Page 37 - Chip Scale Review_May June_2022-digital

dispensing, compression molding, and
then PMC are done. Then, the following
are done: 1) backgrinding of the EMC
to expose the Cu stud; 2) fabricating the
RDLs; 3) and mounting the solder balls.
Those processes are then followed by
scanning a laser through the temporary
glass carrier to the LTHC layer—the
LTHC layer becomes powder, and the
temporary glass carrier is then very easy
to remove. Finally, the reconstituted
wafer (with chips, EMC, RDLs, and
solder balls) is diced into individual
packages. There are three RDLs in
each package and the minimum metal
line width (L) and spacing (S) are 5μm.
For detailed information on the design,
materials, process, fabrication, and
reliability of the chip-first with die face-
up fan-out packaging, please see [4].
TSMC’s integrated fan-out (InFO) [5]
used for Apple’s application processor
is one of the chip-first with die face-up
fan-out processes.
Figure 2: Heterogeneous integration of mini-LEDs for an RGB display (chip first die face down with a
temporary panel process).
Die shift issues
Chip first with die face up during patterning/photolithography In [4], we determined the die shift
Figure 3 shows an example of chip- of the RDLs, the reconstituted carrier caused by compression molding by
first with die face-up fan-out packaging (temporary carrier + chips + EMC) measuring the position of each chip
[4]. The chip size is 10mm x 10mm and is at room temperature. Therefore, before and after molding. (The die size
the package size is 13.42mm x 13.42mm. pitch compensation caused by the is 10mm x 10mm and the minimum
The process steps of chip first with die DAF heating is needed [4]. After EMC metal L/S are 5μm.) Figure 4 shows the
face up is a little more complicated than
that of chip first with die face down.
On the device wafer, one is to
fabricate a Cu stud (about 15μm) on the
original (Al or Cu) contact pads and
the other is to laminate a die-attach
film (DAF) on the bottom side of the
device wafer. The function of the DAF
is to attach (adhere) the die solidly onto
the temporary carrier to avoid die shift
caused by compression molding of the
EMC; and the function of the Cu stud
is to protect the original contact pads
during backgrinding of the EMC, which
is done to expose the Cu stud.
On the temporary glass carrier, a
light-to-heat conversion (LTHC) layer
(about 1μm) is spin coated onto the
temporary glass wafer carrier. The chips
are picked and placed face up on the
LTHC carrier. In order to cure the DAF,
a bonder with temperature and pressure
should be used. The DAF process is
carried out at 120ºC (both bond head
and bond stage) with a bond force of
2kg for 2s for each chip. The temporary
carrier, therefore, will expand during
the pick and place process. However,
Figure 3: A chip-first with die face-up packaging process.

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