Will LEDs light up the world? Assembly packaging could mean a bright future.

Author:Vardaman, E.Jan
Position:ON THE FOREFRONT
 
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CONFERENCES AROUND THE world are buzzing over the growth projections for high brightness light-emitting diodes (HB LED). In Korea, almost 200 people attended the International LED and Green Lighting Seminar in June, while more than 20,000 people visited the colocated LED and OLED Expo. More than 200 people attended special sessions on LEDs during SemiCon West in San Francisco this past July. Companies are looking at the explosive industry growth, and all hope for a piece of the pie. Strategies Unlimited, Credit Suisse, and McKinsey predict that the LED market--driven by three major applications (general lighting, backlighting, and automotive)--will grow at a 40% CAGR through 2015.

According to the Optoelectronics Industry Development Association, three segments--automotive, lighting, and mobile applications--are expected to grow to 89% of all applications in 2021. What is driving the growth? In the case of lighting, much of the growth comes from pending bans on incandescent bulbs and government mandates that lighting be converted to LEDs for energy savings.

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The technology to produce LED die is based on semiconductor diode technology. The emitted wavelength of light depends on the specific semiconductor material used. The key to producing high-quality LED die is the growth of the epitaxial layers and an active p-n junction on an optimum substrate. The p-n junction is critical in determining the device's internal quantum efficiency (IQE), and the substrate is important because it should match the lattice constant of the semiconductor. The matching lattice constant helps reduce dislocation defects. Dislocation defects can adversely affect the performance of the LED.

Key tools for the growth of the epitaxial layers include MOCVD equipment. Wafers are typically two to four inches with a constant pressure to continue moving to larger wafer sizes.

The packaging and assembly process is also critical to the performance, reliability, and lifetime of the LED product. LED packaging tends to be nonstandard, with every package unique to the supplier.

LED packaging options include use of one large LED die in a package versus multiple die. Advantages and disadvantages are still being debated. It is not clear if one method will dominate or if both solutions will be used. In some cases, multiple die are mounted directly on a metal core substrate or on leadframes.

Thermal issues. Thermal issues have been reported to account for as much...

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