Detection and Repair of Common Point Defects in TFT LCD

Common point defects in TFT-LCD (thin film liquid crystal display) production process will have some defects, mainly some display defects, among which point defects are the most serious.

TFT LCD is composed of many sub-pixels, if some sub-pixels are not working properly, it will cause the poor display in some areas.

There are generally two types of LCD monitors, one is a normally white screen; the other is a normally black screen. The normal white screen is white when there is no power on, and the normal black screen is black after power is on. If it cannot turn black after the power is on, then this point is called a bright spot, that is, under a black screen, this point is transparent.

The black dots under the white screen are called dark dots. The inspection screens for the bright spots are the L0 screen and the L92 screen, and the judging criterion is the contrast brightness between the head-up view and the simulated point at 30 cm, that is, there are no visible red, green, or blue light spots within 30 cm. If this point is on and off, it belongs to the flash point, and the flash point is also a kind of bright spot, and its repair method is the same as that of the bright spot.

Both the Array and the Cell segment in the manufacturing process will produce point defects, but only in the Cell can the Panel be lit up for inspection—to detect whether there are defects. The following will introduce the inspection device and inspection method of the Cell segment. The purpose of the inspection is the final inspection of the TFT-LCD Cen section to check whether the product meets the specifications required by the customer. The testing method is a visual inspection. The testing specifications are generally based on the customer's needs. The Cell Integration Engineering Department formulates the product testing specifications. Different Product inspection specifications vary.

The inspection process is mainly to provide the inspection environment from the Panel to the module, so as to detect the point defects, line defects, mura, and other defects of the Panel. It is mainly composed of two parts. Among them, the signal output device of ITEs is a machine that provides signal output. It can set various screens required for testing the Panel, and test whether there is any Defect in the Panel. At the same time, these parameter screens can also be adjusted as needed. The other part is to provide the platform required for Panel testing, which can set up probe platforms of different sizes according to the needs of the production line.

The operation steps of personnel visual inspection are as follows:

(1) When the machine is operating, it is necessary to confirm whether the protective cover is really covered;

(2) When the machine is in operation, it is not allowed to open the protective cover or put your head and hands into the detection area;

(3) When opening and closing the upper cover, pay attention to whether there are people or foreign objects in the dangerous area.

(4) In order to ensure the effectiveness of the visual inspection when the operator performs the test action, the operator must use a "fluorescent lamp" to assist the visual inspection when performing the Cell visual inspection; the position of the eye protection lamp must be fixed, and the production line personnel must The eye protection light can be turned off when visually inspecting the appearance.

At present, point defects of TFT LCD can be repaired by methods such as dark spots, bright spots, ITO isolation, and laser blasting. The first two methods are relatively mature. The following mainly introduces the two repair methods of ITO isolation and laser blasting.

ITO isolation is to use the IT0 isolation method to cut off the IT0 around the foreign matter so that the rest of the area can return to a normal state. The foreign matter in the general pixel can be repaired by the IT0 isolation method theoretically.

Laser blasting is to use of a laser to disperse foreign objects smaller than a certain size, so that the particles become smaller or gasify and disappear, and no longer affect the current flow of pixels.

Laser blasting has certain risks, and it requires high energy stability of the machine. If the energy is unstable, when the energy is low, the foreign matter will scatter and have large particles, which will cause other defects. Therefore Make sure that the energy of the machine is stable.

The formation of point defects is mainly in the Array section and the front section of the Cell. The Array section will have some residues during coating. If these residues are conductive or the area is too large, it will cause a short circuit or an open circuit at the point near it. This point becomes A bright spot or a dark spot, that is, a point defect. At present, the inspection of point defects is mainly based on visual inspection, and some of them are automatically inspected by machines. Point defects can be repaired by methods such as dark spots, bright spots, IT0 isolation, laser-blasting, etc., and the IT0 isolation method proposed in this paper (the method of cutting the IT0 film to achieve repair), the repair effect is the most significant, making the repair success rate Increased from 45% to 80%.