Precautions of design and produce full-color LED display

Precautions of design and produce full-color LED display


LED display may encounter different problems during use, in order to reduce such issues, we need take carefully for the following items during display design and producing.

1) Take care of the anti-static.
LED display assembly plant should have good anti-static measures. Such as dedicated anti-static flooring, anti-static soldering iron, anti-static table mat, anti-static ring, anti-static clothing, humidity control, equipment grounding (especially cut legs machine), are all basic requirements, and must use electrostatic analyzer to test the environment periodically.

2) Design the current value.
The nominal current of the LED is 20mA, the generally recommended maximum current must not exceed the 80% of nominal value, especially for small pitch displays, due to poor heat radiation conditions should reduce the current value. According to the experience, because the red, green, and blue light decay rate are not the same, so it’s better to reduce the blue and green LED current value, and finally maintain the consistency of the white balance in the display after prolonged use.

3) The thermal design.
LED working will produce heating, high temperature will speed LED attenuation and effect LED stability, so the PCB thermal design, and cabinet ventilation design will affect the performance of LED display.

4) The driving circuit design.
The driver IC arrangement in the drive circuit board of display module will also affect the brightness of the LED. If driver IC transmission distance is too far in the PCB, then the transmission path voltage drop is too much, resulting in a lower brightness because the normal operating voltage of the LED is lost during transmission. We often found the LED around module brightness is lower than the middle, and this is the reason. Therefore, to ensure the consistency of the brightness of the display, it is necessary to design a uniform driver circuit maps.

5) Mix LED.
The LED with same color but different brightness need to be mixed, or discrete insert LED lights in PCB, to ensure the color consistency of the entire screen. If there is a problem in this process, there will be the part area brightness is inconsistent, directly influence the effect of the LED screen.

6) Make sure the DIP LED is Perpendicular to the PCB board.
For DIP LED, ensure that the LED is perpendicular to the PCB board before soldering. Any deviation will affect the brightness consistency, and result color blocks.

7) Wave soldering temperature and time.
To ensure the screen quality, must strictly control the reasonable wave welding temperature and time, it is recommended that: preheating temperature is 100 ° C ± 5 ° C, the maximum does not exceed 120 ° C, and the preheating temperature must rise smoothly, soldering temperature is 245 ° C ± 5 ° C, and welding time is no more than three seconds, the PCB should not vibration or shock after soldering, until it reinstate normal temperature. The temperature of the wave soldering machine need to be checked regularly, this is determined by the characteristics of LED, overheating or temperature fluctuations will directly damage the LED or cause the LED quality risks, especially for the small size as 3mm round and oval LED.

8) Welding control.
More than 50% blind LED in display are caused by failure welding, such as LED pin failure welding, IC pin false Welding, signal pin lost welding and so on. Those problems need improve producing process and strengthen the quality inspection. Vibration testing before shipping is a good testing method.

How LED affect display quality ?

How LED affect display quality ?



For a full-color LED display, LED as its most critical components, its quality plays a very important role in the on the LED display. LED screen uses large number LED per square meter, LED directly determines the performance, color saturation and sharpness of full-color LED display.

1) Full-color LED display brightness
LED brightness determines full color LED screen brightness, the use of higher current, the LED brightness is higher. Also, LED have different angle, in the same chip size, the smaller view angle, the higher brightness, but the display’s viewing angle generally is 100 degrees -110 degrees, to ensure LED screen sufficient angle.

2) The failure rate of LED screen
LED display is composed by thousands or even hundreds of thousands of red, green, and blue LED components. Usually failure rate is less than 1/10,000 after 72 hours aging test.

3) The light attenuation of LED display
LED brightness will slowly decay along with long term use, the attenuation is related with LED chip, auxiliary materials, packaging technology and so on. In general, after 1000 hours aging on 20 mA at normal temperature, the red LED attenuation should be less than 7%, blue and green LED decay should be less than 10%. The RGB light decay consistency has great influence on future white balance, thereby affecting the fidelity of the display screen.

