A combined experimental and analytical approach for interface fracture parameters between dissimilar materials in electronic packages

摘要

Failure of materials and interfaces are commonly linked to the fracture parameters such as the stress intensity factors and the energy release rate. However, there exists no experimental procedure for the direct measurement of these fracture parameters. This dissertation reports on the development of a new technique to obtain these parameters by testing specimens created from post-production electronic packages. The results from the experimental testing are then used as the input for an analytical model which computes the desired parameters. The specimens are thin strips of post production electronic packages. A crack is introduced along the interface in the specimen. Loading is applied to the specimen using the bend fixture inside the chamber of a scanning electron microscope, and images are captured following each load step. Digital image analysis on these images provides the displacement field around the crack tip to be used as boundary conditions in the analytical model. A hybrid formulation is developed utilizing the exact solution for the stress and displacement fields based on the eigenfunction expansion method under general loading. The region has two dissimilar elastic or viscoelastic material wedges with perfect bonding, and is not limited to a particular geometric configuration. The solution method is based on the principle of virtual work in conjunction with the use of Laplace transformation to eliminate time dependency. The strength of the singularity is obtained in the time space without resorting to approximate Laplace inversion techniques. However, the intensification of the stress components is obtained by employing an approximate inversion technique. One of the main contributions of this dissertation is the development of multiple techniques for the creation of test specimens from electronic packages. These methods involve different procedures of encapsulation for sectioning and techniques for the introduction of the crack to the interface. A second development is the technique of testing using image capture in conjunction with digital image correlation to find localized displacements. The third contribution from this work is the development of an analytical model to accurately model the region near the junction of two dissimilar viscoelastic materials.