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What Are The Eequirements For LED Packaging Technology For Display Screens

Different application positions will use different specifications of display screens, and different display screens require LED devices with different technical requirements. So what are the technical requirements for LED used in display screens? The following descriptions are based on different categories:

In recent years, with the Beijing Olympics, the Shanghai World Expo, and the Guangzhou Asian Games, LED displays can be seen everywhere. The LED display screen can display changing numbers, text, and graphic images; it can be used not only in an indoor environment but also in an outdoor environment, and has the incomparable advantages of projectors, TV walls, and LCD screens.

LED is widely valued and developed rapidly, which is inseparable from its own advantages. These advantages can be summed up as follows: high brightness, low working voltage, low power consumption, miniaturization, long life, impact resistance and stable performance. The development prospect of LED is extremely broad, and it is currently developing in the direction of higher brightness, higher weather resistance, higher luminous density, higher luminous uniformity, reliability, and full color.

1. Types of LED display

1) According to the color classification

Single-color display: single red or single green; dual-color display: red and green dual-color, 256 gray levels, can display 65536 colors; full-color display: red, green, and blue three-color, 256 gray levels The full-color display can display more than 16 million colors.

2) Classification according to the constituent pixel units

Digital display screen: The display pixel is a 7-segment digital tube, which is suitable for making clock screens, interest rate screens, etc.;

Graphic display: The display pixel is a dot matrix module, which is suitable for playing text and image information;

Video display screen: The display pixels are composed of many light-emitting diodes, which can display various video files such as videos and animations.

3) According to the location of use

Indoor display: small luminous points, dense pixel pitch, suitable for close viewing;

Semi-outdoor display: between indoor and outdoor, not rainproof, suitable for information guidance on the door lintel;

Outdoor display: large luminous points, large pixel pitch, high brightness, can work in the sun, with wind, rain, and waterproof functions, suitable for long-distance viewing.

4) According to the driving mode, there are static, horizontal scrolling, vertical scrolling and page turning display, etc.

2. Types, advantages and disadvantages of LED for display screens

According to the classification of the display screen, the pixel LED used can also be divided into the following types:

1) Dot matrix module

Advantages: low cost, mature processing technology, stable quality; Disadvantages: brightness and color consistency are not well controlled, and Masaige phenomenon is prone to occur;

2) In-line lights

Advantages: Color consistency is relatively easy to control, and the pixel pitch can be freely adjusted and combined according to needs; Disadvantages: the red, green and blue color mixing effect is not good, the angle is not large, it is difficult to control the consistency of the angle, and the processing is prone to unevenness, up and down, left and right. Easy to misplace

3) Patch

Advantages: display color, color mixing effect, angle consistency, etc. are the best; disadvantages: high cost of packaging and processing;

3. LED packaging technology requirements for display screens

Different application positions will use different specifications of display screens, and different display screens require LED devices with different technical requirements. So what are the technical requirements for LED used in display screens? The following descriptions are based on different categories:

1) SMD LED for indoor display.

SMD LED for indoor display screens are divided into "three-in-one" and "three-in-one". The former is mostly used in areas with relatively low cost and low display requirements, while the latter has better display effects and relatively low cost. High, the following mainly explains the "three in one";

(1) Brightness: The first thing to consider is the appropriate ratio of product brightness. At present, the red, green and blue brightness of most full-color displays are matched according to 3:6:1 (that is, the red brightness in a pixel accounts for 30%, and the green brightness is 30%. It accounts for 60% and blue is 10%). Generally speaking, packaging factories and upstream chip manufacturers almost test products according to 20mA, but when applied to display screens, this current is hardly driving LED lights. Yes, generally speaking, the red, green and blue LEDs are composed of different chip materials, and their heating, luminescence, and brightness attenuation in actual use are not proportional. Generally speaking, the red attenuation ratio is smaller, and the blue-green attenuation is larger. Therefore, in order to ensure a relatively long service life of the display, the general designer will lower the blue-green drive current than red; for example: if red is driven at 18mA, green is driven at 15mA, and blue is driven at 12mA, according to the LED Chip IV-If relationship:

