(September 7, 2007) IRVINE, CA — Grote Industries selected a custom-formulated Hysol potting compound from Henkel to enable full automation at its 1-million-parts per year LED lamp assembly line. The compound met 19 engineering requirements for environmental friendliness, thermal conductivity, reliability, and other criteria, and will be deployed for use across 10 product families.
Category Archives: LEDs
By Gail Overton and Valerie Coffey, Small Times guest contributors
September 7, 2007 — SPIE’s Optics + Photonics show, held August 26-30, 2007, emphasized nano and solar technologies, “which are immensely important to our future,” said Akhlesh Lakhtakia, professor of engineering science and mechanics at Pennsylvania State University and editor of SPIE’s Journal of Nanophotonics, which explores the fabrication and application of nanostructures that generate or manipulate light. “But this emphasis on the nano and solar future has its feet firmly planted in the past glories and ongoing research in optics and photonics, a foundation from which all future technologies emerge,” continued Lakhtakia, who was among the event’s plenary speakers.
His presentation, titled “Brave New Nanoworld, without Apologies to Aldous Huxley” discussed the societal issues surrounding nanotechnology and educational strategies necessary for students and the general public to embrace its “socially transformative power.”
The event began, however, with an all-conference plenary consisting of two presentations; the first on “Technology to Enable our Solar Technology Future” by Thomas Feist, manager of the Thin Films Laboratory in Micro and Nano Structures Technologies at GE Global Research, the second on “The Concept of the Photon: Updated” by Marlon O. Scully of Texas A&M and Princeton University. Feist explained that the adoption of new solar-energy technologies will be speeded by systems that seamlessly integrate with existing building architectures such as the use of photovoltaic (PV) roof tiles and organic PV window glass. Feist applauded the Solar America Initiative being led by the U.S. Department of Energy, and provided an overview of the organic and inorganic solar-energy technologies such as roll-to-roll compatible dye-sensitized solar cells and classic silicon or crystalline PV technologies, respectively, that have the potential to achieve 80% conversion efficiencies.
The six nano-focused plenary sessions began with a visually exciting presentation on “Optically Driven Mechanical Micro/Nanosystems in Classical and Quantum Realms” by professor Halina Rubinsztein-Dunlop, head of the School of Physical Sciences and a Director of the Centre for Biophotonics and Laser Science at the University of Queensland (Brisbane, Australia). Her many videos displayed in real time the optically induced rotation of birefringent calcium carbonate nanoparticle spheres and other nanomachines within fluids by using the orbital angular momentum of light. Even though Rubinsztein-Dunlop pointed out that renowned Caltech researcher Richard Feynman said that we don’t have to be useful (when it comes to working in the field of nanotechnology), we can just have fun (which these videos certainly are), she also explained how the properties of these spinning nanoparticles can be used to non-invasively determine the viscosity of fluids in the eye and even of intra-cellular fluids–a tiny “microviscometer” thanks to the ultra-small dimensions of these emerging nanomachines.
In the “Plastic Optoelectronics and Aligned Carbon Nanotube Devices” plenary, Professor of Nanomaterials at the University of Dayton, Liming Dai, described how polymer-infused carbon nanotubes can replicate the feet of a gecko and be used to produce smart membranes that can support tremendous weight on smooth surfaces. Even though Dai joked in his presentation that perhaps we can all be Spiderman someday, the image he displayed of a tiny membrane supporting a rather large weight as it clung tightly to a vertical piece of glass was not a joke; instead, it was a practical application of biomimetics working in concert with nanotechnology.
And if you thought being Spiderman was enough, how about the possibility of making tiny nanomachines that could undertake ‘The Fantastic Voyage’ of entering the human body and performing both diagnostic and curative tasks? Such a scenario was presented by Michael J. Heller, professor at the University of California, San Diego, who presented “Nanotechnology: New Tool for Diagnostics and Treatment of Cancer.” Heller discussed how in-vivo “Motherships” are being developed from a combination of specialized nanoparticles and integrated chip devices that could detect, for example, individual cancer cells and deliver chemotherapy agents directly to the affected cells.
