Page 134 - System on Package_ Miniaturization of the Entire System

Stacked ICs and Packages (SIP) 109

Vertical inline pillar
(gang conductive
epoxy)

FIGURE 3.33 The vertical interconnection process with conductive polymer for chip stacking. [37]

Stacking with Conductive Polymer Side-metallization for vertical interconnection of
stacked chips can also be achieved with conductive polymers. Metallic conducting
elements extending from rerouted chip pads, such as a bond wire or a bond ribbon, are
embedded within the conductive polymer, thus providing an electrical connection
between the stacked chips, as shown in Figure 3.33. Typically, the side-metallization
process requires a lithography process to obtain the desired metallization patterns at
the small area of the sidewall of stacked chips, which includes application of photoresist
(PR) materials, exposure, development, metal etching, and PR strip processes. The use
of conductive polymers for side interconnections can eliminate the lithography step in
the chip stacking process. The typical conductive polymer can be a conductive epoxy
filled with metallic particles such as silver and gold [37].

Stacking with Solder Edge Interconnect Solder balls or bumps have been commonly
used for mechanical and electrical interconnections between electronic components
including chips, functional modules, and substrates. Figure 3.34 shows the solder

Solder
bumps

Chip Chip Chip

Arch-shaped
solder

PCB

FIGURE 3.34 Chip stacking by arched solder column interconnections. [38]