By BizLED Bureau
Feb 1, 2017: With fast development of LED technology, the need for energy-efficient lighting solutions is increasing significantly across the globe. As a result, LED lighting manufacturers are looking for ways to adapt faster product development processes.
The need for cost-effective and energy-efficient LED lighting is placing an emphasis on using COB LEDs that offer ideal cost-effective lighting solutions, which will also accelerate LED adoption across the world.
Evolvement of COB
Till 2005, manufacturers were making several efforts to increase light output of LED lighting products, for example, they started placing multiple die in a package to increase light output and placed phosphor dots on each die to tune color. But in 2005, COB was developed, which is a new type of LED package that placed the die directly on a PCB substrate, which removed the secondary LED package. Now there was no need to place individual phosphor dots on each die as the COBs are incorporated with a yellow-orange phosphor slurry that covers all the die and is at the center of a white substrate.
COB LEDs have several advantages including larger cooling area, thermal resistance, high light efficacy and better lighting effect. With COB, several LEDs can be mounted directly on the printed circuit board (PCB) using wire bonds instead of pins that are used in surface mounting process.
COB also reduces lighting are space significantly. This technology also reduced costs as several LEDs make a single part, and hence, faster time to market, with desirable heat distribution. COB packaging and traditional SMD packaging have almost the same production process, and the same efficiency on die bond and bonding wire. However, COB packaging has higher efficiency than SMD packaging on separation, dispensing, packaging and spectral.
SMT and reflow soldering are not required in application side of COB light source, which significantly reduces the production time and cost and lowers cost of manufacturing equipment. According to industry experts, ?COB technology can reduce light source cost by 19-32% if compared with traditional SMD, reducing the cost of LED products greatly.?
Challenges posed by COBs
However, working with COB isn?t that easy?manufacturers face several challenges while implementing the thermal, electrical and optical interfaces with the LEDs.
With major brands developing products with large areas of light source, COBs were clearly positioned as broad angle emitters, but their large source size became a challenge to effectively focus into a small beam angle. As a result, COBs are generally used in high bay lights and street lights as they require large amount of light to be spread over a large area. However, by using optics like reflectors, COB LEDs can be used in downlights and retrofit lamps as well.
Manufacturers of fixtures also faced the challenge to provide power to these devices and then connect them to the heat sinks inside the lighting fixture. Traditionally it is done by hand-soldering the wires to the pads on the substrate and then fixed the assemblies with screws to the heat sink. But this process is quite time consuming.
However, connector manufacturers offered a solution to this challenge?they manufactured custom sockets. But as the number of COB products started increasing in the market, connector makers realized that one single socket for all COBs will be needed.
Today, COBs are based on ceramic substrates instead of the aluminum substrates that was found in traditional COBs. The physical features of these two substrates differ, and hence, they require special handling as they have different material properties.
Ceramic-based COBs need special attention as they cannot be simply screwed to a heat sink like aluminum-based substrates. Ceramic substrates are brittle and, therefore, need a secondary attachment that can be connected to the heat sink.
The different thickness of COBs also poses challenge to designers. The COB substrates come in different thickness. While the thinner ceramic packages can crack easily, the aluminum substrates are more durable. Obviously, with the thinner ceramic substrates, designing becomes flexible. But, by using a combination of optional thermal springs and housing ledges, different types of COBs can be accommodated.
Another challenge posed by COB technology is the space reduction between the LEDs and small light emitting surface present high heat fluxes that needs to be addressed efficiently. The natural cooling is actually hindered with the small area provided by COB technology. Therefore, COBs create a tough cooling challenge for the designers in terms of watts per square centimeter. But there are many cooling options for the designers to choose from?they can go for passive cooling strategies that spread heat over a large surface area without adding more power to the design, or they can go for active cooling strategies, which involves fans or synthetic jet technology.