Template Design and Solder Paste Selection in SMT High-density Fine-pitch Assembly (3)

Calculations and results

Before and after stopping, the data for each of the stencil's solder paste deposition was collected. For each stencil and solder paste combination, the average amount of solder paste for each component was also calculated before and after stopping to investigate the recovery of the solder paste. Recoverability is the decrease in deposition volume of solder paste after waiting time, which can be defined as the ratio of the average solder paste volume after stopping to the average solder paste volume before stopping.

Figures 1 to 4 show the amount of solder paste before and after the BGA 40, BGA 31 μBGA 20 and QFP 16 solder pastes were printed on 5 templates and 3 different solder pastes. Here, 5-a indicates that a No. 5 template and a solder paste are used. Solder paste c almost completely recovers after waiting time, and the volume loss is minimal or no loss. Solder pastes b and c have better recovery than a. Among the three solder pastes, solder paste c seems to have the best recovery. The recoverability of solder paste also depends on the template.

Figures 5 to 8 show the amount of solder paste before and after stopping 90 minutes at 0402, 0201, SOIC 25 and QFP 20 with 5 templates and 3 different solder pastes. For the 0402 and 0201 CHIP components, none of the solder pastes recovered completely, but for the other two components, all solder pastes recovered 100%. On the whole, after 90 minutes, the solder paste a in the three solder pastes had the best recovery, followed by the solder paste c, which was better than the solder paste b. At 90 minutes, the correlation between the solder paste and the template was obvious.

Figure 9 and Figure 10 show the solder paste recovery and template relationship after 15 minutes of stopping. As can be seen in Figure 9, solder paste C completely recovered after 15 minutes of cessation of all stencils. Solder paste a cannot be completely recovered under any condition, regardless of the use of any stencils; these results are shown in Figures 1 through 4. The results are consistent. In summary, as shown in Figure 10, in all the templates, the 22nd template recovery is minimal, and the solder paste c has the best recovery on the 5th and 11th templates. Solder paste b had the best recovery on the 5th and 21st templates. Although solder paste a did not completely recover all the templates, it was better recoverable than other templates for the 11th template.

Figure 9 and Figure 10 show the solder paste recovery and template relationship after 15 minutes of stopping. As can be seen in Figure 9, solder paste C completely recovered after 15 minutes of cessation of all stencils. Solder paste a cannot be completely recovered under any condition, regardless of the use of any stencils; these results are shown in Figures 1 through 4. The results are consistent. In summary, as shown in Figure 10, in all the templates, the 22nd template recovery is minimal, and the solder paste c has the best recovery on the 5th and 11th templates. Solder paste b had the best recovery on the 5th and 21st templates. Although solder paste a did not completely recover all the templates, it was better recoverable than other templates for the 11th template.