Analyse par éléments finis d'un composant FPA 2k² avec ANSYS MAPDL pour le programme européen ASTEROID
Main objectives of ASTEROID are to develop very
large raw materials compatible with manufacturing of very large detectors in
volume keeping the same level of performance. To improve the thermo-mechanical
stability of 2k² FPA, optimization of the FPA structure and process Flow will
be done though thermo-mechanical modeling by ADDL.The main objective of ADDL in the ASTEROID program is
to develop a methodology to simulate the process flow for a 2k² Focal Plane
Array by use of Finite Elements simulations with ANSYS MAPDL. Results will be
used by LYNRED to optimize the assembly process. Calculation input files
must include ability to change thickness, sizing, material data, boundary
conditions and loads during project.
By considering dimensions of the whole package and the number of Ball for the interconnection layer, some assumptions have been taken into account to build the FPA package Model. The meshing of an assembly that includes a 2088 x 2088 Ball Grid Array where each solder bump is explicitly modelled will lead to a model with more than 4 million solid elements. The current IT capabilities do not allow for the explicit modelling of all Indium balls of the full Ball Grid Array (BGA). To reduce the size of the Finite Element model and keep it reasonable, ADDL has developed a methodology based on homogenization rules used for composite materials to replace the interconnection layer by a Homogeneous Equivalent Material (HEM). The main goal of this approach is to reproduce the stiffness of the interconnexion layer with the HEM. Validation of the HEM is done by comparing results for a thermo-mechanical calculation between 2 FE models at different temperatures. The first one is an assembly with a real 20 x 20 BGA, the other one is an assembly with HEM.
Displacement (µm) in the Z direction in the 20x20 model at polymerization temperature
As objective is to reduce bending for the substrate layer during assembly process, calculation input files must include ability to change thickness, sizing, material data, boundary conditions and loads. APDL scripts are well suited to take into account any change in the FE Model. To reduce the size of the Finite Element model and keep it reasonable, symmetric considerations have been taken into account. A one-quarter symmetry model has been analyzed for this project.
¼ symmetry Finite Element model for the full Focal Plane Array component
Thinning step Uz displacement - (mm)
Thermal assembly process has been decomposed into loading steps (temperatures, boundary conditions, assembly of parts, etc…) that correspond to the steps of the calculations to be performed (Load Step).
Post-processing results from calculations give a trend on the behavior of the full package during the process flow assembly. As regard to the project specifications, calculations have been done to study effect of different factors. The following post-processing results give an example from data and capabilities provided by calculations. The results presented here are extracted from the substrate layer thickness analysis of the ASTEROID project.
Thinning step Von-Mises Stress - (MPa)