11.10.2015
UV LEDs are also creating new applications that arena€™t accessible to traditional UV lamps--applications that are miniaturized and portable. The report points out that traditional UV lamp manufacturers are under the most pressure since they have to compensate for the waning lamp replacement market by diversifying their activities in higher supply chain levels.
AlN on sapphire templates are definitely the substrate of choice for UVA applications, as they provide the right mix between cost and performance.
In addition to substrate issues for UVC LED development, epitaxy represents another challenge for increasing device performance. Sponsored Content is made possible by our sponsor; it does not necessarily reflect the views of our editorial staff. Subscribe to Laser Focus World Magazine or email newsletter today at no cost and receive the latest news and information. Printing processes have drastically evolved over the years, originating in the form of labor-intensive manual printing presses and advancing to modern day offset, flexography, digital and 3D printers. Until recent years, UV LEDs have been faced with a number of technical and economic barriers that have prevented wide commercial adoption. While the adoption of LEDs into consumer devices and applications such as televisions, electronics, displays and lighting has been prolific, this uptake has been predominantly in the longer wavelength spectrum of visible light or infrared. As with most new technologies, acquisition costs tend to be greatest in the early stages of product availability and decline as mass market adoption occurs. Despite much of LED development and adoption being focused on visible light, the growing market, increasing commercial use of LED and investment into the technology itself have helped to drastically improve the cost landscape for UV LEDs as well. While the upfront capital investment in a UV LED curing system for printers may be higher than that for a conventional lamp-based solution, the gap in expenditure has narrowed significantly in the past few years, making the payback period much shorter. Arguably one of the areas under the most scrutiny for UV LED technology is the efficiency and maximum radiant power that is produced. Irradiance is inversely proportional to the junction temperature of the LED die, thus maintaining a cooler die not only extends life and improves reliability, it also increases efficiency and output. The components of LED arrays, thermal management and optics all work together, as optimizing one piece often impacts the others. The challenges of packaging UV LEDs into arrays have been overcome, as there are a number of solutions available today for various applications. Depending on the application and the inks that are used, often 395nm wavelength solutions can adequately cure formulations at a more economical system cost than 365nm alternatives.
Table 1 is an overview of the typical output to input power efficiency of LEDs at various wavelengths. UV LED curing systems typically are composed of an LED head, power supply and interconnect cables. Cooling of discrete UV LEDs does not present a particularly difficult engineering challenge. Water cooling is an extremely efficient method of extracting heat, particularly in applications where high power densities are required over large curing areas. UV LED systems can use optics to provide benefits for specific applications, such as those requiring longer working distances and a narrower, more focused illumination area. A wide range of applications can take advantage of the many benefits that UV LEDs bring, from spot curing to small and large area curing requirements for a range of industries. For instance, in UV label printing, wide-format digital, flexography or 3D printing, air- or water-cooled LED configurations can be used without costs being prohibitive. However, in high speed printing processes that require large scale curing systems with extremely high optical output, the economics of attaining a cost competitive solution using LEDs is an area that is still being optimized.
The gaps that previously existed between traditional lamp solutions and UV LED-based curing systems certainly have been narrowed. Pamela Lee is senior product manager of OmniCure® UV curing solutions at Excelitas Technologies Corporation.
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Such growth is likely to continue as LED-powered UV curing spreads across ink, adhesive and coating industries, forecasts the market research firm.
But this is only if we take into account standard applications, where UV LEDs replace UV lamps. These firms were mostly small and medium enterprises (SMEs), but recently some big companies from the visible LED industry a€“ namely Philips Lumileds and LG Innotek a€“ have also secured a foothold in the UV LED business.
The entry of these two giants will help to further develop the industry, the market and the technology based on their strong experience of the visible LED industry, reckons Yole.
