WHAT IS AN EXCELLON DRILL FILE?

 

Introduction

In the world of printed circuit board (PCB) manufacturing, precision is paramount. Every hole, every connection, and every component placement must be executed with exacting standards to ensure the functionality and reliability of the final product. At the heart of this precision drilling process lies a critical file format that has become the industry standard: the Excellon drill file.

Excellon drill files serve as the blueprint for drilling operations in PCB fabrication, providing machine-readable instructions that guide automated drilling equipment with pinpoint accuracy. These specialized files contain the coordinates, sizes, and specifications for every hole that needs to be drilled into a circuit board, from mounting holes to vias that connect different layers within a multilayer PCB.

Despite their fundamental importance in electronics manufacturing, many engineers, designers, and hobbyists have limited understanding of these essential files. This comprehensive guide aims to demystify Excellon drill files, exploring their structure, format, applications, and best practices for creation and implementation.

Whether you're a seasoned PCB designer looking to optimize your manufacturing process, a student beginning to explore electronic design, or a professional troubleshooting production issues, understanding Excellon drill files is crucial knowledge. By the end of this article, you'll have gained a thorough understanding of these files, their role in the PCB manufacturing ecosystem, and how to work with them effectively to achieve high-quality results.

The History and Evolution of Excellon Drill Files

Origins of Excellon Format

The Excellon format derives its name from the Excellon Automation Company, a pioneering manufacturer of PCB drilling equipment that was established in the early 1970s. As the electronics industry began to standardize PCB manufacturing processes, there emerged a critical need for a universal language to communicate drilling instructions to automated machinery.

Excellon Automation Company developed a proprietary format for their computer numerical control (CNC) drilling machines, which quickly gained adoption throughout the industry. The format was designed to efficiently convey coordinates, tool information, and drilling parameters in a compact, machine-readable form. What began as a manufacturer-specific solution evolved into a de facto industry standard that continues to dominate PCB fabrication workflows to this day.

Evolution Through the Decades

The original Excellon format was relatively simple, designed for the technological limitations of early CNC equipment. As manufacturing technology advanced, so did the capabilities and complexities of the Excellon format:

Decade
Key Developments in Excellon Format
1970s
Original format established for basic drilling operations
1980s
Extended command set to support more complex operations
1990s
Addition of enhanced tool definitions and header information
2000s
Standardization efforts and integration with CAD/CAM systems
2010s
Support for microvias and high-density interconnect (HDI) technologies
2020s
Continued refinement for advanced manufacturing processes

Modern Standard and Variations

Today, the term "Excellon format" encompasses several variations and subformats. The two most common are:

1. Excellon 1: The legacy format that remains widely used due to its simplicity and universal support.
2. Excellon 2: An enhanced format with extended capabilities for modern manufacturing requirements.

Despite numerous attempts to create newer, more comprehensive standards, the electronics industry's deep integration of Excellon formats has ensured their continued prevalence. Even as newer formats like the IPC-NC-349 (also known as IPC-D-356A) have emerged with more standardized approaches, Excellon remains the predominant format for PCB drilling operations worldwide.

Understanding PCB Drilling in Manufacturing

The Role of Drilling in PCB Fabrication

Drilling is a critical step in the PCB manufacturing process. Before examining the technical details of Excellon files, it's important to understand why precise drilling is so essential:

1. Creating Electrical Connections: Drilled holes allow for the insertion of component leads and the formation of vias that connect different layers of a PCB.
2. Mechanical Mounting: Holes provide mounting points for securing the PCB within an enclosure or to other hardware components.
3. Thermal Management: Strategic drilling can create thermal vias that help dissipate heat from power components.
4. Signal Integrity: Properly placed and sized vias help maintain signal integrity in high-frequency circuits.

The drilling process typically occurs after the imaging and etching of the copper patterns but before plating operations. Accuracy in drilling is paramount—even small deviations can render a PCB unusable or compromise its electrical performance.

