Discussion on the application of EMC in LED packaging

1 Introduction

Top LED devices are mainly made of thermoplastic (Thermoplastic plastics, TPP) bracket, which is a mature LED package bracket. At present, the TPP stent molding materials mainly use thermoplastic resins such as PPA and PA6T. The airtightness problem of such stents has not been improved, the water absorption is strong and the PPA itself is discolored, and these problems will affect the reliability of the LED devices [ 1]. In recent years, some foreign LED companies have introduced a new package form from the field of microelectronic packaging, namely Epoxy molding compound packaging, referred to as EMC packaging. EMC is a Thermosetting plastic, which is a very mature technology in Japan. The Taiwan region of China started research and development a few years ago, and the mainland started late [2]. Due to the good performance advantages of EMC packaging, many LED companies are optimistic, and it has gradually become a very popular packaging technology.

2 Introduction to EMC Materials

EMC is an important microelectronic packaging material. The semiconductor chip is coated and protected by the packaging process to avoid damage from the external environment. At the same time, EMC also has a certain heat dissipation effect. EMC has the characteristics of large-scale production and reasonable reliability, and is one of the common packaging materials for semiconductor packaging [3~4].

In the mid-20th century, epoxy and anhydride curing system molding compounds were used in plastic-sealed transistors. With the continuous development of technology, various EMCs with excellent properties such as flame retardant, low hydrolyzed chlorine, low stress, low expansion, low warpage, etc. have been developed to improve the performance and reliability of semiconductor devices [3~4] ]. In recent years, EMC has been introduced into the field of LED packaging, which is of great help to improve the performance and reliability of LED packaged devices.

EMC's main components are fillers, epoxy resins, curing agents, coupling agents, flame retardants, mold release agents, modified additives, etc.; the highest filler content, can improve the parameters and performance of epoxy resin, such as reducing Expansion coefficient, increase thermal conductivity, increase elastic modulus, etc.; epoxy resin as a matrix resin combines other components together, epoxy resin determines the mechanical, electrical, heat resistance and other properties of EMC cured products [3~5] . With the rapid development of semiconductor technology, people continue to study EMC material characteristics and optimize process parameters, so that EMC's performance has been continuously improved.

3 main characteristics of the EMC bracket

EMC has excellent performances such as high reliability, high thermal conductivity, high heat and moisture resistance, low stress, and low expansion coefficient, making it ideal for LED package devices. The LED EMC bracket is a highly integrated bracket known as the third-generation LED bracket. Compared to the first-generation PPA pre-plastic frame and the second-generation ceramic substrate, the EMC bracket can achieve mass production and reduce costs. Advantages such as flexible design and smaller size [2].

Since the LED is a light-emitting device, in addition to ensuring good heat dissipation and airtightness of the device, the package material also has a good light-harvesting effect, that is, the material must have a high reflectivity, a model produced by Hankel, Germany. For the EMC of GR10000402B, the reflectivity of blue light around 460 nm is as high as 94.8%. Although the reflectivity of the traditional PPA can reach about 93%, after 1 000 h of high temperature aging, the reflectivity has dropped below 50%, and the Hankel EMC bracket has passed the high temperature of 1 000 h and 150 °C. After aging, there is still about 80% reflectivity.

Table 1 compares the performance parameters of EMC brackets and traditional PPA brackets. It can be seen from the data in the table that EMC materials have higher reflectance, thermal expansion coefficient and material joint strength after high temperature aging than traditional PPA materials. Great improvement and upgrade, more suitable for high quality, high power LED device package.

Table 1 Comparison of performance parameters of EMC bracket and PPA bracket

4 Advantages of EMC brackets

From the comparative data in Table 1, EMC has obvious packaging performance advantages, which is very suitable for LED packaging devices. EMC brackets have a big advantage over PPA brackets:

(1) The problem of hermeticity of PPA stents has always been a problem for LED devices. EMC has a lower coefficient of thermal expansion, good adhesion and corrosion resistance, and its airtightness is much higher than that of PPA. Improve the reliability of LED devices.

(2) EMC also has UV resistance, which can reduce the yellowing speed of LED brackets. LED devices made with EMC can better adapt to outdoor complex environments.

