Session: 08-01 Mini-Symposium for Professor Dasgupta I

Paper Number: 94505

94505 - Anisotropic Plastic Constitutive Properties of SAC305 Single Crystal Solder Joints 

Heterogeneous integration of different components and functionality into a single chip along with the need for small form factors has driven the size of the solder interconnects to tens of micron-scale. The micro-scale Sn-Ag-Cu (SAC) solder interconnects have oligo-crystalline grain structure with one to three grains in each solder joint. As well documented in the literature, SAC solder joint consisting of 96.5% ß-Sn is highly anisotropic due to the inherently anisotropic mechanical behavior of ß-Sn. Therefore, each joint exhibits a unique mechanical response. However, due to the complexities in the quantification of microstructure and finite element modeling methodology, engineers model solder as a homogenous isotropic volume with an average set of elastic-plastic properties. These approximations cause inaccurate prediction of strain levels in the solder and in turn leads to incorrect lifetime predictions. Another challenge in modeling grain by grain anisotropic solder joint, is the fact that the reliable anisotropic plasticity models are non-existent in the solder literature.

Therefore, the goal of this paper is to determine anisotropic plastic constitutive behavior of SAC305 solder alloy. The paper achieves the goal by conducting monotonic tensile and shear tests on single-grain and multi-grain SAC305 solder joints. Anisotropic plasticity is modeled using Hill-Holloman continuum plasticity model, which utilizes Hill’s anisotropic yield criterion along with a Holloman plasticity model. Mechanistically inspired empirical scaling factors are proposed to extrapolate the stress-strain response across different cooling rates and grain sizes. The Hill-Holloman model constants and scaling factors were estimated inversely using iterative finite element analysis of each test specimen and comparing the FEA results with experimental stress-strain results.

Presenting Author: Abhishek Deshpande University of Maryland