CSP LEDs are coming. COB type LEDs What is cob chip led

In 2014, LED lamps on COB appeared on sale. Made using a new technology that allows you to place and power many crystals in the body of one LED. In the future, the new technology will replace the existing SMD elements.

Crystals are placed on a common substrate, which allows you to remove more heat and get more lumens per square centimeter of area. According to unverified information from the Chinese, one crystal on the substrate gives 5 Lm, that is, the brightness is the same as that of the SMD3528, the 5050 has 3 such crystals. Since, in fact, this is one large LED, and its internal crystals do not require cases, this reduces the cost of 1 Lumen by about 2 times, compared with the old technology. The COB matrix is ​​covered with a layer of phosphor, thanks to which it glows as a whole, and not pointwise. It is not yet necessary to solder numerous SMD diodes, soldered a couple of wires and the lighting device is ready. This also affects the price of budget lamps from China, because some unnamed Chinese manufacturers manage to solder manually.

• 1. Disadvantages of COB lamps
• 2. How to choose COB LED light bulb
• 3. LED corn test for BER
• 4. Results

Disadvantages of COB lamps

COB diode has all the characteristics of conventional previous generation. The technology allows them to be produced in any shape: square, oval, round, with a hole in the middle, which allows you to fit it into any lighting device or simply upgrade an existing one.

The larger the area, the higher its power is, the size of 12 by 3 cm can already be used for street lighting. But in any case, do not forget about a good heat sink, nobody canceled the heating.

New technology has brought new challenges to the operation of LED lamps for the home. Everyone knows how repairable products on SMD LEDs are, repairs are done in 5 minutes. Now the failure of the COB requires the replacement of the entire light emitting element, for example, and not just one of 42, as was the case before. Over time, this disadvantage will not be large, since the cost should decrease significantly for such diodes. Now the prices are too high, because it's new, and you can tell a good lie about the characteristics. When everyone starts to understand this technology, the excitement will drop to a normal level.

How to choose COB LED light bulb

The new technology makes it difficult to choose products of unknown origin, especially Chinese ones. When buying light bulbs on SMD diodes, you could see the marking, count the number and then calculate the power, regardless of what is written in the characteristics.

In our case, it will not be possible to find out its power from the photo and design, since it is impossible to determine the consumption of a COB LED by its appearance. The number, power and density of crystals can be absolutely anything.

Probably, the situation with Chinese COB will be the same as with SMD. Inexpensive Chinese LEDs include a third of the face value for a long service life. In the case of COB, it will probably be the same, budget COB will also include 30% of the power. If the SMD's operating mode could be determined by the number of elements, then in our case the area will not be tied to the characteristics of the LED. Chinese online stores will probably take advantage of this by subtly increasing the luminous flux of products. Indeed, in most cases, an ordinary buyer will not be able to find out if they sold him a lamp on branded diodes or budget Chinese ones.

LED corn test for BER

The dimensions and design are similar to 60-piece corn, only COB plates are installed instead of soldered ones. Exactly the same dimensions are produced lamps for the house on.

They cost $ 9 apiece, the price is certainly too high, similar to the SMD 5730 costs $ 6, a similar one is a little cheaper, but I had to buy it for the sake of interest. The seller promised:

• socle E27;
• power supply 220V;
• current consumption 32 mA;
• warm white;
• power 9 W;
• luminous flux 800-900 lm.

The brightness was compared with the new energy-saving Philips 800 Lm, the same brightness, light and shade. In the chandelier in the photo there are two new ones and two fluorescent ones. The brightness of Chinese COBs is up to 100 lm per watt, as in our case.

Corn COB entrails

Power is made on a ballast capacitor, but an additional capacitor is soldered for. Flicker is present, but it is not as strong as other inexpensive ones, that is, within the normal range. The light bulb heats up, but does not overheat, the area of ​​​​the lateral circle is still considerable, the temperature is within the permissible range.

Testing showed that it corresponds to the declared characteristics, the quality is quite good, I did not find any defects in the assembly.

