How to evaluate and use LED light source devices?

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The type and evolution of LED devices

According to the specific application of LED devices, it can be divided into four categories: backlight, display, lighting, and decoration.

What LED devices can be used in backlights?

We are familiar with the Display LEDs used in mobile phone backlights, including the SMD LED devices we currently use mainly for TV backlights, or in some other backlight applications. There is also a hot solution at present, and the application of CSP in the backlight field has also been widely recognized.

In the display product application, mainly SMD RGB products, there are some direct plug-in Display line products. The main focus of this type of application is on the concentration of colors and the use of colorful colors.

Lighting products are mainly power-type devices, high-power devices in the power devices, and some medium-power and high-power products in the SMD category. These devices are currently used primarily in lighting products. With the modularization of lighting products, more modular products may be gradually promoted.

Decorative applications are also mainly color-sensitive, mainly monochrome. There are Display, as well as SMD classes, as well as some flexible small modules.

The following long picture shows some of the representative devices of LEDs in different periods.

The first red LED has been put on the market since 1962, marking the beginning of the industrialization of the LED industry.

With the development of new semiconductor materials in 1971, LEDs have newer colors, such as green, orange and yellow, and the performance of LEDs is constantly improving.

In 1993, Japanese scientist Nakamura Shuji first invented the first bright blue LED, which has a very efficient blue light-emitting efficiency, and LEDs that fade in the green spectral range are beginning to appear. He then designed the first white LED with some improvement and matching of the phosphor. Our LEDs have since entered the white light era, and the official white LEDs were produced around 1997.

In 2007, high-power LEDs began to appear, starting with the first K2 product developed by Philips.

From 2008 to 2009, some new LED packages appeared, such as COB . The COB shown in the figure is a company that Sharp has started researching and developing in 2007 and officially launched into the market in 2008 and 2009. Very representative LED.

In 2010, the light output efficiency of white light can reach 100 lumens per watt. By 2013, the development of various types of devices is particularly diverse, and the representative ones are super-power LEDs. Not only does it improve in power, but the improvement in light extraction efficiency is also very obvious.

In 2013, some of the LEDs produced by CREE had a luminous efficiency of 150 lumens per watt.

In 2014 and 2015, LED light sources are constantly improving efficiency. The first thing we can see from major manufacturers this year is the improvement of light efficiency. At present, all major production reports of 200 lm / W products began mass production.

The development process of in-line LED

The first in-line LEDs were mainly used on the instructions of electronic products with some 8-byte LED products.

With the development of the display screen, some dot matrix products began to appear. The first thing that appeared was the monochromatic lattice, which then led to the colorful dot matrix, and finally some RGB dot matrix.

The first representative product of the inline type is the straw hat type LED, which is widely used in the indication; the second is the more powerful piranha LED, I believe everyone is particularly familiar with this category. product.

This type of product is mainly used in some red, yellow and green on the computer keyboard indicator. In the process of developing piranha products, it is used on the high brake lights of cars.

Development of SMD products

You may be familiar with SMD LEDs. The first one is LED3528, which is a product that almost all packaging companies have done.

With the emergence of lighting and TV backlight products, there is the emergence of 5630; in order to improve the heat dissipation of the product, there is SMD3014. The SMD3014 product is mainly based on the bottom bracket for better heat dissipation.

Around 2012, the 3528 product formed the SMD 2835 device through the improvement of the bracket. At present, due to the higher temperature resistance of material properties, and the improvement of LED chip technology, the power and light efficiency of single devices have been greatly improved.

The 5050 product, including the 7070 product, will have a higher power boost. At the same time, ORASM S5 products can achieve 5 watts - 8 watts, CREE 7070 can achieve 15 watts.

Through the evolution of these products, we can see that the power of SMD products will become larger and larger, and the technical development of other auxiliary materials will become stronger and stronger. As the technology of auxiliary materials is improving, the overall performance of LED devices is also increasing.

Development of high-power products

The figure shows several representative products, the first is K2 developed by Philips, then the Rebel ES of Philips, including its current LUXEON series, which is a typical replacement product of Cree.

Let's take a look at the comparison of the two products of Philips. What kind of technological changes have there been before and after Philips?

