Analysis and technical solutions for the problem of LED screen yin and yang screen

3 views admin 2025-04-30

With the continuous development of LED display technology, small-pitch LED screens have gradually become the mainstream of the market. However, with the continuous reduction of the pitch and the shortening of the viewing distance, the problem of yin and yang screens has become increasingly prominent. So, what is the problem of LED screen yin and yang screen? How does it come about? What are the effective technical solutions? Let's explore the problem of LED screen yin and yang screen in depth to provide technical support for improving the quality and performance of LED display screens.

An LED display screen can be obtained by mounting LED display devices in an array on the surface of a PCB. In the era of large-pitch LED screens, due to the long viewing distance and the mask blocking, the visual difference caused by insufficient mounting accuracy is not easy to be detected. However, in recent years, as the pitch of LED screens continues to decrease and the viewing distance becomes closer and closer, the accuracy requirements for LEDs, printed circuit boards, and patches are extremely high. At this time, the tilt of the luminous surface caused by minor production and manufacturing process defects becomes obvious when viewed at close range, and the yin-yang screen problem becomes prominent

The so-called yin-yang screen problem of LED screen refers to the fact that when viewed from the left side of the LED screen, the light on this side is obviously darker or brighter; when viewed from the right side, it is the opposite, with a more obvious brighter or darker light, forming a clear brightness contrast between the left and right sides

The root cause of the yin-yang screen problem of LED screen mainly lies in three aspects: LED lamp beads, printed circuit boards and patches
First, let's look at the selection of LED lamp beads. In the small-pitch LED screen, take CHIP type and TOP type LED lamp beads as examples. CHIP type LED lamp beads use BT board as the substrate for solid crystal welding wire, and TOP type LED lamp beads are connected to the printed circuit board by bending copper. For example, when the bending angle of the pin of the TOP type LED lamp bead approaches 90°, when the solder paste distribution on the printed circuit board is uneven, it will cause the LED lamp bead to tilt. Therefore, when selecting TOP-type LED lamp beads, lamp beads with right-angled bends are generally not used, but lamp beads with hook-shaped pins. The advantage of the hook-shaped shape is that there is no need to accurately control the amount of solder paste. When the solder paste is reflowed, the excess solder paste can spread to the redundant space on both sides to ensure that the LED lamp beads can be flatly attached to the printed circuit board. At the same time, Jingtai LED strictly controls the flatness and size difference of the pins to ensure the flatness of the LED after mounting and improve the display effect.

The second is the control of the patch operation. In the LED patch operation, steel mesh printing and furnace temperature control are the key factors to prevent the yin and yang screen. The size of a single pin of the LED lamp beads used in the small-pitch LED screen is between 0.20.2mm and 0.50.5mm. The size of the steel mesh opening is relatively small, which easily causes the solder paste to block the mesh. New coating materials can be added to reduce solder paste drawing, and the steel mesh should be cleaned regularly. The furnace temperature curve control also affects the melting effect of solder paste. The furnace temperature curve is measured and monitored for each production shift to ensure product stability. In addition, each LED lamp bead has a certain directionality, and the direction must be consistent before entering the furnace.

Finally, the printed circuit board. The manufacturing accuracy of the pad on the display surface of the printed circuit board affects the accuracy of the LED patch and is one of the key factors in preventing the problem of yin and yang screens. When designing the PCB, if the pad size is smaller than the window size, the pad may deviate from the center of the window. The window position outside the pad is usually sprayed with ink, and the ink height is higher than the pad height, which will cause ink accumulation problems, blocking the flow of solder paste, causing uneven distribution of solder paste on the pad, and causing the LED lamp bead to tilt. This problem can be solved by reasonably designing the size relationship between the pad and the window and strengthening the control of the production accuracy of the printed circuit board.

In summary, by taking effective measures in three aspects: LED lamp bead selection, patch operation control, and printed circuit board accuracy control, the problem of yin and yang screens