Wireless bonded LED technology, often referred to as “flip chip” or “delta chip”, offers several key performance benefits. Though the technology was first introduced to the industry about a decade ago, the widespread growth in popularity of high-power LEDs in recent years combined with the increasing adoption of LED technologies in high-performance applications have prompted design engineers to begin to look more closely at the unique benefits wireless bonded LEDs offer.
What is a wireless bonded LED?
The main difference between traditional and wireless bonded LEDs is the way they run current. Traditional LEDs use a wire bond to create an electrical pathway at the PN junction. Specifically the electrical bridge is extended from the positively charged top of the LED die to a negatively charged contact pad at the bottom of the die.
Wireless bonded LEDs use the same type of chip wafer as conventional LEDs. During packaging an extra step is added where the chips are formatted to have both P and N terminals placed on the bottom of the pad. The current is passed between the bottom pads creating a wider bonding surface than conventional wire bond LEDs. At the same time, the package profile of wireless bonded LEDs are about half the size of traditional LED packages.
These simple structural differences between traditional and wireless bonded LED technologies have a significant impact on performance in terms of heat dissipation, durability and light performance.
Benefits of wireless bonded LED technology
Wireless bonded LEDs are more robustly designed than traditional LEDs. Wireless bonded LEDs offer superior heat dissipation and are more adverse to shock and vibration. The most striking benefit of bonded LEDs is that they are shadowless, resulting in more uniform, even light performance.
Enhanced heat dissipation. Compared to traditional LEDs, wireless bonded LEDs can withstand higher temperatures without compromising performance. The first reason for this is that wireless bonded LEDs have a greater surface area for heat dissipation. Whereas a standard LED die measures 12 mm x 12 mm, a wireless bonded LED die is larger, often about 10 mm x 23 mm.
At the same time, wireless bonded LEDs are more efficient at removing heat. In traditional LEDs, heat can travel down the 1-mm wide wire bond. In wireless bonded LEDs heat is dissipated faster since the two contact pads are on the bottom and the chip is much closer to the PCB/heatsink.
Together, these two characteristics mean that heat has up to five times more surface space for dissipation in wireless bonded LEDs. Consequently, heat dissipation is up to 30 percent more efficient in wireless bonded LEDs than in traditional LEDs.
Enhanced durability. The enhanced shock and vibration resistance of wireless bonded LEDs compared to traditional LEDs stems from more durable design. Because the wire bond used in traditional LED is attached at two junctures – the ball bond and wedge bond – there is a greater opportunity for malfunction at these two sensitive points. It requires only seven grams of force to sever the wire bond and create performance failure.
With wireless bonded LEDs however, the LED is bonded with a silver epoxy and cured to the die. The die itself is then attached to PCB pads. This approach leads to much more durable performance as it requires 25 to 30 grams of force to sever the connection. This makes wireless bonded LEDs over three times more vibration and shock resistant than traditional LEDs.
Superior light performance. Finally, wireless bonded LEDs provide superior light performance when compared with traditional LED technology. Higher light output is achieved in a more compact space, and the light performance is unencumbered by shadows or other obstacles to consistent performance.
The larger die used in wireless bonded LEDs provides higher light output – up to eight to 10 percent brighter in intensity. At the same time, real estate savings are possible as high intensity light can be achieved using a single wireless bonded LED rather than a larger array of traditional LEDs.
For example, to achieve the same 9W level of brightness, it would be possible to use a single module wireless bonded LED with a footprint of 41.5 mm instead of an array of traditional LEDs with a footprint of over 65 mm.
In addition to providing greater brightness in reduced space, wireless bonded LEDs provide more consistent, evenly distributed light performance. Traditional LED chips emit light from the side of the LED. That light is then bounced through a reflector over the wire bond which generates a shadow and can cause unevenness with light distribution. With a wireless bonded LED, the chip can directly emit light from the top and the side with no wire bond casting shadows or creating uneven light distribution.
The future of wireless bonded LED technology
The applications that will benefit the most from wireless bonded LED technology are ones that specifically require superior heat dissipation, enhanced durability and superior light performance.
These applications include high-power or high-brightness applications such as general lighting, white goods, and automotive that require superior heat dissipation; performance-sensitive applications such as plastic sorting, security applications, precision medical applications and agricultural process that require enhanced durability and consistent performance; and visually sensitive applications such as grain sorting, industrial measurements and small space lighting that require bright, evenly distributed, shadowless light.
As LED technology, particularly high-power LED technology, continues to evolve and become more widely adopted, wireless bonded LED technology provides key benefits to design engineers challenged with providing greater brightness, superior heat dissipation and enhanced durability with increasingly smaller footprints.
Jonathan Domingo is a Product Development Engineer at Lumex, a leading provider of LED and LCD technology. During his seven years of field work in optoelectronics, he has helped design custom LED and LCD solutions for leading brands in industries ranging from appliances to aviation to consumer electronics.