Detailed investigation of ultrasonic Al–Cu wire-bonds: I. Intermetallic formation in the as-bonded state
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Scanning and transmission electron microscopy were used to study intermetallic formation and the interface morphology in copper wire-bonds. The ends of copper wires were melted in air and in a protective environment to form wire-balls. The protective environment enabled formation of symmetrical and relatively defect-free copper balls, together with a smaller heat affected zone (in comparison with wires melted in air). Detailed morphological and compositional characterization of the Al–Cu as-bonded interface was conducted using scanning and transmission electron microscopy, on specimens prepared by focused ion beam milling. Discontinuous and non-uniform intermetallics were found in regions where high localized stress was introduced during the wire-bonding process. The main intermetallic phase was found to be Al2Cu.
KeywordsCopper Wire Transmission Electron Microscopy Specimen Aluminum Metallization Ball Bonding Bond Center
The authors thank A. Berner, Y. Kauffman, and I. Popov for fruitful discussions. This research was partially supported by the Russell Berrie Nanotechnology Institute at the Technion.
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