Modularization: A new trend in LED indoor lighting

As a new light source, LED is increasingly integrated into people's lives, and its development is inseparable from people's demand for lighting. When LED is used as a new light source to replace the previous generation of light sources, it must have more advantages that can be accepted by people than the previous generation of light sources, so that the chance of replacement will be greater.

Compared with traditional light sources (such as fluorescent lamps and incandescent lamps), LEDs are 5-20 times more efficient than traditional light sources when they are close to theoretical conversion efficiency. Even the current mass production efficiency is between 2-15 times, and combined with its directional advantage, the gap will be even greater. Due to the change in the principle of light emission, its life span will also be much longer than that of traditional light sources. In addition, since LEDs also have a series of advantages such as no harm to health and the environment, they have been recognized as the most suitable light source for the next generation at this stage.

Why do we need LED modular packaging?

At present, LED is used as a lighting product. The most direct and simple application is to replace it (including the replacement of bulbs and fluorescent tubes). This is relatively easier to accept. In addition to energy saving, there is no obvious change in the appearance and effect of the product. Of course, as lighting products become more and more personalized, lamps and lamps themselves have gradually evolved into indicators of light quality. However, while LED has many advantages, it also has some factors that are not easily accepted by people, such as glare and cost. For the lamp structure that everyone is more accustomed to, since LED is essentially different from traditional light sources (such as directivity), if it is used with traditional lamp structures now, its own characteristics will be submerged in the simple replacement of existing lamps.

Let's take a simple example: Currently, there are LED downlights and LED bulbs on the market. A light source needs to be placed in a downlight, and for traditional lighting, a bulb is already a light source. If it corresponds to today's LED, the bulb is already a lamp structure. The question we need to think about is: when an LED bulb is installed in a traditional lamp tube, can the light source installed in the LED bulb be directly installed in the downlight structure? The answer is yes. Moreover, its cost effect will be better than the direct installation method of the LED bulb. But the problem with this type of application is that when a non-standard light source structure appears in front of consumers, consumers may not be able to make a simple replacement, etc. In view of this situation, a question currently facing light source manufacturers is: What is a standard light source structure?

Our answer to this question is: the packaging companies should modularize and standardize the light source. Only when the LED light source is modularized and standardized, and this work is completed by the current packaging companies, can the cost be optimized in the entire replacement process. The following will briefly describe the outstanding advantages of modular LED in the light source replacement process from several aspects.

Advantages of light sources in terms of reliability

As one of the top three factors affecting the reliability of LED packaging (heat, static electricity, and moisture), heat is an important cause of LED degradation. According to the Arrhenius model applicable to LED chips, the life of the LED itself will be reduced by half for every 10°C increase in the junction temperature of the LED.

Of course, for LED packaging, factors related to lifespan also include material properties. For example, the decrease in light transmittance of packaging glue and the decrease in reflectivity of various optical materials will cause light attenuation of the entire device. The biggest influence here is still thermal influence.

In combination with LED packaging, an important solution to temperature rise is to reduce the thermal resistance between materials and the thermal resistance of the interface. The modular packaging form can reduce the bonding layer and reduce the overall thermal resistance in structure. Its structure is shown in Figure 1.

Comparing Figure 1 (a) and Figure 1 (b), it can be seen that when LED module light sources are used to assemble fluorescent tubes, the thermal resistance is composed of only three parts: the thermal resistance of the chip itself, the thermal resistance of the die-bonding material, and the thermal resistance of the tube heat dissipation system; while when SMD products are used to assemble the tube, the thermal resistance increases to six parts: the thermal resistance of the chip itself, the thermal resistance of the die-bonding material, the thermal resistance of the lead frame, the thermal resistance of the welding material, the thermal resistance of the heat-conducting substrate, and the thermal resistance of the tube heat dissipation system. It can be seen that the use of LED module light sources can greatly reduce the overall thermal resistance of the series.

Figure 1: Comparison of thermal resistance of optical tubes.

As for the influence of moisture, the design change of LED module structure causes the assembly process to change accordingly. In this way, it will no longer be necessary to use the high temperature process of reflow soldering, thereby reducing the potential damage to the packaging material caused by the high temperature during the reflow soldering process. At the same time, the types of materials used will also be reduced, which can reduce the water vapor penetration between the interfaces of different materials, thereby reducing its potential failure rate. Therefore, the LED module light source can extend the life of the entire system.

Module products can also reduce their hidden dangers of static electricity through anti-static design on the overall circuit.

Advantages in optoelectronic parameters

Most general component light source products use LED blue light chips to excite different phosphors to obtain a more saturated spectrum, thereby improving the color rendering index of the light source. However, at the current stage, since the excitation efficiency of ordinary red light for blue light is very low, and there is mutual absorption between phosphors, the light efficiency of the light source will be reduced to a very low level while improving the color rendering index. For module light sources, implanting color light chips (such as red light, green light, etc.) in the module can make the spectrum of the entire light source saturated, thereby achieving a higher color rendering index; on the other hand, by using chips and phosphors in combination, the best excitation efficiency between the chip and the phosphor can be achieved, and the light efficiency of the light source can be maximized (Figure 2). Then, by using other chips in the module light source and mixing with white light with the best excitation efficiency, a pure light color above the black body line will be obtained. Because the light efficiency of the color light chip itself is much higher than the light efficiency of the phosphor when it is excited, the color rendering of the light source can be improved while eliminating the mutual absorption of phosphors. As a result, the light efficiency and color rendering of the light source can be improved at the same time.

Figure 2: Analysis of the module light source spectrum composition.

Cost advantages

At present, the entire LED industry is continuously working to reduce costs. At present, most application manufacturers use SMD LEDs to assemble various lighting structures. As mentioned above, SMD LEDs will use more materials and processes than module light sources, which are important factors in cost considerations. In module light sources, since many SMD LED materials (such as aluminum substrates, welding materials) and process costs are reduced, the application cost of LEDs can be greatly reduced.

The modular light source is designed according to standard lamp products, and the standard modular light source is produced, which can greatly facilitate the back-end application manufacturers. Since the modular light source already has the array structure and circuit arrangement required for optics, it can directly save some key materials and equipment for terminal lighting manufacturers at the back end, such as PCB, aluminum substrate and patch welding materials (such as solder paste). Due to the modularization of the light source, patch equipment will also become a non-mainstream production equipment in the future LED lighting era (Figure 3).

Figure 3: Comparison of LED production methods.

Furthermore, the low thermal resistance of the module light source system will provide a basic structural guarantee for the high current operation of the chip. During the assembly process of SMD lamps, the overall thermal resistance will be several tens of degrees higher than that of module products, which can increase the operating current provided to the module light source by 20% or even 30%, which is also one of the most critical factors for cost reduction (Figure 4).

Figure 4: Cost versus operating current.

assembly

Traditional light sources are purchased directly by consumers, and LED module light sources may also be directly exposed to consumers one day, which puts forward many higher requirements for module products. Ultimately, both SMD products and module light source products can be used to assemble light sources directly used by consumers, but on the substrate with the best cost, the module light source will have a higher performance-price ratio (Figure 5).

Figure 5: Simple assembly of module products.

Conclusion

The numerous advantages of module light sources have made them more and more popular. However, the structure of module light sources is relatively fixed, and it is a highly targeted light source structure. This feature will limit its application in certain occasions. From the perspective of people's requirements for lighting, LED module light sources have absolute advantages over SMD LEDs in terms of cost performance, reliability and assembly. Therefore, LED module light sources will shine more in future general lighting applications.