4) LED display antistatic ability
Since LED is semiconductor devices, it’s sensitive to static electricity, can easily failure by static, so the anti-static ability is essential for the lifespan of LED display. Generally, LED lamp anti static voltage testing should be no more than 2000V.

How to choose a good LED display ?

Now, LED display is very popular for the advertising, TV studio, touring shows and so on. And many buyers may confused how to find a good quality and suitable screen, will guide you step by step, and teach you how to choose a good LED display, and it’s mainly lies in the following aspects.

1. Flatness: Display surface flatness need to within ±1mm, in order to ensure the display image is not distorted, partial raised or recessed will lead display dead viewing angle. The flatness mainly depends on the design and production process of both mask and cabinet.

2. Brightness: Usually, indoor full color brightness ≥800cd/m2, for outdoor full color display brightness ≥4000cd/m2, if outdoor against the sun, then much ≥6500cd/m2, otherwise it will be too low brightness to see the displayed image. The brightness is determined by LED and LED chip are used, and can be measured by luminance colorimeter.

3. Viewing angle: Screen viewing angle directly determines the amount of audience, and of course the bigger the better. It’s mainly depending on the LED chip package. Usually, for SMD LED with angle of 120° (horizontal) and 120° (vertical), for DIP LED is 120°(horizontal) and 60° (vertical).

4. White balance: White balance is one of the most important indicators for LED display. In color science, it will show pure white color only when red, green and blue ratio meets 1:4.6:0.16. If the actual proportion is different, the white balance will have deviation. Generally pay attention to the LED screen whether there is bluish white or yellowish green color. White balance is affected by display control system and LED chip.

5. Refresh rate: Refresh is a very important parameter for LED screen, especially in TV studio. If low refresh rate there will be scan lines in the image when the camera shoots on it, and the audience will see the flicker though the camera. Usually the refresh rate ≥1000Hz, some high standard application need 3000Hz or more.

6. Color reduction: Color reduction refers to how the image color is produced by display, that means the LED screen color and video source must maintain highly consistent, so as to ensure that the image realism.

7. No mosaic and dead LED: Mosaic is square in the LED screen that always on or off, also means broken modules, mainly because broken cable or connector. Dead LED is the pixel in the display always on or off, and it’s mainly determined by LED chips are used.

8. No color block: Color block is difference color between modules, the block mainly caused by signal transition between modules, this phenomenon is mainly depend on the control system, gray level, and scanning mode.

20bit depth color- leading position in led display

What is 20bit depth color?

• Color depth is the number of bits used to indicate the color of a single pixel in a bitmapped image or video frame buffer.
• Higher color depth gives a broader range of distinct colors.
• 20-bit means 1,048,576 different colors can be showed.

What could 20bit depth color bring?

• Precise performance when the screen in low grey level
• High precision color reproduction, perform exact color of content/brand
• Vivid Color Image look richer and deeper

20bit depth color- leading position in led display

• Compared to main stream technology 16bit depth color in the market, AOTO 20bit be regarded as pioneer, plays a leading position.
• 16bits shows totally 65,536 colors, while 20 bits shows totally 1,048,576 different colors, 16 times color higher.
• With continuously efforts, Aoto is under developing 24bits ‘True color’, which will exceed the color that Human eyes could see. Roughly, Human eyes can see 10 million colors, which would correspond to just over 23 bits.

Differences between LED display light sources

The LED light source is key material for LED display performance, it determines the color consistency, brightness, viewing angle, and the cost for screen. Here introduce the difference between dot matrix, DIP and SMD LED light source.

1. Dot matrix module:

 It is the old design, evolved from the interior pseudo-color dot matrix screen.

• Advantages: low cost of raw materials, simple production process, also stable quality.
• Disadvantages: poor color consistency, has mosaic phenomenon, and poor color reproduction.

Dot matrix module

2. DIP LED: 

In order to solve the color problem of dot matrix screen, and supply outdoor display solution, manufacturers adopt DIP LED for light source.

