LED Lighting Packagers in Taiwan Handle Cooling Differently

Taiwan's light emitting diode (LED) packagers are on a mission: squeeze more illumination and maximize lifespan of LED lamps with ever higher quality thermal-conductivity solutions.

If the heat inside LED packages, or emitters, is not effectively exhausted into the ambient air, the life and luminosity of the packages will be compromised by excessive heat built-up inside the lighting device.

Good packaging methodologies can minimize thermal accumulation inside the package and let more light from the chips fixed on thermal-conductivity substrates (or boards) escape the transparent encapsulant.

The thermal-conductivity substrates used by Taiwan packagers on one-watt-up "high power" LED vary from aluminum-based metal core printed circuit board (MCPCB) to copper-based MCPCB and plastic printed circuit board, ceramic, to silicon.

Over the past few years, they have worked out their own unique packaging solutions to improve the durability and luminosity of their LED lighting products.

Cooling With Copper

Founded in 2004, ProLight Opto Technology Corp. is a proponent of copper-based substrate, which the company's president Michael Hsing says is much superior to aluminum-based board and ceramic boards in thermal-conductivity performance although many packagers still use aluminum-based boards. The company's tests prove its copper substrate's conductivity value is 400 W (watt)/m (meter).K (Kelvin), compared with aluminum's 150-180 W/m.K and ceramic's 25-170 W/m.K.

Pb-free soldering further helps boost conductivity of the company's LED package. ProLight solders LED chip electrode pins to printed circuit boards instead of using thermal conductive adhesive. "Solder's conductivity efficiency is 17-39 W/m.K while the adhesive's is only 0.3-3 W/m.K," Hsing notes. The company affixes chips to copper-based board with silver adhesive for an additional conductivity boost.

The company builds anode and cathode electrodes and thermal-dissipation stripes of the package's copper lead frame on the same pad, eliminating the need of an additional heat sink.

This clever structure, patented both in Taiwan and the United States, sidesteps the need to build the heat sink and electrodes on different pieces. It also enables the company to shrink its package to just 2mm long—a feat that previously would have required the use of ceramic substrate, according to Hsing.

With efficient thermal-dissipation, the company's LED packages deliver excellent luminosity durability: its one-watt package driven by 350mA was field tested at 91.06% brightness after 10,000 hours of non-stop operation. Heat resistance is three degree Celsius per watt.

ProLight encapsulates LED chips with optic-grade silicone, which is considered technologically superior to the epoxy resin used widely in the industry. "Silicone is superior to epoxy in transparency and resilience, as well as heat and ultraviolet resistance," Hsing notes. The company field tested its typical high-power package at 80% of light output after 16,000 hours of non-stop operation, compared with a 5-mm epoxy white LED's 20% of output.

Recently, the company has improved the formula of its silicone encapsulate to make it more reliable in terms of thermal shock and soldering resistance.

ProLight offers 0.3W to 15W RGB, UV, yellow and white packages using chips ranging from 24 mil to 60 mil (0.6mm to 1.5mm) in size and sourced from various suppliers. Most of its packages go into commercial lighting, architectural lighting, entertaining lighting, mine lighting, handheld lights, lighting for high-resolution indoor and outdoor billboard displays, automotive lights and other special-purpose lighting under its eponymous ProLight brand. "We never accept OEM orders because they can reduce our value," Hsing stresses.

Since starting up his own firm, Hsing has always focused on developing in-house technologies. "So we began applying for patents on structure and electrical-circuit designs as well as illumination quality," Hsing notes. ProLight draws on outside designs as a reference in developing its own products, but always with care to avoid patent infringement. "We have unique technologies, and also benefit from shared know-how."

ProLight has introduced circuitry that keeps packages on the same module from mutual interference when one burns up. Also, the company has won patents for its unique packaging process that evenly spreads phosphor powder over LED chips, enabling packages to give off light of consistent color bins. "Our phosphor powders do not infringe anyone's patent rights," Hsing assures. The company has also patented its static-resistance technology.