New product announcements at Optics + Photonics 2007 included the MicroPhase three-dimensional topography solution from PhaseView-USA, a low-cost profiling system based on patented Digital Phase Technology that can measure in the nanometer range and be retrofitted to existing microscopes.
Gail Overton is Associate Editor and Valerie Coffey is Senior Editor at Laser Focus World, a sister publication to Small Times.
September 6, 2007 – Scientists at Princeton U. say they’ve figured out how make gratings on microchips with 60nm half-pitch periodic lines, using what they call a simple, low-cost technique called “fracture-induced structuring.”
The process involves sandwiching a thin polymer film between two substrates, heated to ensure adhesion, and prying them apart. As the film fractures, it automatically breaks into two complementary sets of nanoscale gratings (one on each plate), with the distance between the lines consistently 4x the film’s thickness regardless of molecular weight or chemical composition.
Originally the researchers, led by profs. Stephen Chou and William Russel, was trying to use instabilities in various molten polymers to create patterns, but found that fracturing a solid polymer could generate gratings automatically, and figured out how to optimize the process of grating formation.
The technique has worked to create gratings over 2 sq. cm with 120nm-200nm periodic lines, and patterning of “much larger areas” should be possible once the technique is optimized, the researchers say. The process can also be used in conjunction with other patterning methods — e.g., the nanoprinting method invented by Chou in the 1990s, combining to create a mold enabling mass duplication of high-precision, low-cost patterns.
The research is described in the newest issue of the online version of Nature Nanotechnology.
IMAGE CAPTION:
Fracture-induced structuring results in the self-formation of periodic lines, or gratings, separated by as few as 60nm. (Source: Princeton U.)
September 4, 2007 – Kovio Inc. says it has raised $19.5 million in the first closing of a Series D round of funding, to help develop and commercialize products that use its proprietary printed silicon technology.
The round was led by Pinnacle Ventures with participation from a list of other VC firms: Bessemer Venture Partners, Duff Ackerman & Goodrich Ventures, DEA Capital, Flagship Ventures, Harris & Harris Group, Jerusalem Venture Partners, Kleiner Perkins Caufield & Byers, NCD Investors, and Yasuda Enterprise Development.
The startup says it will use the funding to “design, develop and commercialize printed electronic products” using proprietary printed silicon electronics technology.
September 5, 2007 – Synova SA and Manz Automation say they’ve created a hybrid tool combining their technologies: an inline laser edge isolation system for photovoltaic manufacturing of mono- and multi-crystalline solar cells.
The ILE 2400, integrated with Synova’s “laser microjet” water jet-guided laser technology, targets edge isolation — a technique used to prevent parasitic shunts between the front- and back-sides of the cell, preventing short circuits and improving cell efficiency. Secondary applications include cutting and drilling, the companies noted. The system will be “production ready” by year’s end.
Earlier this year the two companies inked a licensing deal to integrate their technologies for PV applications, with Synova heading up R&D efforts and Manz driving manufacturing, sales, and service operations.
The deal expands markets for Synova’s flagship “laser microjet,” which replaces traditional cutting technologies such as conventional lasers and diamond blade saws, for applications in inkjet print head MEMS, HDDs, and OLEDs. The company already has licensing deals in other markets including medical instrumentation and automotive devices.
Because there are no formal standards for lighting in cleanrooms, contractors and operators must have a thorough understanding of the different types of lighting, fixtures, and installation options available and consider which one will best suit the level of cleanliness required in their critical environments. Here are a few supplier options.
Compiled by Carrie Meadows
 |
Lighter-weight fixture offers flexible ceiling placement
The Bio-Seal is the most technically advanced grid and flange cleanroom troffer available. It is certified for Class 100 (ISO 5), IP66, NSF, and Class 1 Division 2 spaces. The standard seam-welded aluminum body radiates lamp and ballast heat to provide extended transformer life and higher lamp lumens. Its 60 percent lighter weight does not burden a sheet rock ceiling. The one-piece gasket system is dust tight and withstands 26 gpm hosedown without leakage. The fixture can easily provide 30,000 lumens from 6-T5HO lamps. Options include SS doors and housing, surface mounting, and top access re-lamping.