As you can see on the K2 product, there is a copper column on the LED anatomy, which is an embedded bracket structure. We can see from the picture below that the LED is flip-chip soldered with gold balls. At the same time, the gold wire is used to link and realize electrical conduction. And there is a black under the flip chip, we see it in the picture is black, this is a silicon based substrate.

In the Rebel ES series we can clearly see that the first obvious feature is that there is no gold wire; the second is that there is no such gray silicon substrate underneath.

Let's take a look at the two products that are very representative before and after Cree.

The first one is the XRE series. We also use the same way as Philips to use the gold line to achieve the link in the XRE series. There is also a silicon substrate to connect the LEDs. As can be seen in the figure, there are LED phosphor distributions in other areas.

Look at this XML product, the phosphor coating is particularly uniform, just above the LED chip. Through the cut-away view of this product of XML, we can see that there is no silicon substrate at the bottom of the chip. The device achieves lower thermal resistance and thinner weight.

Let's take a look at the development of C0B products.

According to the classification, C0B products are mainly classified by the material of the substrate.

We can see four types of products in the figure. The first type is ceramic substrate. The ceramic substrate mainly forms the circuit directly on the ceramic substrate, and is packaged by dressing or flip chip.

The second type is a press-fit mirror aluminum substrate . The mirror aluminum substrate and the upper FR4 or BT plate are pressed together to fix the chip on the mirror aluminum, and the chip-to-chip soldering method is adopted. The first and last ends are soldered to the upper PCB board to finally achieve the conduction of the circuit.

The third type is directly packaged on a conventional aluminum substrate, which may be widely prevalent in the current Zhongshan area. At present, there are also COBs that are flip-chip mounted directly on an aluminum substrate.

The fourth type of calculation is an integrated class with a high power COB integrated package with a bracket type. The brackets are formed from copper and engineering plastics, and different high-power chips are integrated and packaged to form a single-unit 50-watt or 100-watt device.

LED device evaluation method

There are many device manufacturers that we have passed the LM-80 test report. Does the LM-80 test report mean that there is no need to evaluate it?

Personally feel that the LM-80 report has three shortcomings:

1. The chip size of the undetected device.

2. The batch number of the raw materials used is not reported.

3. The contradiction between long test period and fast technology update.

If you just look at the LM-80 report, personally think that it can only be a life test, it does not mean that this device is the most suitable for us to use.

How to evaluate as a user?

LED devices We may be able to see such an image at the very beginning of the test, which includes the light map, color difference, and other parameters.

Among these parameters we need to pay attention to: first is light; second is electricity; then second is color.

Of course, the order of attention for ordinary use may be different. Then we may have more pictures circulating in the industry. If you look at this report, you will see more and more, and you will not explain them one by one.

Conditional companies recommend measuring the spectrum at different temperature levels while measuring this LED spectrum test report so that you can see how the LEDs exhibit different characteristics at different temperatures. We can evaluate the thermal stability of LEDs through this stability or thermal test.

There are several basic methods for evaluating LEDs, or conventional methods.

High-temperature working life test and high-temperature and high-humidity working life test, followed by a heat-resistance test and thermal shock, the company recommended to strengthen the focus on these four types of tests.

The high-temperature working life test is mainly to simulate the individual parameters of the LED device in the environment of the whole lamp. The high temperature and high humidity are used in some special occasions. For example, in some cases where there is water vapor, we can look at the moisture resistance of the device to humidity. Because humidity is a major manifestation of the performance of the package, it may be said that the water absorption of the material and the characteristics of the phosphor can be expressed more.

The heat resistance test mainly adopts the method of reflow soldering. Generally, three times of reflow soldering, we see whether its functional area is blackened or has a ring change. Looking at the material, the material of the stent has some ring changes, and there is no peeling. The usability and maintainability of the device are also recommended.

All the packaging factories may be the most unwilling to see is black, black is mainly divided into several categories, the first category is as shown in the figure, the bottom of the bracket is completely black; the other type only a small part of the chip Black, other places are not black. These two types of black have been encountered in my work experience, and the way they are produced is different.

There are two fundamental reasons why we can see the blackening. The first one is that the bottom of the LED bracket is silver-containing. At the same time, there may be some volatile organic substances in the excipients. The volatile organic substances have a characteristic, which may be that it has more aggregation characteristics on the LED chip or around it.