Results

The new technology shows good performance, the brightness is already up to 120 lm per watt, instead of the previous 80 lm per watt. But do not rush to buy, the prices are too high for them, such as nanotechnology and the hadron collider are used. Their price should fall below the cost of lamps on SMD elements.

The main direction of lighting engineering is the introduction of LEDs in lamps of all stripes and types. But it should be noted that there is no single direction for this development. Today, in addition to the well-known LED lamps, the so-called COB lamps, which are based on more powerful LEDs, are also entering the market. COB LED bulbs ( chip-on-board)- these are, in fact, all the same LED light sources with which everyone wants to save energy consumption. But disputes are still raging among experts, in which the parties cannot agree on how to choose the right one.

It is believed that in modern lighting technology until 2009 there was only one direction of development - this is an increase in the power of the glow of diodes. And then, and today this direction is called Power LED (powerful LED). Scientists managed to achieve significant results - light-emitting diodes with a power of up to 10 watts were born. Although 3-6 watt devices remained in demand.

What is the essence of the Power LED concept? In principle, everything is quite simple - to reduce the cost of light sources. It was believed that an increase in power, and, accordingly, brightness, would reduce the number of LEDs. But in fact, all this did not happen. The cost of Power LED fixtures has not decreased, and the light output has not increased much. Why did it happen?

• The first reason is that the LED is and always has been a point source of light. But for the basic operating conditions of any lamp, diffusing light is needed. Therefore, diode lamps for the home were provided with special optical systems. Without them, the light source radiated high brightness, and the beam was blinding. But there are two more factors: firstly, the optical systems themselves were expensive, and secondly, through them the lamp itself lost a certain amount of brightness (up to 35%).
• The second reason is that the assembly of LED lamps on COB diodes includes a fairly large amount of manual labor. So here, too, costs strongly influenced the cost of the product.

Breakthrough

Since 2009, SMD diodes have appeared, the power of which is 0.01-0.2 watts. LEDs of this type consist of 1-3 crystals, which were glued to a ceramic square base with sizes from 1.4 to 6 mm. And each point diode is coated on top with a phosphor. Most importantly, the LEDs are connected to the plateau by soldering. And, therefore, the entire technological process can be fully automated, avoiding expensive manual labor.

But that's not all.

• SMD diodes are low-power, for one lamp you have to install them in large quantities (up to 700 pieces). This is 100% diffuse light. That is, there is no need to use expensive and complex optical systems. The best option is a ceiling made of ordinary glass, in which the light loss is only 8%.
• LEDs are arranged on a plateau at regular intervals, which are several times the size of the crystals themselves. Therefore, the diodes themselves are so clearly visible individually, and not in the total mass. In addition, it is possible to increase the optimal glow in the rooms where the computer is located. You can simply install lamps with milky LEDs.

The only disadvantage of SMD lamps is their low maintainability. It is almost impossible to disassemble and re-solder a burned-out diode manually. So it is better if you completely replace the lamp with a new one. It'll be cheap.

Breakthrough continues

So, back to the topic of "diode COB lamp". No one was going to abandon these LEDs, it just became necessary to modify the lamp itself, making it inexpensive. There were several options for changing the design, but one turned out to be optimal.

• First, ceramic substrates were abandoned. That is, the crystals began to be installed directly on the plateau.
• Secondly, all crystals were covered with a single layer of phosphor. Therefore, the luminaire glows evenly without visible individual luminous points.

And here COB matrices began to win over SMD matrices. In the schemes of LED lamps for 220 V, up to 70 crystals per square centimeter were obsessed. That is, the lamp becomes many times smaller, but its brightness was not inferior to other models. In the end, it became possible to use in light sources of this type both reflectors and diffusers that are installed on traditional lamps.

Production process

COB matrices are produced in several automated steps.

• An adhesive composition is applied to the substrate, which will provide high adhesive qualities.
• Crystal assembly.
• Glue curing.
• Matrix cleaning with plasma technology.
• Soldering crystals from a plateau.
• Application of phosphor.