Guth Lighting
St. Louis, MO
www.guth.com
Standard and custom cleanroom lighting systems
 |
Choosing cleanroom lighting fixtures that won’t leak, introduce toxicity or corrosion, add excessive heat, or create potentially unsafe conditions is crucial to each cleanroom environment. Innotech Products offers a quality line of cleanroom lighting such as laminar flow-through, tear-drop, and contaminant-proof sealed housing fixtures, as well as top access, recessed, surface, corner, and UV-shielded lights for clean applications. The fixtures come in standard and custom sizes to fit virtually any ceiling system style. To speak to a cleanroom specialist regarding these and other cleanroom needs, call (888) 270-0458.
Innotech Products
Minneapolis, MN
www.innotechprod.com
NSF-certified lighting suitable for harsh environments
 |
LDPI Lighting’s 376 Series wet/damp fluorescent light fixtures have recently been tested and certified by NSF (National Sanitation Foundation) International to NSF/ANSI Standard 2. The fixtures are designed for use in a variety of areas where harsh conditions exist, such as food and beverage processing facilities, packaging and distribution centers, refrigeration rooms/freezers, cleanrooms, and other areas where extra sanitation precautions are needed. The lights feature a poured-in-place polyurethane gasket and latch that provides continuous positive gasket contact while sealing enclosures from the most hostile environments. Durable components include stainless-steel mounting hardware and a corrosion-resistant non-metallic enclosure. A unique mounting system, which eliminates the need for drilling holes through the housing, reduces installation time. Mounting brackets are designed for narrow and standard lamp housings, and an optional 45° mounting bracket is available.
LDPI Lighting, Inc.
Eau Claire, WI
www.ldpi-inc.com
Light-emitting diode bulbs replace direct incandescent systems
 |
LEDtronics’ latest generation of PAR20 LED short-neck light bulbs replace direct incandescent bulbs, combining advanced light-emitting diode (LED) technology, standard 25 mm Edison screw bases, and a light-optimizing design to produce vivid light. The LED bulbs are available in three light-emitting angles: 15°, 20°, and 22° and in 120 V AC. Other voltages such as 12 to 240 V AC or DC are available to qualified customers. They are well suited to small spotlighting tasks in track or recessed lighting fixtures or high-hat ceiling spotlights. With a power draw of only 2.5 W, energy savings add up over time. Standard colors available are Warm White and XWarm White (3,000 K), Cool White (7,000 K), Super Red (633 nm), and Aqua Green (525 nm).
LEDtronics, Inc.
Torrance, GA
www.ledtronics.com
Packaging Challenges and Solutions
Light-emitting diode (LED)-based applications are growing, and cover a broad range of markets including automotive lighting applications such as indicators, spot utility, and headlamps; camera functions like display backlights and camera flashes; consumer products such as LCD display backlight and projection systems; architectural uses like accent lighting for buildings, and signs; and many others. LEDs are bright, efficient, and quick to react. They have become a substitute for light bulbs in many applications because they use less power, have longer lifetimes, produce little heat, and emit colored light.
Using LEDs for general lighting is becoming more practical as they become increasingly more efficient, generating more lumens per watt. For example, a fluorescent tube equivalent of 3,000 lumens would have required over 1,300 LEDs using 30 lumens/watt at 2 to 3 lumens per LED in 2003. However, by 2005, there was a 20X reduction in the number of LEDs required for the same florescent tube, to around 50, using 50 lumens/watt or higher at 60 lumens per LED.
LED Lighting Levels
There are four different levels – or areas of involvement – in the manufacture of LEDs. The first level is called product level 0, and refers to the device itself. Product level 1 is first-level assembly. This involves connecting the device to the source of electricity through die-attach and wire bonding methods, creating a surface-mountable package. Product level 2 involves second level assembly. The package is put into a structure in multiples to create light output for applications like external signage or outdoor lighting. Product level 3 is system assembly for the whole system or solution.
