Solid state lighting using LED-dies is a rapidly growing market. LED-dies with the needed increasing luminous flux per chip area produce a lot of heat. Therefore an appropriate thermal management is required for general lighting with LEDdies. One way to avoid overheating and shorter lifetime is the use of many small LED-dies on a large area heat sink (down to 70 μm edge length), so that heat can spread into a large area while at the same time light also appears on a larger area. The handling with such small LED-dies is very difficult because they are too small to be picked with common equipment. Therefore a new concept called collective transfer bonding using a temporary carrier chip was developed. A further benefit of this new technology is the high precision assembly as well as the plane parallel assembly of the LED-dies which is necessary for wire bonding. It has been shown that hundred functional LED-dies were transferred and soldered at the same time. After the assembly a cost effective established PCB-technology was applied to produce a large-area light source consisting of many small LED-dies and electrically connected on a PCB-substrate. The top contacts of the LED-dies were realized by laminating an adhesive copper sheet followed by LDI structuring as known from PCB-via-technology. This assembly can be completed by adding converting and light forming optical elements. In summary two technologies based on standard SMD and PCB technology have been developed for panel level LED packaging up to 610x 457 mm2 area size.
LED luminaires are already beyond retrofit systems, which are limited in heat dissipation due to the old fitting standards. Actual LED luminaries are based on new LED packages and modules. Heat dissipation through the first and second level interconnect is a key issue for a successful LED package. Therefore the impact of known bonding technologies as gluing and soldering and new technologies like sintering and transient liquid phase soldering were analyzed and compared. A realized hermetic high power LED package will be shown as example. The used new techniques result in a module extremely stable against further assembly processes and harsh operating conditions.
High precision approaches for active and passive alignment and assembly on optoelectronic micro
benches have been realized at Fraunhofer IZM for various material systems and different scales. The
alignment and reliable mounting of optical subcomponents such as semiconductor laser and photo
diodes, micro lenses and micro prisms require far higher mounting and alignment accuracies than for
micro-electronic parts. When connecting from silicon photonics chip level to single mode optical
fibers, even higher precisions are called for (typically < 100 nm). Alignment and assembly
commonly are performed on specialized lab equipment which needs manual operation, consuming a
lot of time, with less possibilities for automation.
To introduce a higher degree of automatized production, like it has become standard in large volume
electronics, one can choose either active or passive alignment processes - or possibly a combination
of both. In this article we will present examples of micro-optic benches and optical interconnections
that include alignment structures for passive alignment - where the accuracy lies in the components
to be assembled, and mounting takes place on a less accurate machine (“fit into place”). But there is
also a lot of progress on optical "pick, measure and place" machines that realize a flexible and fully
automated active alignment using vision systems and activated components of less cost, with
machine and process robustness for usability in industrial environments.
As connecting elements, passive optical components like optical fibers are commonly used. These
fragile and flexible elements pose additional challenges in secure picking, placing and fixing, at long
lengths vs. small diameters. A very recent and specific approach to use more robust plastic optical
fibers (POF) for very short and cost effective optical interconnects by means of wire bonding
machines will be presented.
It has been previously published how, using two separate Vertical-Cavity-Surface-Emitting-Lasers (VCSELs), a miniature laser-Doppler interferometer can be made for quasi-three-dimensional displacement measurements. For the use in consumer applications as PC-mice, the manufacturing costs of such sensors need to be minimized. This paper describes the fabrication of a low-cost laser-self-mixing sensor by integrating silicon and GaAs components using flip-chip technology. Wafer-scale lens replication on GaAs wafers is used to achieve integrated optics. In this way a sensor was realized without an external lens and that uses only a single GaAs VCSEL crystal, while maintaining its quasi-three-dimensional sensor capabilities.
An important issue for white ultra high power LEDs is the
generation of a homogeneous light with high efficiency and a
good color rendering index. Different from hot light sources
LEDs do not emit the whole range of visible wavelengths. Only
a certain wavelength with a limited full width at half maximum
is emitted. Therefore a combination of wavelengths must be
used to satisfy the human eye for white light. The CIE
chromaticity diagram (Fig. 1) shows, that several combinations
of wavelengths let the brain realize white light. Already the
combination of two wavelengths (e.g. cyan and red or blue and
yellow) let us think, that the source is white, if this wavelengths
hit our receptors. This is completely different, if the light is
illuminating an object. The reflection spectra of this object,
which is crucial for our color feeling about this object, can not
be stimulated in the whole range. For example a red stop sign,
which is absorbing all wavelength excepting red, will absorb
the blue and yellow light from our "white" light source and due
to the missing red, the sign seems to be dark grey or black.
The design of an efficient LED package, with a high luminous flux, stable wavelength emission and long lifetime needs
a good knowledge about the principles of light emitting diodes, thermal and thermomechanical design and the
interaction of materials. The technology development under cost aspects is a general constraint. The following work will
combine known aspects from different research fields with own developments to a complete design for an ultra high
brightness LED package. Topics as material selection, thermal and electrical interconnections, as well as color stable
wavelength conversion will be discussed.