The continuous warming of UVCLED makes the market hot. Everyone knows that UVCLED has a significant sterilization and disinfection effect. It only takes a few seconds to tens of seconds to kill common bacteria under a certain dose and distance. But what everyone doesn't know is that with the hot market, various UVCLED application products on the market have emerged, many of which are shoddy. Often the same level of UVCLED products, the actual use effects are very different.
In the final analysis, it is the difference in technology and craftsmanship.
In the first phase of UVCLED packaging technology science, let us start with the keyword thermal management and look at the secrets behind UVCLED packaging technology.
Thermal management, the key to improving the life of UVCLED
Like any electronic components, UVCLEDs are sensitive to heat.
The external quantum efficiency (EQE) of UVCLEDs is low. Of the input power, only about 1-3% is converted into light, and 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, it will directly affect the service life of the chip, or even it cannot be used. It can be said that thermal management is the key to improving the service life of UVCLEDs.
To do a good job of thermal management, the key is to reduce the welding void rate
Due to the small size of UVCLEDs, 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, how to do a good job of thermal management in the package joint is particularly important.
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, UVCLEDs currently on the market are basically based on flip-chip solutions with high thermal conductivity aluminum nitride substrates. Aluminum nitride (AIN) has excellent thermal conductivity (140W/mK-170W/mK), can withstand the aging of the ultraviolet light source itself, and meet the needs of UVCLED high thermal management.
In terms of process, there are currently several die bonding methods on the market. The first is to use silver paste. Although this method has good binding force, it is easy to cause silver migration and cause device failure. The second is to use solder paste soldering. In this method, since the melting point of the solder paste is only about 220 degrees, after the device is mounted, the re-melting phenomenon will occur after the device is mounted again, and the chip is easy to fall off and fail, which affects the reliability of the UVCLED. Therefore, the third type of die bonding method is mostly adopted on the market: using Au-Sn eutectic soldering. Compared with the first two die bonding methods, it mainly uses flux to perform eutectic soldering, which can effectively improve the bonding strength between the chip and the substrate, and the thermal conductivity is more reliable, which is conducive to the quality control of UVCLED.
Since most of the UVCLED packaging materials and die bonding processes on the market are the same, why is the effect of thermal management so different?
Here, we have to mention the welding void rate.
In simple terms, the soldering void rate refers to the welding process of the LED chip and the substrate. Due to the influence of the process, some areas cannot be soldered, and the formed defects appear as hollow in the shape, which is an important indicator that affects heat dissipation.
In order to show the influence of welding void rate on thermal management more intuitively, we took NationStar UVCLED and UVCLED from partner companies as experimental reference samples to conduct void rate detection, thermal resistance comparison experiment, and product life experiment. Both samples use the same imported LED chips and Au-Sn eutectic welding process.