Backed by its broad LED capability, ProLight provides lighting manufacturers with total solutions. "That's our value. Usually, lighting manufacturers know little about optics, thermal and current-drive issues related to LED. So, we tap our know-how in the three areas to design lighting solutions to suit specific needs," he adds.

Over the past few years, the company has introduced several impressive packages including its Phoenix, Hornet and Crab series. Measuring 4x5x1.55mm, the Crab family of packages is reportedly the industry's smallest high-power package, producing 120 lumens per watt. All packages in the line are made with surface mount technology (SMT) and comply with RoHS.

Set on Silicon

HELIO Optoelectronics Corp. is one of the handful packagers adept at silicone molding injection. According to company general manager, Cater Chen, the injection technology has considerably reduced the chance of lens bubbling and fissuring—a frequent problem when using conventional adhesive methods—enabling light to pass smoothly to the surface of the emitter.

A former manger of the government-backed Industrial Technology Research Institute (ITRI) in charge of a wafer-level-packaging project, Chen has a strong preference for silicon material. "Silicon will win out over other materials because of its excellent performance and low cost," he says.

So far, the company has tried lead-frame packaging, ceramic packaging and silicon packaging approaches, which mount LED chips on polymer-based substrate, ceramic substrate and silicon substrate, respectively. The first two approaches are used widely in the industry now, while silicon is gaining ground thanks to its advantages over other materials. For example, silicon melts at 1,000 centigrade, has a CTE below 4 ppm/C, and has a thermal conductivity in the range of 150-180 W/m.K.

Founded in 2006 by a team of optoelectronics specialists who formerly worked at ITRI, the company has been focusing on high-power LED packages for lighting purposes. Its product line includes 1-, 3-, 5-, and 10-watt emitters for general lighting, auxiliary lighting and auto lighting. Its 1W white emitters have an efficiency rating of 110 lumens per watt, and its 3W white emitters give off 180 lumens. The company sources chips from big-name suppliers, including BridgeLux of the United States, in which silicon foundry giant Taiwan Semiconductor Manufacturing Co. (TSMC) holds stakes.

Integrating packaging with micro-electro-mechanical system (MEMS) technology, which enables IC packagers to encase system-on-chip (SoC) components directly on silicon wafers, is the fourth stage on the company's technology-development roadmap. Chen notes that MEMS technology enables silicon-carrying control integrated circuits to be packaged with a high-power LED chip, reducing packaging costs. Current LED packages generally consist of chips coupled with various external controllers, complicating the manufacturing process and increasing the size and cost of the emitting system. "Our R&D team is mostly composed of MEMS specialists," he says.

Chen's company is testing MEMS integration in cooperation with a big-name silicon-chip assembler on the island. "We're planning to do the packaging on 200mm and 300mm silicon wafers and project to put out 2,000 3.4mm by 3.4mm packages on a wafer in our factory," he says. He estimates the company will begin volume production using the new packaging technology in one year or two.

HELIO has won at least 42 patents, including a patent for AC LED packaging. The company's 40-person R&D team is formed by engineers with degrees in materials, mechanics, physics, optics, and biotech sciences. It also has cooperated with prestigious universities in Taiwan, including National Sun Yat-sen University, National Central University, National University of Tainan and National Chiayi University on medical lighting and bio lighting. The company has also entered into alliance with end-product makers Coretronic Corp., and Foxsemicon Integrated Technology Inc., as well as LED chipmaker Optotech Corp.

HELIO has sold its packages to over 300 lighting-module suppliers, making it one of the top three suppliers of high-power LED packages in Taiwan. The company now puts out 1.2 million emitters and 200,000 modules a month, delivering an equal half of its outputs each to indoor lighting suppliers and outdoor lighting suppliers.

Ceramic Boards

Intematix Technology Center (ITC) Corp., the LED-packaging business of the Fremont, U.S.-headquartered phosphor-technology powerhouse Intematix Corp., is reportedly the exclusive Taiwanese LED packager to win patents on an unorthodox methodology featuring chip array in serial or parallel arrangement on a ceramic board bearing at least two cavities for holding the chips. "This is the result of our philosophy of never operating as an alternative to incumbent packaging technologies," stresses Harik Su, ITC's R&D vice president.

