What are EAGLE DRU Files?

EAGLE, which stands for Easily Applicable Graphical Layout Editor, is a powerful PCB design software used by engineers and hobbyists around the world. One of the key features of EAGLE is the ability to define design rules using Design Rule Check (DRC) files, also known as DRU files.

DRU files are simple text files that contain a set of rules and constraints for PCB design. These rules ensure that the PCB layout meets the manufacturing requirements and electrical specifications of the project. Some examples of design rules include:

• Minimum track width and spacing
• Minimum via size and drill hole diameter
• Clearance between different layers and components
• Copper pour and thermal relief settings

By defining these rules in a DRU file, EAGLE can automatically check the PCB layout for any violations and display error messages to guide the designer in fixing the issues. This saves a lot of time and effort compared to manually checking the layout or relying on the manufacturer to catch any problems.

Benefits of Using DRU Files

Using DRU files in EAGLE offers several benefits for PCB designers:

1. Consistency: DRU files ensure that all the PCBs designed for a particular project follow the same set of rules and constraints, regardless of who designed them. This helps maintain consistency and compatibility across different boards.

2. Efficiency: By automating the design rule checks, DRU files save time and reduce the chances of human error. The designer can focus on the creative aspects of the layout without worrying about the technical details.

3. Flexibility: DRU files can be easily modified to accommodate changes in the manufacturing process or project requirements. The designer can create multiple DRU files for different scenarios and switch between them as needed.

4. Collaboration: DRU files can be shared among team members or with the manufacturer to ensure that everyone is on the same page regarding the design rules. This improves communication and reduces the chances of misunderstandings or delays.

EAGLE V6 and DRU File Improvements

EAGLE V6, released in 2011, introduced several new features and improvements to the software, including enhancements to the DRU file format. Some of the key changes in EAGLE V6 related to DRU files are:

Hierarchical Design Rules

Prior to EAGLE V6, all the design rules were defined in a flat list, which could become quite long and difficult to manage for complex projects. EAGLE V6 introduced hierarchical design rules, which allow the designer to organize the rules into a tree-like structure using categories and subcategories.

For example, the designer can create a category called “Routing” and define subcategories like “Tracks”, “Vias”, and “Pads” under it. Each subcategory can then contain specific rules related to that aspect of the layout. This makes it easier to navigate and modify the DRU file as needed.

Rule Precedence and Wildcards

EAGLE V6 also introduced the concept of rule precedence, which determines the order in which the rules are applied. Rules defined at a higher level in the hierarchy take precedence over rules defined at a lower level. This allows the designer to create general rules that apply to the entire layout and then override them with more specific rules for certain areas or components.

In addition, EAGLE V6 added support for wildcards in rule definitions. Wildcards are special characters that can represent any value or a range of values. For example, the wildcard “*” can be used to match any string of characters, while the wildcard “?” can be used to match any single character. This makes it easier to define rules that apply to multiple layers, signal types, or component classes without having to list them all explicitly.

Improved Error Messages

EAGLE V6 also improved the error messages displayed when a design rule violation is detected. The messages are now more descriptive and include the specific rule that was violated, the location of the violation, and possible solutions to fix the issue. This makes it easier for the designer to identify and correct problems in the layout.

Creating DRU Files for EAGLE V6

Creating a DRU file for EAGLE V6 is a straightforward process that involves the following steps:

1. Open the EAGLE Control Panel and select the “DRC” command from the “Tools” menu.
2. In the DRC window, click on the “Load…” button to open an existing DRU file or click on the “New” button to create a new one.
3. Define the design rules using the hierarchical structure and wildcards as needed. The DRC window provides a graphical interface for defining the rules, but you can also edit the DRU file directly using a text editor.
4. Save the DRU file with a descriptive name and apply it to your PCB layout by clicking on the “Check” button in the DRC window.

Here is an example of a simple DRU file for EAGLE V6:

# Routing
Routing.Tracks.Width = 10mil
Routing.Tracks.Clearance = 10mil
Routing.Vias.Size = 50mil
Routing.Vias.Drill = 20mil
Routing.Pads.Size = 60mil
Routing.Pads.Drill = 30mil

# Polygons
Polygons.Isolation = 20mil
Polygons.Thermals = 4
Polygons.Orphans = 10mil

# SMD
SMD.Density.Level = 5
SMD.MinSize = 30mil

# Text
Text.Size = 50mil
Text.Ratio = 10
Text.Clearance = 10mil

This DRU file defines rules for track width and clearance, via and pad size and drill diameter, polygon isolation and thermals, SMD density and minimum size, and text size and clearance. The designer can modify these values based on the specific requirements of the project.

