Packaging structure, process development status and trend

- Nov 22, 2018-

1.LED packaging is a technology that involves multiple disciplines such as optics, thermals, mechanics, electronics, mechanics, materials, semiconductors, and more. 

In some ways, LED packaging is not only a manufacturing technology, but also a basic science. Excellent packaging engineers need a deep understanding of the physical properties of thermals, optics, materials and process mechanics. . Recently, chip-level package CSP has attracted everyone's attention, so now and future LED packaging technology, it is necessary to carry out the LED package design and chip design at the same time, and need to consider the performance of light, heat, electricity and structure. In the packaging process, although the choice of materials (heat sink, phosphor, potting) is very important, the package structure (such as thermal interface, optical interface) has a great influence on LED light efficiency and reliability. High-power white LED package New materials, new processes, new ideas must be adopted. Small pitch or Mini LED packaging techniques require a deeper understanding of flip chip and reflow or eutectic flip-chip packaging processes. For LED technology practitioners, in addition to cost efficiency and reliability, it is necessary to integrate light source, heat dissipation, power supply and lighting. This article discusses the current status and future of LED packaging technology, and then analyzes the future LED packaging technology and product trends.

2. LED technology development trend

The choice of LED packaging methods, materials, structures, and processes is primarily determined by factors such as chip structure, optoelectronic/mechanical characteristics, specific applications, and cost. After more than 40 years of development, LED packaging has experienced the development stages of stent (LampLED), SMD (SMD LED), power LED (Power LED) and COB.

LED development

To date, where will it go? SMD? EMC? COB? Or CSP? What is flip-chip bonding and no packaging? In the end, LED packaging will go in that direction, and there are still many different opinions. However, from the historical trend, as shown in Figure 3, the packaging materials are getting less and less, the thermal conductivity of the materials is getting better and better, the power density is getting bigger and bigger, and the packaging process steps are becoming more streamlined and the devices are less and less. Trends, of course, this can't leave the advancement of chip technology.

LED development process

The technical blueprint of China LED of the Semiconductor Lighting Center of the Ministry of Science and Technology, from 2004 to the present, China has been moving towards this blueprint. It is expected that the target of 300 lumens will be reached in the next 2022, and the cost of a single lamp will be less than 10 yuan. This is a very big challenge for packaging technology, technological advancement, cost reduction, and Heiz's law will continue to dominate the LED direction in the future, especially the LED lighting industry. In the past decade, the increase in the efficiency of LED chips will reduce the area of chips, which in turn will drive the LED packaging revolution.

Future chip technology will focus on improving efficiency and reducing cost. Fluorescent powder technology will improve efficiency and color rendering index, and LED chip efficiency will be based on stage growth, from 10lm/w to 80lm/ w, 80lm/w~100lm/w, 100lm/w~150lm/w, 150lm/w~200lm/w... When the technology advances to 300lm/w, the efficiency of the existing chip is improved by 1.5~2 times, the chip The calorific value will be greatly reduced (compared to the same volume and the same area), which will lead to the current competition of various packaging technologies, all the technical route trends will be more differentiated and diverse, and what packaging technology will be more fixed. LED will usher in the mainstream, diversified, but not far from the mainstream.

3.LED packaging technology that is changing and will change in the future

As the power density of chips continues to increase, especially the development of semiconductor lighting technology, new and higher requirements are placed on the optical, thermal, electrical and mechanical structures of LED packages.

The development of high-efficiency technology can foresee that existing packaging processes and packaging materials are not suitable for future packaging requirements. As the quantum efficiency of the chip increases, the amount of heat generated is reduced, and the effective current density of the active layer of the chip is greatly increased. The overall heat generation of the chip is reduced, so the heat dissipation area requirement for the package form is also reduced. The heavy heat dissipation package structure currently used will undergo a large change, so the efficiency of the LED chip is greatly reduced, and the chip area is greatly reduced, thereby changing the package. In such a way that the light output of a single device is greatly increased, the area of a single high-efficiency LED chip is now greatly reduced (250 mil 2 = 60 LM). The lack of heat and the high luminous flux requirements for a single LED source make integrated packaging mainstream. The thermal aggregation effect of the integrated packaged LED device makes the overall thermal conductivity of the LED device extremely important. Packaging technology that can significantly reduce thermal resistance may become the mainstream of LED chip packaging technology. Flip-chip reflow soldering technology will solve the problem of chip yield and cost, which will revolutionize the cost of packaging and make non-gold wire soldering. The technology of flip chip packaging technology is applied on a large scale. Of course, silica gel molding technology like PC hardness and aspherical secondary optical lens technology will become the basis of LED packaging technology. The directional quantitative dispensing process, the graphic coating process, the secondary electrostatic spray powder process, the film lamination method, the three-primary phosphor coating process, the chip deposition pressurization method and the like, all of which will be applied in the LED packaging process. It will improve the light extraction efficiency and light color distribution of LED devices.