Pranav Srinivasan, Joseph Hutchinson, and Abhijit Dasgupta
Center for Advanced Life Cycle Engineering, University of Maryland, College Park, MD, USA
For more information about this article and related research, please contact Prof. Abhijit Dasgupta.
Abstract:
Copper pillar μbumps are increasingly being used in heterogeneously integrated semiconductor packages as first-level interconnects to achieve higher interconnect densities than traditional solder bumps. The role of thermomechanical reliability in the co-design process of Cu-pillar microbumps has therefore received increased scrutiny in the literature.In this study, the impact of various design parameters and manufacturing variability on the thermomechanical stresses of the Au-Cu interface in μbumps with Cu pillars bonded to Au pads is assessed using finite element modeling techniques. The severity of the interface stresses is an indicator of the reliability of the interface. The design parameters being considered in this study are: (i) standoff height variability due to die misalignment during manufacturing; (ii) interconnect feature dimensions (Cu pillar diameter and Au pad thickness); and (iii) interconnect pitch.These parametric studies are conducted by using a two-step global-local finite element modeling approach that maps the effect of various design/manufacturing features on thermomechanical reliability. The global model of a semiconductor package, with linear-elastic approximations, simplified geometry, and coarse finite element mesh, is used to identify regions of criticality and to generate local displacement histories near those critical regions. The local displacement fields are then transferred to the boundary nodes of a local model of the critical region(s), consisting of more granularity and fidelity in terms of local geometric details, finer computational spatial resolution, and nonlinear viscoplastic material properties. The stress severity at the interface between the Cu pillar and the Au pad is assessed using equivalent and peel strains at the interface, estimated with finite element modeling.
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