Material characterization of thin coatings and failure analyses of flip-chip packages

Thin films or graded coatings are often anisotropic or partly inhomogeneous. Identification of their properties is very difficult due to their small scales and material complexities. A new procedure, the inverse method, was developed and applied to characterize elastic-plastic graded coatings and transversely isotropic thin films/coatings. Based on Kalman filter technique, the inverse method uses indirect measurable experimental data to extract key unknown parameters. A plasma sprayed graded coating was characterized first in our studies. Compositional profile and effective mechanical properties through thickness were determined without resorting to complex experimental measurements. It relied solely on the load-displacement records of instrumented spherical indentations and the inverse analysis during post-processing. The coating is composed of Yittria Partially Stabilized Zirconia (PSZ) and NiCrAlY whose mixture and elastic-plastic properties vary through its thickness. The elastic moduli of both phases were estimated by Oliver and Pharr method, while the plastic properties of NiCrAlY were determined by modifying the inverse method proposed for graded materials. The later procedure represents a new indentation method for characterization of homogeneous elastic-plastic materials. The simulated load-displacement relations from estimated properties agree with the experimental records very well, which assures a high degree of accuracy in the current measurement procedure. Finite element verifications were carried out successfully for the characterization of transversely isotropic thin films/coatings.; A multi-scale finite element analysis (MS-FEA) procedure was developed to investigate the area-array solder-bumped flip-chip package in which length scales of components vary from sub-micron to several millimeters. Through it, our studies achieved a better understanding of the failure mechanisms by identifying likely fracture modes and potential delamination sites in flip-chip packages. Essentially, the deformation of an entire thermally loaded package was analyzed first to identify the critical solder region. Then, its solution was prescribed as the boundary conditions in a very refined cell model to investigate the micro deformation surrounding the solder bump. Using the two different scale models, detailed stress fields as well as fracture parameters at various interfaces can be determined. Detailed two-dimensional delamination analysis was carried out first under a single temperature drop. Based on the energy release rate calculations, a solder bump located at the corner of chip is more likely to fail first. However, our results also indicate possible delamination growth at solder bumps near the center of chip. In addition, higher energy release rates have been observed for longer cracks under the same thermal loading condition. This result implies a possibility of unstable crack growth in the flip-chip packages. (Abstract shortened by UMI.)...