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.

Title
Microelectronic assemblies having very fine pitch stacking
Application Number
11/318164
Publication Number
20070148819
Application Date
December 23, 2005
Publication Date
June 28, 2007
Inventor
Craig S Mitchell
San Jose
CA, US
Belgacem Haba
Saratoga
CA, US
Agent
LERNER DAVID et al
NJ, US
Agent
Tessera
NJ, US
Assignee
Tessera
CA, US
IPC
H01L 21/44
H01L 21/00
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