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Analysis of chip damage risk in thermosonic wire bonding

: Dresbach, C.; Lorenz, G.; Petzold, M.; Altenbach, H.


Öchsner, A.:
Advanced computational engineering and experimenting : Selected, peer reviewed papers from the Fourth International Conference on Advanced Computational Engineering and Experimenting (ACE-X 2010) held at the Hotel Concorde La Fayette Paris, France during the period 8th-9th July, 2010
Stafa-Zurich: Trans Tech Publications, 2011 (Key engineering materials 478)
ISBN: 978-3-03-785135-7
International Conference on Advanced Computational Engineering and Experimenting (ACE-X) <4, 2010, Paris>
Fraunhofer IWM ()

In current highly integrated microelectronic devices including system-in-package and stacked-die solutions, system reliability is strongly influenced by reliability of the gold and copper wire bond interconnections. Especially in state-of-the-art ICs containing mechanically sensitive low-K dielectric materials, controlling the mechanical properties of the free air ball (FAB) is of utmost significance due to chip damage risks during the bond process. Because of an extreme change in microstructure when forming the FAB, the material properties change significantly. Consequently, it is necessary to determine the properties of the FAB itself, when analyzing chip damage risks via finite element simulations. We present a micro-compression test that allows the determination of the hardening behavior of typical gold and copper FABs with diameters between 45 m and 75 m. In this test a FAB is placed on a diamond support or a test capillary and loaded by a diamond flat punch in a m icroindenter. The hardening was determined from force/displacement behavior via parameter identification using finite element simulations. The identified yield stresses correlate very well with the microstructure which was determined by electron backscatter diffraction method; this means that the yield stress decreases with increasing mean grain diameter in analogy to the Hall-Petch correlation. Compared to unprocessed wires the initial yield stresses are 50% to 60% lower. Considering these material properties, the damage risk during bonding on complex bond pad layouts can be predicted more realistically. This can be shown by results of real bond structures.