Using Element Birth and Death Technique in Modeling Cumulative Molded Substrate Expansion before Singulation

Semiconductor packages are commonly assembled and molded in array format on a substrate strip before they are singulated into individual units. However, cumulative substrate expansion causes problems such as machine vacuum error or misaligned cut during singulation if the substrate expansion is not factored in. This study uses element birth and death technique in modeling the overall expansion of the molded substrate strip so that the predicted expansion could be considered in the singulation tooling design offsets. The expansion of the substrate was modeled with the different package assembly processes and thermal conditions. Modeling results showed that there is a cumulative increase in the length of the substrate as it passes through the different processes. The results are in agreement with actual substrate expansion prior to package singulation. This would not be captured when simulation is done only for the molded substrate without considering the cumulative contribution of the preceding processes. With the element birth and death technique in process-based thermomechanical modeling, substrate expansion could already be forecasted, and package assembly problems avoided.

Thermomechanical modeling of the metallic rivet in friction riveting of amorphous thermoplastics

The present work aims for an initial computational simulation with finite element analysis of the friction riveting process. Knowledge and experimental data from friction riveting of AA2024-T351 and polyetherimide supported the computational simulation. Friction riveting is a friction-based joining technology capable of connecting multiple dissimilar overlapping materials in a fast and simple manner. In this paper, the plastic deformation of the metallic rivet, process heat input, and temperature distribution were modeled and simulated. The plastic deformation of the metallic rivet is of key importance in creating the mechanical interlocking and main joining mechanism between the parts, being this the focus of this work. The influence of the polymeric material was considered a dynamic boundary condition via heat input and pressure profiles applied to the rivet. The heat input, mainly generated by viscous dissipation within the molten polymer, was analytically estimated. Three experimental conditions were simulated. The heat flux values applied in modeling of the different conditions were determined (8.2, 9.1, and 10.2 W/mm2). These yielded distinct plastic deformations characterized by a diameter of the rivet tip, from the initial 5 mm to 6.2, 7.0, and 9.3 mm. The maximum temperatures were 365, 395, and 438 °C, respectively.