Ultraviolet radiation, sitting just below visible light on the electromagnetic spectrum, has been used in a range of different applications for many years. UV radiation is split into three main wavelengths:
- Long wave UVA (400 – 315nm): widely used in the printing industry to cure inks and resins
- Middle wave UVB (315 – 280nm): with applications in medical phototherapy
- Short wave UVC (280 – 200nm): disrupts the DNA of bacteria so has applications in disinfection and purification.
Traditionally UV light was generated using mercury vapour lamps. Whilst these generate the required wavelengths they are extremely inefficient and require a huge amount of power to operate successfully. They are also extremely fragile and contain toxic materials, many of which are being restricted over the coming years.
The development of LEDs capable of operating in the UV spectrum is transforming the market and opening up a host of new applications. Over the last few years long wave UVA LEDs have been rolled out in the printing industry where their longevity and efficiency has led to range of new printing applications.
Short wave (or deep) UVC LEDs are set to have a more profound impact. The ability of UVC to disrupt the DNA of bacteria make it incredibly effective for sterilisation and disinfection applications.
Traditionally UVC applications were restricted to large scale uses such as municipal water purification to cater for a city’s drinking water, or fixed sterilisation units for hospitals or the food industry. The advent of small, cheap and cost effective UVC LEDs opens the door to consumer applications, whether for sterilising babies milk bottles, portable water purifiers, or hand sterilisation stations in hospitals. The scope of potential applications is only just being realised. Industry analysts Yole Développement expect the market for UVC disinfection and purification to grow from $7 million in 2015 to $610 million in 2021.
This level of growth is dramatic. There is however one issue.
UV LEDs are not very good at converting power to light. UVA LEDs convert around 40% of power to light (their external quantum efficiency) whilst the shortest wavelength UVC LEDs barely manage 5%. The power that is not converted to light is converted to heat and needs to be removed as quickly as possible to keep the LED junction temperature within its safe operating temperature. Due to the construction of LEDs the heat cannot radiate out from the surface (as a traditional bulb would) and must be conducted out of the back of the LED, through the PCB and to a heat sink.
To facilitate this process UV LEDs are mounted onto a thermally conductive PCB, either a metal clad PCB (MCPCB) or a ceramic PCB. Whilst most visible light LEDs are mounted onto lower cost MCPCBs, UV LEDs (particularly shorter wavelength LEDs) have the unfortunate effect of degrading organic material. This presents a problem for MCPCBs as the dielectric layer that is used to create the electrical isolation is made from an organic epoxy. This leave ceramic PCBs as the only show in town.
Ceramics come in two varieties: low-cost and low-performance aluminium oxide (AL2O3) and high-cost high-performance aluminium nitride (AIN). This presents a tough call for UV LED module manufacturers, either compromise on thermal performance or pay over the odds. Ceramics have an additional problem – they are exceptionally brittle. This limits the size of tile that can be used to manufacture the circuits on adding further to the cost. It also limits the applications away from anything too rugged – limiting the scope of many portable UVC designs. The need for an alternative is pressing.
This is where Nanotherm DMS comes in.
Nanotherm DMS is a direct metallised single-sided PCB based on Cambridge Nanotherm’s extensively patented Electro-Chemical Oxidation (ECO) process that converts the surface of an aluminium board into a thin alumina dielectric layer. This Nanoceramic alumina has a thermal conductivity of 7.2 W/mK which, coupled with being just tens of microns thick and using a thin-film circuitisation process, gives a composite thermal performance of 152 W/mK. As a thin-film process is used the finished circuit is completely inorganic making it ideal for UV LED applications.
The mechanical robustness of the Nanotherm metal board makes it ideally suited for the new UV LED applications that are emerging, particularity for hand held consume applications, and provides UV LED module designers with a cost-effective alternative to ceramic PCBs.
There is now a material that combines the robust manufacturability and rugged characteristics of aluminium with the high performance and inorganic nature of ceramics. Nanotherm DMS is ideally suited to enable the next generation of UV LED applications.
To find out more about how we can help you with your UV LED application please get in touch with your local sales representative.