Page 34 - ChipScale_Mar-Apr_2020-digital

Figure 4: Process flow schematic for DBI bonding.
diced wafer is cleaned on the dicing frame
and fed directly into the flip-chip bonder
for pick and place. The method not only
simplifies the die preparation process to
reduce cost, it also minimizes die handling
to prevent die breakage and contamination.
Figure 4 illustrates the assembly flow
including wafer and die preparation and
bonding. With this process, we have
achieved assembly yield >90% with
8x12mm size die, as shown in Figure 5.
Assembly process window assessment.
A wide assembly process window is critical
for a high-volume assembly process. Three
factors are critical for the assembly process
window. The first is the plasma process to
enhance the bond energy of the dielectric
surface, the second is the ability to control
Table 1: Throughput comparison table for various bond techniques. Cu recess, and the third is the queue time
Advanced packaging facilities have realized bonding process is possible. Table 1 shows between wafer and die processing and
the importance of micro-environments a side-by-side comparison of bonder bonding. Material held in inventory for up to
for enhanced yield. DBI Ultra assembly throughput for thermocompression bonding 12 months that is able to bond with no issue
requires a minimum of 1K cleanroom (TCB) with nonconductive underfill film indicates a broad process window with no
environment. Some equipment should (NCF), TCB with nonconductive underfill special inventory control.
provide a higher cleanliness requirement, paste (NCP), and DBI Ultra [7]. The very Pitch scaling limitation. Currently,
such as the bonder. We currently retrofitted short bonding time of DBI Ultra is well- the pitch scaling for DBI Ultra is limited
a flip-chip bonder with a class 100 clean kit suited for high-volume package assembly. by the alignment accuracy of the pick
for our bonding experiment. In our assembly process, we slow down and place bonder. We have demonstrated
Assembly throughput and assembly the bonder to approximately 1600 die/hour 40µm pitch bonding using a flip-chip
cost. The new bonding process is using a single bond head to achieve better bonder with 7µm alignment accuracy,
essentially a no-flux pick-and-place alignment accuracy. and 10µm pitch bonding using a bonder
process. The oxide bonding is spontaneous The high bonding throughput is enabled with a 1µm alignment accuracy [8].
once the die surface touches the mating by a die preparation process carried out High-throughput bonders with sub-
surface. Therefore, a high-throughput on a dicing frame. With this process, the µm alignment accuracy are currently

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