Optoelectronics
Optoelectronics
Optical materials and adhesives play a key role in the development and production of wafer-level optics. They are not only used to secure and protect optical elements such as sensors or LEDs. DELO's optical materials are also used to produce microlenses and diffractive optical elements (DOE) which are used in the flash module of smartphone cameras or as microlens arrays in projection systems.
In addition to toughness, optical materials and optical adhesives must also display thermal and UV stability, low outgassing and low shrinkage. DELO offers an extensive range of specially adapted adhesives for these requirements.
Material solutions for wafer-level micro-optics
Micro-optics and nanostructures are key technologies for the latest miniaturized optoelectronic components in smartphones, smart glasses and vehicles. Examples used in consumer electronics include microlenses in time-of-flight or ambient light sensors, diffractive optical elements (DOE) for structured light generation and surface relief gratings with nanometer precision in diffractive waveguides that enable new applications like 3D sensing or augmented reality glasses.
In vehicles, this technology is also used in microlens-based ultra-compact projection systems for headlamps or decorative and functional lighting applications that can be integrated anywhere in a car.
Optically transparent imprint materials
UV-curable polymers are increasingly used for mass production of optical elements via nanoimprint lithography. A matching index of refraction, high transmission and balanced thermo-mechanical behavior, paired with an overall excellent reliability, are their most important features.
DELO’s optical-grade materials offer an almost complete freedom of design, enable complex device architectures and are easy to fabricate at the same time.
Properties:
- High resistance to yellowing at elevated temperatures, especially in reflow processes
- Very high transmission in the visible range
- Low outgassing
- Very low shrinkage
- Excellent adhesion to glass and simultaneous debonding from stamp materials
- Halogen-free (IEC 61249-2-21)
- Broad range of refractive indices available
Applications:
- Microlenses for sensing applications, e.g. Time-of-flight, ambient light sensing
- Microlens arrays (MLA) for projection devices
- Microlens arrays (MLA) for automotive headlamps
- Diffractive optical elements (DOE) for structured light generation (3D sensing)
- Diffractive optical elements (DOE) for flood illumination / diffusor applications
- Diffractive optical elements (DOE) for AR waveguides
Optically functional materials
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 wafer-level.
Besides the optical elements such as lenses or DOEs, an optical system needs additional components, for example spacers, apertures and a housing.
Wafer-level optics deals not only with fabricating each single element, but also how to stack these elements to form the full system.
Applications:
- Package sidewalls
- Light-blocking apertures
- High optical density coatings
- Defined light diffusion
- Spectral filtering
Adhesives for LED packaging
Thanks to their universality, LEDs are used in a wide range of applications. They offer manufacturers great design freedom and enable new types of lighting concepts – in consumer electronics, the automotive industry and sensor technology.
Functional adhesives play a key role in the manufacture of LED packages. They ensure brilliant, homogeneous diode illumination and fast production. DELO has developed a host of suitable products for both first- and second-level packaging. In first-level packaging, the adhesives are applied in the immediate vicinity of the LED semiconductor. In second-level packaging, the adhesives are used to join lenses, cover disks or housings that are used around the LED module.
DELO's adhesive portfolio for optoelectronics includes transparent and low-outgassing, tension-equalizing and electrically conductive adhesives, and die attach to structural bonding. Optical coatings with customized properties regarding transmission, reflection and absorption, as well as encapsulants to protect sensor packages, are also offered by DELO. Users can choose from products with different curing mechanisms depending on the relevant component geometry or substrate combination.
All DELO functional adhesives and sealants in its DELO PHOTOBOND, DELO DUALBOND and DELO KATIOBOND series are particularly suitable for highly automated high-speed processes with high outputs.
Properties of adhesives for LEDs:
- Low-outgassing
- Very low shrinkage
- Optically clear
- Yellowing-resistant
- Reflow-resistant
Adhesives for photonic ICs (PIC)
Photonic integrated circuits (PIC) play a major role for integrating optical functions like signal processing, data transfer and sensing to electronic devices. A PIC is an advanced system on a chip in which multiple miniaturized optical components such as amplifiers, modulators or filters are combined. Operating in the optical/IR range of the EM spectrum (380 – 1650 nm), they allow very high bandwidth and data transfer at high speed.
Packaging and optical interconnecting on chip-level as well as on board-level is technically very challenging. Low coupling loss requires very precise active alignment capable adhesives. Post-processing like the assembly of electronic SMDs by typical reflow processes underlines the need for highly reliable materials.
