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Advances in wireless bonding LED technology

Posted: 24 Oct 2012 ?? ?Print Version ?Bookmark and Share

Keywords:Wireless bonded LED? flip chip? delta chip?

Wireless bonded LED technology, often referred to as "flip chip" or "delta chip", provides 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.

Figure 1: LED with traditional bonding.

Figure 2: LED with wireless bonding: Wireless bonded LEDs provide enhanced heat dissipation, greater durability and superior light performance compared to traditional LEDs.

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.

What are its benefits?
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 12mil by 12mil, a wireless bonded LED die is larger, often about 10mil by 23mil.

At the same time, wireless bonded LEDs are more efficient at removing heat. In traditional LEDs, heat can travel down the 1mil 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% 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 7g of force to sever the wire bond and create performance failure.

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