As the LED display gradually penetrates into the high-end shopping malls, the quality requirements for the LED display equipment are also getting higher and higher. This article discusses the practical experience of high-quality LED display equipment packaging and discusses the key technologies for ending high-quality LED display equipment.
SMD (Surface Mounted Devices) refers to surface mount package LEDs, primarily LEDs with PCB structure and LEDs with PLCC structure. This article focuses on the TOP LED. The SMD LEDs mentioned below all refer to the TOP LED.
The primary materials used in the LED display device package include brackets, chips, die bonding adhesives, bonding wires and encapsulants. The following is a brief introduction of the current situation of some domestic developments in terms of packaging materials.
LED bracket
(1) The role of the stent. The PLCC (Plastic Leaded Chip Carrier) bracket is the carrier of SMD LED equipment, which plays a key role in the reliability and light output of LED.
(2) The production process of the stent. The PLCC stent production process mainly includes metal strip punching, electroplating, PPA (polyphthalamide) injection molding, bending, and five-sided three-dimensional inkjet. In the meantime, electroplating, metal substrates, plastic materials, etc. occupy the primary cost of the stent.
(3) