What is a .PCB File? Complete Protel/Altium PCB Format Guide

If you’ve been working in electronics design for any length of time, you’ve probably encountered a .PCB file at some point. Maybe a colleague sent you legacy design files, or you inherited a project from someone who used older software. As someone who has spent years debugging these exact situations, I can tell you that understanding the .PCB file format is essential knowledge for any serious PCB engineer.

In this guide, I’ll walk you through everything you need to know about .PCB files, from their origins in Protel software to how they work in modern Altium Designer. We’ll cover file versions, structure, conversion methods, and the tools you’ll need to work with these files effectively.

Understanding the .PCB File Format

The .PCB file extension represents a Printed Circuit Board Design File that stores comprehensive layout data for electronic circuit boards. This format originated with Protel, one of the earliest professional PCB design software packages, and has evolved significantly over the past three decades.

When you open a .PCB file, you’re essentially looking at a complete blueprint of a circuit board. The file contains critical design information including component placement coordinates, copper trace routing, drill hole locations, layer stackup definitions, and design rule parameters. Think of it as the DNA of your circuit board—everything needed to reproduce it physically is encoded within.

The .PCB format has been the workhorse of the electronics industry since the 1980s. While newer formats like .PcbDoc have emerged, millions of legacy .PCB files remain in circulation, making this knowledge invaluable for engineers working on maintenance, reverse engineering, or design migration projects.

What Data Does a .PCB File Contain?

A typical .PCB file stores multiple categories of design data:

History of the .PCB File Format: From Protel to Altium

Understanding the lineage of .PCB files helps you navigate compatibility issues more effectively. The format has undergone several major revisions since its introduction.

Evolution Timeline

Protel PCB first appeared in 1985 as a DOS-based design tool developed by Protel Technology in Australia. The software gained international distribution through ACCEL Technologies in the United States, where it was marketed as Tango PCB. These early versions established the .PCB extension that remains in use today.

The transition from DOS to Windows brought significant changes. Protel for Windows 2.8 introduced a 16-bit Windows interface, followed by Protel 98 and 99 which moved to 32-bit architecture. Protel 99 SE, released in 2000, became particularly influential—many engineers still encounter designs from this era.

In 2003, Protel DXP marked the beginning of the modern platform, followed by Protel 2004. Altium Designer 6.0 launched in 2005, officially rebranding the software while maintaining backward compatibility with legacy .PCB files. Since then, Altium Designer has become the industry standard, with versions continuing to support import of older Protel formats.

.PCB File Version Comparison

The version identification becomes crucial when you need to determine which software can open a particular file. You can check a .PCB file’s version by opening it in a text editor—ASCII format files will display version information in the header lines.

.PCB File Structure and Internal Organization

As a PCB engineer, knowing what’s inside a .PCB file helps you troubleshoot problems and understand conversion limitations. The file structure varies between ASCII and binary formats, but both contain similar logical sections.

ASCII .PCB File Structure

The ASCII format (primarily versions 2.8 and earlier exports) uses human-readable text organized into records. Each record contains parameters and values for specific PCB objects. Here’s what the internal organization looks like:

The coordinate system in .PCB files uses internal units where 10,000 units equal 1 mil (0.001 inch). This high resolution ensures precision during design operations while maintaining compatibility with manufacturing equipment.

Binary .PCB File Structure

Binary format files (versions 3.0 and later) pack the same information more efficiently but require specialized software to interpret. The binary structure offers faster loading times and smaller file sizes but sacrifices the ability to manually inspect or edit the data.

How to Open .PCB Files: Software Options

Opening legacy .PCB files can be challenging because the original Protel software is no longer sold or supported. Here are the practical options available to engineers today.

Primary Software for Opening .PCB Files

Step-by-Step: Opening Legacy .PCB Files in Altium Designer

When you attempt to open a legacy .PCB file in Altium Designer, the software automatically detects the older format and launches the Import Wizard. The process works as follows:

1. Select File > Open and navigate to your .PCB file
2. The Import Wizard launches automatically for pre-DXP formats
3. Select the destination folder for converted files
4. Choose whether to extract embedded library components
5. Confirm conversion options and proceed
6. Save the converted .PcbDoc file

During conversion, Altium preserves most design data but some features unique to newer versions may require manual adjustment. Objects like region fills, modern polygon pours, and advanced pad shapes might need recreation.

