it is inevitable that there will be some LED screen enterprises shoddy products, so how to distinguish the quality of LED electronic large screen lamp beads? The following four methods are briefly introduced by the mini photoelectric LED display manufacturers.
Nowadays, SMD (surface mounted devices) is the main packaging method used by LED display manufacturers. This kind of SMD is usually welded on PCB board, which is generally divided into PCB LED (chip LED) and PLCC LED (top LED). Take SMD LED of top LED as an example. The packaging materials of LED electronic large screen include bracket, chip, solid crystal, bonding wire and packaging adhesive.
LED bracket
(1) PLCC (plastic LED chip carrier) is the carrier of SMD LED equipment, which plays an important role in the reliability, luminescence and other functions of LED.
(2) Production process of support. PLCC bracket production process mainly includes metal strip punching, electroplating, PPA (poly (phthalamide) injection molding, bending, five dimensional inkjet and other processes. Among them, electroplating, metal substrate, plastic materials and so on account for the main part of the support cost.
(3) Structure improvement planning of support. Because the combination of PPA and metal is physical, the gap of PLCC bracket will become larger after the high temperature reflux furnace, which will lead to the water vapor easy to enter the equipment and affect the reliability of LED lamp beads.
In order to improve the reliability of LED electronic large screen, some packaging manufacturers improve the structure planning of the bracket. For example, advanced waterproof structure planning and bending and stretching methods are used to prevent water vapor from entering the support, and multiple waterproof methods are used to add waterproof grooves, waterproof steps and drain holes inside the support. This method can not only greatly improve the reliability of the product, but also save the packaging cost. This kind of lamp bead is commonly used in LED outdoor display. And it is found that the LED bracket with SMD lamp bead bending structure has better air tightness after use.
LED chip
LED chip is an important part of LED devices, and its reliability is related to LED equipment, service life and luminous performance. The cost of LED chip accounts for about 70000 of the total cost of LED equipment. With the continuous decline of cost, the size of LED chip is smaller and smaller, and the reliability is higher and higher. The structure of LED blue-green chip is shown in the figure below.
As the size of LED chip becomes more and more straight, the pad of p electrode and N electrode becomes smaller and smaller. The reduction of pad directly affects the quality of solder wire, which leads to the gold ball detachment in the process of packaging and use, and even the electrode itself detachment, leading to failure problems. At the same time, the distance a between the two pads will also be reduced, resulting in the excessive increase of current density at the electrode and the local accumulation of current at the electrode. The uneven distribution of current will seriously affect the chip, resulting in the chip local temperature is too high, the brightness is not uniform, leakage, electrode drop, and even the efficiency will be reduced, which will affect the reliability of the LED electronic large screen.
The function of bonding wire is to connect the chip to the pin, and then to import and export the current from the chip to the outside world. It is one of the key materials for LED packaging, and the common bonding wires for LED device packaging include gold wire, copper wire, palladium plated copper wire and alloy wire. Generally speaking, gold wire is widely used, but because of the high price, LED packaging cost is too high, so it is rarely used.
The glue of LED electronic large screen packaging device mainly includes epoxy resin and silicone. Epoxy resin is easy to aging, poor moisture-proof and heat resistance, and easy to change color under short wave light and high temperature. It has certain toxicity in the colloidal state. The thermal stress does not match with LED, which affects the reliability and life of LED display. Compared with epoxy resin, silicone has higher cost performance, excellent insulation, dielectric and adhesion. But the disadvantage is poor air tightness, easy to absorb moisture, so it is rarely used in LED display device packaging.
In addition, some packaging manufacturers use additives to improve the stress of glue, achieve the effect of matte fog surface, and improve the display effect and quality of LED electronic large screen.
The above is the brief introduction of LED display manufacturers about the four methods of LED electronic large screen lamp beads, including LED bracket, LED chip, bonding wire and glue. Gold wire is better material in bonding wire, which has advantages in heat dissipation, reliability, service life and moisture resistance. However, due to high cost, copper wire or other materials are generally used instead.