Issue link: https://iconnect007.uberflip.com/i/911509
December 2017 • SMT Magazine 51 THE EFFECT OF AREA SHAPE AND AREA RATIO ON SOLDER PASTE PRINTING PERFORMANCE Solder Paste Type Due to the bigger assumed influence using a solder paste with coarser particles the first anal- ysis will be focused on solder paste type 4. The general appearance of the trends in Figure 4 (combined test results) seems to be consistent with Figure 5 (type 4 paste results). The graphs show that the rectangle shape and the orien- tation have an influence. The effect in general seems not so obvious compared to Figure 4 but can still be recognized. The solder paste type 4 shows that the transfer efficiency of the 0.45 area ratios raises about 1.6% for north-south orientation and about 8.7% for east-west orien- tated apertures compared to squares. The investigation of the standard deviation shows that the values for the two orientations are comparable for the variations 5-9. The big- gest aspect ratios for the north-south orienta- tion lead to a slightly increasing standard de- viation for columns 2-4. The east-west orien- tation in column 10-12 implies the highest standard deviation for all area ratios. Based on further examinations slightly better printing re- sults are provided using solder paste of type 5, as illustrated in Figure 6. Especially at area ratios of 0.55 and above a higher transfer efficiency is observed. The effect at area ratios of 0.5 and 0.45 is still measureable, but less marked. The standard deviation is more evenly dis- tributed using solder paste of type 5 and shows less variance compared to a solder paste of type 4. The solder paste type 5 shows that the transfer efficiency of the 0.45 area ratios raises about 5.4% for north-south orientation and about 9.1% for east-west oriented apertures compared to squares. Stencil Thickness Following industry accepted area ratio prin- ciple, thinner stencils are considered to provide better release behavior for miniaturized struc- tures. While use of reduced stencil thickness raises the area ratio for identical apertures, this stencil design strategy also subtracts volume ca- pacity from the aperture. Within our investiga- tions three stencil thicknesses are examined. The effect of the 80 µm stencil thickness is il- lustrated in Figure 7. The graphs in general show Figure 5: Influence of the aperture shape and the orientation for solder paste type 4. Figure 6: Influence of the aperture shape and the orientation for solder paste type 5.