After making the whole machine for so many years, you may have been mistaken about the culprit of LCD light leakage.

Friends who make whole machines have probably encountered this scenario: after the machine is finally installed, when it is powered on and tested, a circle of uneven white light appears at the edge of the screen in pure black.

The R&D team said the screen was not working, but the screen factory said there were assembly issues and they kept pulling back and forth, causing the project to get stuck.

The issue of LCD light leakage can be described as big or small. When it comes to consumers, they don't care about any stress or tolerance,If you can see light on a black screen, it means the quality is poor.Once the complaint arrives, it is once again the fault of the entire machine factory.

Today, let's not talk about anything trivial, but from the perspective of a LCD module factory,Thoroughly explain the issue of light leakage. According to the cases we have handled, the root cause of light leakage basically cannot escape from these four situations.

After reading it, you will find that a considerable amount of light leakage is actually not related to the screen itself.

1、 How does LCD light leakage come about? Speak clearly in one sentence

LCD itself does not emit light, it relies on the backlight module behind it to illuminate. When displaying black normally, the liquid crystal molecules will "twist" at an angle, tightly blocking the backlight.

Leakage of light means that the 'blocking' action was not done properly. The light ran out from where it shouldn't have been.

Why wasn't it blocked? The core reason is in two words:Stress.

The screen is squeezed, pressed, and twisted by various forces inside the machine, causing the shell to warp, the hooks to be too tight, and the foam to be unevenly attached. These external forces can cause the glass to deform and the arrangement of liquid crystal molecules to become disordered.

The light path that should have been tightly sealed to block the light has been 'twisted' like this.

Ultimately, light leakage is not mysticism, but mechanics.

2、 How many of the four common misconceptions have you encountered?

Misconception 1: Light leakage is a quality issue with the screen

This is a big pit. Many whole machine manufacturers' first reaction when they see a light leak is to return it to the screen factory. But the reality is that a large amount of light leakage is "manufactured" during the assembly stage of the entire machine.

The same batch of screens, when installed in shells with different structures, may have vastly different light leakage performance. Blame the screen for coming up, the direction is wrong.

Misconception 2: IPS screens are prone to light leakage, there's nothing we can do about it

IPS panels are indeed more susceptible to light leakage than VA in the black state due to the lateral arrangement of liquid crystal molecules. But this does not mean that light leakage is' taken for granted '.

By optimizing structural design, controlling assembly stress, and improving shading processes, light leakage can be completely controlled within an acceptable range.Panel characteristics are not an excuse, engineering capability is the trump card.

Misconception 3: Accurate leak detection in all black rooms

On the contrary. In dark environments, the sensitivity of the human eye to weak light is infinitely amplified, and the leakage of light that would not be visible under normal light becomes "shocking" as soon as the lights are turned off.

Few companies can pass this standard for card products. The industry standard for leak detection requires ambient light above 150 lux, and that's why.

Misconception 4: Leakage can be completely eliminated

To be honest, it is almost impossible to completely eliminate light leakage.The physical structure of LCD determines its inherent sensitivity to external forces. Our goal is not to make the light leak disappear,But rather keep it within a range that does not affect the user experience.

3、 Where does the light leak come from? Four situations to help you locate

According to the cases we have handled, the root cause of light leakage basically cannot be traced back to these four situations:

The first type: design defects of the panel itself

There are "steps" inside the backlight structure, and the supporting surface is not large enoughChoosing too thick glass will reduce the stress resistance of the screen. The thinner the glass, the better its resistance to light leakage.

Because under the same external force, the deformation of thin glass is smaller, and the deflection of light when passing through is also milder. This is the direction that screen manufacturers should optimize.

Second type: Process issues in screen production

For example, if the temperature is not controlled properly during IC binding, stress points will be left at both ends of the chip, resulting in local light leakage. Or the tape inside the module may be unevenly applied or pulled too tightly. These belong to the process control category of the screen factory.

Third type: Unreasonable overall structural design (common)

The flatness of the shell is not sufficient, so it bends together with the screen after installation; The B-shell hook design is too tight, causing point like light leakage when pressed out directly; The foam support behind the screen is uneven, causing the screen to sag and bend due to its own gravity. This type of problem accounts for the majority of cases of light leakage.

