“In order to make the achievements of UVC LED technology better benefit human beings, as a pioneer in the UVC LED deep ultraviolet sterilization industry, Nationstar Optoelectronics starts from the packaging end, and specially launches a series of popular science articles on UVC LED packaging technology, directly hitting the technical threshold, sharing solutions, and hoping to give the industry Colleagues have more ideas and references to jointly promote the orderly and healthy development of the industry, and provide more technical realization ways for human healthy life.
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write in front
In order to make the achievements of UVC LED technology better benefit human beings, as a pioneer in the UVC LED deep ultraviolet sterilization industry, Nationstar Optoelectronics starts from the packaging end, and specially launches a series of popular science articles on UVC LED packaging technology, directly hitting the technical threshold, sharing solutions, and hoping to give the industry Colleagues have more ideas and references to jointly promote the orderly and healthy development of the industry, and provide more technical realization ways for human healthy life.
The continuous heating up of UVC LEDs has made the market hot. We all know that UVC LED has a significant sterilization and disinfection effect. Under a certain dose and distance, it only takes a few seconds to tens of seconds to kill common bacteria. But what everyone does not know is that with the hot market, various UVC LED application products have emerged on the market, many of which are shoddy, often the same level of UVC LED products, but the actual use effect is vastly different.
In the final analysis, it is the difference between technology and craftsmanship.
The first issue of UVC LED packaging technology popular science, let us start from the key word thermal management and look at the secrets behind UVC LED packaging technology.
Thermal management, the key to improving UVC LED life
Like any Electronic component, UVC LEDs are sensitive to heat.
The external quantum efficiency (EQE) of UVC LEDs is low. Only about 1-3% of the input power is converted into light, while the remaining 97% is basically converted into heat. At this time, if the heat is not quickly removed and the LED chip is kept below its maximum operating temperature, the service life of the chip will be directly affected, or even unusable. It can be said that thermal management is the key to improving the service life of UVC LEDs.
Good thermal management, focusing on reducing solder voids
Due to the small size of UVC LEDs, most of the heat cannot be dissipated from the surface, so the back of the LED becomes the only way to effectively dissipate heat. At this time, it is particularly important to do a good job of thermal management in the packaging joints.
When it comes to thermal management in the packaging process, two aspects are inseparable, one is the material, and the other is the process.
In terms of materials, after years of development, the current UVC LEDs on the market are basically based on flip-chip and high thermal conductivity aluminum nitride substrates. Aluminum nitride (AIN) has excellent thermal conductivity (140W/mK-170W/mK), can resist the aging of the UV light source itself, and meet the needs of UVC LED high thermal management.
In terms of technology, there are several solid crystal methods currently on the market. The first is to use silver paste. Although this method has good bonding force, it is easy to cause silver migration and lead to device failure. The second is to use solder paste soldering. In this way, since the melting point of the solder paste is only about 220 degrees, after the device is placed, there will be a remelting phenomenon after passing the furnace again, and the chip is easy to fall off and fail, which affects the reliability of UVC LEDs. Therefore, most of the market uses the third method of solidification: gold-tin eutectic welding. Compared with the first two bonding methods, eutectic welding is mainly performed by flux, which can effectively improve the bonding strength and thermal conductivity of the chip and the substrate, and is more reliable, which is beneficial to the quality control of UVC LEDs.
Since most of the UVC LED packaging materials and die-bonding processes on the market are the same, why is the thermal management effect so different?
Here, we have to mention the solder void rate.
Soldering void rate simply means that during the welding process of the LED chip and the substrate, due to the influence of the process, some areas cannot be welded, and the formed defects appear as hollow in the shape, which is an important indicator that affects heat dissipation.
In order to more intuitively show the impact of solder void rate on thermal management, we took Nationstar UVC LED and friend UVC LED as experimental control samples to conduct void rate detection, thermal resistance comparison experiment, and product life experiment. Both samples use the same imported LED chips and gold-tin eutectic soldering process.
Legend: The blue-green point in the picture is the product welding void.
After testing and calculation, under the same size LED chip, the void rate of Nationstar UVC LED packaging devices is only 9%, and the void rate of UVC LED packaging devices of friends is 18%.
In the thermal resistance experiment, due to the low void rate of the Nationstar UVC LED, the thermal resistance is also lower than that of the products of friends.
From 0 to 480 hours, the effect of void rate on the optical power maintenance rate did not change much; but after 480 hours, the optical power maintenance rate of the National Star UVC LED (void rate 9%) was comparable to that of the friend UVC LED ( Compared with the void rate of 18%), the gap is more obvious. After 4000 hours, the maintenance rate of the UVC LED light power of Friendship is only about 60%, while the maintenance rate of Nationstar UVC LED light power is lower, and it remains at about 80% after 4000 hours.
Through the above three experiments, we concluded that the lower the solder void rate, the better the heat dissipation effect, the longer the product life, and the better the quality.
It is worth noting that, in reducing the void rate of UVC LED products, Nationstar has formed a relatively advanced and perfect process technology. At present, the overall void area of Nationstar UVC LED products is less than 10%, and the largest single void area is less than 2%. Compared with similar products in the market, the void rate is 15%-30%, which is at the leading level in the industry and has excellent heat dissipation effect. , long product life and excellent product quality control.
Reducing the solder porosity is a key step to improve product thermal management and improve the life of UVC LEDs.
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