With the small-footprint XB-D LED, Cree intends to lower the cost, in terms of lumens per dollar, for SSL lamp and luminaire designs.
Cree has announced the new XLamp XB-D LED family that features components measuring 2.45x2.45 mm, that the company says will deliver double the lumens per dollar achievable at the system level. The small footprint will be especially suited to solid-state lighting (SSL) retrofit lamps, although Cree has said that the LEDs built with a new die structure will serve across a broad application base.
At 350-mA drive current and 85°C operating temperature, the new LED platform delivers 139 lm in 6000K-CCT, cool-white models, and 107 lm in 3000K-CCT, warm-white models. The efficacy is 136 and 105 lm/W respectively.
Hot binning across CCT range
There are several other notable features of the new family according to product marketing manager Paul Scheidt. He said that the XB-D is the first LED family to be hot-binned across all CCTs. Scheidt said, "Competitors only hot bin in the warm-white CCTs."
The new platform includes several elements that Cree says will help reduce system cost. Obviously the smaller die has a direct impact on component cost because Cree can manufacture more components per wafer. Cree did not directly address component cost. But the company did show a table that indicates the XB-D delivers more lumens and better efficacy than competing components that measure 3.5x3.5 mm and larger.
In part the performance comes from a new die architecture and packaging scheme, along with what Cree says are inherent advantages in its manufacturing process, a claim we will discuss a bit later. A photo of an XB-D LED with no phosphor applied revealed a beveled structure around the die designed to maximize light extraction.
Flexible lamp design
The smaller component footprint also provides designers of retrofit lamps far more flexibility in lamp design and the ability to include more LEDs in smaller spaces. For example, Scheidt showed an example of a standard A Lamp where the LEDs can be placed deeper in the neck of the lamp rather than at the equator of the globe, thereby providing better light distribution.
Cree believes the XB-D can increase the penetration of LED lamps in price-sensitive markets such as the residential space. Scheidt cited a Home Depot study in which the same lamps were sold for $20 in some select stores and for $10 in other select stores. According to Scheidt, the stores with the lower-priced lamps realized 6 to 10 times the sales volume.
About SSL lamps, Scheidt said, "The product itself is there in terms of technology. People accept it." He was speaking of aspects such as color and light quality while noting that cost remains the obstacle. But addressing current price levels, he added, "We're at least in the right order of magnitude." And presumably XB-D will help relieve another significant reduction.
Cree also took the occasion of the XB-D launch to emphasize what it belies is a competitive advantage of its gallium-nitride (GaN) on silicon-carbide (SiC) manufacturing process. Cree's Scheidt said that the SiC substrate offers numerous advantages over the sapphire substrates widely used by competitors.
Like many manufacturers of lighting-class LEDs, Cree uses a flip-chip approach in which the substrate side of the die is on the top side of the packaged LED. Scheidt said SiC offers a refractive index that better matches the GaN layers than does sapphire, thereby improving light extraction.
Scheidt further said that SiC offers a better match in terms of coefficient of thermal expansion resulting in fewer cracks. And that SiC results in smaller lattice-structure mismatches between the GaN and SiC layers thereby yielding more efficient LEDs.