• Advantages: better color consistency than dot matrix module; can be waterproof; and work with pixel sharing technology, also named virtual pixel technology.
• Disadvantages: poor pixel mixing effect, small viewing angle, processes more complicated, demand higher antistatic level. Actual pixel resolution is difficult to achieve pixels more than 10,000 per square meter.

DIP LED module

3. SMD LED: 

  This solution usually for smaller pixel pith LED display.

• Advantages: Good color consistency, the viewing angle is the best among the recent used light source; also with very good mixing color, can be for high resolution.
• Disadvantages: Process is very difficult, and high cost, require high antistatic level.

SMD LED module

How to reduce LED display light attenuation?

The light attenuation always is the maintenance problem on the large LED digital display and dot matrix display, in addition to use air conditioning, LED also need to adopt constant current measures. The pixel that composed by a plurality of LED is dynamic when under the control of light up alternately, so the constant current produced by integrated circuit IC and does not match it. And the solution is to use MZD thermistor, it don’t need to change the original circuit configuration, only need to add a WMZD thermistor before or after each pixel, and make the pixel as resistance “bulb”, in this way can reduce the LED display light decay economically.

The choosing of WMZD is according to LED pixel current and parallel number, such as if the pixel is composed by 4 to 6 LED/18 ~ 20mA in series, then can add a WMZD-A20 thermistor in the loop, when the ambient temperature changes from -40℃ ~ 120℃, the pixel current is always maintained at 18 ~ 20mA, it prevents the LED light attenuation effectively, and A20 thermistor power consumption is less than 60 mW.

LED digital display

If LED pixel modules is 100mA, then can use a WMZD-B100 in the circuit, if the module is 200mA, then use a B100, the consumption of B100 is less than 65 mW.

LED dot matrix display

In short, the use of WMZD thermistor in large LED screen is a technological innovation, it don’t need complex changing, you can prove its effectiveness just by a display module, thermometer, ammeter, ovens or heaters.

What’s COB LED?COB package COB LED advantages

What’s COB LED?

COB LED means chip on board LED, it’s one of bare chip technologies, which interconnect bare chip to substrate by conductive or non-conductive adhesive, and then wire bonding to achieve its electrical connection. COB package is attach number of chips directly to the substrate, then packaged together by silica gel, epoxy resin or other materials, the yellow part is phosphor.

Produce process:
The first step of COB package is to cover wafer placement point on the substrate surface by thermal conductive epoxy (usually is epoxy resin mixed with silver particles). Second is put the wafer on the substrate surface directly, then fix wafer to the substrate firmly by heat treatment. Third is to establish electrical connection between wafer and the substrate by wire bonding method.

COB LED advantages:
COB light source can save about 30% cost in the application, mainly lie in LED package cost, light engine production costs and the secondary light distribution costs, which is great significance for applications and promotion of semiconductor lighting.

In performance, through the rational design and micro-lens molding, COB light module can avoid the defects of point and glare light also other flaws existed in discrete light source device. It also can add some red chips appropriately, so that to improve the CRI effectively under the condition of without reduce light efficiency and lifetime significantly.

In application, COB module makes production of lighting manufacturer more simple and convenient, and reduces cost effectively. In production, the existing technology and equipment can support high yield and large-scale COB module manufacturing.

With the development of LED lighting market, lighting demand is growing rapidly, according to different inquires of lighting applications, we can produce a series COB light source module for mass production.

COB LED disadvantages:
COB packaging technology bottleneck is how to improve the reliability of the light source, and its operating temperature. However, most of the current market COB packaging companies are small and they mostly use aluminum substrate as the material. Aluminum COB reliability is low because of its greater thermal resistance, easy to cause death LED or high light attenuation. The ceramic substrate is an ideal COB material, but its cost is relatively high, especially for the power less than 2W, difficult to be accepted by customer.

Also, the demand of COB light source on the market is still low by now. In addition, COB LED exist standardization issues, the standards of package manufacturers and lighting factories are not the same, so the two parties have difficult in integration.

Application:
Currently, the main applications for COB LED are and mining lamps, spot lights, street lights and so on.