Su, one of the seven packaging specialists retained by Intematix a few years ago after acquiring a Taiwanese LED epitaxy-wafer maker, led ITC's R&D guys to work out the unique technology around six years ago. "If we were like other domestic peers with the same technologies as the big players, we would have been trapped in relentless patent battles," Su explains.

The Cetus family of packages is one of the company's main products. This type of packaging is made with ceramic-based chip-array methodology and can be operated with DC or AC voltage, making the company one of just a handful LED packagers able to provide AC LED solutions. According to Su, Cetus employs a unique design to make each cavity connected on a LTCC ceramic lead frame. The design, he says, allows ITC to create any desired array configuration to deliver an illumination profile with a pleasant, smooth and natural looking light. "These arrays really combine the features lighting companies are looking for, including easy design, tight binning, robust thermal management and a simplified and scalable power and area design," he stresses.

The packaging technology boasts several advantages including RoHS compliance, zero moisture, and a 90% illumination reflection rate. "Most of all," Su stresses, "production cost using this methodology is fairly low. Also, it offers a very convenient design environment since any new serial or parallel arrangement does not require changes to the lead frame layouts on the package. This helps our customers to quickly bring new products to market."

ITC uses the unique methodology mostly on LED packages under 10W, which Su thinks is currently a dominant power specification in the LED lighting market. "The power range above 0.5W and below 10W, we think, is the main product ranks now in the market," he estimates. Accordingly, the company has used the methodology to primarily package low-power multiple chips on a lead frame.

Su emphasizes that his company never uses the packaging methodology on red-green-blue (RGB) chips encasing, which he says has lower patent barrier than does the packaging for blue chips wrapped with phosphor. The company's U.S. parent is said to be the world's leading phosphor-power manufacturer in terms of chromatic 'totality' for commercialized phosphor powder, offering one color bin every five nanometers on the spectrum. Ceramic has satisfactory thermal conductivity, at 24-170 W/m.K range, and low CTE, at 4.9-8ppm/K range, according to data complied by ITRI. Both factors add durability to the company's packages, which are marketed with a guarantee that illumination intensity will fall by only a single digit rate after 1,000 hours of operation.

The company's ceramic-based package generates thermal resistance of only 8C/watt, and confines maximum anode-cathode junction temperature to within 90 C. "Our package delivers the best efficacy at 100lm/W and an optimized CRI at 93," Su reports.

The chip-array layout produces optimal light output with a cluster of dot lights on a fairly small ceramic piece, Su says. The company's 10W C1109 package, for instance, gives off a total of 800 lumens on an 11mm x 9mm board.

Output capacity at the company is now 20 to 30 million packages a month. Most of the output is exported to the United States. According to Su, ITC began last year to expand sales in Europe to boost revenue. In Asia, Japanese manufacturers, he adds, are his company's prime buyers. "All of our products are for indoor applications," Su stresses.

The company's packaging technology frees its customers from patent lawsuits and its offer of total solution covering contract design, prototyping and tooling, lighting modules and OEM/ODM-based lighting systems backed up by its parent company saves customers a lot of trouble in dealing with the complexity of LED designs. Thanks to less risky products and convenient service, ITC's revenue for this year is projected to treble from last year, following a similar pace of growth last year, according to Su.

Chip-on-Board

Lustrous Technology Ltd., founded in 2004, fixes LED chips directly on aluminum-based MCPCB instead of lead frame, a methodology known as chip-on-board (COB). "Besides aluminum, we adhere some undisclosed layers to the board and the outcome is our packages generate only 0.5 C per watt," reports H.W. Huang, company account manager.

The company has been developing COB technology, which can lower thermal inside the package as a result of eliminating unnecessary layers between the chips and MCPCB board, since it was founded and used the technology on high-power LED packages driven by current over 300mA. Total PN junction temperature on the company's LED packages is confined under 80 C because of COB's quality thermal dissipation. "We have over 20 patents the COB technology in the United States, Japan and Taiwan," Huang says.

