Low-temperature Solder Paste Process Advantages


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Figure 5 shows the data for the 12-mil circles with AR=0.6, Figure 6 presents the data for 15-mil circles with AR=0.75, and Figure 7 presents the data for 20-mil circles with AR=1.

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Figure 5: Response to pause data for AR=0.6

Alpha-31Oct18-Fig6.jpg

Figure 6: Response to pause data for AR=0.75

Alpha-31Oct18-Fig7.jpg

Figure 7: Response to pause data for AR=1.

Stencil Life

Stencil life was evaluated by measuring the printed solder paste volumes for a given aperture. The classification was made based on the solder paste volume variability between the different printing conditions. The time between prints was used as a process variable (one-hour intervals up to 12-hour intervals were used). Figure 8 shows the data for the 12-mil circles with AR=0.6, Figure 9 presents the data for 15-mil circles with AR=0.75, and Figure 10 presents the data for 20-mil circles with AR=1.

Alpha-31Oct18-Fig8.jpg

Figure 8: Stencil life data for AR=0.6.

Alpha-31Oct18-Fig9.jpg

Figure 9: Stencil life data for AR=0.75.

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Figure 10: Stencil life data for AR=1.

Voiding

For the reflow step, a seven-zone Vitronics oven was employed. The reflow profile employed for the low-temperature alloys and SAC305 spheres is shown in Figure 11.

Alpha-31Oct18-Fig11.jpg

Figure 11: Low-temperature reflow profile.

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