Identifying Unknown .PCB File Sources

When you receive a .PCB file without context, determining its origin becomes the first troubleshooting step. Multiple CAD programs use the .PCB extension:

Opening the file in a text editor (for ASCII formats) or hex editor (for binary formats) reveals identifying strings in the first few hundred bytes.

Converting .PCB Files to Modern Formats

Converting legacy .PCB files ensures long-term accessibility and enables use of modern design tools. The conversion strategy depends on your target format and intended use.

.PCB to .PcbDoc Conversion (Altium Native)

For engineers working within the Altium ecosystem, converting to .PcbDoc provides full access to modern features:

1. Open the .PCB file in Altium Designer
2. Complete the Import Wizard process
3. Use File > Save As and select *.PcbDoc format
4. Run Design Rule Check (DRC) to identify conversion issues
5. Manually correct any flagged problems

.PCB to Gerber Conversion for Manufacturing

When you need to manufacture a board from legacy .PCB files without full design modification capabilities, Gerber export provides a universal solution:

The Gerber format (RS-274X extended) serves as the manufacturing industry standard and virtually all PCB fabricators accept these files directly.

Read more PCB Files format:

What are .GBR and .PHO Files? Gerber File Extensions Guide

What are PCB Panelization Files? Complete Array Format Guide

What is .DSN File? Specctra Autorouter Format Explained

What is .kicad_pcb? KiCad PCB File Format Guide

What is .PcbDoc? Altium Designer PCB Format Explained

What is .PrjPcb? Altium Designer Project File Explained

What is .SchDoc? Altium Schematic File Explained

What is a .ASC File? PADS ASCII Format Explained

What is a .BRD File? Eagle PCB File Format Explained

What is a .DRC File? Design Rule Check Reports Explained

What is a .PCB File? Complete Protel/Altium PCB Format Guide

What is a .SES File? Complete Specctra Session File Guide for PCB Engineers

What is a BOM File? Bill of Materials Format for PCB Assembly

What is a CPL File? SMT Component Placement Guide

What is a Fabrication Drawing? PCB Fab Notes Explained

What is a Gerber Job File? Project Metadata Explained

What is a Netlist? PCB Connectivity Data Explained

What is a Pick and Place File? SMT Centroid Data Guide

What is a Stencil Gerber File? Complete Solder Paste Stencil Guide

What is an Aperture File? Gerber Tool Definition Guide

What is an Assembly Drawing? Complete PCB Assembly Documentation Guide

What is DXF in PCB Design? CAD Drawing Exchange Format Explained

What is Excellon? NC Drill File Format for PCB Manufacturing

What is GenCAD? Universal PCB Data Format Explained

What is Gerber RS-274X? The PCB Industry Standard Explained

What is Gerber X2? The Modern Gerber Format Guide

What is Gerber X3? Component Data in Gerber Files

What is HPGL? PCB Plotter File Format Guide

What is IGES? 3D PCB Model Format Explained

What is ODB++? Complete PCB Data Exchange Format Guide

What is PDF/A for PCB? Documentation Standards Guide

What is STEP File in PCB Design? 3D Model Exchange Guide

What is VRML in PCB? 3D Visualization Format Guide

Converting Between PCB Format Versions

Sometimes you need to move designs between different Protel versions. Altium Designer supports saving to legacy formats through File > Save Copy As:

Note that saving to older formats inevitably loses features introduced in newer versions. Complex polygon fills, advanced design rules, and modern component definitions may not translate backward.

.PCB File Troubleshooting Guide

Common problems arise when working with .PCB files. Here’s how to diagnose and resolve the most frequent issues.

File Won’t Open

When a .PCB file refuses to open, check these factors:

Wrong Software Association: The .PCB extension is used by multiple programs. Verify you’re using appropriate software for that specific file’s origin.

Corrupted File: Download the file again if possible, or try opening in a hex editor to check for truncation or obvious corruption.

Version Incompatibility: Older files may require intermediate conversion. Try opening in older Altium versions first, then upgrading step-by-step.