Best Practices for Using DRU Files

To get the most out of DRU files in EAGLE V6, follow these best practices:

1. Start with a template: If you are new to creating DRU files, start with a template provided by the manufacturer or a trusted source. This will give you a good starting point and ensure that the basic rules are covered.

2. Organize the rules: Use the hierarchical structure to organize the rules into logical categories and subcategories. This will make the DRU file easier to read and maintain.

3. Use descriptive names: Give the rules descriptive names that clearly indicate their purpose. Avoid using abbreviations or cryptic codes that may be difficult to understand later.

4. Test the rules: After creating the DRU file, test it on a sample layout to ensure that it catches all the relevant violations and does not generate any false positives. Make adjustments as needed based on the feedback from the manufacturer or the actual performance of the PCB.

5. Keep the DRU file up to date: As the project evolves or the manufacturing process changes, update the DRU file to reflect the new requirements. Keep a version history of the DRU file to track the changes over time.

6. Collaborate with the manufacturer: Work closely with the PCB Manufacturer to ensure that the DRU file meets their requirements and expectations. They may have specific rules or constraints that need to be added to the file.

By following these best practices, you can create effective and efficient DRU files that will help you design high-quality PCBs with EAGLE V6.

FAQ

1. What is the difference between a DRU file and a DRC file in EAGLE?

2. A DRU file is a text file that contains the design rules and constraints for a PCB layout in EAGLE. A DRC file, on the other hand, is a binary file generated by the Design Rule Check (DRC) tool in EAGLE that contains the results of the design rule check, including any violations and their locations.

3. Can I use the same DRU file for different PCB projects in EAGLE?

4. It depends on the specific requirements of each project. While you can use the same DRU file as a starting point, you may need to modify the rules and constraints based on the unique characteristics of each project, such as the layer stack, component types, and manufacturing process.

5. How do I share a DRU file with my team members or the manufacturer?

6. You can share a DRU file by sending it as an email attachment, uploading it to a shared folder or version control system, or including it in the EAGLE project package. Make sure to include a clear description of the file and its purpose to avoid any confusion.

7. What happens if I violate a design rule in my PCB layout?

8. If you violate a design rule, EAGLE will display an error message indicating the type of violation, its location, and possible solutions. You will need to fix the violation before you can proceed with the manufacturing process. Ignoring design rule violations can lead to problems such as short circuits, signal integrity issues, or manufacturing defects.

9. Can I use EAGLE V6 DRU files in older or newer versions of EAGLE?

10. EAGLE V6 introduced several changes and improvements to the DRU file format, so the files may not be fully compatible with older versions of EAGLE. However, newer versions of EAGLE, such as V7 and V8, should be able to read and use EAGLE V6 DRU files with minor modifications, if any. It is always a good practice to test the DRU file in the specific version of EAGLE you are using and make any necessary adjustments.

Conclusion

DRU files are an essential part of PCB design with EAGLE, as they help ensure that the layout meets the manufacturing requirements and electrical specifications of the project. EAGLE V6 introduced several improvements to the DRU file format, including hierarchical design rules, rule precedence, wildcards, and improved error messages.

Creating effective DRU files requires a clear understanding of the project requirements, close collaboration with the manufacturer, and adherence to best practices such as organizing the rules, using descriptive names, and testing the file on sample layouts.

By leveraging the power of DRU files in EAGLE V6, PCB designers can create high-quality layouts that are consistent, efficient, and error-free, ultimately saving time and cost in the manufacturing process.

Feature	Description
Hierarchical Design Rules	Organize rules into categories and subcategories for easier management
Rule Precedence	Define the order in which rules are applied, with higher-level rules taking precedence
Wildcards	Use special characters to represent any value or range of values in rule definitions
Improved Error Messages	Display more descriptive error messages with specific rule violations and solutions

Remember, a well-crafted DRU file is not a one-time effort but an ongoing process that requires continuous refinement and adaptation as the project evolves. By staying up to date with the latest best practices and collaborating closely with the manufacturer, you can ensure that your PCB designs are of the highest quality and reliability.