With the external quantum efficiency (EQE) of UV LEDs ranging from a few percent in UVC LEDs to 40-50% in UVA and near-UV LEDs, R&D directed at efficient chip manufacturing will be key for the development of UV LED markets, says Yole. To increase EQE, manufacturers need to develop techniques for each efficiency parameter: internal quantum efficiency, electron injection efficiency and light extraction efficiency. Approaches such as flip-chip and photonic structures can be taken directly from the visible LED industry and its decade-plus of experience. In addition to the low power output of UV LEDs, their low efficiency creates additional difficulties at the packaging level.
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Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. IFTLE 75 is a nice round number and if we combine these with their predecessor PFTLE (still accessible here) we are now past 200 and approaching four full years of these weekly updates.
Yole Développement and IC Insights have both released recently some very interesting LED component and packaging market data. It is an IFTLE perception that backlighting for TVs will be equally, if not more important than home lighting. Besides being thinner and lighter, LED-backlit TVs have rapidly gained favor among consumers because they tend to offer broader color range, improved contrast ratios, and use less power. That IC Insights report also notes how the method of delivering programming is quickly transforming broadcast television. While the leading edge of LED packaging is going wafer-level (see below) using bumping and backside TSV technology, the bulk of the packaging as it enters the backlighting market is still on lead frames as shown below for the Osram Golden Dragon. Relative to visible LEDs, UV LEDs are a quiet market at only $30 million, yet recent breakthroughs in radiant power and intensity have enabled the displacement of mercury-vapor lamps in applications including UV curing and counterfeit detection, reports LAURA PETERS. Curing involves the cross-polymerization of a photosensitive material, which can be an ink (printing), adhesive or coating, and is primarily performed at 395 nm, 385 nm or 365 nm, wavelengths which are part of the UV-A spectrum (315-400 nm). In the UV-B spectrum (280-315 nm), applications for UV LEDs include curing, medical light therapy, forensic analysis and drug discovery.
Beyond these applications, UV-B radiation is known to have beneficial health properties including the natural synthesis of vitamin D in humans who are exposed to sunlight.
In the lower UV-C spectral range (100-280 nm), the primary LED applications are air and water sterilization and a range of analytical tools including those that perform spectroscopic and fluorescence measurements. UV in the 250-275 nm range sterilizes water, air and surfaces by breaking-up the DNA and RNA of microorganisms and preventing their reproduction.
In production curing operations, mercury-vapor lamps are hindered by short lifetime (2000-10,000 hr), slow warm-up and cool-down times, and wide spectral power distribution. The mercury lamp has a main peak at 365 nm but several smaller peaks in the visible and infrared regions (Fig. Metcalf added that many people who would not have considered UV curing because of the complexity of standard curing processes a€“ the high voltage, heat of mercury bulbs and environmental issues a€“ will now consider UV-LED curing because it subverts the traditional hassles of the old process. UV LEDs bring such benefits as knowing precisely what power level is being delivered to the curing medium, as well as other advantages LEDs are known for, such as the ability to pulse-width-modulate the output, stated Eskow.
The transition to UV LEDs also opened the door to more environmentally friendly curing formulations.
For the longer-wavelength UV devices, in a similar manner to blue LED fabrication, InGaN-based epilayers are grown on sapphire substrates to produce 385, 395 and 405 nm UV LEDs for curing. In addition to producing more power, the higher-wavelength UV LEDs feature higher wall-plug efficiencies. Stacy Volk, marketing communications specialist at Phoseon Technology in Hillboro, OR, a maker of UV-LED curing systems, pointed out some of the additional advantages associated with UV-LED curing include a controlled curing intensity, scalable equipment, and the fact that the machines are smaller and compact.
One of the issues the curing industry has faced has been inconsistencies in measurement practice and parameter definitions, for example, defining radiometric intensity. Companies that manufacture UV-LED chips include Crystal IS, based in Green Island, NY (Fig. UV-LED manufacturers focus on continually improving the efficiency and lifetime of their devices while reducing cost.
Tim Bettles, director of marketing and sales at SETi stated that its manufacturing agreement with Seoul Optodevice is designed to help SETi drive its volumes of UV LEDs and lamps higher while driving down costs.
