Troubleshoot Autorouter Configuration Problems in Eagle for High-Density Firmware PCB Layouts
When dealing with high-density PCBs for firmware applications in Eagle, the autorouter might struggle due to complex interconnectivity and limited routing spaces. Below are advanced steps to troubleshoot and optimize your autorouter configuration.
Optimize Design Rules
Ensure that your design rules are tightly defined. For high-density boards, it's crucial to set the minimum trace width, clearance, and via size to values that adhere to the manufacturing capabilities while allowing more flexibility for the autorouter.
Open the Design Rules dialog and carefully examine Clearance and Sizes tabs. Make sure these are set to achievable industry standards but are as tight as possible.
Consider setting specific rules for critical nets by using the net classes feature.
Use Appropriate Grid Settings
- Check the grid settings and make sure they provide enough granularity. A finer grid can help the autorouter fit traces between tight components. However, balance this with performance since too fine a grid can slow down the routing engine.
GRID MM 0.1
- Use a larger grid for placement and a finer grid for routing. For example, set the routing grid to tenths of a millimeter for HDI designs.
Increase Number of Routing Layers
When space is tight, consider increasing the number of routing layers, if the budget allows. This provides more flexibility for the autorouter without sacrificing design complexity.
Assign specific purposes to additional layers, such as using one exclusively for power and ground planes to reduce noise and potential crosstalk on signal layers.
Manual Adjustments and Rip-Up & Retry
Before running the autorouter, manually route critical signal paths, such as clock signals, to ensure signal integrity.
Authorize the autorouter to rip-up and retry sections of tracks that are overly complex or congested. This allows it to attempt different pathways to achieve a better layout.
Define Routing Strategies
- In the Autorouter Setup, define a routing strategy that prioritizes crucial nets and specifies the order in which layers should be utilized. Assign cost factors to distances and via placements.
Route
Top -> (preferred layer for digital lines)
Bottom -> (secondary layer)
Inner1 -> (for analog)
Inner2 -> (for power lines)
End Rules
- Utilize exchange layers to specify via costs and limit transition between layers, as excessive via use can complicate the design and increase cost.
Autorouter Script Customization
- Leverage Eagle's autorouter scripts (.scr). Customize these scripts to tweak router behavior, especially in relation to specific requirements of high-density designs.
RUN autorouter-script.scr
- By scripting specific commands, you can instruct the autorouter to emphasize or ignore certain practices, like avoiding certain areas or prioritizing high-frequency nets.
Simulation and Signal Integrity Checks
Use Eagle's integration capabilities with simulation tools to perform a preliminary signal integrity check. This helps detect and avoid routing configurations that might lead to problems like reflections or crosstalk.
After autorouting, employ the DRC (Design Rule Check) to identify and correct violations, such as unauthorized trace widths or clearances that might still be in the layout.
Iterative Testing
The autorouting process might need several iterations. Each run should include adjustments based on earlier results to gradually improve the layout.
Analyze the progress after each iteration to determine if manual intervention is necessary for further blanket refinements.
By paying close attention to these configurations and utilizing Eagle's custom script abilities, you can significantly enhance the comportment and result of the autorouter on high-density firmware PCBs.