Finite element simulation of a nondestructive shear test for TAB bonds

The viability of using a nondestructive micro-shear test to resolve interfacial features in integrated circuits incorporating TAB (tape automated bonding) technology has been confirmed using finite element method (FEM) simulations. Both two- and three-dimensional finite element models were built to determine whether the size and location of interfacial features such as dead zones (nonbonded regions), delaminations and inclusions could be identified by applying one or more forces to the surfaces of a bond and monitoring the resulting deflections. By monitoring the localized Von Mises stress in the model, it was shown that the applied surface forces did not cause irreversible yield within the bond, and could therefore be considered nondestructive. The models, created in NASTRAN, consisted of two- or three-dimensional brick shaped elements (of length 12.5 /spl mu/m per side) whose material properties were set to either copper (representing the lead) or gold (representing the bump). Non-bonded regions within the bond were simulated by either removing elements adjacent to the lead/bump interface, or by implementing gap elements between interfacial nodes. Inclusions were modeled by setting the material parameters of elements adjacent to the interface to those of silicon dioxide. The input force was applied either directly through the surface nodes of the lead, or through a force tool which contacted the lead surface via gap elements. Other issues considered include the relationship between lead overhang length and the bond force deflection curve, as well as the surface force and displacement profiles generated on the bond under the force tool.<
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