A microelectronic
assembly includes two or more microelectronic packages stacked at a
fine pitch, which is finer than the
pitch that is possible when using solder balls for making the joint. Each stackable
package desirably includes a substrate having pins projecting from one surface of the substrate and solder balls projecting from the other surface of the substrate. Each stackable
package may have one or more die attached to one or more of the surfaces of the substrate. In certain embodiments, die may be attached to both surfaces of the substrate. The dies may be electrically interconnected with the substrate using wire bonds,
flip chip bonding, leads and / or stud bumping. The die may be encapsulated in an encapsulated material, under-filled or glob topped. In certain preferred embodiments, the combination of the conductive post height and ball height is equal to or greater than the height of the encapsulated or molded
chip structure. The combination of the conductive post height and the ball height must be at least equal to the height of the encapsulated
chip structure so that the conductive elements are able to span the gap between
layers of the
assembly. After the tips of the conductive pads are in contact with the solder masses, the solder masses are reflowed to form a permanent electrical
interconnection between the stacked microelectronic packages. During reflow, the reflowed solder will wick up around the conductive posts to form elongated solder columns. In addition, when the solder is reflowed,
surface tension pulls the opposing
layers of the
assembly toward one another and provides a self-centering action for the conductive posts.