Plausible origin of electromigration lifetime extrapolation difference between wafer level isothermal test and package level constant current test

Electromigration lifetime, extrapolated from the wafer level isothermal test on a metal line, does not coincide with that from the package level constant current test. The discontinuity of mass flux density in the wafer level isothermal test as the origin of such a difference is identified, based on a temperature profile along the metal line. Once this issue is clarified in advance, improved correlation between both tests can be achieved, and as a result, the wafer level isothermal test is expected to replace the conventional time-consuming package level constant current test.