Types of Holes in PCB Manufacturing

PCB designs incorporate various types of holes, each serving specific functions:

Hole Type
Typical Diameter Range
Primary Purpose
Manufacturing Method
Through-holes
0.3 - 6.0 mm
Component mounting, vias
Mechanical drilling
Vias
0.1 - 0.3 mm
Layer interconnection
Mechanical drilling
Microvias
0.05 - 0.15 mm
High-density interconnects
Laser drilling
Blind vias
0.1 - 0.3 mm
Connect outer to inner layers
Controlled-depth drilling
Buried vias
0.1 - 0.3 mm
Connect internal layers only
Sequential lamination
Non-plated holes
0.5 - 6.0 mm
Mechanical mounting
Mechanical drilling

Drilling Technologies in PCB Manufacturing

Modern PCB manufacturing employs several drilling technologies:

1. Mechanical Drilling: The traditional method using tungsten carbide drill bits, controlled by CNC systems that follow Excellon file instructions. Mechanical drilling remains the most common approach for standard through-holes.
2. Laser Drilling: Utilized for creating microvias and high-precision holes, particularly in high-density interconnect (HDI) boards. Laser drilling offers exceptional precision but at a higher cost than mechanical drilling.
3. Punching: Used primarily for high-volume production of simple designs, punching creates holes by physically forcing a die through the board material.
4. Plasma Drilling: An emerging technology that uses focused plasma to create holes, particularly useful for difficult materials.

The Excellon drill file format has evolved to accommodate these various drilling technologies, providing the necessary instructions for each methodology while maintaining backwards compatibility with existing manufacturing systems.

Anatomy of an Excellon Drill File

Basic Structure and Format

Excellon drill files are fundamentally ASCII text files that can be opened and edited with any standard text editor. However, their structured format is designed for machine interpretation rather than human readability. A typical Excellon file consists of several distinct sections:

1. Header Section: Contains file-level information and global parameters
2. Tool Definition Section: Defines the tools (drill bits) to be used
3. Drilling Instructions: The actual coordinates and commands for drilling operations
4. Footer Section: Concludes the file with end-of-program markers

Header Information

The header section establishes the global parameters that apply throughout the drilling process. Common header commands include:

48 ; Start of header

INCH,TZ         ; Units in inches, trailing zeros format
FMAT,2          ; Format 2

Key header parameters include:

Header Parameter
Description
Common Values
Units
Defines measurement system
INCH or METRIC
Zero Format
How coordinate zeros are handled
TZ (trailing) or LZ (leading)
Format
Version of Excellon format
FMAT,1 or FMAT,2
Absolute/Incremental
Coordinate mode
ICI,ON (incremental) or ICI,OFF (absolute)

Tool Definitions

The tool definition section specifies the characteristics of each drill bit that will be used:

T1C0.0350 ; Tool 1 = 0.035 inch diameter

T2C0.0400       ; Tool 2 = 0.040 inch diameter
T3C0.1250       ; Tool 3 = 0.125 inch diameter

A comprehensive tool definition might include:

Parameter
Description
Example
Tool Number
Unique identifier
T1, T2, etc.
Diameter
Drill bit size
C0.0350 (0.035 inches)
Feed Rate
Speed of tool movement
F100
Spindle Speed
Rotation speed
S65000
Retract Rate
Speed of tool retraction
R300

Drilling Coordinates and Commands

After the header and tool definitions, the main body of the file contains the actual drilling commands:

T1 ; Select Tool 1

X01450Y02375    ; Drill at X=0.1450, Y=0.2375
X01550Y02375    ; Drill at X=0.1550, Y=0.2375
T2              ; Change to Tool 2
X03600Y01750    ; Drill at X=0.3600, Y=0.1750

Common commands within this section include:

Command
Description
Example
Tx
Tool selection
T1 (select tool 1)
X####Y####
Drill coordinate
X01450Y02375
M30
End of program
M30
G05
Drill mode
G05
G00
Rapid movement
G00X01450Y02375

Footer and End of Program

The drilling instructions typically conclude with a footer section that signals the end of the program:

M30 ; End of program

Zero Suppression and Coordinate Systems

One of the most critical aspects of Excellon files is how coordinate values are represented. Two primary approaches exist:

1. Leading Zero Suppression (LZ): Omits zeros at the beginning of coordinate values (e.g., .5 instead of 0.5)
2. Trailing Zero Suppression (TZ): Omits zeros at the end of coordinate values (e.g., 1 instead of 1.0)

Understanding which zero suppression scheme is used is crucial, as misinterpretation can lead to dramatically incorrect hole placements. Most modern CAD systems allow the user to specify which format to use when generating Excellon files.