Attention! In this technology, the phosphor is mixed with silicone. The latter provides complete tightness of the light structure.

The most complex technological operation, which until recently could not be implemented, is the application of a thin adhesive layer. The thing is that the layer of glue must be of a certain thickness. If it is thin, then the crystals will begin to peel off during operation. If it is too thick, then the thermal output of the crystals to the substrate will decrease. This problem was solved by the Chinese, who proposed using the magnetron sputtering method. Therefore, the new matrices are now called MCOB, that is, Multi Chip-on-Board, which means "numerous crystals on the board." True, the device of the LED lamp has not changed from this. It is this technology that currently allows the production of high-power LED lamps.

Parameters and characteristics

So, specifications. Modern COB luminaires can reach 100W. At the same time, the brightness of the glow reaches up to 150 Lm / W, which is even a very decent indicator.

The dimensions of the matrix (it can be square or round) are from 1 to 3 cm. This is for internal use. For outdoor LED lamps, diodes with a matrix size of 3 × 12 cm are used. The service life of LED lamps with COB diodes is 300,000 hours, more powerful analogues last up to 500,000 hours.

Some experts, given the short service life, talk about the low capacity of this type of fixture. But there is one caveat. Lamp life tests were carried out under extreme conditions. After that, mathematical calculations summed up that they will work continuously for 6 years. And during this time, for sure, new lighting devices will appear, more economical, reliable and bright.

Attention! Almost all manufacturers give a warranty period of 200,000 hours, during which they are ready to carry out repairs.

In principle, the technical specifications indicate that LED lamps are by far the most economical option for a home lighting system. Of course, it is also the most expensive in terms of down payment (price). But it is worth paying attention to them if the consumer faces the problem of saving.

Conclusion on the topic

For many, it is probably no longer a secret that many European countries want to abandon the electricity that is generated from the fission of uranium. Nuclear power plants are unreliable. For example, Switzerland will close all nuclear power plants by 2036, although they account for up to 41% of electricity generation. Therefore, Europeans are investing a lot of money in the development of new energy-intensive technologies, where LED lighting is a priority.

And the last on this topic. Many consumers are wondering which LED lamps are still better, how to choose the right one? If you have read the article, then you should understand that this question does not make sense.

LEDs are becoming more and more popular solutions, and in a variety of areas. They can be used as decorative products or to illuminate the premises, as well as various areas outside the buildings. LEDs are supplied to the market in a fairly wide range of modifications. At the same time, the developers of the corresponding products periodically offer innovative solutions that in the future are able to form new market niches. What are the most common types of LEDs today? For what purposes can they be used?

What are LEDs?

Before considering the common types of LEDs, we will study general information about the corresponding devices. An LED is a semiconductor that is capable of converting electrical current into light. At the same time, the semiconductor crystal, which is its main component, consists of several layers characterized by 2 types of conductivity. Namely - hole and electronic.

Conductivity of the first type involves the transition of an electron from one atom to another, on which there is free space. In turn, another electron comes to the first atom, another one to the previous one, etc. This mechanism operates due to covalent bonds between atoms. However, they do not move. In fact, a positive charge is moving, which physicists conventionally call a hole. In this case, when an electron passes to holes, light is released.

In its structure, the LED as a whole is similar to a rectifier diode. That is, it has 2 outputs - an anode and a cathode. This feature predetermines the need to observe the polarity when connecting the LED to a source of electric current.

The corresponding products are generally designed for a direct current of 20 milliamps. In principle, this value can be reduced, however, in this case, the color may change and the brightness of the LED may decrease. In turn, it is undesirable to increase the corresponding parameter. If the current exceeds the optimal value, then in order to reduce it to the required level, a limiting resistor is used.

There are quite a few things to keep in mind when installing LEDs. This is predetermined by their internal structure, form of performance. In some cases, it may be necessary to use a stabilizer for LEDs and other electronic components to ensure the operation of the device in which the product in question is installed.

