Jie-Hua Zhao's blog

I am hiring an Engineering Intern this year. The candidates are expected to be graduate students with solid training in mechanics and programming. The starting date is expected to be this summer, however, it can be also earlier. This opening does not sponsor visa application and the candidates should be currently enrolled in US universities and is expected to return to the same school after the internship.  Please email your resume to jhzhao at apple.com.

You will be working on stress simulation of electronic components and sensors with a group of brilliant minds here in Apple’s Headquarters. You are a graduate student with good academic standing majoring in Mechanical Engineering, Engineering Mechanics or similar engineering fields. You are a good programmer and familiar with Python. You must be authorized to work in US. The intern position is open immediately. Send your resume to Jeff Zhao (jhzhao at apple.com).

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.