Devin Tang, marketing manager of SemiLEDs stated that the company has a full line of bare dice and surface-mount high power packaged LEDs in the 360-400-nm range. Epigap Optronic, based in Berlin, Germany, the main distributor for Dowaa€™s UV LEDs, stated that Dowa manufactures 265, 280, 310, 325 and 340 nm bare dice or packaged LEDs. Recently, Theodore Moustakas of Boston University has pioneered the use MBE (molecular beam epitaxy) to grow more efficient (high internal quantum efficiency) UV LED devices using AIGaN-based layers on sapphire substrates.


Even though UV LED manufacturers have been working hard to improve internal quantum efficiency and optical efficiency, overall efficiency remains below 20%, meaning a great deal of heat must be dissipated from the diodea€™s junction. While some UV LED arrays are packaged on ceramic substrates, many manufacturers, particularly of single-chip devices, use TO-can type through-hole packages with a glass top that offers high transmission of UV. The choice of whether to use hermetic sealing in the package is sometimes determined by the materials in the chip. It is important to recognize that some of the same qualities that make UV LEDs very powerful and useful a€“ their low wavelength and high energy a€“ are also the qualities that make them dangerous. When asked to identify the key issue that might keep UV users from changing over from mercury-vapor sources to UV LEDs, many industry participants say it comes down to breaking existing industry momentum and, of course, cost. Subscribe to the magazine or email newsletter today at no cost and receive the latest news and information. The compact, low cost of ownership, and environmentally-friendly composition of UV LEDs continue to replace incumbent technologies like mercury.
UVC applications are still in their infancy and sales are mainly for R&D purposes and analytical instruments like spectrophotometers. However, for UVC applications (and some UVB applications) the competition with bulk AlN substrate is strong, since such material could allow for improvement at the device level in terms of lifetime, efficiency (IQE and EQE) and power output. While a number of different printing technologies are available, printing with UV inks is a fast growing sector, and UV LEDs are becoming the light source for curing UV inks in many printing applications. High cost and limited availability of LEDs, low output and efficiency, and thermal management challenges, combined with ink compatibility were factors that prohibited market adoption. Until recently, UV LEDs have experienced a more modest adoption because of a number of commercial and technological challenges.
While the LED components themselves contribute most of the total system cost for UV-LED installations, the implementation and efficiency of designs also dictates how well the produced radiant energy is delivered to the working surface. Efficiency and yields have been on the rise while costs have come down – by more than a factor of 10 in the past decade. With growing demand and further advancements in process and technology, the overall cost of UV LEDs will continue to be on the decline. Figure 2 illustrates the lifetime of LEDs at different junction temperatures and the relative output. The effective use of optics, for example, will allow light to be projected more efficiently, thus reducing thermal load, increasing irradiance at longer working distances, reducing the number of LEDs required and, as a consequence, lowering cost.
Both small and larger area UV LED curing systems are available with different wavelength offering, including but not limited to, 365nm, 385nm and 395nm. However, as more processes begin to adopt UV LED curing, the commercial drive has pushed formulators to tailor products with photoinitiators, resins and additives packages that function efficiently with LED emission wavelengths and thus are more effectively cured without any compromise on the quality of cure.
Piecing these components together to create a viable solution is a challenge, with the bulk of engineering development being focused on the UV head design. However, creating a solution using LED arrays that can meet commercial needs is a demanding and technically complex task.
Low junction temperatures can be more easily obtained with this technique and, consequently, higher efficiency, longer lifetime and great reliability are the end result. Since air is inherently less effective at extracting heat than water, special design considerations must be made to enhance airflow, as well as to pack the LEDs and optimize the curing solution by employing the use of optics.
Through the use of optics, the energy from LEDs can be delivered better to the substrate or ink.