Depending on the composition of the semiconductors in the LED, it can be red, yellow, green or blue. For example, if the structure of the corresponding electronic component contains gallium nitride, then the LED will glow blue. Actually, one of the criteria based on which certain types of LEDs are distinguished may be their color.

Application

The first LEDs on the market were produced in metal cases. Gradually it began to be replaced by plastic. At the same time, in color, it is usually selected taking into account the color of the LED glow. However, transparent plastic cases are also quite common.

The considered electronic devices are widely used in various fields. This is due to the fact that almost all are characterized by:

energy efficiency;

Long service life;

The ability to determine the color of the glow, as well as adjust its power;

security;

Environmental friendliness.

If we talk about energy efficiency, LEDs with the same light output can have significantly less power than conventional lamps. The lower power of the LED reduces the overall load on the building's power system. The service life of devices can be several tens of times higher than that of conventional lamps. At the same time, from the point of view of functions, LEDs can not be inferior to them at all.

With the formation of mass demand for such products, as well as their reduction in price, LEDs are increasingly being used for the same purposes as conventional lamps. There are no difficulties in the installation of appropriate solutions in comparison with traditional lighting fixtures. It is only important to make sure that a particular LED is suitable for installation in the power supply of the room. To do this, it may be necessary in advance - before purchasing LEDs - to identify its main parameters.

What other benefits can the solutions under consideration have?

So, it can be noted that the color temperature of the LED can be almost any - including the combination of the above colors. In addition, devices can be supplemented with various light filters, which can significantly expand the scope of LEDs in terms of selecting the required color temperature.

The ability to control the power of the glow is another advantage of the devices in question. This option goes well with their high energy efficiency. The power of the LED can be adjusted automatically - based on the actual conditions of use of lighting devices. And this practically does not affect their service life.

LEDs are environmentally friendly because they do not emit radiation harmful to humans. This characteristic, again, expands the possibilities of using the devices in question.

Classification: indicator and lighting solutions

Experts distinguish 2 main categories of LEDs - indicator, as well as lighting. The former are intended mainly to create a decorative light effect and are used as an element of decorating a building, room, or vehicle. Or as a text styling tool - for example, on an advertising banner.

In turn, there are lighting LEDs. They are designed to increase the brightness of lighting in a room or in a certain area of ​​\u200b\u200bthe territory - for example, if we consider LEDs for cars. The corresponding type of solution is an alternative to the use of conventional lamps and in many cases more advantageous in terms of energy efficiency and environmental friendliness.

Execution types

But back to the classification of LEDs. You can define the widest range of grounds for their assignment to certain categories. A common approach among experts involves the selection of the following main types of LEDs:

Fiber;

Let's consider them in more detail.

What is the specificity of DIP LEDs?

If we study in more detail how these types of LEDs appeared on the market, then DIP class devices can be attributed to the first ones that began to be sold in bulk. These solutions are crystals that are placed in housings with optical components, in particular a lens that creates a light beam.

DIP LEDs belong to the indicator category. They have another name - DIL. They are installed on the board, on which you first need to make holes. It can be noted that within the category under consideration, various types of LEDs can be distinguished, which differ in bulb diameter, color, and material of manufacture. In this case, the corresponding parameters can be represented in the widest range. The solutions under consideration are cylindrical in shape. Among the corresponding LEDs, there are both monochrome and multi-color devices.

Spider LED

This type of LED is generally very similar to previous devices. But they have twice as many pins - 4. While DIP LEDs have 2. The fact that the presented type of solution has more outputs optimizes heat dissipation and increases the reliability of the corresponding components. In practice, they are used in various fields, in particular as LEDs for cars.

SMD LEDs

These solutions are produced using the surface mount concept. That is, they are LEDs that are installed on any surface, while other solutions can be installed through through mounting.

The dimensions of LEDs of this type can be significantly smaller than those of alternative solutions, as well as those structures on which they are installed. Again, in this case it is legitimate to talk about a more optimal heat dissipation. Use of SMD type LEDs in many cases, it allows you to expand the variability of the execution of lighting structures.

