The range of applications for light emitting diodes
(LEDs) continues to grow significantly. One of the fastest growing and most
promising uses for LEDs is in illumination applications.
The LED is penetrating this market rapidly due to its
combination of excellent color saturation, energy savings that satisfies
today’s demand for reduced energy “green” products, and long life
characteristics.
Both white and color LEDs are playing important roles in
a number of market segments including architectural lighting, entertainment,
wall washing, decorative lighting, outdoor façade lighting, and video walls.
The use of red, green and blue (RGB) combinations will become increasingly
popular in these segments due to the resulting flexibility of color selection
and the simplification of the optical aspects of lighting designs.
The largest application in 2006 was
architectural, at $93 million, or 45 percent of the overall market. This was
followed by channel letters/contour lighting and consumer portable applications
(flashlights, lanterns, bicycle lighting and similar devices), at $34 million
(17 percent) and $30 million (15 percent), respectively.
All other applications accounted for less than 10 percent
of the lighting market.
By color, white accounted for 43 percent ($89 million),
blue and green for 35 percent ($72 million), and red, orange and yellow for a
combined 22 percent ($44 million). White represented the largest share, mainly
due to its large penetration in channel letter, consumer portable,
architectural, and retail display lighting. Blue and green is the next-highest
color usage in terms of revenue, mainly in RGB applications where the ratio of
blue and green units to red units is at least 2:1.
Architectural 45.1 percent
ConsumerPortable 14.7 percent
Off Grid 3.7 percent
Machine Vision 6.4 percent
Safety/Security 7.7 percent
Entertainment 1.7 percent
ChannelLetter/Contour 16.7 percent
Outdoor Area 0.1 percent
RetailDisplay 3.1 percent
Residential 0.8 percent
Total: $ 205 Million
Figure 1. LED Lighting Market by Application (2006)
ROY 21.7 percent
Blue-Green 34.9 percent
White 43.4 percent
Total: $205 Million
One of Avago Technologies’ innovative approaches to the
lighting market was the development of the Moonstone LED package.
Avago Technologies’ Moonstone LED emitters are available
in one of the industry’s thinnest packages (15.85 mm x 8.5 mm x 3.3 mm), and are encapsulated in a heat-
and UV-resistant silicone compound for high reliability and long life.
The competitively priced Moonstone LED emitters provide
designers of solid-state lighting with many features, such as a wide viewing
angle radiation pattern, superior heat dissipation, and thin packaging. All
this makes them ideal for use where height is a constraint. Typical applications
include architectural façade lighting, track lights, spot lights, and
decorative lighting applications.
With an exposed pad design on the back of the package,
the Moonstone emitter package has low thermal resistance and is able to
efficiently transfer heat from the package to the motherboard to maintain long
term reliability. These emitters are compatible with standard SMT reflow
soldering processes to provide lighting designers with more freedom and
flexibility in designing their applications.
In addition, the package is qualified to a JEDEC moisture
sensitivity level (MSL) rating of 2A. (For manufacturers, this rating means
that the devices can be kept in the open air (30°C, 60 percent relative
humidity) for up to four weeks after being removed from their sealed package
without the need to remove absorbed moisture).
The Moonstone LEDs are specified for operation in the — 40°C to +95°C temperature range, and are capable of withstanding electrostatic
discharge (ESD) levels of 16 kV (class 3b) per ESD Association standard ESD
STM5.1, Electrostatic Discharge Sensitivity Testing Human Body Model.
Moonstone 0.5 W LED emitters are supplied in warm white
(2600 K to 4000 K) and cool white (4000 K to 10,000 K color temperature), with
a choice of non-diffused or diffused packages and an option of
electrically-isolated or non-isolated slugs. They provide 30 lumens (lm)
(typical) and up to 43 lm cool white light output at 150 mA drive current, with
a 110° viewing angle.
Moonstone 1 W LED emitters are supplied in warm white and
cool white, with a drive current rating of 350 mA and a choice of a 110° or
120° viewing angle. The cool white versions provide up to 80 lm output.
They are also available in AlInGaP:
– amber (582 – 595 nm wavelength/ 35 lm typ. luminous flux)
– red (620 – 635 nm/ 40 lm typ.), InGaN:
– green (515 – 535 nm/ 40 lm typ.)
– blue (460 – 480 nm, 10 lm typ.).
