Current flow across a typical aluminum contact interface occurs only where metallic junctions form at cracks in the insulating aluminum oxide. When the total metallic conducting area is small, current density may be high enough to initiate electromigration failure. These experiments use a solid aluminum specimen having a constricted current path, representing a single metallic contact junction. Specimens are tested with alternating or direct current flow at current density up to 10 6 A/cm 2 . Electromigration failure, observed as a relatively abrupt increase of resistance, occurs in both ac and dc specimens. Electron microscope examination indicates that the deterioration is due to electromigration. Conditions under which electromigration deterioration may occur in practical aluminum power connections are discussed. A method is provided for estimating the minimum possible current density in aluminum connections. The implications for the theory of aluminum contact behavior and the practical considerations of effective life testing are discussed.

11.3Model aluminum contact junctions which have been operated at high current density are examined for evidence of electromigration. Specimens are examined at the surface and cross-sections following metallographic saniple preparation techniques. The analytical electron microscope (AEM) is used to locate the physical andor chemical indicators of electromigration as reported in the literature. Indications of current induced electromigration are evident in both the AC and DC test groups.

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