Opposite to the traditional approach to SSL fixtures, Lighting-fixture maker Albeo Technologies has developed a novel approach to integrating bare LED die directly into fixtures. This exceptional concept has received US Patent 8,056,659 entitled "LED chip-based lighting products and methods of building", but products based on the technology are at least a year away.
Albeo plans to use pick-and-place assembly techniques to install bare die onto a metal substrate that's part of the light fixture with the circuit connections applied through laminate or stencil technology, or even by inkjet printers down the road. Bisberg said, "You turn the fixture into the printed circuit board.
Troffer focus
The company is focused on using small low-to mid-power LEDs such as 0.25-mm chips with a focus squarely on the linear troffer market and the huge installed base of lighting that's in need of replacement in commercial and industrial settings. Already SSL vendors are targeting that application both with purpose-built fixtures and with LED-based T8 retrofit tubes – both offering greater efficiency but struggling to match the cost of fluorescent technology.
Bisberg claims the chip-in-fixture approach will offer lower cost than current approaches. He said that the DOE has estimated that the package in which an LED die is encapsulated is 40% of the cost of the packaged LED component. Moreover, he said the printed circuit board can be 20-30% of the cost of an LED fixture.
One challenge for Albeo will be adapting equipment that can handle bare die to work on the scale of a fixture in terms of size. The equipment used by LED makers to handle bare die is designed to place the die in small packages that max out at the chip-on-board size in the range of a 1-in diameter. The machines used to manufacture larger printed-circuit boards by fixture makers and subcontractors aren't designed to handle bare die.
Assembling bare die
Bisberg said that there are machines that can place bare die on a 1×1-ft substrate today. He said Albeo would likely start with smaller subassemblies, several of which would be integrated into a fixture. And Albeo will likely need a close partner from among the LED manufacturers to accomplish that goal.
The company faces a second challenge in that it intends to use blue LEDs without the phosphor layer applied. The patent covers both direct phosphor application and remote phosphor approaches, although the direct approach would be after the bare die are assembled to a substrate. Bisberg said that inkjet technology can be used to apply phosphor to individual LEDs spread over the scale of a 2x2-ft, or even 4x4-ft substrate.
The concept of working with bare die is likely frightful for anyone that has worked in the traditional semiconductor industry with large ICs that have many connections where packaging is extremely important. But Bisberg says that "LEDs are pretty simple devices with just two terminals." He said the company has built full-size troffers by hand in the lab using the patented techniques.
Bisberg summed up the company's plans saying, "It’s a true fixture play that strips out the cost associated with the traditional supply chain." It's certainly a novel idea, but one that has lots of potential roadblocks.
