Sensitivity Evaluation on Sphere Attachment Shear Strength

A submodeling technique using MSC/PATRAN program and ABAQUS nonlinear finite element code, combined with a Taguchi design-of-experiments approach, was used to optimize the shear strength of spherical ball attachment on an aluminum nitride substrate. In the current design, the sphere is brazed onto a gold solder pad on the backside of the substrate using a gold-tin solder. In the present study, the finite element model was first calibrated by test. Three design parameters were then chosen to evaluate the impact of variation of these parameters on the attachment shear strength. Analysis results indicate that the solder pad size is the most critical parameter affecting this shear strength, and the misalignment between the sphere and the solder pad is the next most critical. Therefore, to effectively improve the attachment shear strength, it is recommended to: (1) Use a larger solder pad; and (2) Minimize the misalignment between the sphere and the mounting solder pad. By implementing only the first recommendation into the current design, i.e., increasing the pad diameter from 0.02 in. to 0.03 in., the attachment shear strength could be improved by 160%. ______________ * Senior Scientist ** Staff Engineer