Moonstone 3 W LED emitters in warm white and cool white
are capable of being driven to 700 mA, providing a light output of up to 161 lumens, and are
available with a 110° or 120° viewing angle.
The newest version is the 3-in-1 Moonstone emitter,
combining red, green and blue LED chips into a single package (Figs 3 and 4).
Each color can be driven at up to 350 mA, for a typical flux output of 108 lm
(40 lm red, 55 lm green, and 13 lm blue). Color mixing provides hundreds of
thousands of colors, making the 3-in-1 emitter ideal for applications including
instrumentation, interior or exterior illumination, mood lighting, and special
effects.
The conventional approach to assembling RGB LEDs for illumination applications is to use separate,
discrete packages for each color, arranging the packages on a printed circuit board to achieve an RGB light source. In
applications such as architectural, entertainment, outdoor facade and decorative lighting, this will be more
challenging for secondary optic designs, including a collimated lens for RGB that is used to illuminate an area some distance away. The lens and printed circuit board sizes
will have to be enlarged once the pitch size between the LEDs increases. At the same time, the cost of a secondary
optic design and materials will also increase.
In contrast, the 3-in-1 approach directly mounts the RGB LED die into the same package. Each die can be
individually addressed, which means that each has its own electrical channel to provide a range of colors. This enables the
light source to be compact, compared with separately packaged devices, and the pitch between individual light sources
to be significantly reduced, which is important in achieving the best color quality. The minimum pitch required for LED light sources to achieve good color mixing is
approximately 5 mm. The 3-in-1 approach reduces the pitch to as little as 1.5 mm [Figure 5]. Once the pitch is reduced,
the area required for effective color mixing also is reduced.
In the Avago Technologies’ 3-in-1 package, high
performance polyphthalamide plastic is used as both the package housing and the reflector. This material can operate under conditions of high-temperature, high-UV light levels for long periods while maintaining surface reflectivity. If the wrong material is chosen as a
reflector, however, the light output performance can drop
significantly because of its white surface, which becomes yellow or brown over time after experiencing high temperatures.
A copper lead frame (substrate) enables the lowest
thermal resistance. The heat generated by the operating LED chips can be efficiently transferred to the heat sink through the frame; copper’s thermal conductivity is superior to ceramic, mild steel and aluminum.
LED JunctionMCPCBLED Junction to ChipChip to DA
AdhesiveDA Adhesive to substrateSubstrate to SolderSolder to MCPCBThermal
PathSolderPaste
Discrete LED
5mm pitch1.5mm pitch3-in-1 Solution: reduced chip to chip
pitch
LED Chip
SubstratePCBReflectorReflectorMetal
SubstrateEncapsulationLED Chip
Encapsulation
Good Thermal and Reliability Performance
The thermal resistance has been verified using the FLOTHERM computational fluid dynamics (CFD) program from FLOMERICS Group PLC. In the simulation model, the reflector, lead frame, encapsulation, die attach layer
and dice are created. A 1W power source is created on top of each die.
The simulated thermal resistance from junction to pin (Rjp) for the red, green, and blue die are 23°C/W,
20°C/W, and 20°C/W, respectively. These thermal resistance values have also been verified by actual measurement using the forward voltage method. The results of actual
measurements are very close to the simulation.
Furthermore, the package thermal performance has also been validated through operating life tests of up to 5000 hours.
Reliability testing was performed in a temperature chamber and showed low degradation after 5000 hours at +100°C operation. The InGaN die show an
approximate 12 to 18 percent Iv drop and the AllnGaP die, an 10 percent Iv drop.
Conclusion
The 3-in-1 package solution provides better performance than conventional discrete LED packages in terms of
characteristics such as color mixing and space requirements, while featuring good thermal performance and reliability characteristics. It also provides greater flexibility for system designers in developing their applications.
Avago Technologies offers extensive technology and products in the LED illumination field, providing mid-
and high-power LED devices ranging from mid-power PLCC surface-mount emitters in both warm and cool white and a range of colors, to the Moonstone emitters, Star-1 and Star-2 PC assemblies, 3.5 and 5-watt multi-chip white LED modules and 24-watt multi-chip LED modules. For detailed information on these or other Avago
Technologies’ lighting products, go to http://www.avagotechlighting.com/.
By GreentechLead.com Team
editor@greentechlead.com