Bug in thermals?

[_Marek]

Hello, 

Probably I discovered a bug. It didn't appear month ago when I created previous version of project, based on the same components. Please take look at GND signals routed from polygon.

On the first image - connection is broken. I tried to determine the reason. For test purpose  single path, adjacent to GND route was removed - it didn't help. When second path was removed - GND signal appeared automatically - please refer #2. On the 3rd approach thermals on polygon were disabled. GND signal is properly connected. Obviously I want to use thermals. 

Situation is related to small pitch numbers. In this case ATmega128 is used (pitch 0.8mm). I discovered rule when thermals will connect polygon and pad. The thermal isolation in DRC must be at least 2 times lower than thermal width set on the polygon.

In previous project these values were set to 10 mils both and everything was ok. The consequence is extremely small thermal isolation - sometimes difficult to achieve in final PCB. 

Is it possible to brake above size dependency and force somehow GND connections from Polygon to small pads?

[jorge_garcia]

Hi @_Marek ,

There are several things that can affect the thermals getting filled it's not just the relationship between thermal isolation and thermal width. You also have to look at any clearances that may be involved such as a netclass clearance. Make sure to set the thermal isolation to whatever your board house can do. The thermal obviously can't be thinner than the minimum width. So if you factor those into account you may find that another setting is keeping the thermal from being filled.

Let me know if there's anything else I can do for you.

Best Regards,

[_Marek]

This is full configuration.
Can you see potential reason of such a behavior? 

[jorge_garcia]

Hi @_Marek,

What is your DRC clearance? Your pad pitch is 0.8mm what is the pad width?

I think that's all I'm missing.

Best Regards,

[_Marek]

Hello,

Here is clearance settings. 

Pad width is 0.45mm. This is Atmega128 - so you can get any further package information. 

In the meantime I discovered that there is workaround to disappearing connections to the ground, If there is no option to create thermals from GND polygon to particular pads, it is still possible to create stub from not connected pad to polygon.

In this particular case, every pad of this IC requires to create 2 stubs: inner and outer. In my opinion - it shouldn't happen. If ground plane can almost touch the pad, there is no reason why thermals are not created. The logic of deciding when thermals are created should be more intelligent. 

[jorge_garcia]

Hi @_Marek,

I hope you're doing well. After working through the numbers and all the information you've given me, I agree with you. I don't see a reason for the thermals to no be produced. Would you be willing to share the design with me so that our devs can reproduce and fix the issue?

I'll make a bug report for this. Let me know if there's anything else I can do for you.

Best Regards,

[jorge_garcia]

Hi @_Marek,

I hope you're doing well. One other thing came to mind could you turn on all of your layers and get me a screenshot? I want to make sure you don't have a restrict or something else blocking the thermal.

Let me know if there's anything else I can do for you.

Best Regards,

[_Marek]

Hi Jorge,

I disabled top layer. I think that screenshot will be mor clear to analyze. Also removed GND stubs from polygon to pads to see effect. There are 2 GND pads unconnected now.

[_Marek]

Of course I can share design. Give me som hints how to do that - I never did such a things.

[m.ensing2UAQJ]

does it show as airwire? and will it appear as an error after running the DRC? 

[jorge_garcia]

Hi @_Marek,

I hope you're doing well. I've sent you a DM with instructions to export the files and my email so you can send them to me.

Let me know if there's anything else I can do for you.

Best Regards,

[m.ensing2UAQJ]

I am really interested in the outcome of this research, and hope this will be shared @jorge_garcia 

[_Marek]

FYI. We have appointment on Monday regarding to this issue.

[m.ensing2UAQJ]

any news?

[_Marek]

Hi,
Engineers start working on it.  We must be patient. For now, use workaround as I did (wire stubs imitating thermals). They encourage polygons (ground planes) to pass through narrow pads.  

[jorge_garcia]

Hi @m.ensing2UAQJ,

The developer responsible for thermals is looking into it this week. If I here anything new, I'll let you know.

Best Regards,

[HelenChen-ElectronicsQA]

Hi @_Marek , @m.ensing2UAQJ ,

Hope all is well.

Great news that the fix is ready in the latest Fusion Production build 2601.0.90. Could you please upgrade to latest Fusion version to have a try? Looking forward to your feedback.

Hope you have a great day.

Best regards,

Helen