LED chiplet packaging technology is difficult to analyze

In recent years, with the development of LED chip materials, as well as the optimization of light extraction structure and packaging technology, the power (W) of single chip size is higher, the light efficiency (lm/W) and cost performance (lm/$) of the chip. It is getting better and better. With the support of this background, the miniaturization of LED chips has become a trend. The meaning behind the miniaturization of the chip size, in addition to the overall size of the light-emitting components can better meet the trend of light, thin, short and small in future products, the number of small chips that can be cut by a single epitaxial wafer is more, and the fixed power is The number of chips to be used is smaller, which is of great help in reducing the production expenditure of LEDs. After all, "cost" is always a big problem.

In the field of high-power lighting, the technology of using multiple small chips in series and parallel has been used very mature and extensive. Compared with a single high-power chip, the chip cost of this process is lower, the overall heat dissipation is better, the light efficiency is higher, the light decay is slower, and the goal of high efficiency and high power can be achieved at the same time, although the process is complicated. There are hidden concerns such as low reliability, but it is also difficult to shake its position. Secondly, in the field of display applications, RGB multi-chip packaging is a mainstream process. As the density of pixels is higher (ie, the resolution is higher), the size of a single pixel per unit area must be smaller and smaller. At the same time as the direction of "small pitch" is gradually developed, the size of the R, G, and B color chips that can be used must also be smaller and smaller, thereby meeting the high resolution requirements in the market. From the above trend, how to make a small-sized chip package becomes an important issue.

In the technology of LED packaging, it is still based on the traditional solid-crystal and wire-bonding process. As for the current Flip Chip or Chip Scale Package (CSP), other new processes, Due to current yield, cost, equipment investment and other considerations, it is still difficult to replace the existing process in a short time. As the chip size shrinks, the most direct impact is the difficulty of the die-hardening process; at the same time, the electrodes on the chip must be smaller, the wire diameter of the bonding wire used must also be reduced, and the matching porcelain mouth is also Must be optimized synchronously. Therefore, after entering the field of "small chip packaging", the first difficulty to overcome is the solid crystal glue, bonding wire, and porcelain nozzle used in the solid crystal and wire bonding processes.

About the challenges of solid crystal

Solid crystal glue is the key consumable of the solid crystal process. Its function includes fixed chip, (conducting) and heat dissipation. Its main component is composed of polymer or silver powder plus polymer material. By different distribution ratios, different shear strength, thixotropic index, glass transition temperature, volume resistivity and the like are formed, and different solid crystal effects and reliability are achieved. In addition, as the chip size shrinks, the amount of solid crystal glue must be reduced. If the amount of glue is too large, the chip slips easily. If it is too small, the chip may fall due to stickiness. How to handle it? It is also an art.

How to choose bonding wire

The so-called good bonding wire must have the following requirements:

1. Meet the mechanical and electrical performance of customer specifications (such as melting current, arc length arc height, spherical size, etc.)

2. Precise diameter

3. No scratches on the surface, clean and no pollution

4. No bending, torsional stress

5. Internal organization structure is even

In addition to the above requirements, small-diameter wires may face the need for series-parallel connection between multiple chips, or special ball-threading methods such as BSOB (Bond STIck On Ball) and BBOS (Bond Ball On STItch). It is also a challenge in the manufacturing process. For example, the process of serial connection of chips involves the bonding of Pad to Pad between chips. If copper or pure silver wire is used for soldering, it will have poor workability and good yield. The high problem is far less than the performance of pure gold and high gold and alloy wire. These are all considered.

In addition, as the wire diameter becomes smaller, the load of the bonding wire (Breaking load, BL) will decrease, which will affect the tensile force and reliability of the wire; in addition, with the distribution ratio of various wires, the uniformity of the alloy Control, as well as drawing and bonfire conditions, will produce different wire hardness, load, elongation (ElongaTIon, EL), heat affected zone (Heat AffecTIon Zone, HAZ) and resistance, etc., while the wire is tapered How to resist the external force such as mold flow without collapse, the shape of the drawn arc can be stabilized without damage, how can the wire pull force value be achieved, how to control the size of the small wire diameter, how to not affect The main characteristics of the case to reduce costs for customers, and to maintain the resistance of the wire sulphide resistance, etc., are the direction that bond wire suppliers can work hard. For the difference of the characteristics of different bond wires, please refer to the comparison table below. From the table, we can clearly see that the use of high-gold wire, alloy wire and other related products can not only reduce the cost by 20%-40%, but also It can meet the performance of pure gold wire, and has been widely used in the industry through the recognition of many world-class customers. In other words, the choice of a good high gold wire or alloy wire is the key to reducing costs and at the same time making small chip packages, as shown in Figure 1.

Table 1, comparison table of related characteristics of pure gold wire, high gold wire and alloy wire

Figure 1. Selecting a good high-gold wire or alloy wire is the key to reducing costs and at the same time making small chip packages.

Porcelain mouth and wire parameters

Parameter optimization of the porcelain mouth is also critical. Under the premise that the bonding wire diameter must be reduced to meet the electrode pad size, a single chamfering shape can be used to match the roughened porcelain tip to achieve a better first welding. Point strength; in addition, a larger needle diameter (T), surface angle (FA) and a smaller outer arc radius (OR) can achieve better second weld strength and fishtail stability. Of course, it is also very important to adjust the appropriate wire parameters such as ball burning current, wire bonding time, wire bonding power, etc. through actual conditions and experience.

In general, due to the obvious advantages, the application of small chips is one of the trends of LED in the future. Whether it is the development of high-power lighting or small-pitch display, it is closely related to this, and small chip packaging is the key to achieve this goal. technology. In order to produce a good wire, in addition to the appropriate parameters, the correct porcelain mouth, it is very important to choose a good quality bonding wire. This is indispensable, and only this one is perfect, small chip packaging The technology will be better. (Author: Liao Yi-taek (1985-), Taipei, Taiwan, engaged in research related to aspects of the LED package)

Three major problems to be solved in the popularization of LED filament lamps

China IOT Conference Series [The 3rd China LED Intelligent Lighting Innovation Application Summit Forum ] will invite Zigbee Alliance, WiFi, Bluetooth and 2.4G technology major supplier executives to share their market insight and latest development results, I hope you can grasp This rare opportunity to exchange, find better business opportunities, and find a higher partner.

Shaded Pole Ac Motor

Shaded Pole Ac Motor,Ac Shaded Pole Motors,Shaded Pole Motor,Shaded Pole Induction Motor

Changzhou Sherry International Trading Co., Ltd. , https://www.sherry-motor.com