Roughly we can calculate that the actual brightness of the LED, the relationship between red, green and blue is:

R: 3÷90%

G: 6÷75%

B:1÷60%

At the same time, the brightness should be classified. The purpose of the classification is to make the display screen not be able to see the difference in brightness by the naked eye. Generally speaking, the brightness difference that the human eye can be more sensitive to distinguish is 30%, deducted For the test error of the equipment and the error of the installation mechanism, it is better to design the light splitting according to 10%~20%.

(2) Color: According to the optical effect, the white light is decomposed into a gradual transitional color spectrum after passing through the prism. The colors are red, orange, yellow, green, cyan, blue, and purple, which is the visible spectrum. Among them, the human eye is most sensitive to red, green, and blue. The human eye is like a three-color receiver system. Most colors can be produced by combining the three colors of red, green, and blue in different proportions. Similarly, most monochromatic light can be decomposed into three colors of red, green and blue.

This is the most basic principle of colorimetry, the principle of three primary colors. The three primary colors are independent of each other, and no one primary color can be combined with the other two colors. Red, green and blue are the three primary colors, and the color range of these three colors is the most extensive. The three primary colors of red, green and blue are added in different proportions to form a mixed color called additive color mixing. The three primary colors are three colors that are independent of each other, and any one of them cannot be produced by mixing other two colors.

The color obtained by adding the three primary colors of different proportions is called additive color mixing. The law is:

Red + green = yellow

Red + blue = purple

Blue+green=cyan

Red + blue + green = white

The best color matching of LED for display screens is: red 620-630nm, green 520-530nm, blue 465-475nm, of course, this range can be reduced according to actual needs, such as red with 3nm as the first gear, blue and green with 2.5nm For the first gear.

Angle: In fact, for the angle, of course, the bigger the better, but the more important thing is that the angle is not only big, but also the angle curve must be full and smooth, and the red, green and blue must be consistent, otherwise the display screen will appear. After that, dark areas will be displayed in some locations, or a certain color will be particularly bright or dark;

3) Electrical parameters: The electrical parameters of LED are mainly manifested in forward voltage (vf), reverse current (Ir) and anti-static (ESD). Generally, the display screen is driven by a constant current of 5v DC power supply, so: LED's Vf generally does not require high consistency, as long as it is controlled within a reasonable range (generally red 1.8-2.2v, blue-green 3.0-3.4v); generally speaking, the larger the ESD, the better, because ESD is everywhere, so The greater the ESD of the LED, the less likely it is to cause problems when processing the display; the reverse current requirement is Vr=5v, Ir≦10uA

Oval direct plug LED for outdoor display

LED for outdoor display screens generally use straight plug-in lights with an oval structure. Compared with LED for indoor displays, oval lights for outdoor use mainly have horizontal and vertical angles in the light-emitting angle. Generally speaking, the display screen is outdoors. , The horizontal visual range is relatively large, and the vertical visual range is relatively small;

Generally speaking, the horizontal angle of the outdoor display LED is about 110 degrees, and the vertical angle of about 50 degrees is better. Because the angle of the direct plug-in lamp has many factors, the main manifestations are:

(1) The appearance and shape of the LED package;

(2) The bowl and cup structure of the bracket;

(3) The structure of the chip and itself;

(4) The refractive index of the packaging glue;

(5) Consistency of material quality;

(6) Packaging process (that is, the position of the light emitting height of the chip);

Therefore, the angle of LED used in outdoor displays is more difficult to grasp, not only requires a good design, but also has a better level of process design and quality control.

With the continuous improvement of technology, the requirements for display screens will become higher and higher. Of course, the requirements for LED packaging technology will also be equally high. I hope that colleagues in the industry will work tirelessly to make better products.