Throughout the embodiments of the present disclosure, as shown in FIGS. 2 through 9, elongated openings 158A are centripetal. In accordance with some embodiments, the longer axis 134 (FIGS. 10A and 10B) of elongated centripetal openings 158A extend toward the neutral-stress point 140 (FIG. 2 through 4), which may be at, or at least close to, the center of bottom package 100 (in the top view). Alternatively stated, the longer axis 134 (FIGS. 10A and 10B) of the centripetal elongated openings 158A pass through the center of bottom package 100, or at least, the longer axis 134 of the centripetal elongated openings 158A are closer to the center of bottom package 100 than the respective shorter axis 136.