Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Interface reactions during Au-ball/wedge and AlSi1- Wedge/wedge bonding at room temperature
    ( 2007)
    Schneider-Ramelow, M.
    ;
    Lang, K.-D.
    ;
    Geißler, U.
    ;
    Scheel, W.
    ;
    Reichl, H.
    Tlie presentation addresses results of Au Ball/Wedge Bonding and AlSi1 Wedge/Wedge Bonding from 125 deg C down to room temperature (RT). In this context, also interfacial reactions on Flash-Au PCB-metallizations as well as microstructural changes in AlSi1 wire material in relationship to bonding conditions are discussed. This emphasizes the understanding of bonding process remarkable. One topic is the verification of RT bondability of different types of Au wire on specific Al pad metallizations and PCB-substrates with Cu/Ni/Pd/Flash-Au metallization. Investigations include mechanical tests of Au loops and ball contacts as well as microstructural observations of the contacts (FIB (Focused Ion Beam ), SEM, TEM). A most important result in this context is, that Au/Al intermetallic phases with thicknesses of a few hundred nanometers were found below the Au contacts on Al metallization directly after bonding at room temperature. Secondly new results of the Au-Au interface between wire and Flash-Au finish metallization are presented. Another related purpose was to investigate wedge microstructures of AlSi1 wire bonds as well as the interface between the bonding wire and a Cu/Ni/Flash-Au metallization layer. FIB and TEM have been the dominant analytic methods. The interface between the AlSi1 wire and the Cu/Ni/Flash-Au metallization layer of the optimized bonds consists of a closed crystalline Au layer with a thickness of nearly 80 nm. Above this Au layer, a second smaller zone consisting of an intermetallic phase was analyzed and identified by electron diffraction as Au8Al3. Further a correlation of wire material structure changes (fiber texture to recrystallized grains) and ultrasonic power during bonding were determined. With this results understanding of room temperature wire bonding could be improved exceedingly.
  • Publication
    High temperature and element alloying influences on Kirkendall voiding in Au ball bond interconnects on Al chip metallization
    ( 2007)
    Schneider-Ramelow, M.
    ;
    Schuch, B.
    ;
    Lang, K.-D.
    ;
    Reichl, H.
    The presentation addresses the reliability of Au ball bond interconnects on Al chip metallizations of different thicknesses and compositions. Interfacial reactions, intermetallic phase (IP) and Kirkendall void growing are discussed. The results contribute to a better understanding of failure mechanisms caused by interdiffusion and Kirkendall voiding. The mentioned failure mechanism is influenced by numerous factors, such as curing temperature and time, Au wire and Al metallization composition and ratio of mixture as well as the real area of interconnect formation under the ball. These influences are mainly responsible for ball lift offs under load. It was discovered that numerous lift offs already occur with Al metallization thicknesses more than 1 micron and temperatures in the range of 175 deg C, while temperatures of 150 deg C or 200 deg C are less critical. Therefore interpolation or extrapolation of aging temperature results without considering certain bonding conditions is no longer expedient. Investigations include mechanical tests of Au wires as well as microstructure observations of the contacts in correlation to material composition, aging temperature and Al metallization thickness. Au/Al intermetallic phase thicknesses below the Au contacts on Al metallization are typically a few hundred nanometers thick directly after the bonding process, depending on bonding conditions like process parameters and material combination. These phases grow under temperature influence and Kirkendall voiding can occur. A most significant result in this context is that pull and shear lift offs occur if the chip metallization consists of pure Al (not Si and Cu alloyed) and clearly thicker than 1 micron and the temperature is in the range of 175 deg C.