Abstract
A materials investigation of Au wire bonds to Al pads revealed the evolution of a multiphase system whose terminal phases depended on the composition of the Au wire. Scanning transmission electron microscopy/energy-dispersive spectroscopy and electron diffraction data are presented for Au/Al wire bonds using both Pd-doped, 99% pure Au wire (2N) and 99.99% pure Au wire (4N) in the as-formed state, upon completion of overmold operations, and after reflow and aging. The reacted interfaces of both the 2N and 4N bonds were found to take on a bilayer intermetallic compound (IMC) microstructure that persisted with aging and phase changes; it is the interface of this bilayer that is believed to be susceptible to mechanical degradation. Pd was found to accumulate in the IMC near the Au/IMC interface for 2N wire bonds and appears to lead to a phase evolution different from that for 4N wire that may be responsible for enhanced reliability of the 2N wire bond with high-temperature aging.
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DeLucca, J., Osenbach, J. & Baiocchi, F. Observations of IMC Formation for Au Wire Bonds to Al Pads. J. Electron. Mater. 41, 748–756 (2012). https://doi.org/10.1007/s11664-011-1805-8
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DOI: https://doi.org/10.1007/s11664-011-1805-8