Effect of load sequence interaction on bond-wire lifetime due to power cycling

Experimental investigations on the effects of load sequence on degradations of bond-wire contacts of Insulated Gate Bipolar Transistors power modules are reported in this paper. Both the junction temperature swing (ΔTj) and the heating duration (tON) are investigated. First, power cycling tests with single conditions (in ΔTj and tON), are performed in order to serve as test references. Then, combined power cycling tests with two-level stress conditions have been done sequentially. These tests are carried-out in the two sequences: low stress/high stress (LH) and high stress/low stress (HL) for both ΔTj and tON. The tests conducted show that a sequencing in ΔTj regardless of the direction “high-low” or “low–high” leads to an acceleration of degradations and so, to shorter lifetimes. This is more pronounced when the difference between the stress levels is large. With regard to the heating duration (tON), the effect seems insignificant. However, it is necessary to confirm the effect of this last parameter by additional tests.