Excellon File Formats and Variants

Excellon 1 vs. Excellon 2

The Excellon format has evolved into two primary variants, each with distinct characteristics:

Excellon 1 (Traditional Format)

The original Excellon format remains widely used due to its simplicity and universal support. Key characteristics include:

• More compact file size
• Limited header information
• Basic tool definitions
• Simpler command structure

Example of an Excellon 1 format snippet:

M48

INCH,TZ
T1C0.0350
T2C0.0400
%
T1
X01450Y02375
X01550Y02375
T2
X03600Y01750
M30

Excellon 2 (Extended Format)

The enhanced format offers extended capabilities for modern manufacturing requirements:

• More comprehensive header information
• Extended tool definitions with additional parameters
• Support for advanced drilling operations
• Better compatibility with newer CNC equipment

Example of an Excellon 2 format snippet:

M48

FMAT,2
INCH,TZ
;FILE_FORMAT=4:3
T1C0.0350F100S65000
T2C0.0400F100S55000
%
G90
T1
X01450Y02375
X01550Y02375
T2
X03600Y01750
M30

Common Variations and Manufacturer Specifics

While Excellon formats have become industry standards, variations exist based on manufacturing equipment and regional preferences:

Variation
Key Characteristics
Common Usage
Sieb & Meyer
Alternative format with similar structure
European manufacturers
IPC-NC-349
More standardized approach with enhanced metadata
Aerospace and military
Extended Excellon
Manufacturer-specific extensions
High-end PCB fabrication

These variations maintain the core principles of the Excellon format while adding specific features or syntax adjustments to accommodate specialized equipment or manufacturing requirements.

Format Specification and Standards

Despite its ubiquity, one of the challenges with Excellon drill files is the absence of a formal, universally accepted specification. The format evolved organically from Excellon Automation's proprietary system, leading to variations in implementation. However, several industry organizations have worked to standardize aspects of the format:

1. IPC (Association Connecting Electronics Industries): Has published guidelines for drill file formats as part of their PCB design standards.
2. JPCA (Japan Electronics Packaging and Circuits Association): Maintains standards that include drill file specifications.
3. Equipment Manufacturers: Companies like Excellon, Sieb & Meyer, and others publish their own format specifications that become de facto standards.

This lack of complete standardization necessitates clear communication between PCB designers and manufacturers to ensure correct interpretation of drill files.

Creating Excellon Drill Files

CAD Software and Export Options

Modern PCB design software packages automate the creation of Excellon drill files. Popular CAD tools offer various options for generating these files:

CAD Software
Export Location
Format Options
Special Features
Altium Designer
File > Fabrication Outputs
Excellon 1/2, Metric/Imperial
NC Drill Manager
Eagle
File > CAM Processor
Excellon, Metric/Imperial
Custom CAM processor
KiCad
File > Plot > Drill Files
Excellon, Metric/Imperial
Separate plated/non-plated files
OrCAD
Manufacturing > NC Drill
Excellon, Sieb & Meyer
Advanced drill control
PADS
Post Processing > NC Drill
Multiple formats
Customizable templates

When exporting drill files, designers typically encounter several configuration options:

1. Units: Selecting between metric (mm) and imperial (inches) measurements
2. Zero Suppression: Choosing leading (LZ) or trailing (TZ) zero suppression
3. Format Precision: Specifying the number of integer and decimal places
4. Tool Numbering: Defining how tool numbers are assigned
5. File Separation: Determining whether to generate separate files for different hole types

Manual Creation and Editing

While most Excellon files are generated automatically by CAD software, understanding how to manually create or edit these files can be valuable for troubleshooting or specialized applications. A basic workflow for manual creation includes:

1. Start with the header section defining global parameters
2. Define all required tools with appropriate diameters
3. Organize drilling operations by tool to minimize tool changes
4. Enter coordinates methodically, ensuring consistent formatting
5. Conclude with proper end-of-program markers

Text editors suitable for editing Excellon files include:

• Notepad++ with syntax highlighting plugins
• UltraEdit with custom syntax definitions
• Specialized PCB editors like CircuitWorks

Best Practices for File Generation

To ensure manufacturing accuracy and avoid common issues, follow these best practices when generating Excellon drill files:

1. Consistent Units: Maintain consistency in measurement units throughout the design process
2. Document Format Settings: Clearly document the chosen format settings for future reference
3. Tool Optimization: Minimize the number of different drill sizes to reduce manufacturing costs
4. Clearance Verification: Ensure adequate clearance between holes for manufacturing feasibility
5. Layer Alignment: Verify alignment with other manufacturing files (Gerber, etc.)
6. File Naming: Use clear, consistent naming conventions that indicate the file purpose

Common Export Settings and Their Effects

The export settings chosen when generating Excellon files significantly impact manufacturing outcomes:

Setting
Options
Effect on Manufacturing
Units
Inches vs. Millimeters
Affects interpretation of all dimensional values
Zero Suppression
Leading vs. Trailing
Critical for correct coordinate interpretation
Format Specification
2:4, 2:5, etc.
Determines coordinate precision
Separate Files
Combined vs. Multiple
Impacts manufacturer's workflow
Tool Numbering
Sequential vs. Optimized
Affects drilling efficiency

Incorrect export settings can lead to manufacturing defects, including misplaced holes, incorrect hole sizes, or complete fabrication failures. Always verify settings before submitting files for manufacture.

Reading and Interpreting Excellon Files

Decoding File Content

While Excellon files are designed for machine interpretation, engineers and designers often need to read and understand these files for verification or troubleshooting purposes. Here's a systematic approach to decoding an Excellon file:

1. Identify the Header: Look for the M48 command that marks the beginning of the header section
2. Determine Units and Format: Check for INCH/METRIC declarations and zero suppression settings
3. Catalog Tool Definitions: Note each tool number and its corresponding diameter
4. Map Drilling Operations: Trace through the coordinate commands to visualize hole locations
5. Verify Ending Commands: Ensure proper termination with M30 or similar commands

Tools for Viewing and Validating Files

Several software tools facilitate the visualization and validation of Excellon drill files:

Tool Type
Examples
Primary Functions
Gerber Viewers
GerbView, ViewMate, GC-Prevue
Visual representation of drill files
CAM Editors
CircuitCAM, FAB 3000
Editing and optimization
Verification Software
CAM350, DFMStream
Design rule checking
Conversion Utilities
Gerbv, GerbMagic
Format conversion and standardization
Online Services
PCBShopper viewers, EasyEDA
Quick visualization without software installation

These tools typically offer features such as:

• Graphical display of hole positions
• Overlay capabilities with other manufacturing files
• Measurement tools for verification
• Statistical analysis of hole counts and distributions
• Export to alternative formats

Common Errors and Misinterpretations

When interpreting Excellon files, several common errors can lead to manufacturing problems:

1. Unit Mismatches: Misinterpreting whether coordinates are in inches or millimeters
2. Zero Suppression Confusion: Incorrectly applying leading or trailing zero suppression
3. Origin Discrepancies: Different assumptions about the coordinate system origin
4. Tool Number Misalignment: Mismatching tools between design and manufacturing
5. Format Precision Issues: Truncation or rounding errors in coordinate values

Verification Procedures

Before submitting Excellon files for manufacturing, implementing verification procedures can prevent costly errors:

1. Visual Inspection: Overlay drill files with other PCB layers to verify alignment
2. Tool Diameter Verification: Confirm that tool definitions match design requirements
3. Hole Count Validation: Compare the number of holes with design expectations
4. Boundary Check: Ensure all holes fall within the board outline
5. Clearance Analysis: Verify minimum spacing between holes meets manufacturing capabilities

A comprehensive verification process should include both automated checks through software and manual inspection by experienced personnel.

