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September 2015 • SMT Magazine 47 evALuAtING mANuAL AND AutOmAteD HeAt sINK AssembLy continues ArtiCle strength, strain gauge misplacement, or pin di- mensions. However, the objective is to establish a trend in the finite element model. In this case, both lines increased until a peak strain is noted at the end of the process. The predicted maximum principal strain plot is shown in Figure 8. The yellow arrow points to the approximate location of sensor 15 in the strain gauge testing, wherein strain val- ues are higher. Typical in a press-in process, the push pin develops plastic deformation in the snap-fit features. The resulting contact forces generate the strain on the board. For the manu- al process, the highest strain is predicted when the push pin is about to exit the PCB hole. FeA (Automated Assembly Analysis) Several iterations of the analysis were con- ducted to approximate the automated assembly process. As shown in Figure 9, the graph indi- cates an early peak strain and decreases into a consistent value. Both the experimental and simulation graph lines show similar trends. For the automated process, the push pin is assem- bled to the board at a faster rate. Strain is stable when the push metal rods maintain maximum displacement for a few seconds. The predicted maximum principal strain plot is shown in Figure 10. The yellow arrow points to the approximate location of sensor 14 in the strain gauge testing, wherein strain val- ues are higher. Similar to the manual process, the highest strain is predicted when the push pin is about to exit the PCB hole. As the pin is pushed deeper in the PCB hole, the contact area figure 7: Max. strain graph (comparison for manual process). figure 8: Max. principal strain (manual).