John Cafferkey of Cambridge Nanotherm, a British firm, said there had been a previous saying that "The heat produced is more than light", and now this sentence sums up the "heat challenge" of the growing market for UVC LEDs. Currently, UvC LEDs are mainly used for disinfection of medical devices, water and other daily consumables.
UVC technology originated in early 20th century, when mercury lamps were first produced for mass production.
The ultraviolet light emitting lamp was used for drinking water disinfection in 1910. However, the prototype factory was shut down because it proved to be unreliable.
In the 1950s, the new UVC water treatment system was tested, and by the mid 1980s there were about 1500 factories in Europe.
In addition to water treatment, UVC is used in a range of applications, including clean medical equipment and hospital rooms, to disinfect air-conditioning systems to prevent the spread of pathogens.
Although mercury vapor lamps are very effective in these large applications, light bulbs are fragile and the use of dangerous mercury means they are not suitable for more portable and environmentally friendly applications.
In recent years, led manufacturers have developed more and more effective UVC LEDs. Although not as effective as UVA LEDs (for curing inks and paints), they can be used for low-power applications.
As a result, industry analysts believe the UVC led will grow rapidly in the next few years. This prosperity is based on the UVC led for portable, consumer-friendly UVC applications created the market. For example, consumers will buy portable disinfection "wands" that can be used to sterilize daily necessities such as smartphones, tablets or keyboards.
Consumer-goods manufacturers can embed led UVC technology into their products to sterilize themselves. For example, after the toothbrush has been used to put back on the shelf, can be disinfected automatically, can press the button, the baby bottle can be automatically sterilized; when used, the faucet can sterilize the water. These possibilities are endless.
The potential to save lives
However, some of the more in-depth applications of UVC are of concern. Portable sterilization bottles can improve the way in which developing countries provide clean water to their citizens, and when they need to be consumed, water can be disinfected. This is particularly valuable in some areas, such as areas where there is no centralized water disinfection infrastructure, or where safe water can be quickly provided.
In addition to new applications, even hospitals (UVC have been used for years in hospitals) can benefit. Globally, more than 700,000 patients are infected in hospital each year and 75000 are killed. UVC technology can be embedded in medical devices, such as stethoscope and scalpel, and can be disinfected in a matter of seconds.
UVC LEDs have the potential to bring UVC disinfection capabilities into the mass market and may have a significant impact on public health.
The technology is still in its infancy, and one of the challenges is the thermal management of UVC LEDs. Like any electronic component, LEDs are sensitive to heat.
UVC LEDs have exceptionally low external quantum efficiencies (EQE)-they convert only about 5% of the power input into light. The remaining 95% of the power is converted to heat, and the heat must be quickly removed to keep the LED chip below its maximum operating temperature. If the LED chip is not cooled in time, it will eventually shorten its service life, or even use it.
As UVC LEDs become stronger, manufacturers need to consider new ways to meet this challenge. Now, the problem is still how to deal with the high demand of UV led, while ensuring that components remain cost-effective, durable and capable of UV light source itself wear.
Because the UV LED is too small, a lot of heat can not spread from its surface, so the only way to effectively let the heat discharge is through the back of the LED. Heat must be derived from the LED chip, through the module PCB, to reach the heatsink, and then released into the atmosphere.
Heat is also the problem of PCB
The installation of LED PCB must have high thermal conductivity, for visible light LED is usually a metal base printed circuit board (MCPCB). However, these do not apply to UVC applications. The MCPCB is made of a piece of metal (usually aluminum or copper), with a layer of dielectric layer attached to it, consisting of electrically conductive but electrically insulated epoxy resins.
MCPCB based on epoxy dielectric can be used in visible light applications, but UV (especially UVC) degrades organic matter, such as epoxy resins, and thus significantly reduces the MCPCB life of UV applications. The only viable alternative is the use of electronic grade ceramics.
Aluminum Nitride (AIN) has excellent thermal conductivity (140W/MK-170W/MK), but is expensive. Alumina ($literal) is a more cost-effective alternative, but does not provide the thermal conductivity required by UV LEDs (20W/MK-30W/MK). At the same time, both are fragile and easily damaged, which means they are not easy to install with screws and are not suitable for more powerful applications.
The alternative solution is nano-ceramic with sputtering circuit layer. This provides thermal conductivity above/and is within the desired heat range.
The British Cambridge Nanotherm uses a patented electrochemical oxidation (ECO) process that converts the surface of the aluminum sheet into dozens of micron thin alumina ($literal) ceramics.
The alumina ($literal) ceramic layer acts as an electrical medium between the above circuit and the aluminum below. Because the alumina ceramic layer produced by eco process is very thin, heat can be easily passed, so that it has good thermal conductivity.
The film processing or sputtering step follows the ECO process, and the copper circuit layer is attached directly to the nanometer ceramic dielectric to further improve the thermal efficiency. Because no organic epoxy is used at any stage, ultraviolet radiation has nothing to degrade.
This method can produce MCPCB with the thermal properties of AlN (AlN), but there are no problems related to production or brittleness.
The UVC disinfection technology implemented by LEDs can bring real transformative effects, but manufacturers and designers need to be sure to overcome the thermal challenges of UV LEDs.
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