Level 1 LED packages range from a single LED to a complex matrix of LEDs. In a standard-array LED, each LED is wire bonded to a substrate pad. LEDs can be addressed individually or tied together. Many of these type assemblies are die-attached with epoxy. For high-brightness LED applications, such as outdoor lighting or rear projection screen lighting, a matrix configuration of LEDs is used. In this configuration, the LEDs are placed in tightly packed rows and columns to generate the most light. Figure 1 shows a matrix of LEDs ganged together to produce a massive amount of lumens. The number and closeness of LEDs requires good thermally conductive die attach to keep the LEDs as cool as possible.
 Figure 1. Matrix LED |
Matrix LED assemblies are the basis of many systems found in production. Their emerging popularity is derived from their ability to get more lumens per watt from this configuration. However, matrix LED packages present challenges for both die attach and wire bonding compared to single-die packages. High-brightness LED applications require maximum thermal transfer to achieve performance requirements.
Packaging High-brightness LEDs
Matrix LED process steps include material preparation, pick-and-place, pulsed reflow, clean, wire bond, and test. This discussion will focus on pulsed-reflow (eutectic attach) and wire-bonding steps. The example is a 9×8 matrix of 290-µm LEDs using AuSn attachment. LEDs are electrically connected together in rows. The goal is to place LEDs as close as part tolerances allow (~1mil gap) using a metallurgical eutectic interconnect of the LEDs to the substrate. Figure 2 shows the 290-µm LED matrix.
 Figure 2. 290 micron LED attachment to AuSn before wire bond. |
Pulsed Reflow
Critical to the LED assembly process is a void-free eutectic solder interface between the diode and its substrate that provides the thermal and electrical connections needed to generate a stable transmission of light. Eutectic die attachments transfer the tremendous amount of heat generated by the diodes to maintain the temperature stability of the device. Controlling the eutectic attach process is critical to yield and reliability.
Precision eutectic component attach includes pick-and-place of the diode; in-situ reflow of pre-form or pre-tinned devices with programmable x, y, or z-axis agitation; and programmable pulse heating or steady-state temperature. To yield the optimal thermally conducting solder interface, the temperature profile of the attachment process must be repeatable and have the capability for a high-temperature ramp rate. Once the interface is brought up to the proper eutectic temperature, the heating mechanism must maintain that programmed temperature with minimal overshoot. After the required amount of reflow time, the heating mechanism must controllably cool to minimize damage to the diode and to allow the eutectic material to reach metallurgical equilibrium. This equilibrium is reached through simultaneous application of active thermoelectric pulse heating and cooling gases.
LED matrix assembly is an extremely temperature-sensitive process that requires careful control during assembly. The reflow profile during an in-situ eutectic die-attach process is engineered to provide consistent melting and a void-free attach interface. This is necessary for consistent heat transfer from the diode and contributes significantly to temperature stabilization during LED operation.
In this example, a ganged pulse-heat reflow was used. During the pulsed heat cycle, temperatures were ramped from a pre-heat temperature to the reflow temperature using a servo-controlled ramp profile with low overshoot compared to traditional heater stage systems. The reflow temperature is held for a prescribed duration and then the cooling profile is commanded using both servo-control temperature and cooling gas. Temperature profile repeatability is critical to the process to allow proper eutectic wetting with low voids without damaging the LEDs. Required temperature profiles depend on the substrate materials, geometry, and solder composition. Programmable point-and-click profiling was used for establishing the temperature command profile. The system also captures actual temperature profiles during bonding for process traceability. Pulsed-heat profile control allows batch reflow of the LED matrix for reduced overall cycle time and minimum time at temperature for the protection of temperature-sensitive LED devices.
