LCD Backlight Leakage

I. Definition of LCD light leakage

LCD liquid crystal display is widely used in the information age of flat panel display equipment, it has low energy consumption, thin and lightweight, lightweight features, by the liquid crystal display, connectors, integrated circuits, electronic circuit boards, backlight boards, and other structural components combined into a liquid crystal display LCD is the main flat panel display equipment. Television and LCD liquid crystal display often appear panel light leakage phenomenon, which in the end what causes, is not normal? Light leakage in the end, in fact, light leakage and panel structure has a very big relationship, first of all, mainly by the liquid crystal display (TFT-LCD), backlight (BLU) and flexible circuit boards (FPC) composed of these three major parts of the liquid crystal display LCD (TFT-LCM) in general light leakage is a very normal phenomenon, because light leakage will not affect both the brightness of the LCD TV and the LCD display itself, not to mention that it will not affect the LCD TV and LCD display itself, the brightness of the LCD TV. Will not affect the response speed and service life of LCD TVs and LCDs, the only thing that will affect the panel's overall display effect. When the brightness of the backlight LED lamp port position is significantly higher than other areas of the bright spot or bright columns appear in the lamp port position is called: light leakage.

Second, the causes of light leakage of the LCD screen to generate reasons

1, LCD liquid crystal display leakage caused by reasons

According to the statistical analysis of some manufacturers, the LCD display produces light leakage bad reasons, including 93% is caused by bad glare, therefore, it can be concluded that the main key problem of light leakage bad is to solve the problem of glare.

2. Reasons for glare

One of the reasons for the glare is the LCD LCD screen in the backlight in the LED lights emitted by the light is directly shot, rather than in accordance with normal circumstances through the light guide plate uniform diffusion out, at the same time, there is also a situation is that the production of the light guide plate is not good will also produce a similar situation. From the above two situations and then subdivided, can lead to 7 aspects of the reason.

(1) LED lamp thicker than light guide plate

When the thickness of the LED lamp over the light guide plate, then the excess part of the light will radiate directly from the top of the light guide plate, it is not through the guide plate uniformly dispersed light to form a glare. Through the use of spiral micrometer on the light guide plate and LED lamps were measured statistics, statistical measurements of the mean value of the comparison of the resulting statistics show that the average value of the measured data are significant differences: LED lamps are thicker than the light guide plate.

(2) FPC reflexion force is greater than FPC double-sided adhesive force.

When the reflexion force of FPC is too large, the LCD will be pulled up, resulting in the formation of misalignment between the light guide plate and the LED lights, resulting in the light can not be normal through the light guide plate uniformly dispersed and produce glare. However, there is no quantitative method to test the reflexive force of FPC, so the adhesive coefficient and adhesive area of double-sided adhesive are reduced to check whether it will cause glare. By comparing the rate of glare generation under different adhesive areas, it is confirmed that the assumption that the reflexive force of FPC is greater than the adhesive force of double-sided adhesive of FPC is not valid.

(3) Employees squeezing the LCD screen

By observing and comparing the production line staff's work practices found that there are indeed employees in the processing process will occasionally occur in the case of extrusion of the LCD, in this way, through the LCD pinched by the force of the pressure test, found that the pinch pressure will make the LED contact with the LCD, when the LCD contact with the LED and by the extrusion of the LED on the top of the double-sided adhesive tape will be stuck to the LED and move with it. Therefore, the assumption of glare caused by employees squeezing the LCD is valid.

(4) There is a gap between the LCD and the LED.

When the LCD is pressed to make the gap between the LCD and the LED disappears, the double-sided tape will stick to the LED and drive it to shift, resulting in light leakage. In order to be able to confirm the fitness of the gap size, we use 0.1mm plug gauge on the gap for the different thickness of the test, the final conclusion is: the use of 0.1 + 0.06 + 0.02 of the vinyl combination can be plugged into the gap, and the use of 0.15 + 0.06 of the vinyl combination can not be plugged into the gap, due to the vinyl itself is the maximum thickness: 0.06mm, so the size of the gap for: 0.12 The maximum thickness of the vinyl itself is: 0.06mm, so the size of the gap is: 0.12mm, which means: the hypothesis that there is a gap between the LCD and the LED to cause glare is valid.

(5) Glare caused by the small distance of the window from the LED light emitting surface

Take the model with a backlight D2 design length of 2.9mm as an example, because the operation of the staff will lead to the deviation of the effective D2, we conducted a comparative test on the glare rate of the D2 with a length of 3.1mm as well as two different conditions of 2.9mm, to check the differences generated in different situations, test results: under these two conditions, the undesirable rate of the glare is on a decreasing trend as the distance of the D2 is increased. Therefore, it shows that the small distance between the window and the LED light-emitting distance is also one of the elements of glare generation.

(6) Possibility of glare caused by poor guide plate dots and poor guide plate serrations

Detection of poor guide plate mesh and guide plate serration bad need to test IQC, the length of D2 were 3.1mm and 2.9mm two lengths of 20 pieces of guide plate bad rate test, the results are: guide plate effect is acceptable 10, guide plate effect is not acceptable also 10 pieces. And then by two inspectors on the 500 pieces of guide plate were extracted from the test, were not found to guide the light guide plate defective, so it shows that the guide plate dot bad and guide plate sawtooth bad is not the main factor in the production of glare.

Third, the LCD display LCD screen glare improvement methods

To address the factors that create glare, we can use the following improvement programs.

1, the use of paste light-absorbing strip to solve the problem of LED lights thicker than the light guide plate

If the LED lamp directly changed to 0.4mm thickness, to adapt to the thickness of the light guide plate, but so the cost of the backlight will increase 20% or so, and, after the LED lamp change, whether it can match the light guide plate also need to be tested, therefore, after repeated speculation, we chose the backlight on the reverse side of the LED lamp, LED lamp mouth paste absorbent strips, the light guide plate cushioning, this way To adjust the matching degree between the LED light and the light guide plate, to reduce the generation of glare.

2、Improve the gap by increasing the size of the polarizer under the LCD.

By changing the original 42.10 x 34.40mm polarizer to a 44.10 x 34.40mm polarizer, by lengthening the polarizer, the polarizer can completely cover the LEDs and at the same time fill the gap between the LCD and the LEDs.

3. Increase the distance of the viewport

Due to the black and white adhesive glued on the visual zone of the LE D can not be carried out, and black and white adhesive assembly after the standard deviation S is 0.058 mm, so if the production process will be the edge of the AA area of the LED and black and white adhesive edge distance to leave 0 . 0 8 m m space, at the same time according to the maximum length of 3.4mm D2 calculated, 3.4-0.08-3 × 0.058 = 3.14 So, the view window distance from the LED light-emitting surface of the LED lamp from 2.9mm to 3.14mm.

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