7 Fundamentals and Failures in Die Preparation for 3D Packaging
183
form BSC. The FSC and BSC also heavily depends on street structures in a given
wafer. High metal content streets can increase the blade loading and increase the
number of chips formed in the street. It may also lead to micro cracks, originating
from Si sidewall. The chipping size, occurrence and the die thickness and residual
stress of the die can dictate the reliability risk. A typical failure in reliability is die
crack due to assembly and test interaction. In some cases, it may lead to the crack of
molding compound or epoxy fillet. One of the challenges for BSC detection is the
DAF material in certain products as it prevents BSC to be monitored with typical
measurement tools. In general, the BSC is acceptable in most cases as long as the
chip depth is minimal and not extending towards the active area.
Multiple papers discussed the factors impacting FSC or BSC [48, 81–84]. In
summary, the key factors to be considered in eliminating or reducing the chipping
are:
1. Blade type:
a. Grit size of a blade can impact the chipping size and frequency. If the grit
size is increased, the cutting power increases [84] and hence reduces blade
loading. However, the study also shows that the backside chipping increases
if the grit is larger on wafer thickness less than 200 um [84].
b. Higher diamond concentration results less chipping due to smaller load on
each grit.
c. A softer bond material allows the blade for self-sharpening and hence reduces
the chipping. However, the softer bond material can lead to faster blade wear
and hence increases the frequency of blade change.
2. Blade thickness: is generally dictated by scribe width. However, this factor needs
to be assessed carefully to determine the right size. Wider blade may cause higher
force applied to the dies and higher backside chipping. On the other hand, the
smaller blade can tend to wobble during dicing and can cause higher chipping.
The wobbling can be associated to die thickness and also metal structure density
in street.
3. Process conditions and factors such as pre-cut dressing conditions [81], coolant
flow [85] and direction, blade setup and surfactant flow. It is important to monitor
these parameters and setup condition to ensure friction on the blade is maintained
during dicing. Blade torque can be monitored on-line to ensure process stability
is maintained and meets current challenges of the dicing process [85].
As indicated in Fig. 7.21, in order to calculate the stress level on a chip, the blade
deflection distance δ can be calculated [48] using Eq. (7.19):
δ =
6Fr
3
1
Er 2 e 3
(7.19)
where δ: displacement at the blade tip,
F: total side thrust force in N which is equal to ql,
183
form BSC. The FSC and BSC also heavily depends on street structures in a given
wafer. High metal content streets can increase the blade loading and increase the
number of chips formed in the street. It may also lead to micro cracks, originating
from Si sidewall. The chipping size, occurrence and the die thickness and residual
stress of the die can dictate the reliability risk. A typical failure in reliability is die
crack due to assembly and test interaction. In some cases, it may lead to the crack of
molding compound or epoxy fillet. One of the challenges for BSC detection is the
DAF material in certain products as it prevents BSC to be monitored with typical
measurement tools. In general, the BSC is acceptable in most cases as long as the
chip depth is minimal and not extending towards the active area.
Multiple papers discussed the factors impacting FSC or BSC [48, 81–84]. In
summary, the key factors to be considered in eliminating or reducing the chipping
are:
1. Blade type:
a. Grit size of a blade can impact the chipping size and frequency. If the grit
size is increased, the cutting power increases [84] and hence reduces blade
loading. However, the study also shows that the backside chipping increases
if the grit is larger on wafer thickness less than 200 um [84].
b. Higher diamond concentration results less chipping due to smaller load on
each grit.
c. A softer bond material allows the blade for self-sharpening and hence reduces
the chipping. However, the softer bond material can lead to faster blade wear
and hence increases the frequency of blade change.
2. Blade thickness: is generally dictated by scribe width. However, this factor needs
to be assessed carefully to determine the right size. Wider blade may cause higher
force applied to the dies and higher backside chipping. On the other hand, the
smaller blade can tend to wobble during dicing and can cause higher chipping.
The wobbling can be associated to die thickness and also metal structure density
in street.
3. Process conditions and factors such as pre-cut dressing conditions [81], coolant
flow [85] and direction, blade setup and surfactant flow. It is important to monitor
these parameters and setup condition to ensure friction on the blade is maintained
during dicing. Blade torque can be monitored on-line to ensure process stability
is maintained and meets current challenges of the dicing process [85].
As indicated in Fig. 7.21, in order to calculate the stress level on a chip, the blade
deflection distance δ can be calculated [48] using Eq. (7.19):
δ =
6Fr
3
1
Er 2 e 3
(7.19)
where δ: displacement at the blade tip,
F: total side thrust force in N which is equal to ql,