Outdoor Video LED Signs and Display

Outdoor Video LED Signs and Display

Application Areas:

·---Outdoor advertising, led panel, commercial led display, advertising for big companies

·---Sports halls, fields, playgrounds.

·---Airports, bus stations and railway passenger terminals.

·---Facades of shopping malls, department stores, banks and car dealerships.

·---Architecture and social projects, information systems in cities.

·---Highway, road, streets or other public full color led display projects.

Applications:

This kind of Full Color LED Display is applied for advertising, city beautifying, information publicity, and relative activities.

Specifications:

Outdoor full color LED Display
Module	Pitch/mm	p10	p12	p16	p20
	Module size/mm	160x160	192x192	256x128	320x160
	Density of pixel/(dots/m2)	10, 000	6, 944	3, 906	2, 500
	Pixel composition	1R1G1B	2R1G1B	2R1G1B	2R1G1B
	Led encapsulation	DIP	DIP	DIP	DIP
	Resolution of module	16X16	16X16	32X16	32X16
Main	Optimum viewing distance	≥10	≥12	≥15	≥17
	View angle / °	110 H, 60 V	110 H, 60 V	110 H, 60 V	110 H, 60 V
	Average power consumption/W/M2	450	450	400	350
	Max power consumption/W/M2	950	950	900	850
	Size of cabinet/mm	960X960	960X960	1024X768	1280X960
	Resolution of cabinet	96X96	80x80	64x48	64X48
	Weight of cabinet/kg	65	65	60	75
	Driving method	1/4 scan constant current	1/4 scan constant current	Static constant current	Static constant current
	Frame frequency / Hz/S	≥60	≥60	≥60	≥60
	Refresh rate Hz/S	≥600	≥600	≥600	≥600
	Luminance of white balance	≥7000 nits	≥7000 nits	≥6500 nits	≥6000 nits
	Operation of Environmental Temperature/℃	below 30  to  above 50
	IP rating	Front, IP65;Rear, IP43
	Working vlotage	110-220 VAC/+/- 10%
	Grey scale/color	displaying colors≥16.7M(synchronized)
	Brightness adjustment	256 levels of each color(manually), 100 levels of each color(automatically)
	Input signal	RF, S-Video, RGB, RGBH, YUV, YC&Composition , etc
	Control system	linsn(sending card, receiving cards and Hubs)
	Average of non-failure life	>50, 00h
	Life span	>100, 000h
	Functionaless dot rate	<0.0001

Competitive Advantage:

1. Quality stability and reliability;

2. High refresh rate and low power consumption;

3. Complete project solution provider

4. Two years warranty

RGB Video aluminum module tile LED Screens

RGB Video aluminum module and tile LED Screens 

 

Technical Specification:

 

 

 

aluminum module LED Display Screen
Module	Pitch/mm	P8
	Module size/mm	256x128
	Density of pixel/(dots/m2)	15600
	Pixel composition	1R1G1B
	Led encapsulation	SMD3230
	Resolution of module	32x16
Main	Optimum viewing distance	≥8
	View angle / °	160 H,120 V
	Average power consumption/W/M2	500
	Max power consumption/W/M2	900
	Size of cabinet/mm	1024x1024
	Resolution of cabinet	128x128
	Weight of cabinet/kg	30
	Driving method	1/4 scan constant current
	Frame frequency / Hz/S	≥60
	Refresh rate Hz/S	≥1200
	Luminance of white balance	≥7000 nits
	Operation of Environmental Temperature/°C	below 30  to  above 50
	IP rating	Front:IP65;Rear:IP43
	Working vlotage	110-220 VAC/+/- 10%
	Grey scale/color	displaying colors≥16.7M(synchronized)
	Brightness adjustment	256 levels of each color(manually),100 levels of each color(automatically)
	Input signal	RF,S-Video,RGB,RGBH,YUV,YC&Composition ,etc
	Control system	(sending card,receiving cards and Hubs)
	Average of non-failure life	>50,00h
	Life span	>100,000h
	Functionaless dot rate	<0.0001