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Polygon Differences in Fusion vs Eagle Cause Footprint to be Malformed in Fusion

Message 1 of 3
86 Views, 2 Replies

Polygon Differences in Fusion vs Eagle Cause Footprint to be Malformed in Fusion

We have a footprint in Eagle that we have been using on many boards. I have included only the relevant portion of this footprint in the images of this post. It deals with a polygon. I played around with this polygon. The original is on the left, and my "fixed" one is on the right. This is an Eagle screenshot:




There is a minor difference between the two. It is this portion:


I lowered down that bottom hump on the polygon that is on the right to fix my issue.


Now, here is how these look in Fusion:


Same footprint. The original just produced that little square on the left. The right, with the hump lowered, is okay. I think I realize why this happened, and it is how Fusion handles polygons differently than Eagle. In Eagle, the polygon edge itself has a thickness that is incorporated into the poured area. For example, I can highlight that exact top piece of the hump by right-clicking:


In Fusion, this is not the case. The Polygon edges seem to be "dimensionless". If I highlight a random polygon edge in Fusion, we can see the following:


The edge is dimensionless, and the centerline of the edge is to what the area of the pour extends to. So, it seems that Fusion, in order to maintain the same polygon pour as Eagle, it actually changes the edges to be along what used to be the edge of the pour. I have proved this, too.


Looking at the original "fixed" polygon in Eagle vs Fusion, in Eagle you can see the y position of that previously-highlighted hump is -5 mil:



That position of "-5" was the centerline of that. I have drawn this in purple:


In Fusion, you can see for the very same footprint, the polygon edge y position is located at -2.5mil:


This is because what used to be the portion of the pour that belonged to the edge itself in Eagle has been incorporated into the interior fill of the new dimensionless edge in Fusion, with those edge dimensions adjusted automatically by Fusion based on the original edge position and fill width in Eagle.


That is a lot, but I see so clearly what happened. When Fusion changed the polygon edge positions, it actually ended up causing two edges to touch that previously were not touching. You can visualize how this would happen. I have drawn it here.


Therefore, Fusion saw this as an enclosed square whereas Eagle did not.


I would also like to raise a concern over "rounded corners" in Eagle being straight now. Notice before I had rounded corners, but in Fusion they are perfectly right-angled cuts.


Has anybody encountered things like this before?


I agree with the design decision in Fusion to go with edges that have no thickness in and of themselves. I never liked how in Eagle the thickness of the edge itself mattered. But I wanted to bring to attention potential edge cases where this automatic alteration of edges can cause issues.

Message 2 of 3

Hi. Thanks a lot for the detailed and thoughtful reply.


You are right that this is due to a change in Fusion Electronics compared to EAGLE where we are getting rid of the edge width. It seems however, that when using library components from EAGLE libraries, there is some issue with properly bringing the polygon portion over. We are currently investigating this issue and hopefully can provide a fix for this.


To get unblocked for now, I would suggest to re-do the polygon portions in Fusion. We are very sorry for this.

Pieter-Jan Van de Maele
Senior Engineering Manager, Fusion Electronics
Message 3 of 3

All good, the changes were quick to make on my end. Appreciate the response and acknowledgement!

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