The irradiance levels of an LED solution utilizing optics are maintained at longer working distances when compared to a solution that does not employ optics. Optics also can be designed for flexibility, allowing systems to be joined to create larger illumination areas while maintaining the same uniformity between the units. However, depending on the print application, the practicality of implementing UV LED solutions may vary. In digital UV inkjet printing, the flexibility and customization that can be afforded with the technology has driven growth in this segment. The technological advances that have been realized in the past few years have enabled cost reductions, higher output and efficiency and better thermal performance and system design. Whether it is performance, cost or availability of formulations that are compatible with UV LEDs, the technology has unquestionably made considerable advances to allow UV LED curing solutions to become commercially viable. She holds an MBA and Bachelor of Science degree in electrical engineering from the University of Toronto, has authored several publications and has presented at a number of industry-related speaking engagements.
The potential is even greater if we consider the ability of UV LEDs to enable new concepts in areas like general lighting, horticultural lighting, biomedical devices, and in fighting hospital-acquired infections (HAIs). Since then, more than 50 firms have entered the field, over 30 of these between 2012 and 2014, mostly attracted by the high margin when overcapacity and strong price pressure from the 'LED TV crisis' had taken its toll on the visible LED industry.
A good example of this is that they have made a nearly full transition of their process to 6" sapphire substrates. With most of the input power being transformed into heat, thermal management represents a key topic for reliability in devices and associated systems. Certainly no other information source available has been following 3D IC on a weekly basis for as long. Hopefully there continues to be something for each of you to learn from each and every blog. But that doesn’t mean that there are no other very significant packaging evolutions and market opportunities going on at the same time. In 2011, LED-backlit TVs are expected to account for an estimated 37% of global TV shipments, up from 15% in 2010. Also, LED TVs are said to be more reliable, offering over 100,000 hours of life compared to traditional cold cathode fluorescent lamp (CCFL) LCD TVs, which are often rated at 20,000 hours.
However, India, China and other countries throughout the Asia-Pacific and Latin America are forecast to enjoy strong DTV growth.
Package development for LEDs appears to be in its infancy similar to where bumped WLP devices were a decade ago. Ranging from 100 to 400 nm, the radiation can effectively be used to sterilize cosmetics, perform forensic analysis, cure materials (Fig. UV-B also accelerates the production of polyphenols in certain leafy vegetables such as red lettuce. Specifically, 275 nm is believed to be the most effective wavelength for eradicating pathogens such as E-coli in water.
With the next generation of products that ink, coating and adhesive companies were developing, they used the opportunity to phase-out volatile organic compounds (VOCs) associated with the solvent-based formulations of past chemistries. Metcalf describes large flat-bed banner printers as being able to use lower-power LEDs, but higher speed digital, offset and flexographic technologies require closely-spaced banks of high-flux-density LEDs. Seoul Optodevice has a manufacturing partnership agreement with SETi, which manufactures a broad range of UV LEDs and lamps, and performs everything from wafer processing to custom lamp design. The replacement of epoxy lenses with flat or dome-shaped glass capable of UV transmission is a relatively new development, and one that has allowed an extension of lifetimes from around 5000 hours up to as high as 30,000 hours. The warning labels on UV LEDs and their products are clear but bear noting: UV-LEDs emit invisible ultraviolet radiation when in operation, which may be harmful to eyes or skin, even for brief periods. Lim thinks that a rounding out of the wavelength portfolio would go a long way toward adoption. The UV LED business is expected to grow from $45M in 2012 to nearly $270M by 2017, at a compound annual growth rate (CAGR) of 43%--whereas the traditional UV lamps market will grow at a CAGR of 10% during the same time period. Once UVC LEDs achieve sufficient performance, therea€™s no way a manufacturer will allow the opportunity to pass them by. With advancements in UV LED technology, utilization of UV LEDs for curing in printing processes has become increasingly prominent in the market. Some of these barriers included high cost, low output power and efficiency, as well as thermal management challenges. For instance, the better the implementation of optics and cooling, the fewer LEDs will be required. This all has contributed to wider adoption, increased volumes and increased support for UV LED compatible inks and materials available for the marketplace. High power systems are created by grouping arrays of LED die together, increasing both the packing density and, in principle, the radiated power. A good implementation of UV LED systems requires expertise in each area and an understanding that each piece is interwoven to work as a system. As mentioned previously, high power systems are created by densely populating LED die in arrays.