The fourth type: non-standard assembly process

The compression fixture does not match the screen, and the pressure distribution is uneven; The worker's method of plugging and unplugging the cable is incorrect, which introduces local stress. These may seem like minor issues, but they will be magnified exponentially on the production line.

A real case: the same screen, different lives

Last year, we cooperated with a laptop customer to handle a batch of light leakage complaints. The same batch of screens, when installed on their newly launched model, suddenly had a light leakage defect rate skyrocketing to double digits.

According to conventional thinking, the customer's first reaction is that there is a problem with this batch of screens. But when we went to the scene and saw that the same screen was replaced with the old model, the light leakage was normal.

Where is the problem?The new shell is designed to be lightweight and the flatness standard is set too wide,After installing the screen, I bent the ribbon directly. The screen itself is fine, it's just the shell that 'broke' the screen and leaked light.

The solution is simple: tighten the control of the flatness of the shell,The rate of poor light leakage has directly decreased to normal levels. The screen and fixture were not replaced, only a new specification was changed.

What does this case illustrate? Leakage is often a system issue, not a component problem.

4、 Encounter batch light leakage, check in this order

If there is a batch of light leakage on the production line,Don't just come up and dismantle the device to replace the screen.Disassemble and assemble again, the stress state has completely changed, and the more you disassemble, the more confused you become.

Our suggested troubleshooting sequence is as follows:

Step 1: Classify first, don't do anything.Separate the leaking machines according to their position and shape (dot or sheet). The same phenomenon of light leakage often has the same cause, and this judgment can help you save 80% of the detours.

Step 2: Confirm the phenomenon.Record the location of the light leakage on a completely black screen, gently press the light leakage area with your finger, and observe the changes. If it becomes lighter after pressing, it indicates compression type light leakage; Getting heavier indicates that the structure itself has problems.

Step 3: Disassemble the B shell for verification.Be careful to remove the screen frame. If the light leakage is significantly reduced, the problem lies in the B shell, where the hook is too tight and the gap is not enough.

Step 4: Disassemble the screen for verification.Remove the tape that secures the screen and let it sit for half an hour. If there is a change in light leakage, the problem lies in the shell, insufficient flatness, and excessive assembly stress.

Step 5: All of the above are excluded, then look at the screen itself.

Special reminder: Try not to perform ABA cross validation. Remove the screen from chassis A to chassis B and reinstall it.The disassembly process itself will change the stress state, and the conclusions drawn are likely to be inaccurate.

5、 Here are three suggestions for you

Suggestion 1: Move the light leakage control forward

Don't wait until the whole machine is installed before testing for light leakage. In the structural design phase, it is necessary to evaluate the flatness of the shell, the gap between the hooks, and the foam support scheme. Solving one problem during the design phase is more cost-effective than solving a hundred problems during the mass production phase.

Suggestion 2: Establish your own anti leakage standards

The light leakage performance varies among different batches of screens and shells with different structures. I suggest working with the screen manufacturer to establish a mutually recognized light leakage judgment standard for your specific model. What is considered qualified and what is considered defective, write it in the specification book.

Suggestion 3: Conduct a joint review with the module factory

An effective approach is to involve the screen manufacturer in the overall design phase. Screen manufacturers know what their screens are afraid of. You tell them how your structure is designed, and they tell you where problems may occur. Evaluating together is a hundred times stronger than blaming each other afterwards.

Speaking of which, the issue of LCD light leakage has never been a problem with a single component, but rather a system problem.

What screen manufacturers can do is to improve the stress resistance of the screen; What a complete machine factory can do is to ensure that the structural design and assembly process are in place. If both sides take half a step forward, the problem won't be so difficult to solve.

Next time you encounter a complaint about light leakage, why not ask yourself three questions first:

Does the same screen leak when installed on other models?

Has the light leakage become lighter after removing the B shell?

Is this light leakage point like or patchy?

The answer is out, and the responsible party becomes clear.

Leakage is not scary, what's scary is finding the wrong direction.

If you are troubled by light leakage issues,Welcome to discuss specific phenomena in the comment section. Different forms of light leakage often point to completely different root causes. Maybe we can help you avoid some detours.

#LCD Leakage # Screen Leakage # Monitor Quality Control # Leakage Standards # LCD Screen # LCD Screen # LCD Display Screen # LCD Module # Screen Detection