SMD LEDs belong to the lighting category. They are characterized by a rather complex structure. So, the LED itself consists of a metal substrate. A crystal is fixed on it, which is soldered directly to the contacts of the substrate body. A lens is placed above the crystal. In this case, 1-3 LEDs can be installed on one substrate. SMDs include common types of ultra-bright LEDs, such as 3528. These solutions are in high demand.

COB LEDs

The next popular LED type is COB. It is made using a technology that involves the installation of a crystal directly on the board. This solution has many advantages:

The protection of the compound from oxidation;

Small dimensions of the structure;

Heat dissipation efficiency;

Reducing the cost of installing LEDs - in comparison, in particular, with SMD devices.

If we consider the above types of LEDs, it can be noted that COB brand solutions can be attributed to the most innovative. For the first time, this technology was implemented by Japanese engineers in the late 2000s. Now these types of LEDs continue to gain popularity.

According to experts, the solutions under consideration may even become the most popular on the market, especially if we talk about the commercial segment, about the sphere of household lighting. It is worth noting that there are areas in which the application of COB LEDs can be difficult. Among them is the production of professional lighting equipment. The fact is that the LEDs in question are not very optimal in terms of adaptation to the organization of lighting with an established luminous intensity curve. In such cases, SMD type devices may be more suitable.

The described diodes are related to lighting. According to experts, they can be attributed to the best, based on the characteristics of the luminous flux. They are available on the market in different colors such as red, green, blue and also white. The luminous flux of these models has a dispersion angle of 40-120 degrees.

More than 9 COB LEDs can be installed on one substrate. They are covered with a phosphor, as a result of which they acquire high brightness. It can be noted that the luminous flux of these solutions is higher than that of SMD type devices. Thus, if we consider which type of LEDs is better, then according to the indicated criterion, a COB class solution may have an advantage.

COB type LEDs also find application in the automotive industry. They can be used as a component of front, rear lights, turn signals. The main thing is to install the purchased devices correctly. To do this, it makes sense to turn to experienced professionals.

Fiber LEDs

Fiber LEDs are innovative. They appeared on the market recently, in 2015. The considered solutions were developed by engineers from South Korea.

You can use these types of LEDs in the production of clothing. That is, from them it is quite possible to sew a shirt or T-shirt that can glow. The production of clothing based on fiber LEDs also involves the use of various polymers, as well as aluminum compounds.

Filament LEDs

Another example of innovative LEDs is Filament type solutions. Their main advantage is high energy efficiency. At the same power, for example, with LEDs such as COB, Filament solutions can provide a higher level of illumination.

Considered most often used in the manufacture Among the notable characteristics of the production of the corresponding LEDs is the implementation of mounting directly on a substrate made of glass. This approach makes it possible to spread the light emitted by the LED through 360 degrees.

How to choose the best option?

How to determine the type of LED that is optimal for a particular design? There are a large number of criteria that can be guided in this matter. In principle, it is quite legitimate to determine the scope of the LED based on its classification according to the features that we discussed above. We will study the specifics of choosing the appropriate electronic components, taking into account the features of devices:

LED Selection: Features of DIP Solutions

As we noted above, DIP LEDs are among the earliest products to hit the market. Thus, quite old, but still in demand technologies are involved in them. Their main advantages are ease of installation, convenience of form, low power consumption, low heating, as well as a fairly high degree of protection from external influences.

Most often, the considered LEDs are available in diameters of 3 and 5 mm. If we compare LEDs by type, we can conclude that the solutions under consideration are the most optimal for use:

As elements of car tuning;

As decorative components;

As part of low-power - as a variant of home-made - lanterns.

The considered LEDs have a relatively low cost and availability on the market. It can be noted that among the most common modifications are 12 volt LEDs. They can be found in various online catalogs, as well as in specialized stores in a wide range. Actually, any 12 volt LEDs are characterized by a fairly high demand in the market.

Choosing LEDs: Features of SMD Type Solutions

The corresponding type of solution in appearance fundamentally differs from others in that they have a flat shape. The installation of these electronic components is carried out without the use of legs. The current for SMD type LEDs is supplied to the terminals that are located on their reverse side.