Technical Specifications and Parameters

Coordinate Systems and Precision

Excellon drill files rely on a Cartesian coordinate system to specify hole locations. Understanding the technical aspects of these coordinates is essential:

Origin and Orientation

The default origin (0,0) in most Excellon files is the lower-left corner of the board, with positive X to the right and positive Y upward. However, variations exist:

Origin Convention
Description
Common Usage
Lower-left (Default)
Origin at bottom-left, +X right, +Y up
Most CAD systems
Center
Origin at board center, +X right, +Y up
Some European systems
Upper-left
Origin at top-left, +X right, +Y down
Specialized applications

Precision and Resolution

The precision of coordinate values impacts manufacturing accuracy:

M48

;INCH,TZ
;FILE_FORMAT=2:4

In this example, "2:4" indicates:

• 2 digits before the decimal point (integer part)
• 4 digits after the decimal point (fractional part)

This format allows positions to be specified with a resolution of 0.0001 inches (or about 2.54 microns).

Tool Parameters and Specifications

Beyond simple diameter values, tool definitions can include various parameters:

Parameter
Code
Description
Example
Tool Number
T##
Unique identifier
T01
Diameter
C####
Tool diameter
C0.0350
Feed Rate
F####
Drilling speed
F100
Spindle Speed
S#####
Rotation speed (RPM)
S65000
Retract Rate
R####
Z-axis retraction speed
R300
Depth
Z####
Drilling depth for blind holes
Z-0.062

Advanced manufacturing may require additional tool parameters for optimal results, particularly for specialized materials or high-precision applications.

G-Codes and M-Codes

Excellon files incorporate various G-codes (preparatory functions) and M-codes (miscellaneous functions) to control drilling operations:

Code
Description
Usage
G00
Rapid Movement
Positioning without drilling
G01
Linear Interpolation
Controlled-rate movement
G05
Drill Mode
Standard drilling operation
G85
Slot Mode
Creating slots through multiple drills
G90
Absolute Positioning
Coordinates reference absolute origin
G91
Incremental Positioning
Coordinates reference previous position
M00
Program Stop
Temporary halt of operations
M01
Optional Stop
Conditional halt
M18
Tool Up
Raise the drill
M25
Beginning of Pattern
Start of repeated pattern
M30
End of Program
Terminate program execution
M48
Beginning of Header
Start of parameter section
M71
Metric Mode
Switch to millimeter units
M72
Imperial Mode
Switch to inch units

Not all CNC systems support the full range of codes, and some manufacturers use proprietary extensions for specialized functions.

Header Commands and Parameters

The header section establishes global parameters for the entire drilling operation:

M48

INCH,TZ
FMAT,2
ICI,OFF
VER,1
;Layer_Color=9474304
;FILE_FORMAT=2:5
DETECT,ON

Important header parameters include:

Parameter
Description
Options
INCH/METRIC
Unit system
INCH or METRIC
TZ/LZ
Zero suppression
TZ (trailing) or LZ (leading)
FMAT
Format version
FMAT,1 or FMAT,2
ICI
Incremental mode
ON or OFF
VER
Version number
Varies by system
DETECT
Broken tool detection
ON or OFF
ATC
Automatic tool change
ON or OFF

These parameters must be correctly interpreted by the manufacturing equipment to ensure proper drilling operations. Miscommunication regarding these settings is a common source of production errors.

Applications and Use Cases

Standard PCB Manufacturing

The primary application of Excellon drill files remains standard PCB manufacturing, where they guide automated drilling systems in creating holes for:

1. Component Mounting: Through-holes for traditional leaded components
2. Vias: Electrical connections between different PCB layers
3. Mounting Holes: Mechanical attachment points for the assembled PCB
4. Thermal Relief: Heat dissipation structures for high-power components

In standard manufacturing workflows, Excellon files are typically submitted along with Gerber files as part of a complete fabrication package.

High-Density Interconnect (HDI) Applications

HDI technology pushes the boundaries of PCB density and complexity, requiring specialized drilling techniques:

Feature
Typical Specifications
Drilling Method
Excellon File Considerations
Microvias
50-150μm diameter
Laser drilling
Special tool definitions
Stacked vias
Multiple connected microvias
Sequential processing
Layer-specific drill files
Buried vias
Internal layer connections
Layer-by-layer processing
Multiple drill files
Blind vias
Surface to internal connections
Controlled-depth drilling
Depth parameters

For HDI applications, Excellon files often require enhanced precision and may be split into multiple files for different drilling stages.