(3) EMC's low thermal expansion coefficient allows the device to withstand higher temperatures without affecting device reliability. For the same volume of LED devices, EMC LEDs can pass higher currents. For 3014 Top LED devices with conventional PPA materials, the forward current IF does not exceed 40 mA; and the EMC package's 3014 forward current can reach 150 mA, resulting in LED power of 0.5 W. For the 3030 and 3535 EMC packages, the LED can pass 350 mA and the power can reach more than 1 W [2].

(4) Since the development of LED technology, its light efficiency (lm/W) has been improved rapidly. With the improvement of LED light efficiency, people began to pay attention to the cost of unit lumens, namely lm/$. Compared to traditional PPA materials, EMC enables LED devices to achieve higher power and achieve higher luminous flux in the same or even smaller volume. Although EMC's current price is more expensive than PPA, EMC's cost advantage is obvious from the cost of unit lumens. In addition, due to the characteristics of its production process, EMC has a much higher processing accuracy than traditional packaging, and the degree of integration is very high, and the production efficiency can be greatly improved, further increasing the cost advantage.

5 EMC bracket process

EMC is mainly made by melt-mixing extrusion method [5]; while LED EMC brackets use etching technology to heat EMC and etched copper substrates in the molding equipment package [2].

The LED EMC stent process is shown in Figure 1. It includes etching, plating, slicing, injection molding, molding baking, and flash removal. The injection molding is the main process, which is completed by molding equipment. It is a schematic diagram of the process of EMC stent injection molding and some key process parameters.

6 EMC applications in the LED package

Some problems in EMC application in LED packaging EMC has been applied to LED brackets, becoming the third generation of LED brackets. Compared with the previous two generations of LED brackets, it has obvious performance advantages and outstanding application effects, but there are still some problems. (1) EMC is a thermosetting plastic. After being introduced into the LED package, the material composition is improved according to the characteristics and performance requirements of the LED product, but the filler and epoxy are similar to those of the microelectronic package, so EMC is Some common defects in microelectronic packaging also exist in LED packaging, such as porosity, pitting, cracking, flashing and airtightness, and brittleness after curing [6~8].

(2) Although the airtightness of EMC is much better than that of PPA, the material itself is still absorbent, and the problem of airtightness cannot be completely avoided [9]. Although the problem of air tightness cannot be completely solved, the subsequent improvement can be further improved, such as researching and adding some modified additives or controlling from the process to optimize the process parameters; in particular, paying special attention to controlling the temperature variation causes the difference in thermal expansion coefficient of the interface material. The difference affects the relative displacement of the EMC and the copper lead frame [1], which in turn forms a channel through which water vapor infiltrates.

(3) Since the EMC of the LED package still needs to be imported from abroad, the current EMC price is more expensive than the PPA. With the continuous development of EMC's material level and process technology and the increasing use of EMC in LED packaging, the cost advantage of EMC packaged LED devices will gradually become prominent.

(4) If the LED package is to be introduced into EMC, it requires large capital and R&D investment [2], mainly because the structure of the EMC bracket is different from the traditional PPA bracket, as shown in Figure 3, the 3014 EMC bracket and Figure 4 The 3014 PPA bracket is shown. The structural differences between the two stents lead to differences in the packaging process. For example, in the process of cutting the ribs, the PPA bracket is formed by punching with the matching tooling; while the LED of the EMC bracket is cut by the dicing machine. If you want to introduce EMC, you need to adjust or improve the fixtures of some original equipments, and even some equipment needs to be replaced. This will inevitably increase more investment. This is why many domestic bracket manufacturers and LED packaging manufacturers are still hesitating. The main reason for the introduction of EMC.

7 Conclusion

At present, due to overcapacity in the LED industry, competition is fierce, and in the market fight, prices are the first to bear the brunt. The price of LED lamps is still higher than that of traditional lamps, and further price reduction is needed to fully open the largest general lighting market. To this end, all LED companies are actively researching new materials, new technologies and new processes to improve the performance of LED products, reduce costs, and ultimately improve the overall competitiveness of products.

Due to the excellent characteristics of EMC and simple process, the EMC bracket is very suitable for LED devices with power between 0.5 and 2 W. The cost advantage is obvious, and the performance and reliability of LED devices are also greatly improved. Therefore, LEDs in EMC bracket packages will gradually become the mainstream choice for medium and high power LED devices. With the introduction of EMC, the price of LED products will have more room for price reduction, which is bound to accelerate the pace of LED lighting into the general lighting market.

Edit: Cedar

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