LED miniaturization/thinning
As mobile devices become thinner and smaller, the market demand for small-pitch products is growing stronger year by year, and parts are also facing more requirements to reduce height and size. In addition, since most outdoor full-color display devices use LEDs, in order to improve performance, full-color LED packaging is also moving towards higher density (Figure 4).
Figure 4 Full-color LED packaging is moving towards higher density.
Take ROHM as an example. Since it started producing SMD LEDs in 1996, it has been continuously moving towards miniaturization and thinness of its products every year. In 2007, it successfully launched the world's smallest and thinnest product - the 1006 (0402 inches) (t=0.2 mm) size "PICOLED series" mass production, and has now successfully developed the 0603 (0201 inch) size "PICOLED-mini" (Figure 5). The following details the key technologies for small and thin packaging of LED lighting products.
Figure 5 Miniaturized LED chip
Component Technology
In order to make the package smaller and thinner, the internal LED components must also adopt small and thin specifications. Therefore, the industry adopts self-developed process technology from the film formation of the light-emitting layer on the wafer to the chip formation, and finally successfully reduced the component size of aluminum gallium indium phosphide (AlGaInP) light-emitting LED to 0.13 mm (mm) at the corner and t=50 μm (μm) in thickness, achieving the goal of miniaturization in one fell swoop.
Molding Technology
In order to ensure the strength of the product, the industry has proposed a method for resin sealing of semiconductor components. The resin sealing process adopts the transfer molding method, but the mold cavity of the casting mold will become thinner and thinner (the mold cavity thickness is 0.10 mm), so the fluidity of the resin must be ensured. In addition, in order to ensure the optical properties of the LED, it is impossible to add filler materials to ensure the strength of the parts, which will cause the mechanical strength of the product to decrease, but the above problems have been solved.
Assembly technology
In the production of LED chips, LED components must be wire-bonded in a sealing resin with a thickness of t=0.10 mm. Therefore, the industry uses a self-developed wire bonding machine to successfully reduce the spacing and reduce the loop.
Currently, the world's smallest ultra-small LED is only 1006 in size and 0.2 mm thick. This product is not limited by the installation space and uses high-brightness LED components. Through the LED light, the light can penetrate and illuminate the inside of the mobile phone shell.
In addition, ultra-small LEDs can also be used in dot matrix displays. The minimum pitch of conventional 1608-size products is 2 mm, while ultra-small LEDs can be installed at a high density with a minimum pitch of 1.5 mm, thus showing a more delicate display effect.
In terms of other features, since the package size of this solution is extremely small, it can be used in seven-segment displays and dot matrix display modules, and omits processes such as die bonding, wire bonding, and resin bonding that are required in chip-on-board (COB) technology.
Automotive LED lighting attracts attention
As LED bulbs and lighting applications become increasingly popular, automotive LED lighting is more popular than ever before. In vehicle interior applications, LED light sources are now almost fully used for car audio, car navigation systems, air conditioning panels, and other major backlighting. Next, interior lights and warning lights that still use traditional bulbs, as well as dashboard backlights that use cold cathode tubes, will gradually face the fate of being replaced.
In recent years, traditional bulbs such as taillights, turn signals, and positioning lights have been gradually replaced in vehicle exteriors. Even headlights have been replaced by LED lights instead of traditional halogen lamps and high-intensity discharge (HID) lamps. From the perspective of environmental recognition, the trend of using LED lights as daytime running lamps (DRL) is even more noteworthy.
In order to meet the diverse needs of automotive applications, the industry will focus on the following two areas in the development of automotive LED technology.
Customized requirements for color and brightness
In terms of car interiors, the colors of light sources around dashboards, such as air conditioning panels, are mostly specified by car manufacturers. The aluminum gallium indium phosphide component-based LED series products launched by the industry have the advantage of self-made components, and both color and brightness can be customized according to customer requirements.
Other white and pink LED series, which are successfully created using indium gallium nitride (InGaN) and phosphor-containing resin, also provide color customization. For example, the backlight of the main key, which is used frequently, can highlight the difference between it and the adjacent keys through subtle color differences to arouse the user's attention. This aluminum gallium indium phosphide component adopts technology to suppress wavelength differences during the epitaxial growth stage, so it can meet the strict specifications of customers.
Develop anti-sulfurization measures/expand new products
On the other hand, the market's biggest requirement for LED lights for vehicle exterior applications such as taillights is heat resistance and tolerance to harsh climates. However, since the lead frames of traditional LED packages are made of silver-plated materials, they are prone to sulfurization and beam degradation, and this problem is now beginning to receive attention.
In view of this, the industry has adopted nickel plating/palladium plating/gold plating as the lead frame material, successfully solving the problem of beam degradation caused by sulfurization. In addition, for the disadvantage of reduced brightness caused by nickel plating/palladium plating/gold plating, the industry has also developed a new series of products (Figure 6), which solves the problem by improving the output efficiency of the components themselves, showing a beam intensity that is no less than that of silver-plated products. In the future, the industry will adopt nickel plating/palladium plating/gold plating as a countermeasure to improve package sulfurization, and actively expand new product series to meet the diverse needs of customers.
Figure 6: The industry uses the improvement of LED light output efficiency to reduce the disadvantage of reduced brightness caused by replacing packaging materials.
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