Thus, the installation of these devices is carried out without the use of holes. The placement of LEDs can be done very compactly. As a result, the structure on which the corresponding devices are located may also decrease.

The main ways of using the devices in question are the same auto-tuning, various types of interior lighting. Among the most significant advantages of these options are high brightness, light output. Combined with their small size, these solutions offer significant advantages over alternative product models.

Among the most common on the modern market is the type of LED 3528. These products are widely used in the production of LED strips. The design of the corresponding products allows the production of three-color LEDs - with red, blue, and green glow colors. Based on the 3528 solutions, many other electronic components are produced, such as the SMD 5050 type LED.

The products in question are also characterized by affordability. They are usually presented on the market in a wide range.

LED Selection: Features of COB Solutions

First of all, it is worth noting that a significant part of the LEDs of the corresponding type are very powerful designs. Their characteristic feature is the rapid dissipation of light, thanks to the placement of crystals on the surface, which provides dynamic heat removal.

The LEDs in question are very bright. This makes them in demand just for use in the design of car headlights. It is worth noting that these products should be installed taking into account a number of significant nuances - these can only be known to experienced specialists. Therefore, it is recommended to contact the competent service departments for the installation of appropriate solutions.

A. SuperFlux(Russian SuperFlux) (or Piranha, Russian - Piranha) - a technology in which the chip is "packed" in a square box with four pins. And already this box is directly mounted on a conductive substrate.

SMD crystals, in turn, differ in numerical indices: 3528, 5050, 5630, 5730, 7060. These indices should be understood only as chip sizes. So, for example, the most popular SMD 3528 and SMD 5050 chips are 3.5x2.8 mm and 5.0x5.0 mm, respectively. At the same time, SMD 5050, for example, is actually not one, but three chips integrated together, so some manufacturers and sellers add the 3Chip designation in the abbreviation or call such chips multi-chip. Accordingly, a large area of ​​the chip means its high luminosity.

C.CoB(Russian - KOB) - Chip-on-Board, the technology of "soldering" the chip directly onto the board substrate. This technology allows you to effectively remove heat from the crystal.

1. Introduction

Simultaneously with the improvement of silicon wafer production technology, increasing the reliability of chips and improving their heat dissipation properties, an incredible reduction in the size of semiconductor devices has occurred. Japanese electronics manufacturer Mitsubishi was the first to launch Chip-Scale Package (CSP) technology in 1994. Now CSP components are standard. However, until recently, CSP technology was not used for LEDs due to the inability to remove heat from such tiny devices. But the increase in efficiency and resistance to high temperatures (which was a problem for previous generations of LEDs) changed the situation. And now, manufacturers such as Nichia, Lumileds, Samsung and Toshiba have announced the start of mass production of CSP LEDs.
Let's consider how the technology of packaging (case) of LEDs was developed, what opportunities CSP provides for designers to create new compact form factors that are impractical with the use of LEDs of the previous generation.

2. Development of packaging technology

Moore's Law, which recently celebrated its 50th anniversary, states that the number of transistors on a chip of a given size doubles every 18 months as manufacturing techniques improve. However, this law also implies that every 18 months a chip with a certain number of transistors shrinks in area to half its previous size. And this miniaturization of components is a boon for designers faced with space constraints imposed by design. For example, wearable devices (gadgets).

But the size reductions due to technological improvements have not been enough to meet the demand for greater miniaturization. To further reduce the size of electronic components, chip manufacturers have systematically modified packaging by removing parts of little use. Surface mount components (SMD) were the first major advance in this direction. SMDs dispensed with leads that passed through holes in the PCB, providing the component with support and electrical connection. Mounting of SMD components was carried out directly on the surface of the printed circuit board, by reflowing solder paste, which provided mechanical and electrical connection while saving significant free space.

