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November 2017 • SMT Magazine 67 Results and Discussion DDR4 Test Vehicle Mixed VIPPO and non-VIPPO BGA foot- prints with different drill hole sizes were direct- ly compared for this DDR4 test vehicle study. Post-secondary SMT reflow electrical resistance measurements were taken and physical anal- ysis via dye and pry was performed for solder separation failure verification. The experimen- tal control test leg with an all VIPPO pad BGA footprint showed no solder cracks. On the oth- er hand, as shown in Figure 12, all of the de- signs with mixed VIPPO and non-VIPPO pads within the BGA footprint showed solder sepa- ration at the component side of the VIPPO sol- der joint. The solder separation failure occurred with both 7.9 mil and 9.8 mil drill hole sizes, and hence, confirms that the failure mecha- nism is independent of drill hole size used in the VIPPO pad structure. Fine Pitch VIPPO and non-VIPPO Test Vehicle Employing the same analysis technique, the results obtained for the fine-pitch, mixed BGA VIPPO and non-VIPPO study further confirmed that mixed VIPPO and non-VIPPO pad designs within the same BGA array would result in sol- der separation at the component side and is in- dependent of BGA pitch and VIPPO drill hole size. However, the data also indicates that BGA body size can influence the outcome of the sol- der joint integrity for this type of defect. VIA-IN-PAD PLATED OVER DESIGN CONSIDERATIONS Figure 11: Mixed VIPPO and VIPPO with backdrill test vehicle with multi-package types. Figure 12: VIPPO pads with 9.8 mil and 7.9 mil DHS post second reflow. Figure 13: Solder separation interface observed on DDR4 VIPPO + non-VIPPO test vehicle.