Detailed methods for creating LED high-efficiency COB packaging products

March 17, 2020

With the continuous innovation of LED packaging technology and the implementation of energy saving and emission reduction policies at home and abroad, the proportion of LED light source applications in the field of lighting is increasing, and new packaging forms are constantly being introduced. Yuan Lei senior engineer Ouyang Minghua said: "LED performance in heat dissipation, light efficiency, reliability, cost performance is still a concern, if these are not broken, or new products in the future can achieve breakthroughs, then lighting The choice of the field may not be LED.” COB is the LED packaging product introduced by the industry in this context. Compared with the traditional discrete LED packaging products, it has better primary heat dissipation capability and high-density luminous flux output. In addition to explaining some of the characteristics of COB, this paper focuses on how to improve the light efficiency of COB from the basic principles and seek ways to meet the core value points of lighting.
COB has good heat dissipation capacity
When designing the LED package structure, the junction temperature of the chip should be reduced as much as possible. The COB packaged chip has the shortest heat dissipation path, and can directly transfer the heat of the working chip to the metal substrate and then to the heat sink. Therefore, the COB has better heat dissipation capability than the conventional discrete component assembly. The material of the current COB metal substrate is copper, aluminum, aluminum oxide, aluminum nitride, etc. In terms of overall cost, heat dissipation capability, corrosion resistance, etc., aluminum is mainly used as a metal substrate to produce COB. The following figure shows Yuanlei COB products. Structure diagram.
COB enables high-density luminous flux output
When using LEDs in a modular design, we usually give a small amount of space to the light source. At the same time, we hope to have a high enough brightness output in a small size. However, this solution can hardly be found on discrete component LEDs. Of course, some possibilities are possible. 3535 ceramics or other products with relatively small light fluxes are selected, but they are not comparable to the high-density luminous flux output of COB or MCOB. So the advantages of COB in product modularization are reflected: it helps the modular design and maintains a high luminous flux.
The drive design of the COB is very flexible, and the application side can select COB in combination with existing driving conditions to meet various solutions from low pressure to high pressure.
Disadvantages of COB packaging
Although COB has many advantages, it is still not mainstream in the current lighting market. While we are optimistic about COB, we should see the shortcomings behind it in order to find the reasons for its application. First, the light efficiency of COB is still low. Since COB is a flat-emitting light, it cannot be used as a discrete LED, and PPA will output the side light of the chip, resulting in partial light loss. Secondly, COB does not currently have a standardized shape. Most domestic manufacturers manufacture COBs according to their respective partners, matching the corresponding lamps and driving methods. Each shape is not uniform, which limits the large-scale use of COB.
Method for improving COB light efficiency
Based on the problem of low COB light efficiency, the author believes that the solution should be considered from the principle of the substrate. LED package light efficiency improvement We usually talk about external quantum efficiency, that is, how to improve the luminous flux of packaged products or the entire module in the same situation of the chip. First, the high reflectivity of the substrate material, the reflectivity of the chip placement area directly affects the entire luminous flux output, whether it is a copper substrate, an aluminum substrate , or a ceramic substrate, this rule must be followed. Moreover, it must be noted that when assembling the COB, the area outside the light-emitting surface of the substrate should also be considered. If no reflector is added to the light-emitting surface, a reflective material should be added to the area other than the light-emitting surface. Secondly, large particles, high-intensity phosphors, and high-transmittance encapsulated silica gel are the same as conventional discrete LED light-efficiency enhancement methods. Again, the arrangement spacing and driving method of the chip during the solid crystal should be reasonable. Under the same power, the driving current is small as much as possible to avoid excessive heat remaining inside the substrate. In addition, when the size of the light-emitting surface is small, the lens shape of the silica gel on the surface of the phosphor can not only increase the angle but also further improve the light efficiency.
to sum up
Our understanding of LEDs should return to ordinary electronic components, just like capacitor resistors, except that LEDs function as illuminators, and other components function as separate electronic components, as long as the entire system is sent out. The light output meets the market's value requirements, and it is not a bad idea to choose COB.

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