Fig.1. SMD components dispense with pin-through-hole and are mounted directly to the PCB

Then, the chip manufacturers went further, removing even a small amount of plastic from the SMD package. Up to the fact that the components supplied to the client were little more than bare silicon.
The results of such optimization can be quite significant. For example, Nordic Semiconductor, a manufacturer of microcircuits for wireless communications, offers its systems on a chip (SoC) in two versions. The SoC in the QFN surface mount package occupies 36 mm 2 on the PCB, while the CSP version occupies only 9.6 mm 2 . Space saving - almost 76%.

However, making a CPS version of a conventional chip is not easy. It took many years for semiconductor manufacturers to improve their manufacturing processes before delivering silicon chips that are robust enough to be directly mounted on a printed circuit board and able to withstand the rigors of everyday use.

Although (with some exceptions) LEDs are not manufactured on silicon, but most often are structures based on semiconductor nitrides (GaN and its solid solutions) grown on a substrate of sapphire (Al 2 O 3) or silicon carbide (SiC), they fall under the same manufacturing processes that led to the downsizing of conventional electronics.

High temperature is the main degradation factor for LEDs. The higher the temperature, the shorter the service life. However, over the years of testing, a large amount of data has been accumulated, and it is increasingly clear that each new generation of semiconductor devices is becoming more reliable, capable of a longer service life. For example, LEDs operated at a very high junction temperature of 105°C have shown a useful life in excess of 36,000 hours.

3. Less is more

The main advantage of CSP technology is obvious - it significantly reduces the size of the package (body) of the LED (Fig. 2).

Fig.2. The evolution of LEDs downsizing to a chip-scale package

But there are other important benefits as well. For example, these tiny solid-state lighting (SSL) fixtures are substantially cheaper to manufacture, allowing customers to significantly reduce the cost of producing lighting equipment.

CSP LEDs have formed a new concept of minimal packaging, representing a real step into the future, even compared to flip-chip technology ("flip-chip" - a method of directly mounting chips on printed circuit boards and other substrates). The pads are located on the bottom surface of the LED CSP with a pitch compatible with standard SMD hardware. This feature did away with the need for chip manufacturers to add wafers, bases, or any other form of additional packaging.

There is no clear definition for a CSP, but the industry generally considers a "chip-scale package LED" to be any device equal in size to or up to 20 percent larger than the active area (the light emitting area of ​​the LED).

Devices of this size give engineers more design flexibility. For example, they provide the freedom to change the geometry of the radiating surface, the level of luminosity of LEDs, and make it possible to reduce the size of fixtures.

Fig.3. The dimensions of the contact pads of the CSP LED correspond to the standard SMD mounting technology

Assembly shops are also interested in using CSPs with their standard pitch pads (both anode and cathode based on the LED) because they make the assembly process easier and cheaper. Devices can be mounted directly to the PCB using standard "pick-and-place" hardware and there is no need for additional wire splicing required by other miniature package types such as flip-chip. In addition, CSP LEDs can be tested using standard automatic test equipment (ATE).
Another important advantage of CSP is the lower thermal resistance than conventional LEDs. For example, Toshiba's TL2F2 SMD LED has a package thermal resistance of 30K/W (junction to solder pad). For comparison, the TL1WK series LED from the same company (Figure 4) is available in CSP format and has a thermal resistance of 17 K/W (junction to solder pad). CSP LEDs with thermal resistance below 5K/W have already been announced.

Fig.4. Toshiba's TL1WK LED has low thermal resistance

The low thermal resistance allows CSP LEDs to operate at higher currents than LEDs in conventional packages, to increase brightness without undue risk of premature failure due to overheating. Because of their small size, CSP LEDs emit as a point source of light rather than the more diffuse source of traditional packaged LEDs. This allows lighting fixtures to use smaller lenses, thereby reducing cost, and to use smaller form factors that were previously impractical. Another optical advantage of the CSP comes from emitting light from all five sides of the chip (a conventional SMD LED package only emits from the top side), which increases the luminous flux at a given current.

