Tech Briefs Magazine - May 2022 - PIT-24

Acrylic
Acrylic
Epoxy
Epoxy
01000200030004000500060007000
050100
Young's modulus [MPa]
Glass transition temperature [°C]
Figure 5. Depending on the application, soft or hard imprint materials might be beneficial. Both epoxy and acrylic materials can cover a broad range of Young's
modulus (left graph) and glass transition temperatures (right graph).
from 72h to 1000h or more), as well as
temperature cycling and temperature
shock tests (-40°C to +120°C or higher)
for consumer electronics and other applications
that are used at ambient temperatures.
For demanding high-temperature
applications, like those found in automotive
scenarios with their 150°C requirements,
UV-curable epoxies are normally
the material of choice. These polymers
can withstand reflow soldering, as they
prove in MSL (moisture sensitivity level)
testing (THT followed by 3x reflow process
with 260°C peak temperature), making
them suitable for optoelectronic components
that face a reflow process in their
downstream final assembly.
Given these options, and many more
that have not been mentioned, including
non-yellowing, low shrinkage and
low outgassing, it is obvious how important
it is to balance all these properties
to achieve the best performance in
different application and production
scenarios, based on simulations and experimental
tests. Both acrylic and epoxy-based
materials have their individual
strengths. As a rule of thumb, acrylic
materials tend to be stronger in covering
a wide refractive index range, whereas
epoxies are beneficial with higher
temperature and low shrinkage requirements.
In the end, the final application
will dictate which to use to achieve the
best performance.
True Power of Wafer Level Optics
UV imprint of single optical elements is
just a small aspect of wafer-level optics. Its
true power comes into play when full optical
systems are manufactured in parallel on
24
150
200
Figure 6. Schematic cross section through a typical optical sensor. Elements like lenses and spacer
wafers can be fabricated using NIL. The system is finally formed by stacking these elements on a
wafer-level. The single component, e.g. the optical sensor, can be obtained by blade or laser dicing.
(Image: DELO)
a wafer-level. Besides the optical elements,
such as a lens or a DOE, an optical system
needs additional components, like spacers,
apertures and a housing. Wafer-level optics
deal not only with fabricating each single
element, but also how to stack these elements
to form the full system.
UV-Curable Polymers Help To
Reach Optoelectronic
Innovations
UV-curable polymers, which are essentially
adhesives, are increasingly used for
mass production of micro- and nanoscale
optical elements via nanoimprint lithography.
A matching refractive index, high
transmission, and balanced thermo-mechanical
behavior, paired with an overall
excellent reliability, are their most important
features.
Given the large number of optical
functions which can be implemented
in the design of a new device, these,
and many other properties need to be
considered for, and tailored to, a specific
application. When this is done
properly, the optical-grade materials
offer an almost complete freedom of
design, enable complex device architectures
and are easy to fabricate at the
same time. With their help, consumer
electronics and automotive OEMs are
able to successfully reach optoelectronic
innovations with regard to 3D
sensing, automotive headlamps and
projectors as well as AR.
This article was written by Karl Bitzer,
PhD, Head of Product Management, DELO
(Windach, Germany). For more information,
visit http://info.hotims.com/82321-222.
Photonics & Imaging Technology, May 2022
PIT Application Briefs 0522_1.indd 24
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4/20/22 10:42 AM

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