Performance, space and system size constraints, noise, environmental conditions and ease of integration are factors that dictate the design of a solution. Another advantage of water cooling is the compact UV LED head size, permitting integration into applications where space around the curing area is limited.
The benefits air cooled systems bring are the ease of integration, being light weight and reducing costs, with no need for external chillers, tubing or coolant. Different methodologies ranging from reflection to focusing light with lensing can be employed to enhance the output and minimize loss of energy. By providing high output and custom optics to deliver high irradiance at flexible working distances, UV LED curing systems enable users to increase productivity by maximizing the use of UV energy.


Taking into consideration the type of print process, required throughputs and print area, the use of UV LED curing systems may be a viable option, and one that can help overcome many challenges. The ability to have tighter controls on the process results in high quality prints and fast turnaround times.
It is anticipated that as the technology continues to mature, more and more processes will adopt UV LED curing solutions. The UV LED business is therefore expected to grow from $90m in 2014 to about $520m in 2019. Compared to a process based on 2" substrates, this can provide an overall productivity increase of at least 30%, which would help to further reduce manufacturing cost. Here too, expertise developed in the visible LED industry will help to accelerate UV LED development, concludes Yole. I’ll try to come up with something special for IFTLE 81, which would be the beginning of Year Five.
Fast-growth economies, increased disposable incomes, and large populations will drive this expansion. An estimated 20% of television shipments in 2011 were smart TVs, but this is expected to increase to nearly 40% of in 2012. Amongst these applications, UV curing is the most dynamic and most important market, due to significant advantages offered over traditional technologies (lower cost of ownership, system miniaturization, etc.). UV-LED flashlights in this range are used to detect fraudulent identification and currency, and offer the benefit of use in well-lit environments, which is difficult using a mercury-vapor lamp.
He added that the UV output of a mercury vapor lamp drops off rapidly over its operational life because some of its electrode material vaporizes, depositing a film on the inside of the quartz tube which the UV cannot penetrate. A downside to these extraneous peaks is the generation of heat during printing and other curing operations.
At 385 nm, this efficiency improves, but only to ~15%, making the higher-wavelength chip the better choice. Depending on the equipment and curing application, the media can be 1 to 100 mm from the emitter window, for which AMS has produced special optics. Even though the radiation is not visible, collimating optics are utilized to deliver the radiation with a uniform power level across the target media. The association also seeks to help speed development of applications especially suited to UV LEDs, educate researchers, integrators and end users regarding the benefits of UV LEDs, and provide a forum for industry communication and collaboration.
The company provides UV emitters in hermetically-sealed metal-glass packages (TO-18, TO-39 and TO-3), with standard products and custom solutions spanning the wavelength range from 240 to 355 nm. We are now gearing SETia€™s capacity for high-volume manufacturing to cater to new demands coming from mainstream consumer markets,a€? said Bettles. Crystal IS manufactures 260 nm UV LEDs and is the only company to produce LEDs on AlN substrates.
Nonetheless, AlN substrates are only available in small sizes and remain much more expensive than sapphire wafers, thereby limiting this market. This is only possible with an LED package capable of handling extreme power densities for the life of the product.
UV accelerates degradation of the epoxy material in a non-linear manner, directly impacting lifetime. The new copper- and glass-based package from Schott offers the advantages of high thermal conductivity and hermeticity. When that moment comes, the whole supply chain will become a mess due to an increasingly competitive environment, and consolidation will be necessary. There are several technological advances that have enabled the use of UV LEDs for ink curing, as well as specific advantages UV LEDs bring to printing processes. Significant progress has been made to address these shortfalls and, as such, has helped advance the acceptance and viability of UV LEDs as a curing solution. However, in practice, there are limitations to the packaging as a higher packing density results in a greater power per area (an increased irradiance), but with that must also come the handling of an increased heat density and power consumption. Thermal management has become a crucial technological component in UV LED advancements and will be further discussed in this article. The complexity in the packaging of arrays alone is one aspect, but these arrays must also be housed, driven, cooled and optimized.
