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66 SMT Magazine • November 2017 vehicle (shown in Figure 10) is used to study the impact of different BGA body sizes, ranging from 10x10 mm sq. up to 37x37 mm sq., in ad- dition to BGA pitches, ranging from 0.7 mm to 1.0 mm, with respect to the solder joint integri- ty within a mixed VIPPO and non-VIPPO BGA footprint on the PCB. An advanced 7.9 mil DHS VIPPO was used in order to accommodate the DHS-to-pad size design rule for BGA pitches < 1.0 mm. The components are designed on both sides of the PCB and utilize the same set of con- trolled PCB factors as defined in the DDR4 test vehicle for thickness, material and stack-up. Lastly, the VIPPO and VIPPO + backdrill test vehicle (shown in Figure 11) is designed to in- vestigate the influence of a mixed VIPPO and VIPPO + backdrill BGA footprint on the sol- der joint integrity. Different backdrill depths (to layer 03, layer 05 and layer 07 on a 28-lay- er, 130 mil thick PCB design) are studied based on PCB backdrilling depth capability and tol- erance. Different daisy chain component BGA body sizes ranging from 10x10 mm sq. to 37x37 mm sq. are again used for this test vehicle. For all of these test vehicles, each board is subjected to pre- and post-assembly (i.e. after primary and secondary reflow processes) pro- cess resistance measurement followed by phys- ical analysis verification with dye and pry and cross-section techniques. VIA-IN-PAD PLATED OVER DESIGN CONSIDERATIONS Figure 9: Mixed VIPPO and non-VIPPO test vehicle with multi-drill size. Figure 10: Mixed VIPPO and non-VIPPO test vehicle with multi-package types.