Missing or Incorrect Data After Conversion

Conversion artifacts typically fall into predictable categories:

Verifying Converted Files

After any conversion, verification ensures manufacturing success:

1. Run Design Rule Check in the new software
2. Generate Gerber files and review in a Gerber viewer
3. Compare critical dimensions with original if available
4. Check netlist integrity against schematic
5. Verify drill file hole counts and sizes

Useful Resources for .PCB File Work

Having the right resources available streamlines .PCB file work. Here are essential references for PCB engineers.

Official Documentation

Free Tools for .PCB Files

PCB Manufacturing Services with Online Viewers

Several fabrication services offer integrated viewers that accept various formats:

Best Practices for .PCB File Management

Proper file management prevents the compatibility headaches that plague legacy designs.

Archive Strategy

Maintain multiple format versions of important designs:

1. Native format: Keep the original .PCB or .PcbDoc file
2. ASCII export: Save an ASCII version for text-based archiving
3. Gerber set: Generate complete manufacturing files
4. PDF documentation: Create visual records of each layer
5. BOM export: Preserve component information separately

Version Control Considerations

Modern version control systems work best with text-based files. The ASCII .PCB format enables diff comparison and merge operations, while binary formats require specialized tools or simple versioning by date.

Documentation Requirements

Include these items when archiving .PCB projects:

Frequently Asked Questions About .PCB Files

What program opens .PCB files?

The primary software for opening .PCB files is Altium Designer, which supports all Protel legacy formats through its built-in Import Wizard. Free alternatives include the Altium 365 online viewer for basic viewing, though it may not support all legacy Protel versions. For files from other sources (PADS, P-CAD, CADSTAR), you’ll need software from those respective vendors or specialized converters.

Can I convert .PCB files to Gerber without Altium?

Yes, but options are limited. CAM350 can read some .PCB variants and export Gerber files. Some online conversion services claim to handle .PCB files, though results vary depending on the source format. For reliable conversion of legacy Protel files specifically, Altium Designer remains the most consistent option. If you only need to manufacture an existing design without modifications, consider contacting a PCB fabrication service—many have engineering support that can assist with file conversion.

Why can’t I open my .PCB file in Eagle or KiCad?

Eagle and KiCad use their own native file formats (.brd for Eagle, .kicad_pcb for KiCad) and don’t directly import Protel .PCB files. To move a design between these tools, you’ll need an intermediate format. The typical workflow involves opening the .PCB file in Altium, exporting to an interchange format like ASCII or IDF, then importing into your target software. Some community-developed scripts exist for specific conversions, but results require careful verification.

How do I identify which version of .PCB file I have?

Open the file in a text editor (Notepad, VS Code, or similar). For ASCII format files, the version information appears in the first few lines. Look for strings like “PCB FILE 6 VERSION 2.80” (Protel 2.8), “KIND=Protel_Advanced_PCB|VERSION=3.00” (Protel 98/99/99SE), or specific version markers. Binary files require hex editor inspection or attempting to open in Altium, which reports the detected format during import.

What’s the difference between .PCB and .PcbDoc files?

The .PCB extension represents older Protel formats (versions through Protel 2004), while .PcbDoc is the modern Altium Designer native format introduced with Altium Designer 6.0 in 2005. The .PcbDoc format uses a more sophisticated internal structure supporting advanced features like embedded 3D models, enhanced design rules, and improved multi-channel support. Altium Designer can open both formats, but .PcbDoc offers full access to current capabilities while .PCB files may lose features during conversion.

Conclusion

The .PCB file format represents decades of PCB design history, from the early DOS days of Protel through the modern Altium Designer platform. Understanding these files enables engineers to work with legacy designs, migrate projects to current tools, and maintain long-term design archives.

Whether you’re reverse engineering an old board, migrating a proven design to new software, or simply trying to view files from a colleague, the knowledge covered in this guide provides the foundation for successful .PCB file work. The format may be legacy, but its importance to the electronics industry continues.

For ongoing work with .PCB files, I recommend building a toolkit that includes current Altium Designer (even the viewer version), a good Gerber viewer, and text editing tools for ASCII file inspection. This combination handles the vast majority of situations you’ll encounter with these ubiquitous design files.