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Micro-Nanostructural Investigations of AlSi1 Bondcontacts

: Geißler, U.; Schneider-Ramelow, M.; Reichl, H.

Michel, B.:
MicroNanoReliability 2007, 1st World Congress MicroNanoReliability : Berlin, September, 2 - 5, 2007
Dresden: ddp Goldenbogen, 2007 (Micromaterials and Nanomaterials 6.2007)
World Congress MicroNanoReliability <1, 2007, Berlin>
Fraunhofer IZM ()

The wedge microstructure of AlSi1 wire bonds as well as the interface between the bonding wire and the Cu/Ni/Au metallization layer especially for Chip on Board (COB) assemblies was investigated by Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and micro-hardness measurements. With increasing ultrasonic power the results indicate recrystallization of the grain structure and decreasing micro-hardness inside the bonded wedges contacts. The very fine grain structure in the interface region is the precondition of a closed interface, high bond strength and reliable bond contacts.
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. Above this Au layer, a second zone consisting of intermetallic phases was analyzed and identified by electron diffraction as Au8Al3. After a few milliseconds first spots of the 30- 50 nm thick intermetallic phase are grown. The covered area increases during the bonding time and results for perfect bond contacts in a gold layer completely overcast by the Au8Al3 phase.