Export Configuration

Check	Action
Format version	RS-274X or X2 as required
Units	Consistent across all files
Coordinate format	Same for Gerbers and drills
Zero suppression	Same for Gerbers and drills
Layer selection	All required layers included

Post-Export Verification

Never send Gerber files to manufacturing without verification.

Verification Steps

Step	Tool	What to Check
Visual inspection	Gerber viewer	All layers present and correct
Layer alignment	Gerber viewer	Overlay copper and drill layers
Drill alignment	Gerber viewer	Holes center on pads
Board dimensions	Gerber viewer	Correct size and shape
Feature sizes	Gerber viewer	Traces and pads at expected widths
DFM check	Manufacturer tool	Design rule compliance

Recommended Verification Tools

Tool	Type	Features
Gerbv	Free, open source	Layer viewing, measurement
KiCad GerbView	Free, open source	Part of KiCad suite
ViewMate	Free (basic)	Professional viewer
CAM350	Commercial	Full CAM functionality
HQDFM	Online, free	DFM checking
Manufacturer viewers	Online, free	JLCPCB, PCBWay, etc.

Useful Resources

Gerber Specification Documents

Resource	Source	URL
Gerber Format Specification	Ucamco	ucamco.com/gerber
Excellon Format Reference	Industry standard	Various sources
IPC-D-356 Netlist Standard	IPC	ipc.org

CAD Software Documentation

Software	Documentation URL
Altium Designer	altium.com/documentation
KiCad	docs.kicad.org
Eagle/Fusion 360	autodesk.com/support
OrCAD	cadence.com/support

Manufacturer Guidelines

Manufacturer	Guidelines URL
JLCPCB	jlcpcb.com/help
PCBWay	pcbway.com/blog
OSH Park	docs.oshpark.com
Eurocircuits	eurocircuits.com/help

Frequently Asked Questions

What coordinate format should I use for high-density designs?

For HDI and fine-pitch designs (0.4mm pitch BGAs, 3/3 mil traces), use 2:5 format with metric units. This provides 0.00001mm resolution, sufficient for features down to 0.05mm (2 mil). The 2:4 format may not provide adequate precision for these designs. Always verify your manufacturer supports your chosen format—some budget services have equipment limitations that restrict format options.

Why do my drill holes appear offset from pads in the Gerber viewer?

This almost always indicates a mismatch between Gerber and drill file settings. Check three things: First, verify both files use the same units (inches or mm). Second, confirm the coordinate format matches (both should be 2:4 or both 2:5). Third, check zero suppression settings—if Gerbers use leading zero suppression and drill files use trailing, coordinates will be misinterpreted. Re-export both file types with identical settings.

Should I use Gerber X2 format instead of RS-274X?

Use Gerber X2 if your manufacturer supports it and your CAD tool exports it reliably. X2 adds layer function attributes that help CAM software automatically identify layer types (top copper, bottom solder mask, etc.), reducing manual interpretation and errors. However, RS-274X remains universally supported, so if you’re unsure about X2 compatibility, stick with RS-274X. Some engineers export both formats as a safeguard.

What’s the difference between leading and trailing zero suppression?

Zero suppression removes unnecessary zeros from coordinate numbers to reduce file size. Leading zero suppression removes zeros from the beginning (00152500 becomes 152500), while trailing suppression removes them from the end (15250000 becomes 1525). The receiving software must know which method was used to correctly interpret coordinates. Leading zero suppression is more common and widely supported—use it unless your manufacturer specifically requires trailing suppression.

How do I verify my solder mask polarity is correct?

Open your solder mask Gerber file in a viewer and compare it to your copper layer. Pad locations should appear as openings (clear areas) in the solder mask, not as filled areas. If pads appear solid in the solder mask file, your polarity is inverted. Most CAD tools export solder mask as negative polarity (drawn areas = openings), but some viewers display this differently. The safest check is overlaying solder mask on copper—openings should exactly match pad locations where you want exposed copper.

Conclusion

Proper Gerber file output settings form the foundation of successful PCB manufacturing. The settings covered in this guide—format version, coordinate format, units, zero suppression, and aperture configuration—must be correct and consistent across all files. Get these right, and your boards will manufacture exactly as designed.

The most important takeaways: use RS-274X format with embedded apertures, maintain identical coordinate format and units between Gerber and drill files, use leading zero suppression, and always verify your output before sending to manufacturing. Save your export configuration once it’s working correctly, and you’ll eliminate this source of errors for future projects.

Take the extra time to verify your Gerber files in a viewer before every manufacturing order. The few minutes spent checking alignment, dimensions, and layer content can save days of delay and significant cost when problems are caught before fabrication instead of after.