SemiLEDs' recent announcement of the availability of its newest line of white LEDs in chip-scale and enhanced flip-chip packages caught my attention because I've seen several applications which could benefit from the space savings and potential cost savings they provide. And since I'm still in the process of getting to know the many players in the Asian sector of the LED industry, it also seemed like a good opportunity to learn a little about the company. 

If SemiLEDs' claims measure up, the new packaging option should give light-engine and luminaire manufacturers a more flexible and potentially more cost-effective alternative to the packaged die solutions they use today. The same advantages could also help make SemiLEDs one of the better alternative sources of LEDs for North American SSL equipment manufacturers who encounter difficulty dealing with "The Tirad" which dominates the region's market today.

After a first look at of SemiLEDs' new LEDs and the technology behind them, I found something to like about both – even if I ended up with a few more questions which will take some time to answer.

Here's what I've learned so far: 

SemiLEDs' ReadyMount white chip scale LEDs are produced using an enhanced chip-scale (EC) packaging technique which combines the company's Enhanced Flip chip (EF) structure and their ReadyWhite phosphor technology. The EC packaging is based on SemiLEDs' EF Series FlipChip, which moves the electrical contacts to the bottom of the chip. This allows manufacturers to assemble products using their existing SMT equipment. In addition, the rear contacts eliminate the emitting surface of wire bonds or top-side electrodes which would normally obstruct a portion of the LED's output (more about this shortly). 

The result is a white emitter that's been fully packaged as a 1.4 x 1.4mm x 0.4mm high SMD component which can produce up to 300 lumens at 1A. It can be surface mounted on any board level module or chip-on-board (COB) application, making it suitable for many general lighting applications including indoor and outdoor lighting, architectural lighting, and torches/flashlights. Depending on the thermal characteristics of what it's mounted to, the device is rated for input power of up to 3W. The EC package allows tight co-placement of multiple LEDs, making it easy to implement extremely high lumen density configurations. 

The EC packaging option is intended to provide an alternative to their bare die products which require wire bonding and passivation for improved flexibility, reliability and manufacturability. I suspect that the improved reliability is due in good part to eliminating the need for customers to do their own wire bonding, the manufacturing step with the greatest potential for introducing defects in any assembly process. It also avoids the possibility of a customer's machine introducing excessive mechanical stresses which could impair the performance of the unusual photon injection elements embedded within the equally unusual structure of these LEDs which include a copper alloy backing that provides mechanical support (and a great thermal junction) after they're separated from the sapphire substrate they're fabricated on. 

Fig.1- Although the SemiLEDs emitters in this photo don't have EC packaging, they are made using the same "Vertical LED on metal alloy" process which enables re-use of the sapphire substrates they are grown on. 

SemiLEDs claims EC-style LEDs reduce final component cost up to 50%, giving system-integrators and luminaire manufacturers a way to offer products which can compete in tough, commodity markets where lumens-per-dollar is an important differentiator. This is probably an arguable point, but only for manufacturers who are tooled up to take advantage of SMT technologies, and have the engineering chops to do their own thermal and electrical designs can take advantage of this. They also claim it can reduce capital costs, by which I'll guess they mean it can be integrated using standard tape and reel surface mount manufacturing, without the need for costly wire bonding equipment.

The other less obvious benefits of the chip scale package is that eliminating the wire bonds improves the optical characteristics of the light produced by tightly-packed EC LED arrays. Without the usual obstructions, the LEDs can be assembled into a uniform, nearly edge-to-edge emitting surface, eliminating the need for complex mixing lenses which are used to control ghosting and shadows in narrow beam applications. The LEDs also have an integral glass top surface which helps protect it against handling damage. SemiLEDs says that their EC-style LEDs typically demonstrate a 145 degree field of view with good color-over-angle characteristics.

SemiLEDs' EC series is available in standard ReadyWhite correlated color temperatures ranging from 2700K to 10,000K with color rendering indices up to 90 minimum. I was unable to find much information about the ReadyWhite phosphor in the short time available to prepare this review but, from what I did locate, it seems to be a proprietary coating process which produces a very uniform layer directly on the emitter surface. I need to learn more about the process as well as take a closer look at the product binning diagrams in their product brochure before I make any further comments. 

Fig.2: - SemiLEDs vertical LED on metal alloy" process allows the sapphire substrate to be removed and re-used. 

In the process of researching the ReadyWhite coating I also learned a bit about the unconventional "vertical LED on metal alloy" process SemiLEDs uses to fabricate many of its LEDs. The details they provided are vague about most of the details but it appears that the process does involve a traditional sapphire wafer but the GaN LED structures are deposited along with a copper alloy layer (Fig.2). The alloy appears to serve as both an electrical contact and a handy mechanical backing which supports the LED once it's removed from the original sapphire substrate. How the sapphire is removed is not explained but SemiLEDs says it allows them to be "recycled" to grow more batches of LEDs. The copper substrate's low thermal resistance should give the LEDs most or all of the thermal properties SemiLEDs claims, making thermal management much easier and help preserve the lifetime and quality of light in high-density applications (Fig.3). 

Fig.3: - A cross section of a SemiLEDs LED reveals several unique features.

This unusual process is one of the reasons that my first impression of SemiLEDs is that they are innovators rather than imitators. This is a marked difference from some of the manufacturers from that part of the world whose products are based at least partly on "borrowed" IP which, at least for the moment, locks them out of North America and some other markets. That's not to say SemiLEDs has not had its own brush with patent issues but it appears that the 2012 settlement of a patent infringement suit brought by Cree was more likely the result of parallel development than deliberate use of someone else's IP. This appears to be validated by SemiLEDs' continued presence in the North American market. 

Although I am still unsure SemiLEDs' EC package will deliver completely on the promised cost savings, I think many manufacturers will take advantage of the price, performance and design flexibility it offers. This may be especially true for manufacturers doing business in regions where patent enforcement has limited their choice in LED vendors to a handful of manufacturers until recently.