IMC growth and DR4 open on TSOP package

One kind of TSOP package (Device 98M16 encapsulated by mold compound 7351LS) encountered serious open failure after Data Retention 4 test (DR4, 5000 hours baking at 150 degC) and the failure rate is almost 100%. But a similar package (Device 98R16 encapsulated by mold compound G700L) is normal after test. Failure analyses were done for the two packages. The results show that the wire bond IMC are different for failed package and good package. Kirkendall voids and cracks were found on the wire bond area for failed package. FEA simulation results show that the mold compound used in failed package induces high stress status in wire bond area and leads to the bad performance of the wire bond.