Interface reactions during Au-ball/wedge and AlSi1- Wedge/wedge bonding at room temperature

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.