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52 SMT Magazine • December 2017 a consistent behavior of the transfer efficien- cy. The measured values rise along with higher area ratios. Apertures with east-west orientation again show higher transfer efficiencies. Against the overall view, the effect seems to have a max- imum for columns 5 and 9 at area ratios of 0.5 and above. AR of 0.45 shows a continuous trend to higher transfer efficiencies with a decrease in the outer shapes. The analysis of the standard deviation for the 80 µm stencil thickness shows the clear trend for more unwavering distribu- tions at higher area ratios. Again, the rectangu- lar aperture shows a reduced standard deviation but against the overall view no significant vari- ance in the outer columns occurs. The analysis of the measured data for the 100 µm stencil thickness shows significant dif- ferences in the transfer efficiencies, as shown in Figure 8. Area ratios above 0.55 consistent- ly print above 75% transfer, while a strong de- crease is observed for the area ratios 0.5 and es- pecially 0.45. Compared to the 80 µm thickness no significant decrease of the transfer efficien- cy can be observed. Excluding the area ratio 0.5 data, all others have the common trend where the highest aspect ratio rectangles track low- er in transfer efficiency relative to neighboring data points. The standard deviation of the 100 µm sten- cil follows the overall trend with higher devia- tions for the area ratios 0.45 and 0.5. Area ratios above 0.5 show the minimum for the variance in the area of the rectangular shape. A strong influence is detected for north-south orientated apertures resulting in higher values for the stan- dard deviation towards column 2. The average values of the 120 µm stencil show the highest transfer efficiency of all sten- cils and it seems to be the stencil with the high- est ability to perform the prints. The increase of the transfer efficiency for the east-west aperture orientation is clearly recognizable as illustrated in Figure 9. Similar to the trends shown in Figure 4, the two smallest area ratios have marked transfer efficiency differences between the two aperture orientations, particularly at high aperture as- pect ratio. Conversely, the transfer efficiencies produced by the north-south aperture orienta- tion for the two smallest area ratios are less sen- THE EFFECT OF AREA SHAPE AND AREA RATIO ON SOLDER PASTE PRINTING PERFORMANCE Figure 7: Influence of the aperture shape and the orientation for the 80 µm stencil. Figure 8: Influence of the aperture shape and the orientation for the 100 µm stencil.