Introduction
A centroid file, also known as a pick and place file, is crucial for automated PCB assembly. It contains the precise coordinates and orientation of every component on a circuit board, enabling pick and place machines to accurately place components during manufacturing. This comprehensive guide explores how to create these files efficiently and accurately.
Understanding Centroid Files
Basic Components
A centroid file contains essential information for each component:
| Information | Description | Example |
|---|
| Reference Designator | Unique component identifier | R1, C4, U2 |
| X Coordinate | Position along X-axis | 25.4 mm |
| Y Coordinate | Position along Y-axis | 15.7 mm |
| Rotation | Component orientation | 0, 90, 180, 270 degrees |
| Layer | Board side for placement | Top, Bottom |
| Package Type | Component footprint | SOT-23, SOIC-8 |
File Format Types
| Format | Extension | Advantages | Common Usage |
|---|
| ASCII | .txt, .csv | Human-readable, universal | Most common |
| Excel | .xls, .xlsx | Easy editing, sorting | Documentation |
| Custom | Various | Manufacturer-specific | Special requirements |
Creation Methods
Automated Generation
Most modern PCB design software includes centroid file generation capabilities:
| Software | Native Format | Export Options | Special Features |
|---|
| Altium Designer | .txt | Multiple | Component grouping |
| KiCad | .pos | ASCII, CSV | Layer filtering |
| Eagle | .mnt | Text, CSV | Rotation handling |
| OrCAD | .txt | Multiple | Batch processing |
Manual Creation Steps
- Component Placement Documentation
- Coordinate System Definition
- Reference Point Establishment
- Component Orientation Verification
- Layer Assignment
File Format Requirements
Standard Format Elements
| Element | Format | Required | Notes |
|---|
| Header | Text | Optional | File information |
| Units | mm/mil | Required | Consistent throughout |
| Coordinates | Decimal | Required | Precision to 0.01mm |
| Rotation | Integer | Required | 0.1-degree precision |
| Comments | Text | Optional | Documentation |
Industry Standards
Common industry standards for centroid files:
- IPC-7351
- JEDEC
- ISO 9001 requirements
- Manufacturing specific guidelines
Quality Control and Verification
Verification Process
| Step | Purpose | Tools Required |
|---|
| Format Check | File structure verification | Text editor |
| Coordinate Verification | Position accuracy | CAD software |
| Rotation Check | Orientation confirmation | Viewer tool |
| Layer Assignment | Side verification | Assembly software |
Common Errors
| Error Type | Cause | Prevention Method |
|---|
| Coordinate Offset | Reference point mismatch | Standardize origin |
| Rotation Inversion | Different conventions | Document standards |
| Missing Components | Export settings | Complete verification |
| Unit Mismatches | Mixed systems | Enforce consistency |
Common Software Solutions
CAD Software Integration
| Software | Key Features | Automation Level |
|---|
| Altium | Direct export, verification | High |
| KiCad | Built-in tools, customization | Medium |
| Eagle | Basic export, manual options | Medium |
| OrCAD | Advanced options, scripting | High |
Third-Party Tools
Specialized tools for centroid file management:
- File format converters
- Verification utilities
- Batch processors
- Custom script generators
Best Practices
File Naming Conventions
| Element | Format | Example |
|---|
| Project Name | Text | Project123 |
| Revision | Number | Rev2 |
| Date | YYYYMMDD | 20240103 |
| Side | T/B | Top |
Documentation Requirements
Essential documentation elements:
- File format specification
- Coordinate system definition
- Unit system declaration
- Revision history
- Special instructions
Version Control
| Stage | Action | Documentation |
|---|
| Creation | Initial generation | Version 1.0 |
| Revision | Component updates | Change log |
| Release | Manufacturing approval | Sign-off |
Advanced Techniques
Automation Scripts
| Script Type | Purpose | Language |
|---|
| Format Conversion | Standardization | Python |
| Batch Processing | Multiple boards | Shell |
| Verification | Error checking | Python/Perl |
| Integration | Tool connection | Various |
Multi-board Handling
Strategies for managing multiple boards:
- Panel array coordinates
- Common reference points
- Nested assignments
- Batch processing
Manufacturing Considerations
DFM Requirements
| Requirement | Purpose | Implementation |
|---|
| Fiducial Marks | Registration | Standard positions |
| Origin Location | Reference | Consistent placement |
| Component Spacing | Assembly clearance | Design rules |
Machine-Specific Requirements
Different machines may need specific formats:
| Machine Type | Format | Special Requirements |
|---|
| Universal | Generic CSV | Basic positioning |
| Yamaha | Custom | Extended attributes |
| Panasonic | Custom | Special rotation |
| ASM | Proprietary | Enhanced data |
Troubleshooting Guide
Common Issues
| Issue | Symptoms | Solution |
|---|
| Offset Components | Misalignment | Check origin |
| Wrong Rotation | Incorrect orientation | Verify conventions |
| Missing Data | Incomplete placement | Review export settings |
| Format Errors | File rejection | Validate format |
Resolution Steps
- Verify source data
- Check export settings
- Validate file format
- Test with viewers
- Perform trial runs
Frequently Asked Questions
Q1: What is the most common format for centroid files?
A1: The most common format is CSV (Comma Separated Values) or plain text (.txt) files. These formats are universal, human-readable, and easily imported into various pick and place machines. They typically contain columns for reference designator, X-coordinate, Y-coordinate, rotation, and layer information.
Q2: How do I handle component rotation in centroid files?
A2: Component rotation handling requires attention to:
- Reference orientation (0 degrees)
- Rotation direction (clockwise vs. counterclockwise)
- Machine-specific conventions
- Pin 1 location
Always verify rotation conventions with your manufacturer and document any special requirements in your assembly notes.
Q3: What are the essential coordinates for a centroid file?
A3: Essential coordinates include:
- X and Y positions relative to a defined origin point
- Z coordinates for height-sensitive components
- Rotation angle
- Reference designator
- Component side (top/bottom)
All coordinates should be in consistent units (typically millimeters) and referenced to a clearly defined origin point.
Q4: How can I verify my centroid file is correct?
A4: Verification steps include:
- Using PCB design software's built-in viewers
- Cross-checking against the original design
- Using third-party verification tools
- Performing manual spot-checks of critical components
- Running a test assembly if possible
Q5: What are common mistakes in centroid file creation?
A5: Common mistakes include:
- Incorrect origin point selection
- Mixed units (mixing millimeters and inches)
- Wrong rotation conventions
- Missing components
- Incorrect layer assignments
These can be avoided through careful verification and following established procedures.
