In the field of LED packaging, COB stands for Chip on Board, an integrated surface light source technology that affixes LED chips directly to the substrate. LED light source using COB technology, the chip directly dissipates heat to the substrate, withstanding high thermal power density; chip dense arrangement, high optical power density; single luminous body size is small, ideal for commercial lighting field with strict requirements on light source size. Compared to a single chip package LED devices, COB package multiple chips, multiple solder joints, high power density also led to an exponential increase in the difficulty of the packaging process. It can be said that COB light source on the one hand is the leading commercial lighting applications, on the other hand, is also the crown jewel of the LED packaging field.
The main function of the light source is lighting, for LED to add a limit to the premise of lighting – energy saving, so the first stage of development of COB light source is also in pursuit of light efficiency, due to COB light source using metal-based circuit board or ceramic substrate reflectivity is not as good as silver-plated bracket, lower reflectivity superimposed on the mutual absorption of light between multiple chips Absorption, COB light source luminous efficiency is lower than SMD devices more than 30%, and later the introduction of mirror aluminum substrate to solve the reflectivity problem, but the mutual absorption of multiple chips still makes COB light source luminous efficiency is lower than discrete devices. With the chip outside the quantum efficiency and phosphor light conversion efficiency, COB light source luminous efficiency reached industry acceptance of the “sweet spot” – 100lm / W, the arrival of this sweet spot than discrete devices assembled light source 2-3 years later.
In different scenarios, changing the color temperature of the light source can bring better lighting experience. When there is no space limitation, it is easy to realize the color temperature change, as long as the high and low color temperature devices are mixed and driven separately, the color temperature change of COB light source is also the same idea, the chips in COB light source are divided into two groups and coated with different types and concentrations of mixed phosphor, so that the two groups of chips produce different color temperature white light. Change the current size of the two groups of chips, you can make the light source emit different color temperature of white light. small size of COB light source, after the light can not see two different color temperature of the light-emitting point, but a uniform light-emitting surface, which is the advantage of COB light source, but the small size, but also to the production of color mixing COB light source has caused a lot of confusion. After years of exploration, for different chip structures, people have invented and improved several technologies such as printing, spraying, and fluorescent chips to achieve a fixed domain and quantitative coating of different kinds of phosphors in COB light sources.
The types and ratios of two kinds of color temperature fluorescent glue in the color-tuning COB light source are optimized to achieve high apparent index and high luminous efficiency in the whole color change range. Figure 2 shows the spectral curves of high and low color temperature of a color-changing COB light source provided by LightSense Semiconductor. The phosphor of this light source is optimized so that the color rendering index can reach more than 95 at any color temperature during the color-changing process of 3000-6000K, and the R9 index, which is of great concern, is greater than 80.
Color temperature adjustment expands the application field of COB light source, but the color obtained in the color gamut diagram can only appear in the high and low color temperature color coordinates on the dotted line. In the field of commercial lighting, the use of different color coordinates of the lighting source, you can highlight the visual effect of different colors of goods to meet people’s aesthetic needs, from this point of view, only color temperature adjustment or not enough, in this case, with the ability to adjust the color gamut of COB light source was born.
Post time: Jun-03-2019