FIG. 6 illustrates some components in the top view of bottom package 100 and openings 158 in accordance with yet alternative embodiments. In these embodiments, a plurality of device dies 102 is closely located from each other to form device die group 148. Device die group 148 includes corners 146. In accordance with some embodiments of the present disclosure, there are four corner regions 147, each at a corner 146. There are four openings 158 in each of corner regions 147, wherein the four openings 158 are closest to the respective corner 146. Each of the four openings 158 in each corner region 147 includes one opening that overlaps die group 148 and three openings 158 that do not overlap die group 148. All four openings 158 in each corner region 147 are elongated openings 158A, while other openings 158 in the regions surrounding each of corner regions 147 are non-elongated openings 158B.

There is also a plurality of edge regions 149 that overlaps the edges of die group 148. In each of edge regions 149, there are two rows of openings 158, with each of the two rows extending in the direction parallel to the respective edge of die group 148. One of the rows of openings 158 overlaps die group 148, and the other row of openings 158 does not overlap die group. In accordance with some embodiments of the present disclosure, edge openings 158 in edge regions 149 are non-elongated openings 158B. In alternative embodiments, edge openings 158 in edge regions 149 are elongated openings 158A.