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3D stackable packages with bumpless interconnect technology

Novel 3D stackable packages fabricated with bumpless interconnect technology are presented. Each stackable package contains a chip, an array of planar routing traces and a series of copper pillars and/or vertical conductive channels on the chip periphery for 3D stacking assembly. To keep each stackable package ultra-thin, bumpless interconnect methods such as electro-chemical plating (ECP) or ball bonding are applied to directly connect the traces to the die pads of the chip. No wire bonding, lead-bond, solder bumps, substrate or vacuum sputtering films are involved. The traces route the pad to one or more copper pillars that all extend uniformly and orthogonally downwards from the trace and are pre-coated with solder paste; or to one or more terminals that extend simultaneously downward and are precoated with solder paste and vertical conductive channels that extend upward through the package for inter-package interconnect. The bottom-most package of the 3D stack has surface mount compatible terminals for board level assembly. During 3D stacking assembly, the stackable packages are positioned in a vertical stack with their pillars or conductive channels aligned to one another. A single reflow operation simultaneously bonds all stackable packages together to form a 3D stack. The compliant and deformable nature of solder paste and the routing traces provide flexible vertical interconnections that accommodate chips with a wide range of thicknesses and sizes. The traces, pillars and vertical conductive channels serve as the interconnect matrix between chips, which may be functionally similar or different from one another; thereby increasing packaging density and functionality. The use of different materials for inter-package and board level interconnect maintains package integrity and controls package warp. Compliant terminals may be used to increase board level reliability in the 3D stack. Details of the package design and the underlying bumpless interconnect technology are discussed along with key applications and advantages for test and assembly of these 3D stackable packages.