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84 SMT007 MAGAZINE I MAY 2024 Additionally, both samples exhibit the abil- ity to reset the moisture condition through prebake. For these samples the number of pre- bakes and the moisture exposure between them plays no significant role. However, the study does not show the effect of extended exposure to prebake temperatures or numerous cycles in an oven on a sample warpage. With only two prebake cycles it is difficult to exclude the pos- sibility that prebake conditions can affect sam- ple warpage. 10 x 11 mm, 11 x 12 mm, and 14 x 14 mm samples Overall warpage levels of the smaller dimen- sioned samples, particularly the 11 x 12 mm samples, are much smaller than the larger dimensioned samples. is makes the warpage offset caused by moisture an even larger factor than visually shown in the graphs. Certainly, larger samples will tend to have larger solder balls and solder ball pitch, thus larger allowable warpage 7 . However, the offset here is signifi- cant as seen in Figure 19. Figures 10 to 12 showing warpage over tem- perature for the different moisture conditions are difficult to interpret. e sample-to-sample variation at starting room temperature plays a large role in the coplanarity variation. In order to better understand the differences in thermal warpage caused by moisture, the coplanarity can be analyzed with all surfaces shown as rela- tive changes from the room temperature shape. Figures 20 to 22 replicate the data from Fig- ures 10 to 12, but are shown as relative warp- age plots instead of absolute shape. Taken from the relative warpage perspec- tive, the MSL3 data on the 14 x14 mm sam- ple, Figure 22, begins to stand out. is isn't true for the 10 x 11 mm or 11 x 12 mm samples, which seem to show no clear trend in terms of higher warpage with increased moisture expo- sure. So, there are three package types show- Figure 19: Overall coplanarity by sample size. Figure 21: Average relative coplanarity, 11 x 12 mm. Figure 20: Average relative coplanarity, 10 x 11 mm. Figure 22: Average relative coplanarity, 14 x 14 mm (with outlier from Figure 18 removed from average).