signal electromigration
Electromigration is the movement of metal ions in a conductor, which depends upon the current density , if ur current density say 2mA is flowing in a metal layer of 1micron then u will get electromigration problems which causes metal layer to break , That is if the current flow is unidirectional then you will get electromigration. And it happens only in the case of Power lines not signal lines,
The problem which occurs in Signal nets is called as Self Heating and it is because the signal flows bidirectionally.
Hope it is clear
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