Wire Bonding
Once LEDs are attached, wire interconnect is completed using strings of wire bonds. The high-density, high-frequency LED matrix format requires LEDs to be interconnected using wires. Although there are several methods of wire bonding, such as ball and wedge bonding, test data indicate that chain bonding interconnects using a ball bonder achieves the best results. In standard ball/stitch bonding, a ball is placed and bonds are placed on top of the stitches to create a string of interconnected LEDs. Chain bonding is a variant on ball/stitch bonding where the stitch is not terminated and another loop-stitch combination is repeated to complete a chain bond wire set. Figure 3 shows chain bonding using a wire bonder to place a ball-loop-intermediate stitch-loop-intermediate stitch-loop. It ends with a loop-end stitch which is followed by a security ball bump on the end stitch. This is not new technology, but it has been further developed through materials selection and software tools. Chain bonding enables higher throughput since there is no need to create free air balls for standard ball bonding. Additionally less light occlusion exists due to chain bond stitch geometry, and pull test results indicate better pull strength.
Conclusion
Placing LEDS in a matrix configuration can result in high intensity, brighter LEDs. This configuration creates challenges in assembly because of the high concentration of heat and the need for high-frequency wire-bonded connections that must be accurately placed in tight areas, have consistent loop structure, and have a connection strong enough to withstand mechanical shock and stresses due to large thermal variations. Three steps in the assembly process are key. The first step involves high accuracy die pick-and-place for matrix LED applications to within LED geometric tolerances. Second, using a pulse-heat-controlled batch eutectic reflow die-attach process is necessary for assembly throughput, LED protection, and high thermal conductivity while providing high quality, low risk performance. Third, chain bonding provides excellent electrical and mechanical connection of the arrays across the LEDs. Adhering to these assembly processes results in high brightness while achieving thermal dissipation and maximum light extraction.
 Figure 3. Chain bonding with security bond |
DAN EVANS, senior scientist, may be contacted at Palomar Technologies, Inc 2728 Loker Ave. West, Carlsbad CA 92010-6033; 760/931-3600; E-mail: [email protected].
According to Pat Moore, MILMEGA managing director, Cree’s MESFETS enable amplifier products that are up to three times smaller and lighter than those using conventional transistor technology, providing MILMEGAA with a unique advantage in terms of performance and cost. MILMEGA Ltd. has been designing, developing and manufacturing solid-state, high-power broadband amplifiers for commercial and government purposes since 1987.
(August 29, 2007) MANASSAS, VA — ZESTRON officially announced the opening of its Worldwide Center of Competence and Excellence for Inline Cleaning. Speedline Technologies, Stoelting and Trek Industries are among the international companies whose state-of-the-art equipment is installed in the new facility.
In addition to front-end materials such as polishing pads, slurries, and pad conditioners for CMP, Rohm and Haas supplies SMIC with electroplating processes for wafer bumping and under bump metallization, photoresists and anti-reflectants used in lithography, and ion exchange resins used to produce ultrapure water needed in semiconductor manufacturing.
(August 29, 2007) DURHAM, NC — In a move to reduce form factor while increasing power of its UHF power amplifiers, MILMEGA Ltd. has chosen Cree silicon carbide (SiC) MESFETS to power its new line. Cree’s SiC MESFETs are said to provide greater power density than conventional semiconductor materials, allowing for improved efficiency and more capabilities in a smaller form factor.
August 17, 2007 – Technologies and Devices International Inc. (TDI) says it is now producing indium-gallium-nitride (InGaN) substrates for packaging GaN-based high-brightness LEDs and blue and green laser diodes, targeting volume production for early 2008.
The material’s crystal lattice and thermal properties are composed to match the given overgrown GaN device, which can reduce defects, improve device efficiency and output, and boost lifetime and power usage, according to the company.
The InGaN substrates are grown by proprietary hydride vapor phase epitaxy (HVPE) processes (on equipment designed and built by TDI), which build in InGaN layer through deposition onto 2″ GaN/sapphire templates. InN content ranges from 5 to 20 mol. %, and deposition rate, doping levels, composition range, and density are adjusted to meet customer parameters. TDI plans to scale the process to 6″ and larger wafers in high-throughput volume production.
InGaN materials, a match for GaN-based epitaxial structures, can supply the light-emitting regions of laser diodes and LEDs and determine device parameters. The US Department of Energy (DOE) and Department of Defense (DOD) supported development and production qualification for the technology.