RS-274X (Extended Gerber)

What is Gerber Format?

Gerber format is a standard file format used to describe the layout and design of PCBs. It was initially developed by the Gerber Systems Corp. in the 1960s and has since become the de facto standard for the electronics industry. The Gerber format consists of a set of ASCII text files that contain vector-based image data representing the different layers of a PCB, such as copper traces, solder mask, silkscreen, and drill holes.

Advantages of Gerber Format

1. Widely accepted and supported by PCB design software and manufacturing equipment.
2. Simple and compact file format, making it easy to store and transfer PCB design data.
3. Provides a clear and unambiguous representation of the PCB Layers.
4. Enables accurate and reliable PCB Fabrication and assembly.

Evolution of Gerber Format

The Gerber format has undergone several revisions and extensions over the years to accommodate the increasing complexity and requirements of PCB designs.

RS-274D

The original Gerber format, known as RS-274D, was introduced in the 1980s. It used a simple set of commands to describe the PCB features, such as apertures, flashes, and draws. However, it had limitations in terms of coordinate precision, aperture definitions, and layer stackup information.

RS-274X

To address the limitations of RS-274D, the Extended Gerber format (RS-274X) was developed in 1998. RS-274X introduced several enhancements and new features, including:

1. Improved coordinate precision (up to 6 decimal places).
2. Support for aperture macros, allowing custom aperture shapes.
3. Inclusion of layer stackup information and file attributes.
4. Negative image polarity for solder mask and other layers.
5. Improved support for embedded apertures and primitives.

These enhancements made RS-274X more powerful and flexible, enabling designers to create more complex and detaiLED PCB layouts.

RS-274X File Structure

An RS-274X file consists of a sequence of commands and parameters that describe the PCB features. Each command starts with a letter (D, G, M, or X) followed by a specific code and optional parameters. Here are some of the key components of an RS-274X file:

Aperture Definitions

Apertures define the shapes and sizes of the features to be drawn on the PCB layer. RS-274X supports a wide range of aperture types, including circles, rectangles, ovals, and custom shapes defined using aperture macros.

Example aperture definitions:

%ADD10C,0.5*%
%ADD11R,1.0X2.0*%
%ADD12O,0.75X1.5*%

In this example:
– %ADD10C,0.5*% defines a circular aperture with a diameter of 0.5 units.
– %ADD11R,1.0X2.0*% defines a rectangular aperture with a width of 1.0 units and a height of 2.0 units.
– %ADD12O,0.75X1.5*% defines an oval aperture with a width of 0.75 units and a height of 1.5 units.

Drawing Commands

Drawing commands specify the operations to be performed on the PCB layer using the defined apertures. The most common drawing commands are:

• D01: Sets the current position without drawing.
• D02: Moves the aperture to a new position and draws a line.
• D03: Flashes the aperture at the current position.

Example drawing commands:

D10*
X1000Y1500D02*
X2000Y1500D01*
X2000Y2000D01*
X1000Y2000D01*
X1000Y1500D01*

In this example:
– D10* selects the aperture defined by %ADD10C,0.5*%.
– The subsequent commands draw a rectangle by moving the aperture to specific X and Y coordinates and drawing lines between them.

Polarity and Rotation

RS-274X supports the specification of image polarity and rotation for each layer. Polarity determines whether the drawn features are additive (dark) or subtractive (clear) on the layer. Rotation allows the layer to be rotated by a specific angle.

Example polarity and rotation commands:

%LPD*%
%IR45*%

In this example:
– %LPD*% sets the polarity to dark (additive).
– %IR45*% rotates the layer by 45 degrees counterclockwise.

Gerber File Extensions

RS-274X files use specific file extensions to identify the different PCB layers. Some common file extensions include:

These file extensions help identify the specific layers and their purposes in the PCB fabrication process.

Frequently Asked Questions (FAQ)

1. Q: Can RS-274X files be viewed and edited manually?
   A: While it is possible to view and edit RS-274X files using a text editor, it is not recommended. The files contain complex commands and parameters that are best handled by specialized PCB design software.

2. Q: Are RS-274X files backward compatible with RS-274D?
   A: RS-274X files are generally backward compatible with RS-274D, as they include additional features and enhancements. However, older software and equipment that only support RS-274D may not be able to fully interpret and process RS-274X files.

3. Q: How do I ensure the accuracy of my RS-274X files?
   A: To ensure the accuracy of your RS-274X files, follow these best practices:

4. Use reputable PCB design software that generates valid RS-274X files.
5. Verify the file content using Gerber Viewers or validation tools.

6. Communicate clearly with your PCB fabrication vendor about the file requirements and specifications.

7. Q: Can RS-274X files contain information about the PCB Stackup?
   A: Yes, RS-274X files can include information about the PCB stackup using the %FSLAX*% command. This command specifies the file attributes, including the number of copper layers, layer order, and thickness.

8. Q: What is the difference between RS-274X and other PCB data formats like ODB++?
   A: RS-274X is a vector-based image format that focuses on describing the PCB layers and features. Other formats, such as ODB++ (Open Database++), provide a more comprehensive database-like structure that includes additional information like component placement, netlist, and test points. However, RS-274X remains the most widely used and supported format in the PCB industry.

Conclusion

RS-274X (Extended Gerber) is a crucial data format for the electronics manufacturing industry, enabling the accurate and reliable description of PCB layers and features. Its enhanced capabilities, such as improved coordinate precision, aperture macros, and layer stackup information, make it a powerful tool for PCB designers and fabricators.

By understanding the structure and components of RS-274X files, designers can create detailed and precise PCB layouts that can be efficiently manufactured. The widespread adoption and support of RS-274X in the industry ensure its continued relevance and importance in the PCB fabrication process.

As PCB designs continue to evolve and become more complex, the RS-274X format serves as a robust and flexible foundation for representing and communicating PCB data. Its simplicity, compatibility, and extensive ecosystem of software and equipment make it an indispensable standard in the world of electronics manufacturing.