Company Profile: NeoBulb takes heat out of high-power LEDs

June 6, 2005
A new system-in-package solution from NeoPac Lighting is capable of dissipating 500 W/cm2 from high-power LED chips.

October 2005 - Download a PDF of the latest NeoPac product line (520 KB)

[The following article was written in June 2005. Recent news from NeoPac can be found in the Links at right.]

NeoBulb NeoPac Lighting, a Taiwanese LED lighting system manufacturer, has unveiled its system-in-package ultra-high-power LED light bulb, in which the first-level package is integrated with a highly efficient heat sink. The NeoBulb is a “plug-and-play” solution that contains a small-diameter, high-power LED light source, drivers, optics and efficient thermal heat sinking.

The key to the product is in its approach to thermal management. Since LEDs are temperature-sensitive devices, a rise in an LED’s junction temperature will decrease its light output, cause a shift in its color, and reduce its life. Thermal management represents one of the main challenges in improving the efficiency, durability and spectral characteristics of high-power LEDs.

Cross-section In the NeoBulb structure, heat is effectively removed from the vicinity of the LED junction using a micro-heatpipe, and then dissipated using a series of circular fins surrounding the heatpipe. Heat removal is enhanced by using a longer heatpipe or larger-diameter fins. The chips are packaged and mounted onto the proprietary heat-pipe, eliminating a number of interfaces typically found in high-power packages and assemblies. Jeffrey Chen, president of NeoPac, told LEDs Magazine that the thermal conductivity of the finned heatpipe (made of copper ) is 100 times higher than copper itself, which is sometimes used as a heat-sink slug in high-power LED packages.
NeoBulb demo The NeoBulb Light Engine configuration can result in a very low Rj-a (the thermal resistance from junction to ambient). For an 80-mm-long heatpipe with a fin diameter of 20 mm, Rj-a = 12.0. Increasing the heat pipe length to 110 mm reduces Rj-a to 9.9, while increasing the diameter to 30 mm results in Rj-a = 6.6 (for 110 mm heatpipe length). These figures all arise using natural convection, and can be improved with the use of forced convection.

High performance light engines

Neopac has achieved some very impressive results, for example from a light engine with a 66-mm-long heat pipe and 30-mm-diameter fins (similar in size to an A battery). The package's light source has a diameter of only 5.5 mm (i.e. an area of only 0.24 cm2), but can dissipate at least 5 W from a single 1 mm2 chip and still keep the junction temperature of the device at 103°C. The safe limit for high-power LEDs is usually quoted as 120°C. NeoPac estimates that its technology is capable of dissipating up to 30 W for natural convection, and 60 W for forced convection.

Power dissipation The Graph shows power dissipation results recorded in a natural convection environment for different package dimensions. All the packages contained 1 mm2 flip-chip LED chips supplied by a local chip manufacturer.

Dissipating 5 W of power in a 1mm2 chip corresponds to a heat flux of 500 W/cm2, which is 10 times the amount generated in a conventional microprocessor chip. Jeffrey Chen believes it is impossible for an LED chip to withstand such a huge power density using even the most advanced package technology currently in use.

New packaging approach
Track light application NeoPac Lighting claims to have developed the world's brightest point-source LED bulb by utilizing current chip technology within a small-footprint package. The platform can accomodate chips from different vendors. Because thermal considerations are so fundamental to this approach, the first-level chip package is effectively integrated into the second-level heat sink assembly - hence the "system in package" description.

"For ultra-high-power applications, the concept of LED packaging and assembly must be essentially changed,” says Jeffrey Chen. “For the NeoBulb approach, 14 patents have been filed internationally, from package and light engine level to bulb and luminaire levels. We are confident that NeoBulb will be the best solution for accelerating LEDs toward general lighting.”