Relation between delamination and temperature cycling induced failures in plastic packaged devices

The occurrence of electrical failures in temperature cycling tests is studied by means of test chips. The observed failures are all caused by top metal deformation, leading to electrical opens. Investigation of the test chips using scanning acoustic tomography demonstrates that the failures are introduced by delamination at the plastic/die interface. A similar correlation is observed between hazardous metal shifting and delamination on 1-Mbit SRAMs. Delamination at the plastic/die interface is found to give rise to a strong degradation of the wire bond quality. These observations can be explained by the increased freedom of the plastic to move with respect to the die surface in case of delamination, as well as by the concentration of shear stresses on a small area. The overall conclusion from these experiments is that plastic/die adhesion is the key factor to be considered in temperature cycling tests.<
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