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and the traditional 5µm MRSI-705 with eutectic process is performed in an inert precision fluid control technology. The
horizontal turret. Both platforms support environment to prevent oxidation of the substrate surface is measured by a three-
AuSi and AuSn process requirements bonding surfaces, as the RF PA device point laser height system that maps the
and have high-performance stamping and is subjected to heat. We used a specially plane to ensure that the gap between the
dispensing options. designed gas cover over the eutectic needle and surface is maintained at all
Both of our products come with an station. The flow of forming gas is locations. We also provide an option for
integrated turret that can hold up to 12 tips. carefully managed to create an oxygen- a confocal height sensor to measure bond
The turret enables “on-the-fly” tool changing free environment for the eutectic process. line thickness. Consistent bond lines
to achieve zero-time between tip changes. The standalone eutectic station can achieve are achieved through a combination of
Figure 1 illustrates our “on-the-fly” tool a <100ppm oxygen level environment and precision epoxy volume control and closed-
changer. Any version of custom die pick up the indexing eutectic station can achieve loop force control.
tip or epoxy stamping tip can be used in the a <500ppm oxygen level environment,
turret. It can flexibly handle multiple dies, using pure nitrogen forming gas. Both RF PA process results
multiple processes, and multiple products cases far exceed the process requirements Below, we share the performance
in one machine. This helps users to create mentioned earlier. results achieved using the MRSI-H-
flexible production lines that can be rapidly Scrubbing process. Scrubbing is a LDMOS. This system included an
reconfigured for different products. critical process step in the formation of a indexing conveyor for high-volume
Furthermore, high-volume production common material (bond) between AuSi and manufacturing. We used 60 industry
is aided by the in-line eutectic die bonding AuSn by forcing out air to reduce voiding. standard glass dies to test the machine’s
system we developed. By utilizing a Also, the solder is better distributed pick and place accuracy, the 3σ results
progressive heat stage system that indexes across the die and the pressure assists the of x<1.21µm and y<0.84µm surpassed
through heat zones, eutectic die attach can diffusion process. As a starting point, the machine specification <1.5µm @3σ.
be performed on parts transported in “boats” our software includes a pre-programmed The machine oxygen level at the eutectic
or carriers that are loaded, processed, and library of scrub patterns to guide users bonding station was tested by using a Pro
unloaded to cassettes automatically. The as they quickly develop their process. OX-100 Digital Oxygen Purge Monitor.
in-line eutectic system is a “Universal” The scrubbing parameters are completely The results show the oxygen level at the
P r og re ssive I nd ex i ng Conveyor programmable for customization to the eutectic bonding area is <100ppm.
(Figure 2). It is a modularly-designed specific process. Scrubbing consists of The real AuSn process was done for
common architecture across multiple applying vertical and lateral forces to a two different size GaN chips bonding on a
machine platforms (MRSI-705, MRSI-M3, chip during its placement. The chip is substrate by using AuSn solder preforms.
MRSI-H), and supports both AuSn and usually moved in a figure eight pattern that Chip sizes were about 3 x 1mm and 4 x
AuSi eutectic processes. This in-line mode is repeated for several cycles. Movements 1mm. Both chips were 100µm thick. Au-
is also applicable to the epoxy process. in alternate directions are also possible. Sn solder preform sizes were slightly
Temperature profile control. To Rotational scrubs are sometimes employed. smaller than the chips. As the carriers were
achieve eutectic bonding, a heating Scrub parameters consist of amplitude, indexed through the machine, parts were
station is typically employed that speed, and frequency in the x, y, and theta heated to a pre-heat temperature before
can ramp up and ramp dow n the directions. Parameters are determined by arriving at the bond station. The bond
temperature rapidly and precisely to process requirements, such as the surface station was ramped from the preheat to
maintain good temperature uniformity area of the chip, and process constraints, reflow temperature during the processing.
on the hotplate. Our eutectic station such as proximity to adjacent die. Optimal force and scrub parameters were
is a pulsed heating station, with a Bond line control for the epoxy found through process development.
maximum temperature of 450°C, a process. Our epoxy stamping process Metrology revealed that the bonding
temperature control accuracy of <±1°C, uses a rotating stamping-well with process accuracy met the requirements
a temperature ramp-up speed of up to multiple epoxy grooves presenting epoxy well. The results are shown in Figure 3.
40°C/s, and a cool-down speed of 30°C/s. for stamping. The dispensing process The left image shows 15 samples, the right
Oxygen environment control. The uses time-pressure dispensing units with image shows the real size sample. These

Figure 2: “Universal” progress indexing conveyor. Figure 3: 15 samples show solder flowed evenly without oxidation.

32 Chip Scale Review March • April • 2021 [ChipScaleReview.com]
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