Huang stresses that COB has recently emerged as the packaging technology of choice due to its superior thermal and cost efficiencies and streamlined thermal-management design relative to existing technologies. "This is an ideal packaging solution that meets the needs of the lighting market," he says. Huang claims that packaging using the COB technology can operate at full luminosity for 50,000 hours before a 30% decay sets in.

The company has applied the COB technology to a dimmable single multichip package, which the company claims is the industry's first of its kind. The 15W package, code-named Crystal, is embedded with 12 chips and driven at 700mA.

The 34mm x 36mm x 10.4mm Crystal is composed of a white-light half and a warm-white half packages, allowing it to produce 650 luminous flux of white light and 480 luminous flux of warm white light at a 75 color rendering index (CRI). The package is an ideal light source for recessed downlights, light bulbs, ambient lighting fixtures, and dimmable lighting fixtures.

Also, the company has turned out alternating-current (AC) LED package based on its COB technology, making it the industry's first COB AC LED package.

Lustrous' another proprietary edge in paring down thermal accumulation inside package is the use of molding lenses. According to Huang, the domed lenses, covering the chip, let 20% more of the light escape the encased body, averting the same percentage of electrical power consumed by the chip turning into heat.

Lustrous has built up its "Lustrous" brand in the U.S. since 2004, when it set up a factory in Taiwan.

Huang's company has rolled out one-watt, three-watt, five-watt and 10-watt emitters built around the technology. Major applications for the company's packages include MR16, sunken lamps, down lights, wash wall lamps, and streetlights.

To avert disputes over chip intellectual property, the company builds Epistar Inc.'s chips into packages for domestic sales and Cree Inc.'s chips into products for exports. Epistar is Taiwan's No.1 LED-chip maker.

The company's R&D team brings together considerable talent in thermal-dissipation and optoelectronics, allowing it to develop self-sufficient technologies that free the company "from being trapped in patent disputes." Mastery of package-structure, phosphor, and chip know-how also puts the company two to three years ahead of rivals in terms of R&D, Huang claims.

Huang notes that, in many cases, the company's packages are developed in cooperation with lighting manufacturers and retailers. "Actually, we provide them tailor-made solutions," he says.

Copper/Silver Heat Beater

Kaylu Industrial Corp. fixes chips on a pure-copper substrate with silver adhesive and plates the frame with silver to protect it from tarnishing and help boost reflection of the light from LED. The result is the packaging solution conducts thermal at a staggering 398W/m.K rate.

Outstanding thermal conductivity allows the company to embed both the anode and cathode of its LED packages on the bottom of the lead frame, in contrast to using a stand-alone anode and cathode extending from sides of packages-a design adopted by many packagers. The unique anode-cathode design frees the company from reliance on outside patented technology.

Each of Kaylu's packages can hold up to four chips and have four pairs of embedded anodes and cathodes. The package is applied to high-power chip rated above one watt.

"Our package design is protected by patents in the U.S. and Europe, so we can now export to those markets without fear of patent infringement," stresses Paul Chang, the company's sales representative.

The company's packaging is not only protected by its own patents but also by patents from its phosphor-powder and chip suppliers. "So, our customers need not to worry about using our products," Chang stresses.

Chang points out that LED package buyers are most concerned about the stability of color rendering, which is closely associated with thermal-conductivity and phosphor qualities.

Buyers have built the company's packages into MR16, recessed lamps, T8 lamps, garden lamps, flood lights, streetlights, road lights, and tunnel lights. The company supplies lighting manufacturers with not only LED packages but also custom-made lighting modules.

Kaylu has built up its LED packaging capability on its PCB-processing equipment business, which has been its main business since it was opened in 1987. "Designing electrical circuits on the boards is quite similar to package structure design. So, that's our advantage," Chang stresses. Another advantage is the company's competitive pricing. The company broke into the LED packaging segment in 2000 with a lead-frame design for Cu substrate, and it debuted its own LED packaging in 2007.

Industry Leader

Everlight Electronics Co., Ltd., currently Taiwan's No.1 LED packager founded in 1983, has a wide range of solutions. Ceramic lead frame is the one for several of its new products including "Sheun" and "Shwo" families of high-power packages.