The demand for increased "lumen density" - driven in part by the need to reduce the number of LEDs for a given light output (light output), which in turn cuts materials and assembly costs - is likely to be the catalyst for CSP to replace traditional LEDs. In this case, the effect can be significant. For example, a typical LED might have a light output of 120 lm from a light emitting area of ​​12.25 mm 2 at a lumen density (luminosity) of 9.8 lm/mm 2 . By comparison, a CSP LED could deliver 30 lm from a 1 mm 2 light emitting area, providing a luminosity of 30 lm/mm 2 - three times that of a conventional LED.

The improved luminosity results in more compact light engines, including fewer LEDs in the emitting array. What will be in demand for the production of standard, ready-to-use Chip-on-Board (CoB) modules that simplify the design of new lighting products for engineers, even non-lighting specialists.

4. CSP LEDs on sale

Leading LED chip manufacturers are active in the CSP solutions segment. For example, Samsung Electronics introduced its second generation of CSP LEDs in mid-2015. The devices are made using the flip-chip method using a blue emitter and a phosphor (to produce white light) applied directly to each face of the crystal, except for the bottom surface.
According to the manufacturer, these LEDs provide a 10% improvement in efficiency and luminous flux compared to the previous generation. The company offers both single-chip LEDs (Fig. 5) and CSP arrays of 2x2 or 3x3 LEDs. The matrices are small enough to allow the use of a single lens, while LEDs in conventional packages would require many separate lenses.

Fig.5. Samsung LM101A CSP LED has an area of ​​1.4mm 2

Lumileds also produces its own CSP LEDs in 1x1mm (LUXEON FlipChip White 05) and 1.4x1.4mm (LUXEON FlipChip White 10) chip sizes. The latter has a thermal resistance of 2 K/W and provides an efficiency of up to 141 lm/W (at 350 mA).

Nichia announced in the spring of 2015 the commercial launch of Elemental LEDs (ELEDS) - flip-chip LEDs with a size of 1/9 of the previous generation of similar products. The company's CSP LEDs later received the serial name Direct Mountable Chip (DMC) and are available in two versions - 1 mm 2 (NCSLE17AT 1717) and 2 mm 2 (NVSLE21AT 2121). They are a cost effective replacement for conventional high power (1-4W) LEDs and offer efficiencies between 120 and 150 lm/W.

Toshiba introduced the previously mentioned TL1WK series LEDs to the CSP market. The device measures 0.65x0.65mm (0.42mm2) and can handle 180mA without the risk of overheating, giving the designer some leeway within the company's thermal design guidelines.

Cree also develops CSP LEDs, currently the smallest package commercially available, the 1.6x1.6mm (2.56mm2) XLamp XQ series. The LEDs are based on SC3's technology, which uses a SiC (silicon-carbide) substrate.

Seoul Semiconductor, Epistar, Lextar and a number of other well-known manufacturers already have CSP products in their portfolio. Moreover, Epistar produces not only CSP LEDs, but also modules based on them (Fig. 6), in the power range of 20-40 W, offering customers an inexpensive alternative to COB modules.

Fig.6. Epistar modules are equipped with CSP LEDs

5. Dominant trend

There is no end in sight to the search for how to make electronic components smaller. Compact products such as wearable devices (gadgets) are increasingly miniaturized.

LEDs experienced a much slower shrinkage in size than other electronic components because they were susceptible to thermal degradation, especially in miniature packages. But the demand from the lighting industry to minimize assembly costs, increase "lumen density," has forced LED chip manufacturers to overcome technical challenges. Modern chips have become much more reliable and can now withstand higher temperatures, especially in the CSP format.
As a consequence, these new fixtures can operate at higher direct currents, increasing luminous flux.

Today, CSP LEDs are not for everyone. They are too fragile and too small to be accepted by any assembly company. But the benefits of these tiny "creatures" are plentiful, and all major LED chip manufacturers are working on commercial products for mass production in the next 6-12 months. Analysts report that if in 2013 CSP LEDs accounted for only 11% of the total number of high-power LEDs, then their share in 2020 will approach 40%.
While the market is waiting for the transition of CSP technology into the dominant LED lighting trend, KTL already manufactures almost all lighting equipment using CSP LEDs today.