Optical coupling
There are several approaches to couple a PIC with optical fibers. In general, single mode fibers with core diameter of just a few microns are used, requiring very high precision active alignment. The fibers can be directly bonded to the PIC with the adhesive within the light path. Using the adhesive outside the light path by bonding the fiber to an interposer is typically followed by filling the gap between fiber and PIC with an optical adhesive that matches the index of refraction (RI), minimizing the transmission loss caused by Fresnel-reflection. Another approach is to use microlenses on the PIC, allowing higher tolerances or enabling contactless connection (expanded beam connector).
Adhesive properties:
- Low shrinkage
- Fast fixation
- Low CTE
- High Tg
- RI matching
- High transmission
- Reflow stability
| Products | DELO DUALBOND OB6268 | DELO DUALBOND OB6769 | DELO DUALBOND OB6799 | DELO DUALBOND OB787 |
| Schrinkage | 0.7 Vol.-% | 1.7 Vol.-% | 0.4 Vol.-% | 1.5 Vol.-% |
| Young's modulus | 6,300 MPa | 11,000 MPa | 13,000 MPa | 7,000 MPa |
| Glass transition temperature | 202 °C | 160 °C | 140 °C | 185 °C |
| CTE1 | 37 ppm/K (-40 °C – -20 °C) | 26 ppm/K (-40 °C – -30 °C) | 17 ppm/K (-40 °C – 0 °C) | 45 ppm/K (+30 °C – +50 °C) |
| CTE2 | 78 ppm/K (+140°C – +170 °C) | 69 ppm/K (+160°C – +180 °C) | 49 ppm/K (+150°C – +190 °C) | 79 ppm/K (+140°C – +170 °C) |
| RI @ 1550 nm | 1.495 | 1.478 | 1.473 | 1.486 |
| Transmission @ 1550 nm (50 µm) | > 98 % | > 98 % | > 98 % | > 98 % |
V-groove bonding
The use of V-groove structured substrates is common for passive alignment of fibers. Instead of connecting several single fibers to the PIC one by one, they can be pre-assembled by using V-grooves. The whole part, consisting typically of 12 fibers or more, can then be connected to the PIC in one step. The fibers are kept in the V-groove by bonding a lid on top. DELO adhesives can be dispensed before joining the lid or afterwards by an underfill process.
Adhesive properties:
- Suitable viscosity
- Low CTE
- Reflow stability
| Products | DELO KATIOBOND OM614 | DELO KATIOBOND OM6116 | DELO DUALBOND OB749 |
| Viscosity (Rheometer 10/s) | 400 mPa*s | 430 mPa*s | 3,000 mPa*s |
| Young's modulus | 3,000 MPa | 3,500 MPa | 6,200 MPa |
| CTE1 | 53 ppm/K (-35 °C – -10 °C) | 58 ppm/K (-40 °C – +80 °C) | 44 ppm/K (+30 °C – +70 °C) |
| CTE2 | 200 ppm/K (+125°C – +170 °C) | 153 ppm/K (+185°C – +220 °C) | 93 ppm/K (+130°C – +170 °C) |
Cladding
Short distance PIC to PIC or fiber to PIC connections can be achieved using photonic wire bonding. Similar to electrical wiring, an optical wire is used for interconnecting already assembled PICs and/or fibers. The photonic wire bonds can be 3D written by means of two-photon polymerization (2PP). For protecting the tiny wires, DELO offers a low index of refraction (RI) adhesive cladding that allows wave guiding by total inner reflection.
Adhesive properties:
- Low RI
- Low viscosity
- High reliability
Chip attach
Attaching the PIC to a substrate or interposer is essential for photonic packaging. Reliable bonding with low CTE and sufficient bond strength are required. Additionally, DELO offers adhesives with light fixation that are beneficial for high accuracy and reducing the cycle time.
Adhesive properties:
- High bond strength
- Low CTE
- Low shrinkage
- High reliability
| Products | DELO DUALBOND OB6268 | DELO DUALBOND OB787 |
| Viscosity (Rheometer 10/s) | 27,000 mPa*s | 46,800 mPa*s |
| Schrinkage | 0.7 Vol.-% | 1.5 Vol.-% |
| Elongation at tear | 1.0 % | 0.8 % |
| Young's modulus | 6,300 MPa | 7,000 MPa |
| Glass transition temperature | 202 °C | 185°C |
| CTE1 | 37 ppm/K (-40 °C – -20 °C) | 45 ppm/K (+30 °C – +50 °C) |
| CTE2 | 78 ppm/K (+140°C – +170 °C) | 79 ppm/K (+140°C – +170 °C) |
| DSS – Silicon on glass (inital) | 38 MPa | 50 MPa |
| DSS – Silicon on glass after THT & reflow | 38 MPa | 23 MPa |
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