Therefore, if we want to deal with this kind of event in the packaging factory, we must first look at whether the whole lamp company has some volatile substances in the auxiliary materials, mainly detecting the adhesive, that is, the glue type products; the second is in the power supply. Some of the components are also in-depth and must be tested to see if there is mainly sulfur.

In order to avoid testing afterwards, it is recommended to initially disassemble the LED device. So how to disassemble is better, or what can be seen by dismantling?

The glue is peeled off directly by slicing experiments or violent disassembly. The situation of the LED chip and the material of the LED bracket can be clearly seen. The metal material of the LED bracket, whether it is an iron bracket or a copper bracket, can be seen at a glance.

The other is the size of the LED gold wire or the connecting wire. If there is a high magnification microscope, we can also see how big the LED phosphor particles are.

These reports are ready for us to guarantee a correct route based on usage.

How to use LED devices correctly

One more problem solving

How do you solve this problem? Or let's take a look at what technical methods are used at different time periods.

This light bulb is invested by Li Ka-shing. The devices used are beyond our expectations. All of them use a 1 watt high-power product to achieve full-circumference. This light effect is also known as the highest light-efficiency light bulb in the industry. .

Panasonic's implementation is to use a special C0B. Cree also uses its own high-power devices. Philips uses a remote phosphor excitation and adds a blue LED device to achieve this full-circle bulb.

Another possibility is our most common LED bulb in Zhongshan or Shenzhen.

Some SMD devices are used. At the same time, we still have a bigger solution. On the filament, the full-circle light bulb realized by LED filament is a hot bulb.

A light bulb has such a solution. That corresponds to the specific luminaire. How do we choose the device? This problem is placed on our head. For linear luminaires, or for luminaires that emit light.

The type of luminaire has some obvious features, and its light-emitting area is relatively wide, and some translucent covers are used. These transmissive covers have some dispersion effect on the light and some dispersion.

So what are our requirements for the device? Our devices require a particularly high degree of chroma concentration, high spectral uniformity, and no color cast or metamerism.

The difference in voltage is small, because we are especially on the panel light, we may use a multi-connection scheme. If the voltage difference is relatively large, there will be some different current sizes, which will result in uneven brightness and brightness. There will be some low. This type of luminaire is recommended to use SMD-based low-power products, which can be achieved with multiple layouts.

For floodlights such as downlights, ceiling lights, or ceiling lamps. How do we choose the right device?

Linear luminaires and surface-emitting luminaires: The illuminating surface is wide, and the translucent cover (panel) is prone to dispersion.

Device requirements: high color temperature concentration, high spectral consistency, small voltage difference, and low brightness.

Applicable devices: SMD low power devices

What kind of "potential" will LED devices have?

SMD class's contrarian rise (integration, material improvement)

Bracket material temperature rise

Chip integration

Personally think that SMD products, it is a trend of rising against the trend. The SMD class starts with a chip inside a bracket, and now two or more can be placed in one bracket.

Osram's S8 and H10 can now be 15 watts in a single unit, which can directly form a lamp. This development has broken through some of the original features of the SMD class, so I defined it as a contrarian rise.

At the same time, the SMD bracket was initially transferred from PPA to PCT. Then the EMC bracket is widely used now, and SMC products will gradually become more widely used.

The characteristics of these materials, the temperature resistance will be higher and higher, which also drives our single SMD class to use higher power.

The development of the COB category

High light flux density

High color quality

COB eliminates the need for reflow soldering and placement of different devices, and it eliminates the need for a PCB board. A single lamp uses only one source, and its color difference is well controlled.

What kind of development trend does the COB use today?

We can look at Cree's products and see the main direction of the COB category through Cree's products.

First, the light-emitting surface will become smaller and smaller, and the light-emitting surface will be as small as we said above, in order to match a better optical design, a secondary optical lens, which is more cost-effective and easier to achieve a small angle. Second, the power may be higher and higher, and the luminous flux per unit area output will be higher and higher.

In addition, since the COB category is mainly used for commercial purposes, the requirements for color quality will become higher and higher. At present, some companies have achieved some professional subdivisions. For example, Oulante has specialized mahogany furniture, specializes in vegetables, and lighting fixtures for fresh meat are also used more and more.

