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Looking at the advantages and disadvantages of different types of packaged LED light headlights
Mar 29, 2018

Automotive headlamp bulbs made of LEDs have significant advantages such as long life, high brightness, and long throw distance, and have become a preferred light source for replacing halogen lamps and xenon lamps in large areas, and adaptive automobiles manufactured by multi-beam intelligent strong light LEDs. Headlamps have also become the trend of the next generation of car headlamps.

Figure 1 shows that, from the point of view of road lighting, the headlights with LED lights are significantly better than the headlights with halogen lamps in terms of visual, brightness, and throw distance. The life of the former is more than tens of thousands. Times.

▲ Figure 1: The picture shows the near (left) far (right) light effect of a car headlight with a halogen lamp, and the (near) (left) far (right) light effect with a car headlight using an LED.

Although LEDs are a new kind of lighting source, in terms of auto parts and aftermarkets, because the original lamp body system of the car headlights must be used, the dimensions and fixing method of the headlight bulbs of the LEDs are used in the design. Interfaces, power supply and control, lighting area shape, brightness, and luminous flux should be consistent with halogen bulbs and xenon bulbs.

When replacing halogen bulbs and xenon bulbs, there is no need to make major changes to the lamp body. As a new alternative light source, car headlights using LEDs must bring new experiences to the user, not only in terms of life and reliability, but also significantly increase without reducing or even reducing glare. Increase ground illumination and throw distance.

▲ Figure II: Halogen Bulb (Left) and Xenon Bulb (Right)

As can be seen from Figure 2, the halogen bulb and xenon bulb are linear light sources, the length of the light area is about 4-6mm, and the diameter is about 1-1.2mm. It is ideal as an LED headlamp bulb that replaces halogen bulbs and xenon bulbs. The light emitting area should be 4-6mm x 1.1-1.2mm. Obviously, LEDs with linear light emitting regions are the preferred light source for manufacturing LED headlight bulbs.

As a mature light source, LEDs have been widely used in lighting, backlighting, display, and other fields. High-power LEDs are characterized by their small size, high current, and high reliability. They are mainly used in directional projection lighting, such as headlights and motorcycles. Lights, pico projectors, stage lighting, portable high-light lighting, long distance searchlights, etc. At present, the light-emitting LED packages used for automotive headlights and motorcycle lights include COBs (short for chip on board), CSP (short for chip scale package), COBs, 2016-LEDs or CSP-LEDs, and high-power ceramics. Base LEDs and headlights dedicated LED modules.

▲ Figure 3: Car headlight bulbs made with COBs

Figure 3 shows car headlight bulbs made using COBs. The luminous flux of this kind of light source can be very high, mainly depends on the size of the light emitting area. Generally can reach 2000-3000LM. COBs are usually surface light sources and do not belong to linear light sources. Even if the light emitting regions of the COBs are surrounded by strips, ceramics or superconducting aluminum with good thermal conductivity as the substrate may not be able to achieve the goals of small size, large current, and high reliability due to the limitation of the package type. Headlamp bulbs made of COBs are far from the halogen bulbs and xenon bulbs due to the shape of their light emitting areas. Many light from outside the linear region becomes harmful stray light and glare, not only cannot be improved. The effective illumination of the road surface also destroys the light shape and brightness distribution of the projection beam. Blindly increasing the luminous flux not only brings more serious heat dissipation problems, but serious light glare and deformed light intensity distribution will become a hidden safety issue. The headlight bulbs made of COBs, though they are low in cost, are relatively poor in reliability and light shape and can only belong to primary products and have been eliminated from the mainstream market.

▲ Figure 4: Automotive headlight bulbs made from high-power ceramic-based LEDs

Figure 4 shows automotive headlamp bulbs made using high-power ceramic-based LEDs. High-power ceramic-based LEDs are small-size, high-current, high-reliability and strong-light LED light sources, which are represented by CREE's XHP35, XHP50, XHP70, and XML-2. Because high-power ceramic-based LEDs have lenses with conventional LEDs and vertical chips that often use high-efficiency light, their luminous efficiency is usually higher than other LEDs. The ceramic substrate used has a low thermal resistance so that high-power ceramic-based LEDs can be used normally under the condition of an overdrive.

Due to the limitations of the package type, the chips in the high-power ceramic-based LEDs can only be arranged in a square shape. After passing through the lens, the light emitting area appears as a circle. Obviously, when the high-power ceramic-based LEDS headlight bulbs are installed in the whole lamp, many light from outside the linear area becomes harmful stray light and glare, not only can not improve the effective illumination of the road surface, but also The shape and brightness distribution of the projection beam will be destroyed. In addition, high-power ceramic-based LEDs are affected by the size of the substrate and are very bulky. The mainstream products are 7070, 5050, and 3535. If in order to increase the luminous flux, two high-power ceramic-based LEDs are closely arranged on a narrow car headlight circuit board, a dark area will occur, and the luminous flux will be wasted more wastefully.

Although high-power ceramic-based LEDs have insurmountable disadvantages when used in automotive headlights, they are favored by the market because of their relatively mature package form and high light efficiency. At present, most LED automotive headlamp bulbs use high-power ceramic-based LEDs. Major suppliers at home and abroad include US CREE, South Korea LG, Taiwan Weitian, and Jiangxi Jingrui. With the advent of linear light LED sources with better price/performance and user experience, such as 2016-LEDs and CSP-COBs described below, the application of high-power ceramic-based LEDs to automotive headlamps may be gradually replaced.

