industry

Jie-Hua Zhao, Peng Su, Min Ding, Sheila Chopin, and Paul S. Ho

A 3-dimensional finite element method (FEM) model considering the elasticity anisotropy, thermal expansion anisotropy and plasticity of β-Sn is established. The Voronoi diagrams are used to generate the geometric patterns of grains of the Sn coating on Cu leadframes. The crystal orientations are assigned to the Sn grains in the model using the x-ray diffraction (XRD) measurement data of the samples. The model is applied to the Sn-plated package leads under thermal cycling tests. The strain energy density (SED) is calculated for each grain. It is observed that the samples with higher calculated SED are more likely to have longer Sn whiskers and higher whisker density. The FEM model, combined with the XRD measurement of the Sn finish, can be used as an effective indicator of the Sn whisker propensity. This may expedite the qualification process significantly.

Electronic active device is built on the strained silicon-on-insulator (sSOI), e.g. strained Si layer on oxide, which in turn is bonded on bulk silicon wafer. Because no misfit dislocation can exist in strained silicon layer any more, will the dislocation be generated during later processing and operation? If there are still lots of dislocations in the strained silicon layer, where do they come from? Is there any experimental work to discover the dislocation nucleation sites? I guess they will nucleate from the triple junctions of gate-sSOI-cap, because the stress is singular in the triple junction. But I am not sure. So I want to know something about the experimental observations.

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