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First, teardrops and fillets are interchangeable words in PCB design, and both terms are used here in this post. Second, I’m going to go over fixed fillets from start to finish so you can avoid the problem when you are ready for Fab.
Your design is done, you finished the routing, added fillets, and you want to make sure the fillets do not change.
Allegro PCB Editor has a fixed fillet routine for you.
Sounds easy, right? Finish the design, review the fillets for correctness, and run the Missing Fillets report to verify the design is complete.
You are done and ready to output manufacturing media.
Since dynamic fillets can change, and manually added fillets can be deleted when minor editing is performed, you might want to prevent the fillets from moving, or changing their geometry. You might use a third-party tool to generate fillets and need them to be fixed.
Set the environment variable, restart Allegro® PCB Editor and look for the new commands Fix Teardrop and Unfix Teardrop in the Route – Teardrop menu. You should see this menu addition:
You can be selective on which fillets you fix, or to make this easy, make use of the right-click option Fix All (to fix all fillets in the design).
When executed, the command window echoes the following message:
"Fixed status added to < # > of teardrops in design
Once you have fixed the fillets, you might ask, "How do you identify them?"
1. Show element will report them as locked.
2. Run the Missing Fillet report.
A new column will display with the header Lock Status
Each fixed fillet will report with a Lock Status of yes
The report continues to list any missing fillets, and the lock status will be empty for the true missing fillets
This example missing fillet report shows a net with 1 missing fillet on the Bottom and 2 fixed fillets on Top.
You are done! Those fillets are not moving! They are fixed until you chose to unfix them. You can confidently output artwork and archive the design.
What happens when you need to modify the design? Perhaps you need to refresh symbols, move something, add something, or change the routing. ECO’s are inevitable in any design cycle. If you pick up a part and move it, dynamic (non-fixed) fillets regenerate on the net when the part is placed again.
Doing the same placement change with a fixed fillet disconnects the fillet from the net. When you pick up a symbol, slide a cline, or delete a via that has a fixed fillet connected, that fillet loses its connectivity to the original net and cannot be re-attached.
More problems occur as you continue to edit the database while fillets are fixed. For example:
If the above process was not followed, and you find yourself with a database that is already edited and contains fixed fillet problems, then you need the following solution:
Dbdoctor reports a warning for each fillet processed.
That’s it! You are ready to use fixed fillets!