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48 SMT Magazine • September 2015 and force increases leading to the high devel- oped strain. FeA (Impact of bGA Location) For this analysis, the FE model for the au- tomated process assembly is used for reference. The original design is referred to as Case 1. For Case 2, the BGA was moved in the Y axis (vertical), 1 mm away from the board edge. In Case 3, the BGA was moved in the -X axis (hor- izontal) direction by 1 mm. As shown in Figure 10, a significant decrease in strain is observed in Case 2 while in Case 3, there was a slight increase in the predicted maximum principal strain. summary The finite element models for FEA of a heat sink assembly by manual and automated pro- cesses have been presented in this paper. Based on results, automated assembly is preferred to the manual assembly process. The results of the analysis were compared to experimental data gathered through strain gauge testing. After several iterations, the differences between ex- perimental and numerical results were reduced and trends were noted to achieve optimized FE models. These FE models can be used to per- form other studies to improve strain values and avoid damaging board flexure. One such factor is the location of the BGAs on the PCB. Further studies can help improve the FE model. Actual testing for material properties can be performed. Other factors affecting BGAs can also be included in a DOE matrix. smt figure 9: Max. strain graph (comparison for automated process). figure 10: Max. principal strain (automated). evALuAtING mANuAL AND AutOmAteD HeAt sINK AssembLy continues ArtiCle

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