▲ Figure 5: Car headlight bulbs manufactured using 2016-LEDs

Figure 5 shows the automotive headlamp bulbs made with 2016-LEDs. The feature is that LEDs with external dimensions of 2mm x 1.6mm are linearly arranged on the lamp panel of the car headlights. The LUXEON Z and ZES of Philips Lumileds are currently used. The original design of 2016-LEDs is for flash, which is a small size, high current, high reliability and strong light source. In order to ensure sufficient light efficiency, good thermal conductivity, and the ability to control the light emission angle within 120° under high power usage conditions, 2016-LEDs often use large-scale flip-chip, vertical or thin-film flip-chip and ceramic substrate packaging technologies. Its manufacturing costs and use costs are relatively high. At present, 2016-LEDs are mainly used for manufacturing high-end LED car headlight bulbs. The major suppliers of 2016-LEDs include Philips Lumileds of the United States, Samsung of South Korea, Taiwan Everlight, Shenzhen Avenue Semiconductor, Guangzhou Hongli, Guangzhou Jingke and Jiangxi Jingneng.

CSP-LEDs featuring small size are also used in LED headlights. At present, there are many types of CSP-LEDs, and the manufacturing processes and technologies vary widely. At present, CSP-LEDs are mainly five-sided. Because the phosphor layer on the CSP-LEDs is three-dimensionally wrapped around the flip chip, the adhesiveness is poor. In the process of die bonding and reflow, any mechanical impact, difference in solder melting and coefficient of thermal expansion can cause the fluorescent adhesive layer to The flip chip is detached and fails.

Obviously, compared to 2016-LEDs, CSP-LEDs are not suitable for producing highly reliable headlights. At present, major domestic and foreign suppliers of CSP-LEDs include South Korea’s Samsung and Seoul, Taiwan’s Jingdian, Shenzhen’s Dongshuguang, and Zhongshan Sanguang.

▲Figure 6: Conversion of CSP-COBs manufactured by Shenzhen Avenue Semiconductor to the headlights made of high-power LEDs as shown in Fig. 4

Figure 6 shows car headlight bulbs made using CSP-COBs. The CSP-COBs are first applied to the surface of the aluminum nitride ceramic substrate in a linear array of flip chips, and then the phosphor is three-dimensionally wrapped around the flip chip with a spray coating method, and its appearance and patch are applied to the surface of the circuit board. CSP-LEDs are similar, so they can be called CSP-COBs.

In CSP-COBs, the perfect combination of flip-chip and aluminum nitride ceramic substrates allows CSP-COBs to have the lowest thermal resistance, allowing a high current density of operation. The light emitting region formed on the CSP-COBs by the linearly arranged flip chip not only does not produce a dark region but has a high center luminance and a high illuminance at the center of the irradiated surface. After the headlights are installed in the car, there is no waste of stray light and the luminous flux is highly utilized. In general, the central illumination of car headlamps with CSP-COBs whose luminous flux is only 1200-1500 LM as the light source can achieve the central illumination of car headlights with high-power ceramic-based LEDs with luminous flux exceeding 2000 LM as the light source, and the reduced heat. More than 20%.

In addition, the substrate size of CSP-COBs is usually 5mmx5mm or 7mmx7mm, and the electrode pads and heat-dissipation pads on the back are the same in size as CREE XHP50 and XHP70. When used, 5050 and 7070 CSP-COBs can be directly replaced CREEXHP50 and XHP70, without changing the original circuit board and lamp body design. Because the area of the thermal pad on the back of the CSP-COBs is large, even if the CSP-COBs are soldered to the automotive headlamp circuit boards made of conventional copper-clad metal substrates, there will be no board burn-out problems and the reliability is high.

The CSP-COBs have no molded lens on the surface, making the shape of the CSP-COBs closer to halogen and xenon lamps, and the projected light shapes are more similar to the light intensity distribution. Because there is no molded lens protection, the phosphor layer wrapped on the surface of the flip chip is relatively easy to lose relative to the lens, and some products are easy to fall off, so that the yield of the CSP-COBs in the solid crystal reflow is relatively low. When installing the lamp, be careful not to touch the surface of the light emitting area of the CSP-COBs.

▲ Figure 7: The left picture shows the Osram headlight special module, and the right figure shows the Philips car headlight special module

Figure 7 shows the automotive headlight special LED modules of OSRAM and Philips, which are mainly used in the front loading market and are auto headlamps and auto parts markets that are designed with special LED modules for headlights. The main suppliers are Germany OSRAM, United States Philips Lumileds, South Korea LG, Japan Nichia, etc. Among them, OSRAM and LG use UX3 vertical chip, Philips Lumileds use TFFC film

Flip chip and Nichia have adopted new technologies such as flip-chip plus dams and fluorescent glass. At present, the traditional dress, flip-chip and vertical chips used by domestic and Taiwanese companies cannot meet the demanding requirements of the LED headlamps for optical headlights, lighting angles, heat conduction, and reliability.

From the above simple analysis, it can be seen that in the auto parts and aftermarket, the traditional halogen bulbs and xenon bulbs are still the main alternatives. Automotive headlight bulbs made with high-intensity LEDs should be consistent with halogen bulbs and xenon bulbs in terms of physical dimensions, mounting methods and interfaces, power and control, lighting area shape, brightness, and luminous flux. Although traditional COBs have low manufacturing costs, their reliability and light shape are relatively poor and they have been eliminated from the mainstream market.

Due to insurmountable shortcomings and high cost, the application of high-power ceramic-based LEDs to automotive headlights will be gradually replaced by cost-effective linear LED light sources with better user experience. Linear light LED light sources can be 2016-LEDs in a linear arrangement on a circuit board, or 5050 and 7070 CSP-COBs. Five-faceted CSP-LEDs are not suitable for producing highly reliable headlights. The headlight special LED modules for automobiles are mainly used in the front loading market and are auto headlights and aftermarkets that are designed with special LED modules for headlights.

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