296
S. Lee
10.4.3.1 TSV Memory Stacking
The High Bandwidth Memory (HBM) will be the first commercially available product
using TCB. The data in Table 10.5 describes its specification. NCF is used with
TCB in the current POR building block for mass production of top two DRAM
manufactures, Samsung and SK Hynix who are producing the 3D TSV DRAM.
The fine pitch I/O and low gap height prohibit the use of a traditional underfilling
process for encapsulation of the 3D TSV DRAM (see Fig. 10.42). The gap height
is too small to be assured of a flux cleaning process, which requires a gap greater
than 100 μm, the limit of deflux process known to packing industry. Consequently,
the underfilling process, combined with the limited efficacy of flux cleaning process,
limits process downselections of two flux based materials among four major materials
designed for TCB assembly building blocks.
In addition, stacking die will expose interconnections to multiple times of solder
reflow. If the TCB step for the second die applies the forces and temperatures to the
first die when no encapsulation is present, the first bonded die is overcompressed to
the bottom substrate. (see Fig. 10.43). Namely, stacking with no encapsulation can
result in solder interconnections bridging during TCB process.
Table 10.5 Samsung 3D
TSV DRAM specification
Die size
<6.0 × 6.25 mm
Bump pitch
~60 μm
Die thickness
~50 μm
Gap height
~15 μm
Fig. 10.42 Flowchart of building block selection
S. Lee
10.4.3.1 TSV Memory Stacking
The High Bandwidth Memory (HBM) will be the first commercially available product
using TCB. The data in Table 10.5 describes its specification. NCF is used with
TCB in the current POR building block for mass production of top two DRAM
manufactures, Samsung and SK Hynix who are producing the 3D TSV DRAM.
The fine pitch I/O and low gap height prohibit the use of a traditional underfilling
process for encapsulation of the 3D TSV DRAM (see Fig. 10.42). The gap height
is too small to be assured of a flux cleaning process, which requires a gap greater
than 100 μm, the limit of deflux process known to packing industry. Consequently,
the underfilling process, combined with the limited efficacy of flux cleaning process,
limits process downselections of two flux based materials among four major materials
designed for TCB assembly building blocks.
In addition, stacking die will expose interconnections to multiple times of solder
reflow. If the TCB step for the second die applies the forces and temperatures to the
first die when no encapsulation is present, the first bonded die is overcompressed to
the bottom substrate. (see Fig. 10.43). Namely, stacking with no encapsulation can
result in solder interconnections bridging during TCB process.
Table 10.5 Samsung 3D
TSV DRAM specification
Die size
<6.0 × 6.25 mm
Bump pitch
~60 μm
Die thickness
~50 μm
Gap height
~15 μm
Fig. 10.42 Flowchart of building block selection