Research on Solutions to the Poor Light Leakage Phenomenon of Liquid Crystal Display Modules

I. Introduction

With the rapid development of science and technology, the information revolution has brought us into an electronic era. The development of electronics and communication equipment has enabled flat panel display technology represented by liquid crystal display modules to quickly enter millions of households. Therefore, liquid crystal display modules Whether there is poor light leakage has become one of the key factors in the inspection of flat panel display devices. This article analyzes the causes of poor light leakage of liquid crystal display modules and uses detection methods to determine the factors that cause poor light leakage of liquid crystal display modules. This puts forward suggestions for handling.

2. Definition of light leakage of liquid crystal display module

Liquid crystal display is a flat display device widely used in the information age. It has the characteristics of low energy consumption, thin and light appearance, and light weight. It is composed of liquid crystal display, connectors, integrated circuits, electronic circuit boards, backlight boards and other structural parts. Liquid crystal display module is the main equipment of flat panel display. TVs and LCD monitors often have panel light leakage. What causes this? Is it normal? What is light leakage? In fact, light leakage has a great relationship with the panel structure. First of all, the liquid crystal display module (TFT-LCD), the backlight (BLU) and the flexible circuit board (FPC) are mainly composed of three parts. LCM) Under normal circumstances, light leakage is a very normal phenomenon, because light leakage will not affect the brightness of the LCD TV and the LCD itself, nor will it affect the response speed and service life of the LCD TV and the LCD. The only thing that will affect it is It is the overall display effect of the panel. When the brightness of the backlight LED lamp socket is significantly higher than other areas, the bright spot or bright column that appears at the lamp socket is called: light leakage.

Third, the cause of light leakage of the liquid crystal display module

1 Causes of light leakage of liquid crystal display modules

According to the statistical analysis of some manufacturers, 93% of the causes of poor light leakage in LCD TVs and LCD displays are caused by poor glare. Therefore, it can be concluded that the main key problem of poor light leakage is to solve the glare problem.

2 Causes of glare

One of the reasons for glare is that the light emitted by the LED lamp in the backlight of the liquid crystal display module is directly emitted instead of uniformly spreading out through the light guide plate according to the normal situation. At the same time, there is another situation that the light guide plate Poor production results can also produce similar situations. Subdividing from the above two situations can lead to 7 reasons. As shown in Figure 1: Analysis of the causes of glare.

(1) The LED lamp is thicker than the light guide plate

When the thickness of the LED lamp exceeds the light guide plate, the excess light will radiate directly from the top of the light guide plate, and it is the light that does not evenly diverge through the light guide plate to form glare. Through the use of spiral micrometer to measure the light guide plate and LED lamp separately, the statistical data obtained from the comparison of the mean value obtained by the statistical measurement shows that there is a significant difference in the mean value of the measured data: the LED lamp is thicker than the light guide plate.

(2) The reflex force of FPC is greater than the adhesive force of FPC double-sided adhesive

When the reflex force of the FPC is too large, the LCD will be pulled up, causing the light guide plate and the LED lamp to form a misalignment, so that the light can not normally diverge evenly through the light guide plate, resulting in glare. However, for the FPC's large reflex force, there is no quantitative method to test the reflex force, so the double-sided adhesive's viscosity coefficient and adhesive area are both reduced to test whether it will cause glare. By comparing the glare generation rate under different adhesive areas, it is confirmed that the assumption that the FPC's reflex force is greater than the FPC's double-sided adhesive force is not valid.

(3) Staff extrusion module

By observing and comparing the working methods of the employees on the production line, it is found that there are indeed cases where employees occasionally squeeze the module during the processing. In this way, through a strong pinching test on the module, it is found that the pinching will cause the LED and LCD When the LCD touches the LED and is squeezed, the double-sided tape on the top of the LED will stick the LED and move with it. Therefore, the assumption of glare caused by employees squeezing the module is valid.

(4) There is a gap between LCD and LED

When the liquid crystal display module is pressed so that the gap between the LCD and the LED disappears, the double-sided adhesive will stick to the LED and drive it to shift, causing light leakage. In order to confirm the suitability of the gap size, we used a 0.1mm plug gauge to test the gap with different thicknesses. The final conclusion is that the black glue combination of 0.1+0.06+0.02 can be inserted into the gap, while the black of 0.15+0.06 is used. The glue combination cannot be stuffed into the gap. Since the maximum thickness of the black glue itself is: 0.06mm, the size of the gap is: 0.12mm, indicating that the assumption that there is a gap between the LCD and the LED that causes glare is established.

(5) The small distance between the window and the light-emitting surface of the LED lamp causes glare

Take the model with a backlit D2 design length of 2.9mm as an example. Due to the deviation of the effective D2 due to the operation of the staff, we conducted a comparative test on the glare rate of the two different conditions of the D2 length of 3.1mm and 2.9mm, and checked them. Differences in different situations, test results: Under these two conditions, with the increase of D2 distance, the defective rate of glare shows a downward trend. Therefore, it is also one of the factors that show that the window is small from the LED light emitting distance.

(6) Poor dots on the light guide plate and poor serrations on the light guide plate may cause glare

IQC is required to detect poor dots on the light guide plate and poor serrations of the light guide plate. IQC is required to test the defective rate of 20 light guide plates with two lengths of 3.1mm and 2.9mm. The result is: the light guide plate has an acceptable effect of 10. There are also 10 unacceptable light board effects. Two inspectors conducted separate inspections on 500 pieces of light guide plates, and none of them found defective light guide plates. Therefore, it shows that poor light guide plate dots and poor light guide plate serrations are not the main factors for glare.

Fourth, the method of improving the glare of the liquid crystal display module

In view of the factors that produce glare, we can adopt the following improvement schemes.

1 Adopting a light-absorbing strip to solve the problem that the LED lamp is thicker than the light guide plate

If the LED lamp is directly changed to a thickness of 0.4mm to adapt to the thickness of the light guide plate, the cost of the backlight will increase by about 20%. Moreover, after the LED lamp is changed, whether it can match the light guide plate needs to be tested Therefore, after repeated scrutiny, we chose to add a light-absorbing strip to the lamp socket of the LED lamp on the reverse side of the backlight to heighten the light guide plate, so as to adjust the matching degree of the LED lamp and the light guide plate to reduce the generation of glare.

2 Increase the size of the polarizer under the LCD to improve the gap condition

Change the original 42.10×34.40mm polarizer to 44.10×34.40mm polarizer. By lengthening the polarizer, the polarizer can completely cover the LED and fill the gap between the LCD and the LED.

3 Increase the distance of the window

Since the visual area of the LED cannot be used after the black and white glue is attached, and the standard deviation S after the assembly of the black and white glue is 0.058mm, if the distance between the edge of the AA area of the LED and the edge of the black and white glue is set at 0 during the production process. 0 8 mm space, and calculated based on D2 with a maximum length of 3.4mm, 3.4-0.08-3×0.058=3.14. Therefore, the distance between the window and the light-emitting surface of the LED lamp is increased from 2.9mm to 3.14mm.