How to Check Gerber Files for Manufacturing Problems

 The process of checking Gerber files for manufacturing problems is crucial in printed circuit board (PCB) production. This comprehensive guide will walk you through the essential steps and considerations to ensure your Gerber files are manufacturing-ready, helping you avoid costly mistakes and production delays.

Understanding Gerber Files

What Are Gerber Files?

Gerber files are the standard format used in the PCB industry to communicate design information to manufacturers. They contain vector data that describes the various layers and features of a PCB design, including copper traces, solder masks, silkscreen, and drilling information.

Types of Gerber File Formats

Format Type
Description
Current Status
RS-274D
Legacy format with limited features
Obsolete but still supported
RS-274X
Extended format with embedded apertures
Industry standard
X2
Latest format with additional metadata
Growing adoption

Essential Pre-Check Steps

Collecting Required Files

Before beginning the verification process, ensure you have all necessary Gerber files:

Layer Type
File Extension
Purpose
Top Copper
.GTL
Main conductor layer
Bottom Copper
.GBL
Secondary conductor layer
Solder Mask
.GTS, .GBS
Protective coating
Silkscreen
.GTO, .GBO
Component markings
Drill Files
.TXT, .XLN
Hole locations
Outline
.GKO
Board boundaries

File Naming Conventions

Maintaining consistent file naming is crucial for avoiding confusion during manufacturing:

Layer Description
Recommended Prefix
Example
Top Layer
TOP_
TOP_COPPER.GTL
Bottom Layer
BOT_
BOT_COPPER.GBL
Inner Layer
IN[X]_
IN1_POWER.GTL
Drill File
DRILL_
DRILL_THROUGH.TXT

Detailed Verification Process

1. Layer Stack-up Verification

The layer stack-up must be clearly defined and consistent. A typical 4-layer PCB stack-up might look like this:

Layer Order
Layer Name
Layer Type
Thickness (mm)
1
Top Copper
Signal
0.035
2
Inner Layer 1
Power
0.035
3
Inner Layer 2
Ground
0.035
4
Bottom Copper
Signal
0.035

2. Design Rule Checks (DRC)

Critical DRC Parameters

Parameter
Recommended Minimum
Description
Trace Width
0.15mm
Minimum copper trace width
Trace Spacing
0.15mm
Minimum space between traces
Drill Size
0.3mm
Minimum hole diameter
Annular Ring
0.125mm
Minimum copper around holes
Edge Clearance
0.3mm
Distance from traces to board edge

3. Common Manufacturing Issues

Copper Layer Checks

Issue Type
Description
Prevention Method
Copper Islands
Isolated copper areas
Remove or connect to ground
Acid Traps
Acute angles in traces
Use 45-degree angles
Slivers
Thin copper remnants
Adjust design rules

Solder Mask Considerations

Feature
Requirement
Reason
Solder Mask Dam
Min 0.1mm
Prevent solder bridges
Mask Opening
±0.05mm tolerance
Ensure proper pad exposure
Edge Relief
Min 0.25mm
Prevent mask lifting

Advanced Verification Steps

1. Panelization Requirements

Parameter
Specification
Notes
Panel Size
450mm x 350mm max
Standard production size
Board Spacing
2.5mm minimum
For depaneling clearance
Fiducial Marks
3 recommended
For assembly alignment

2. Impedance Control

Layer Type
Target Impedance
Tolerance
Microstrip
50Ω
±10%
Stripline
50Ω
±10%
Differential Pairs
100Ω
±10%

3. Special Features Verification

Plated Through-Holes

Feature
Specification
Application
PTH
≥0.3mm diameter
Component leads
Via
≥0.2mm diameter
Signal routing
Micro Via
≥0.1mm diameter
HDI designs

Manufacturing Documentation

Required Documentation Checklist

Document Type
Purpose
Format
Fabrication Drawing
Overall board specifications
PDF
Assembly Drawing
Component placement guide
PDF
BOM
Component list and quantities
Excel
Pick & Place File
Assembly machine coordinates
CSV

Layer Identification

Layer ID
Color Code
Standard Name
L1
Red
Top Layer
L2
Green
Ground Layer
L3
Blue
Power Layer
L4
Yellow
Bottom Layer

Quality Assurance Process

1. Verification Software Tools

Tool Type
Purpose
Key Features
Gerber Viewers
Visual inspection
Layer visibility control
DFM Analysis
Manufacturing checks
Automated rule checking
CAM Tools
Tool path verification
Manufacturing simulation

2. Common Quality Checks

Check Type
Description
Acceptance Criteria
Registration
Layer alignment
±0.1mm max offset
Copper Balance
Distribution of copper
20-80% coverage
Hole Quality
Drill specifications
±0.1mm tolerance

Frequently Asked Questions

Q1: What are the most critical Gerber files needed for PCB manufacturing?

A1: The essential Gerber files include top and bottom copper layers (.GTL, .GBL), solder mask layers (.GTS, .GBS), silkscreen layers (.GTO, .GBO), drill files (.TXT or .XLN), and board outline (.GKO). Inner layer files are required for multilayer boards.

Q2: How can I verify that my Gerber files are complete and correct?

A2: Use specialized Gerber viewer software to check each layer visually, verify layer alignment, confirm drill locations, and run DRC checks. Compare the viewer's rendering against your original PCB design to ensure all features are present and correctly positioned.

Q3: What are the common reasons for Gerber file rejection by manufacturers?

A3: Common reasons include missing or incomplete files, incorrect file formats, design rule violations (trace width/spacing), missing drill information, undefined board outline, and incorrect layer stack-up definition.

Q4: How do I ensure proper layer stack-up in my Gerber files?

A4: Include a detailed stack-up diagram in your fabrication drawing, clearly indicating layer order, material types, and thicknesses. Verify that layer names in Gerber files match your stack-up documentation.

Q5: What's the importance of checking copper balance in Gerber files?

A5: Proper copper balance helps prevent board warping during manufacturing and ensures even plating distribution. Aim for 20-80% copper coverage on each layer and consider adding copper pour areas to achieve better balance.

Conclusion

Thorough verification of Gerber files is crucial for successful PCB manufacturing. Following this comprehensive guide will help ensure your files meet manufacturing requirements and reduce the risk of production issues. Remember to:

• Verify all required files are present and properly formatted
• Check against common manufacturing issues
• Use appropriate verification tools
• Document specifications clearly
• Maintain open communication with your manufacturer