Specialized Manufacturing Processes

Beyond standard PCB production, Excellon files find application in various specialized manufacturing scenarios:

1. Flex and Rigid-Flex PCBs: Drilling through flexible materials requires specialized parameters
2. Back-Drilling: Removing portions of plated through-holes to improve signal integrity
3. Controlled Depth Drilling: Creating cavities or partially penetrating holes
4. Sequential Lamination: Building complex multilayer boards through stepwise processes

Each of these applications may require specific extensions or modifications to the standard Excellon format.

Non-PCB Applications

While developed for PCB manufacturing, the Excellon format has been adapted for other precision drilling applications:

1. Front Panel Fabrication: Creating instrument panels with precisely placed holes
2. Mechanical Part Drilling: Manufacturing mechanical components requiring precise hole patterns
3. Stencil Production: Creating solder paste stencils for SMT assembly
4. Artistic Applications: CNC artwork involving precise hole patterns

These alternative applications leverage the format's ability to efficiently communicate precise drilling instructions to automated equipment.

File Processing in Manufacturing

From Design to Drilling Machine

The journey of an Excellon file from designer to manufacturing equipment involves several processing steps:

1. CAM Processing: Computer-Aided Manufacturing software processes the raw Excellon file
2. Tool Assignment: Physical drill bits are assigned to match the tool definitions
3. Panelization: Multiple boards may be arranged into a production panel
4. Machine-Specific Conversion: Translation to the specific format required by drilling equipment
5. Optimization: Drill paths are optimized to minimize drilling time
6. Verification: Final checks before committing to physical drilling

Large manufacturers typically maintain specialized CAM departments dedicated to processing and optimizing these files for production efficiency.

CAM Processing and Optimization

CAM software enhances raw Excellon files for manufacturing efficiency through various optimization techniques:

Optimization Technique
Purpose
Benefit
Tool Path Optimization
Minimize travel distance
Reduced production time
Tool Sorting
Group operations by tool
Fewer tool changes
Entry Point Selection
Optimize starting points
Improved drill bit life
Drill Sequence Planning
Minimize stress on material
Higher quality holes
Panel Optimization
Efficient use of material
Cost reduction

Professional CAM software can significantly improve production metrics through these optimizations while preserving the design intent of the original file.

Quality Control and Verification

Manufacturing facilities implement various quality control measures for drill operations:

1. Optical Inspection: Automated systems verify hole positions and sizes
2. X-Ray Verification: For buried features in multilayer boards
3. Statistical Process Control: Monitoring drill performance over time
4. First Article Inspection: Detailed verification of initial production pieces
5. In-Process Verification: Real-time feedback during drilling operations

These verification procedures ensure that the physical drilling accurately reflects the specifications in the Excellon file.

Common Manufacturing Challenges

Several challenges commonly arise when processing Excellon files in production environments:

1. Format Misinterpretation: Confusion over zero suppression or units
2. Tool Availability: Specified drill sizes not available in inventory
3. Material Limitations: Some hole specifications may not be feasible with certain materials
4. Registration Issues: Alignment problems between drilling and other fabrication steps
5. Optimization Conflicts: Path optimizations that may affect quality

Experienced fabrication partners develop procedures to address these challenges proactively, often involving direct communication with designers when issues arise.

Advanced Topics and Techniques

Controlled Depth Drilling

Controlled depth drilling creates holes that only partially penetrate the PCB, essential for blind vias and special features:

Parameter
Description
Example in Excellon Format
Z-Axis Depth
Specifies drilling depth
Z-0.031
Dwell Time
Pause at bottom of hole
D15
Pecking
Multiple partial depth cycles
P3

Proper implementation requires additional parameters in the Excellon file and specialized drilling equipment capable of precise Z-axis control.

Back Drilling

Back drilling removes portions of plated through-holes to reduce stub length, improving signal integrity in high-speed designs:

M48

INCH,TZ
T1C0.0400
T2C0.0450
%
T1
X01450Y02375
T2
B01450Y02375Z-0.031
M30

The "B" command indicates back drilling, often with precise depth control to remove the unwanted portion of the plated hole without damaging the functional part.