Both families of packages come in 1W and 3W types in terms of power specification, with 1W packages producing 10-15 C per watt and 3W types generating 6-8 C per watt.

One-watt Sheun packages are driven by 350mA to give off 100 luminous flux while 3W packages are driven by 700 mA to put out 170 luminous flux. Both packages feature a compact and slim design measuring 3.05mm x 4.5mm x 2mm and are SMT devices offering high light output, making them suitable for a variety of lighting applications including general luminaires, flash, spot, signage, commercial and industrial lighting.

Sheun packages come with an electrically-isolated thermal pad designed around the idea of improved thermal and electrical characteristics. Depending on their applications, the packages offer a range of CRI from 79 to 90. Commercial production of the packages has begun this quarter.

Shwo packages are also SMT devices measuring 3.5mm x 3.5mm x 1.85 mm, an ideal design for various lighting applications including general luminaires, flash, spot, industrial and commercial lighting.

One-watt Shwo packages come in warm white and cool white types, with the former delivering a 3000K light and producing 80 lumens and the latter delivering a 6500K light and giving off 100 lumens at 350mA.

Three-watt Shwo packages are driven at 700mA, with warm-white type producing 160 lumens and delivering a 6500K and cool-white type producing 120 lumens and delivering a 3000K.

High-voltage packaging is another Everlight specialty. In sharp contrast to high-power packages mostly using single-digit voltage to boot up, the high-voltage "HV" package uses 50 volt. The company defines HV as the third generation LED after AC LED. "Basically, HV LED shares much common process technology with AC LED, bearing several micro-dies on it as AC LED. The only exception is it does not have a bridge diode, which strings all these micro devices to fit alternating current," says Kenny Wang, an R&D associate engineer of Everlight's solid-state lighting unit.

The semi-AC design, Wang goes on, gives the company's customers latitude to decide the current specification of the LED according to their needs. "If they use the LED as a DC device, they don't need to change anything on the LED. They simply add a power-management IC to make it an AC LED," Wang adds.

Currently, AC LED, which can be directly plugged in household power outlets without a current adapter, which DC LEDs require, remains pricier than DC LED because of the more complicated manufacturing process involved. With high drive voltage, HV LED can produce higher light output than their low-voltage cousins do. HV LED also has an impressive CRI of 85 to 90 with a 3000K warm white light.

Flat-panel Package

Edison Opto Corp.'s high-power SMD and flat-panel packages produce thermal resistance of 5-15 C per watt depending on product types and show less than 5% illumination degeneration after 1,000 hours of non-stop operation, according to Christopher Tu, the company's deputy engineer for R&D.

Edison Opto's SMD packages contain one single high-power chip each, while the flat-panel packages carry multiple chips. The company packs LED chips mostly on copper-based MCPCB according to its SMD package formula and fixes multiple chips on a ceramic board using flat-panel package techniques. "The two categories cover almost all lamps with dot-shape and broad area light," Tu says.

The company can pack 100 1W chips on a 9mm x 9mm ceramic panel to produce 8,000 lumens. It also makes a 3W SMD package measuring only 1.5mm x 3mm x 4.5mm. "The trend is now towards small size and high light output, but with the precondition of good thermal dissipation," stresses Tu.

Tu says that his company is Taiwan's first LED packager to produce high-power products when it diversified into LED packaging in 2003 from manufacturing of fiber-optical sensor and fiber-optical transition equipment, the company's core business when it was founded in 2001. "In 2006, our 100W LED project won government funding," he says.

Edison Opto uses patented high-power chips from heavyweight players like Cree and BridgeLux. Its package designs are also patented. "With patent backing, we could freely ship our products to Europe and North America," says the deputy engineer.

The company provides not just commodity packages but also built-to-order packages. "One of our tailor-made designs can be seen in the color bin range. We can fine-tune the range according to customer demands," Tu says.

Packaging is not the company's only charm. It also designs lens and thermal-dissipation modules for customers. "To do this, you really need know-how on optics, mechanics and electronics," Tu stresses. The company's packages have been built into commercial lights, streetlights, garden lights, and household lights. Europe and North America, mainland China, and Taiwan each account for one third of the company's sales.