Transfer printing: an emerging technology for massively parallel assembly
Transfer printing: an
emerging technology for
massively parallel assembly
by C. A. Bower, E. Menard, P. E. Garrou, Semprius, Inc., Research Triangle Park, NC, USA
Surface mount technologies, such as pick- 10,000 placements per hour), but this comes
Transfer printing is a newly
and-place assembly, are well established and at the expense of placement accuracy. Even
developed process that enables
used in the packaging of many microelectronic while operating at slow speeds, many pick-
the massively parallel as-
devices. Standard assembly equipment and-place processes do not achieve placement
sembly of high performance
is also being used to pick-and-place small accuracies better than +/- 20 µm.
semiconductor devices onto
high-efficiency compound semiconductor There have been several efforts to
virtually any substrate mate-
solar cells in the concentrated photovoltaics advance fluidic self-assembly approaches
3,4
as
(CPV) industry. Regardless of this ubiquity, potential routes to low cost parallel assembly
rial, including glass, plastics,
serial pick-and-place technology is not well of small devices. However, to date these
metals or other semiconduc-
suited for a number of applications that call efforts have not produced a technology
tors. This semiconductor
for large assemblies of sparsely populated, platform capable of competing with
transfer printing technology
precisely positioned microscale devices
1
. traditional pick-and-place technology.
relies on the use of a micro- Current assembly technology also places Transfer printing using an elastomeric
structured elastomeric stamp
constraints on the numbers and sizes of stamp has the potential to deliver higher
to selectively pick up devices
solar cells that can be economically handled. throughput (parallel vs. serial assembly),
from a source wafer and then
Standard pick-and-place tools using vacuum better placement accuracy and easier
print the devices onto the
collets are not well suited for handling handling of microscale devices compared to
target substrate. The key en-
devices smaller than 100µm
2
or devices standard pick-and-place with vacuum collets.
abling technique is the ability
thinner than
~
20 µm. Modern pick-and- Transfer printing is essentially a massively
place tools operate at very high speeds to parallel variant of traditional surface mount
to tune the adhesion between
achieve reasonable process throughput (> assembly and therefore is considerably less
the elastomeric stamp and the
disruptive compared to fluidic self-assembly.
semiconductor devices. The 1a
transfer process is massively
1c
parallel as the stamps are
designed to transfer hundreds
to thousands of discrete
devices in a single pick-up
and print operation. Studies
of the process yield indicate
that print yields in excess of Figure 1a. The transfer stamp is aligned to the source
99.9% can be achieved. In
wafer. The stamp is moved down into contact with
addition, experiments show
the released devices. The tethers holding the devices
Figure 1c. The transfer stamp is aligned to the target
in place are not shown in this drawing.
substrate and moved into contact with the surface.
that the chips can be printed
with placement accuracies
better than ± 4 µm @ 3
1b 1d
σ.
Keywords: Transfer Printing,
Concentrated Photovoltaics,
Semiconductor Solar Cells
Figure 1b. The transfer stamp is lifted away from Figure 1d. The devices are transferred to the target
the surface and the stamp posts are now populated substrate as the transfer stamp is moved away from
This paper was originally presented
with devices. the surface.
at SMTAI 2008.
18 – Global Solar Technology – November/December 2008 www.globalsolartechnology.com
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