COB products currently have a potential competitor, which is what we just said, such as Osram and Philips, some medium and high power devices, single SMD.

Future COBs may not have much advantage in small wattages.

The trend of CSP

With or without substrate

Light angle

Single, integrated

Application

If the CSP products are classified according to classification, they can be mainly divided into two types, the first type has a substrate; the second type has no substrate. At the same time, the emergence of CSP products also benefited from the development of LED chips.

CSP products must first use flip chip, which is more conducive to its placement and use. The CSP launched by Samsung has already developed into a single direction.

At the same time, CSP products have different angles and narrow angles of CSP according to different applications. At present, some manufacturers also apply CSP to products similar to COB.

Personally feel that such an application may be a direction, but not necessarily all. Mainly depends on the manufacturing cost of CSP and the process of placement, and I believe that CSP is a trend in light source development. Because CSP is smaller and thinner, it is like any of our electronic products. It will become smaller, thinner and lighter. Looking forward to the future CSP products will bring more surprises to the lighting industry.

The use of filaments

Flip chip imagination

Substrate selection

The development of flip chip will make the filament have more imagination space, and the substrate of the filament is sapphire, white ceramic, glass, and even some flexible PCB board, which will give us more ideas.

The development of LED has not always been isolated. Whether it is the replacement of materials, the replacement of component sizes and the development of packaging technology will affect the development of LED.

But with the development of LEDs we can see, before on the sapphire substrate, or silicon substrate, and some are silicon nitride substrates. Above these substrates, the LED re-gallium nitride substrate may produce quantum defects.

Now some companies are producing GaN on GaN substrates. As everyone knows, Nakamura Shuji's current company is doing this. What are the benefits of doing this? Reduce the defect, it can drive more power in the epitaxial layer.

With linear luminaires, the development of linear power supplies requires higher and higher voltages for LED devices, especially for single devices.

The method of adopting a high voltage chip is very worth learning.

The development of the LED from the epitaxial chip will drive the development of downstream devices. We can now see that a single device with 18 volts or even 45 volts on the market is implemented with one chip. And as the defects of the epitaxial layer are reduced, the light efficiency generated by the epitaxy will become higher and higher, and the luminous efficacy of the LED will become higher and higher in the future. Even if one day, all the LEDs are emitting light, and no heat is known.

In addition to the basic materials, the development of the packaging process will also make LEDs produce many differences. At the beginning, it is like a straight-in type of product, and some use aluminum wire bonding and ultrasonic wire wedge bonding of aluminum wire. This welding method is easy to cause LED leakage.

With the development and advancement of technology, spherical gold wire welding has been produced. This soldering method avoids the possibility of leakage of the LED chip and has higher soldering reliability.

There are still some companies that use flip-chip welding, and flip-chip welding is also divided into two categories. The first type is the flip-chip welding of the gold ball; the second is the direct gold-tin flip-chip welding; and some are the solder paste flip-chip welding.

These soldering methods will bring more and more choices for LED devices, so there will be more and more types of LEDs.

The coating of the phosphor on the white light device has a great influence on the LED device, and the main coating method of the phosphor can be classified into three types. The first type is potting; the second type is spraying; the third type is using a fluorescent film.

The first type of potting can be seen that there is very little distribution of phosphors directly on the side of the chip. At this time, color is easy to produce, and the phosphor coating process overcomes the fact that the side of the potting is less and the side is more.

Spraying can achieve the same thickness of the phosphor on the side and front side of the chip. Of course, the method of using the fluorescent film may have better color quality and color consistency of the device. Different types of phosphor coating methods can have different effects on the color of the device.

The LED device will eventually have a development. At present, there may be many different keywords to summarize the development of LED devices, whether modular or CSP can dominate the world, and flip-chip C0B, light engine or high voltage device. There are different LED devices for different applications.

With the subdivision of applications, LED devices may become more and more, but the variety of generalized products will be less and less. The subdivision will determine the future of our device. The last picture on the picture is the LED light source used by the Panasonic bulb we saw before. If it is not standardized by standardization, it is A specially customized device.

So subdivision is the future of LED device development. Different technologies and different applications will ultimately determine the development of our LEDs.

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