Laser Drilling and Microvias

Laser drilling for microvias requires specialized Excellon file configurations:

Feature
Excellon Implementation
Manufacturing Consideration
Microvia Size
Ultra-precise tool definitions
Laser power/duration settings
Layer Targeting
Layer-specific drill files
Sequential processing
Stackup Integration
Correlation with layer structure
Careful registration

Laser drilling systems often require manufacturer-specific extensions to the standard Excellon format to control laser parameters effectively.

Programming for Special Hole Types

Beyond standard round holes, Excellon files can support various specialized hole types:

1. Slots: Created through sequences of overlapping drills or routing operations
2. Non-Round Holes: Implemented through special tooling or post-drilling processes
3. Countersunk Holes: Requiring multiple operations with different tool sizes
4. Plated/Non-Plated Combinations: Often separated into different Excellon files

For example, a slot might be specified through a sequence of closely spaced holes or through specialized commands in extended formats:

T1C0.0400

G85
X01000Y01000
X01500Y01000
G05

The G85 command initiates slot mode, creating a continuous slot between the specified coordinates before returning to standard drilling mode with G05.

Troubleshooting and Common Issues

Format and Interpretation Problems

Many drill file issues stem from format misinterpretation:

Problem
Symptom
Resolution
Zero Suppression Confusion
Holes dramatically out of position
Verify TZ/LZ settings
Unit Mismatch
Holes scaled incorrectly (25.4x difference)
Confirm inch/mm settings
Format Precision Issues
Minor position errors
Check format settings (2:4, etc.)
Origin Discrepancy
Systematic offset of all holes
Verify coordinate origin

When troubleshooting, comparing visualizations of the drill file with design expectations can quickly identify these systemic issues.

Tool-Related Issues

Problems related to tool definitions and availability:

1. Non-Standard Tool Sizes: Specified diameters not matching available drill bits
2. Tool Number Conflicts: Inconsistent numbering between files
3. Tool Parameter Mismatches: Feed rates or speeds incompatible with equipment
4. Missing Tool Definitions: Coordinates referencing undefined tools

Proactive communication with fabrication partners regarding tool availability can prevent manufacturing delays.

Coordinate and Positioning Errors

Precision drilling requires careful management of coordinate data:

1. Truncation Errors: Loss of precision in coordinate translation
2. Rounding Issues: Inconsistent rounding between design and manufacturing
3. Registration Problems: Misalignment between drilling and other fabrication steps
4. Scaling Discrepancies: Incorrect application of scaling factors

Modern PCB CAD tools implement various strategies to minimize these errors, but designers should verify critical dimensions in generated files.

Debugging and Validation Methods

When issues arise, systematic debugging approaches can identify and resolve problems:

1. Visual Comparison: Overlay drill file visualization with design files
2. Statistical Analysis: Check for anomalies in hole distributions or counts
3. Reference Point Validation: Verify key reference holes against design specifications
4. Test Drilling: Produce sample pieces for verification before full production
5. Format Conversion: Export to alternative formats to identify conversion issues

Professional PCB design workflows typically incorporate validation steps before files are released for manufacturing.

Integration with Other PCB Manufacturing Files

Relationship with Gerber Files

Excellon drill files and Gerber files form complementary parts of a complete PCB fabrication package:

File Type
Contains
Format
Relationship
Excellon
Drilling instructions
ASCII text
Specifies hole locations
Gerber
Copper patterns, silkscreen, etc.
RS-274X
Defines conductive patterns

These files must maintain perfect alignment for successful manufacturing. Modern CAD tools generate both file types from the same design database, ensuring consistency.

Alignment and Registration

Proper alignment between drill locations and copper features is critical:

1. Fiducial Markers: Special alignment markers included in both file types
2. Registration Points: Designated reference points for alignment
3. Panel Framework: Additional structures for production panelization

Manufacturing systems use these features to ensure precise registration between drilling operations and other fabrication processes.

IPC-D-356 and Testing Integration

Beyond fabrication, drill data integrates with testing procedures:

317NET130 UA01X+012350Y+023750X0350 S0

The IPC-D-356 format provides test point information that correlates with drill locations, enabling automated electrical testing after fabrication. This format specifies:

• Net names
• Hole locations (correlating with Excellon coordinates)
• Expected connections