I. Definition of LCD module light leakage
Liquid crystal display is widely used in the information age of flat panel display equipment, it has low energy consumption, thin profile, light weight, characterized by liquid crystal display, connectors, integrated circuits, electronic circuit boards, backlight boards, and other structural components into a combination of liquid crystal display module is the main flat panel display equipment. TVs and LCD monitors often appear panel light leakage phenomenon, which in the end what causes it, 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 components of the liquid crystal display module (TFT-LCM) in general, light leakage is a very normal phenomenon, because light leakage will not affect the brightness of the LCD TV and LCD monitor itself, more Will not affect the response speed and service life of LCD TVs and LCD monitors, the only thing that will affect the overall display effect of the panel. When the brightness of the backlight LED lamp port position is significantly higher than other areas of the bright spot or bright columns appearing in the lamp port position is called: light leakage.
Second, caused by the liquid crystal display module leakage causes
1、LCD module leakage causes
According to the statistical analysis of some manufacturers, LCD TVs and LCD monitors produce bad light leakage, which has 93% because of bad glare, therefore, it can be concluded that the main key problem of bad light leakage is to solve the problem of glare.
2. Reasons for glare
One of the reasons for glare is that the light emitted by the LEDs in the backlight of the LCD module is directly emitted, rather than uniformly diffused out through the light guide plate in accordance with the normal situation, and at the same time, there is also a situation in which the production of the light guide plate is not good enough to 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) Employee Extrusion Module
By observing and comparing the working methods of the employees on the production line, it is found that there is indeed the case that the employees will occasionally squeeze the module during the processing, in this way, by carrying out the pinch test on the module, it is found that the pinch will make the LEDs contact with the LCDs, and when the LCDs contact the LEDs and are squeezed, the double-sided adhesive tape at the top of the LEDs will stick to the LEDs and move along with them. Therefore, the assumption that the employees caused glare by squeezing the module is valid.
(4) There is a gap between the LCD and the LED.
When the LCD module is pressed to make the gap between the LCD and the LED disappear, 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 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 is: 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, liquid crystal display module 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.