Excellon is a drill instruction file format used in PCB manufacturing workflows to define hole locations, drill sizes, and drilling operations. Excellon files are primarily used to control automated PCB drilling machines during board fabrication.
The format is commonly generated alongside Gerber files during PCB export workflows.
Excellon files commonly use extensions such as .drl, .drd, or .txt.
What Is Excellon?
Excellon is a machine-control format specialized for PCB drilling operations.
Excellon files typically define:
- drill hole coordinates
- tool diameters
- via holes
- mounting holes
- plated holes
- non-plated holes
PCB manufacturers use Excellon data to automate drilling processes with CNC drilling machines.
Excellon in PCB Manufacturing
PCB manufacturing commonly combines multiple fabrication formats.
A typical workflow includes:
- Creating a circuit schematic
- Designing the PCB layout
- Routing copper traces
- Exporting Gerber files
- Exporting Excellon drill files
- Manufacturing the PCB
Gerber files define graphical PCB layers, while Excellon files define physical drilling operations.
PCB Drilling Operations
Excellon files are used to manufacture drilled features such as:
- vias
- through-holes
- component mounting holes
- alignment holes
- tooling holes
Accurate drilling is critical for electrical connectivity and component placement.
Excellon File Structure
Excellon files are text-based instruction files.
Typical data includes:
- tool definitions
- drill coordinates
- unit settings
- spindle commands
- drilling sequences
Example Excellon content:
M48
METRIC
T01C0.800
%
T01
X025000Y030000
X040000Y050000
M30
Different PCB software systems may generate slightly different syntax variations.
Tool Definitions
Excellon files commonly define multiple drill tools.
Each tool definition specifies:
- drill diameter
- tool identifier
- machining operation
Example tool usage:
| Tool ID | Diameter | Typical use |
|---|---|---|
| T01 | 0.8 mm | Through-hole vias |
| T02 | 1.0 mm | Component leads |
| T03 | 3.2 mm | Mounting holes |
Drill sizes must match manufacturing requirements and component specifications.
Coordinates in Excellon
Excellon files define drill locations using coordinate systems.
Important concepts include:
- X and Y coordinates
- unit definitions
- origin points
- coordinate precision
- zero suppression
Incorrect coordinate interpretation may produce unusable PCBs.
Plated and Non-Plated Holes
PCB drilling workflows commonly distinguish between:
| Hole type | Purpose |
|---|---|
| Plated hole | Electrical connectivity |
| Non-plated hole | Mechanical mounting |
Some PCB workflows export separate Excellon files for plated and non-plated operations.
Excellon and CNC Drilling
Excellon files are interpreted by CNC drilling systems.
These machines perform:
- high-speed drilling
- automated tool changes
- precision hole alignment
- multi-layer drilling operations
Modern PCB drilling systems operate with extremely high positional accuracy.
Excellon vs G-code
Excellon and G-code are both machine-control formats.
| Format | Primary use | Industry |
|---|---|---|
| Excellon | PCB drilling | Electronics manufacturing |
| G-code | General machine control | CNC fabrication |
Excellon is specialized for PCB drilling workflows, while G-code supports broader manufacturing operations.
Excellon and Gerber
Gerber and Excellon files are complementary manufacturing formats.
| Format | Manufacturing role |
|---|---|
| Gerber | PCB graphical layers |
| Excellon | Drill operations |
Both formats are typically required for complete PCB manufacturing.
Manufacturing Precision
PCB drilling requires extremely precise alignment.
Important manufacturing considerations include:
- drill tolerance
- layer registration
- hole diameter accuracy
- via alignment
- spindle precision
Improper drill settings may cause electrical failure or assembly issues.
Advantages of Excellon
Excellon provides several important advantages.
- standardized PCB drilling workflows
- broad industry compatibility
- efficient CNC drilling integration
- precise hole definition
- compact file structure
- automated manufacturing support
These characteristics make Excellon a core PCB manufacturing format.
Limitations of Excellon
Excellon also has several limitations.
- drilling-only specialization
- limited graphical representation
- software-specific syntax differences
- limited metadata support
- dependency on separate Gerber files
Because of these limitations, Excellon is used alongside other PCB manufacturing formats rather than independently.
Common Software Supporting Excellon
| Software | Excellon support type | Typical use |
|---|---|---|
| KiCad | Native export | PCB design |
| Altium Designer | Native export | Industrial PCB workflows |
| EAGLE | Native export | Electronics prototyping |
| FlatCAM | CAM processing | CNC PCB manufacturing |
| EasyEDA | Native export | Browser-based PCB design |
Excellon Verification
Excellon files are commonly verified before manufacturing.
Verification processes may include:
- drill alignment inspection
- hole-size validation
- plated-hole checking
- manufacturing preview rendering
- drill-to-copper clearance analysis
Proper verification helps prevent PCB fabrication errors.