In this paper, we presented several practical aspects for building robust and reliable finite element models in thermomechanical modeling in electronics packaging using finite element analysis. Firstly, for layered or patterned structures, a homogenized equivalent model, with equivalent orthotropic material properties, gives excellent agreement with the exact finite element model solutions. Such a simplified finite element model provides an efficient way for structural parameter optimization. Secondly, the finite element mesh should keep the fixed size and shape at the location of interest where the singular point exists. This approach provides a simple way for relative stress comparison in different designs, although the absolute value of stress components has no actual meaning. Thirdly, to further eliminate the mesh dependency, the volume averaging method can be used. We extended the local volume averaging method for large-area die attach problems. Fourthly, in this paper, we presented a comparison study between linear elastic and nonlinear viscoplastic analysis, and demonstrated that in some cases, two different types of analysis give opposite trend results. Lastly, we demonstrated that with the use of different stress components, the conclusions may be different. We also provided an ANSYS APDL script in the supplemental material as a benchmark example.

The contact stress of flexible joint is an important factor affecting the safety of ultra-short-radius drilling tools. However, calculating the contact stress accurately is difficult, because the method for solving the multibody collision of the flexible joint is complex. A novel analytical method for the contact stress of ball cage flexible joint is presented in this study. The method was used to establish the relationship between the parameters and contact stress of the flexible joint during the drilling process. The contact stress analytical models of the ball head, ball key, and ball seat were established based on Hertz contact theory, and the finite element method was used to analyse the variations of contact stress under the weight of bit and torque. The influences of borehole curvature and deflection angle on contact stress were discussed for parameter optimization. Results demonstrate that the contact stress values on the ball key, inner raceway, and outer raceway are concentrative. The ball key is the most dangerous part of the flexible joint, and its safety can be improved by increasing its diameter. When the deflection angle between the flexible joint was increased from 0 ° to 18 °, the contact stress value also increased to 220 MPa. However, the contact position was random on the inside of deflection. The proposed method provides a good prospect to optimize the structure parameters of the flexible joint and ultra-short-radius drilling parameters