Mechanical Measurements and Simulations for Nonlinear Interlocking Structures

Abstract

This thesis reports investigations of mechanical joining for heterogeneous integration in electronics manufacturing. It expands on previous work using sliding contact point boundary conditions in the interaction of interlocking cantilever structures. Design methodology, simulation setup, and analysis along with design considerations are discussed. Calculation of designs’ contact force and von Mises stress were performed with COMSOL Multiphysics 5.3a and 5.6. Physical tests were also designed and performed in support of experimental verification of an elliptic integral analytic model for curved cantilevers. Experiments generally showed the simulations followed the modeling curve until the sample deformed plastically, and physical testing generally undershot the analytical model, likely because of plastic deformation. Meanwhile, many of the computational simulations tended to overshoot the model by 2.04% to 31.9%. Maximizing the aspect ratio of the flat interacting cantilevers to maintain pure elastic deformation resulted in a low bond strength of 250 Pa, therefore a design strategy accommodating a small degree of plastic deformation may allow for the higher bond strength. In addition to flat cantilever performance, several other designs were evaluated computationally and experimentally. Of these, the design called "inverted S" showed the best performance. The distinct features that contributed to this performance were a demonstrated improvement in its force ratio push-in(insertion force) versus pull-out (retention force), as well as a significant reduction in von Mises stress compared to the flat cantilever pairs. These were achieved by physical testing of this design in stainless steel differed from the computational model by a small 0.006% error for the pull-out force and an error of 6.78% for the push-in force. The knowledge gained from these studies points towards several recommendations for best practices and improvements in future designs, namely that future designers consider the implementation of radii at the corners, minimize the cantilever aspect ratio within the elastic region, choose materials with high yield strength, and include angled interacting cantilevers for the highest possible bonding stress. Furthermore, a list of troubleshooting methods are provided as a guide to aid future researchers, along with comments on the maximum aspect ratios that can be simulated within a reasonable time. Fundamentals of modeling plastic deformation for interacting structures are also discussed as a foundation for future designs. Many further improvements in performance may be made with further optimization of the design and verification techniques.