Rory, Doug from CSL is correct. Electromigration is like fire, without one of the elements contamination, moisture, bias, you don't get migration. What you may be observing is dendritic growth of some lead based crystal (we have observed a crystal growth on silver conductors as the result of sulfer exposure.) Aris Christou has recently published a compilation of electromigration papers; "Electromigration and electronic device degradation". This may have some helpful information. -Mitch Austin [log in to unmask]