As outlined above, the performance, reliability and lifetime of LEDs, particularly those in high density and high output arrays, are dependent on how effectively the heat is dissipated. While in its infancy, air cooled solutions could be utilized only for low output UV applications. Depending on the application, optics can be customized to meet the performance requirements, including working distance and curing area.
While the new applications do not yet have a strong impact on market size, Yole expects them to possibly count for nearly 10% of the total UV LED market by 2019. Asia-Pacific is undergoing a digital TV boom that some believe will result in 70% of homes having a DTV in 2015, up from approximately 35% in 2010. This trend is reinforced by the whole supply chain, which is pushing for the technology’s adoption: from UV LED module and system manufacturers to ink formulators and (of course) the associations created to promote the technology.
Today, as is the case with LEDs in the visible spectrum, UV LEDs are only beginning to replace the established UV sources in a likewise diverse array of markets. As a result, the user cannot easily predict the amount of UV generated at a later time; often this is a critical process parameter. All the major providers of curing formulations (photoinitiators and resins), have recently brought higher-wavelength inks and coatings to market to fill this need. Digital inkjet curing was the first segment to adopt UV LEDs due to the required close distance to the media for the print heads to optimally perform.
Figure 6 shows examples of UV-LED arrays in lamps designed to deliver radiation in the 300-320 nm range for phototherapy applications such as the treatment of skin conditions such as psoriasis or eczema. SETi recently announced the purchase of a new facility, where it plans to manufacture over 100 million UV LEDs per year.
A thermally matched stress-free package and glass lens help eliminate common packaging failure modes associated with UV LEDs,a€? said Thomas. Bulk GaN was the ideal technical candidate, but cost was too high and sapphire was widely adopted instead. According to market research from Yole Developpement, "the UV LED business is expected to grow from $45M in 2012 to nearly $270M by 2017," with majority of this being accounted for by UV curing. The performance of the die is better at longer wavelengths, thus cost per watt output is lower while delivering more energy.
The roles that thermal management and optics play in a system design are profound, as they help dictate the efficiency, form factor and implementation.
High peak irradiance and delivering sufficient energy density are necessities in UV curing.
The need for chillers and water pipes requires extra infrastructure that some applications or print environments cannot afford. However, in recent years, considerable advancements have been made, such that higher power air cooling implementations can be achieved without negatively impacting lifetime and reliability. Interestingly, we have evidence that when those plants are exposed to UV-B LEDs a short time before harvest, their polyphenol content is boosted without compromising plant mass,a€? explained Cary Eskow, global director of advanced LEDs and illumination for Avnet Electronics Marketing in Phoenix, AZ, which distributes UV LEDs. SETi has demonstrated disinfection of drinking water in an in-line flow-through system using less than 40 mW of UV power.
He gave examples that include plastic gift cards or credit cards, which use sheet-fed lithographic printing. This was a natural fit for UV-LED lamps as the curing intensity is highest at the emitter window. He described LED Engina€™s patented multi-layer ceramic substrate with extremely low thermal resistance that quickly conducts heat from the die junction (Fig.
Another alternative is to combine a glass lens with silicone encapsulant to accommodate even higher flux density and higher efficiency yet shorter lifetime (15,000-20,000 hr). Thermal management is often overlooked but plays a crucial component in the successful execution of a design to achieve the required performance parameters. Having a window or flood that illuminates onto a wide area for such a process would mean the majority of energy is wasted.
He continued a€?This is a novel method for increasing the appeal of some foods without using chemicals.
There are currently two implementations of thermal management – water and air cooling. But given some newly published results (increase of EQE over 10%, etc.) and the recent commercialization of the world’s first UVC LED-based disinfection system (2012), the market should kick into gear within the next two years. LED irradiance can be very high at the emitting window but decreases with distance because, without optics, the light is diffused and unfocused. To mitigate the effects of an increased working distance, employing optics to focus the UV light helps to optimize the output and results in a more efficient solution.



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