DEVELOPMENT OF MOIRÉ INTERFEROMETRY FOR REAL-TIME OBSERVATION OF NONLINEAR THERMAL DEFORMATIONS OF SOLDER AND SOLDER ASSEMBLY

An experimental apparatus using moiré interferometry is developed to characterize the thermo-mechanical behavior of solder joints. A compact moiré interferometer is combined with an environmental chamber to allow real-time observation of non-linear and time-dependent solder and solder assemblies. The first apparatus is based on convection heating and cooling to simulate an accelerated thermal cycling (ATC) condition. Vibrations caused by an environmental chamber are circumvented by unique rigid links that connect the specimen to the moiré interferometer. Displacement fields are documented while the chamber is being operated. The system is utilized to analyze thermo-mechanical behavior of a ceramic ball grid array package assembly and a plastic ball grid array package assembly. The effect of thermal cycling on the accumulated permanent deformation is documented, which reveals the temperature-dependent non-linearity of solder joints. The second apparatus is based on conduction heating and cooling to achieve a high ramp rate. A special chamber is designed and fabricated using a high power thermoelectric cooler to achieve the desired ramp rate. The system is utilized to investigate the time-dependent behavior of solder joints. A new solder joint configuration is designed and fabricated to be tested with the conduction based apparatus. The specimen is an extension of the conventional bi-material joint configuration but the unique design offers two important features; it negates the inherent shortcoming from cross sectioning required in moiré interferometry and produces a virtually uniform shear strain field at the solder joint. The deformation of solder joint is documented at a controlled ramp rate over several thermal cycles. The experimental results are analyzed and compared with those of Finite Element analysis to investigate the validity of solder constitutive models available in the literatures

Analysis of column interconnects for wafer level packages

Master'sMASTER OF ENGINEERIN

Rapid Assessment of BGA Fatigue Life Under Vibration Loading

Ball Grid Array (BGA) packages are a relatively new package type and have rapidly become the package style of choice. Much high density, high I/O count semiconductor devices are now only offered in this package style. Designers are naturally concerned about the robustness of BGA packages in a vibration environment when their experience base is with products using more traditional compliant gull or J leaded surface mount packages. Because designers simply do not have the experience, tools are needed to assess the vibration fatigue life of BGA packages during early design stages and not have to wait for product qualification testing, or field returns, to determine if a problem exists. This dissertation emphasizes a rapid assessment methodology to determine fatigue life of BGA components. If time and money were not an issue, clearly one would use a general-purpose finite element program to determine the dynamic response of the printed wiring board in the vibration environment. Once the response of the board was determined, one would determine the location and value of the critical stress in the component of interest. Knowing the critical stress, one would estimate the fatigue life from a damage model. The time required building the FEA model, conducting the analysis, and post-process the results would take at least a few days to weeks. This is too time-consuming, except in the most critical applications. It is not a process that can be used in everyday design and what-if simulations. The rapid assessment approach proposed in this research focuses on a physics of failure type approach to damage analysis and involves global and local modeling to determine the critical stress in the component of interest. A fatigue damage model then estimates the life. Once implemented in software, i.e. the new version of CALCE_PWA, the entire fatigue life assessment is anticipated to be executed by an average engineer in real time and take only minutes to generate accurate results