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Diplom- und Master-Arbeiten (eigene und betreute):

J. Gager:
"Numerical Simulations of Delaminations and Cracks in Glued Die-Attach Semiconductor Devices";
Betreuer/in(nen): H. E. Pettermann; Institut für Leichtbau und Struktur-Biomechanik, TU Wien, 2010; Abschlussprüfung: 09.02.2010.



Kurzfassung englisch:
During service most semiconductor devices are exposed to temperature variations or thermal cycles. Because of the multi-material-design of the devices these thermal loads often induce considerably tractions at the interfaces. These tractions might initiate cracks and delaminations and, therefore, can lead to a device failure due to a loss of electric contact. Hence, it is important to understand the influences of the temperature loads and the resulting stress fields on the cracks to develop reliable semiconductor devices.

The interpretation of the crack situation is based on linear elastic interface fracture mechanic methods. Here, the stress intensity factor, the mode-mix, and the energy release rate are used to assess the crack. To obtain these fracture parameters, the displacement extrapolation method and the virtual crack closure technique are implemented as post processing routines. To compute the underlying stress and displacement fields the finite element method is used. The fracture mechanics methods are verified by means of two example problems for which analytical solutions exist.

Under the assumptions of linear elastic fracture mechanics, two-dimensional models with various cracks located in the interface between the die-attach - mould compound, lead frame - mould compound, and die-attach - die, respectively, are created. For a better accuracy special crack tip elements, which are capable of representing the 1/sqrt(r) singularity, are used. Some of these crack configurations suffer from crack face overlapping, thus, for these special cases contact capabilities are introduced. Furthermore, for all models a manufacturing simulation is performed to predict residual stresses. A thermo-elastic simulation covers the cooling down part of a thermal cycle, and a subsequent fracture mechanics analysis gives the fracture mechanics parameter.

A design study is performed in which various geometry and crack configurations are investigated. It reveals that a variation of the effective clearance has no influence on the fracture parameters as long as the crack remains in the die-attach - mould compound interface. Rather, the bleed-out angle is the parameter with the main influence on the crack tips in this basic configuration. If the crack is extended into the lead frame - mould compound interface the effective clearance shows a strong influence on the crack tip in this interface. By means of a more realistic bleed out shape model the concave shaped bleed out turns out to be an preferable design. A crack extension to both sides, into the lead frame - mould compound and die-attach - die interface shows that the crack tip in the latter interface is not affected by the delamination length on effective clearance side. This means, that under the given modeling assumptions, the delamination of the lead frame does not alter the predicted stress state at the die-attach - die interface.

Erstellt aus der Publikationsdatenbank der Technischen Universität Wien.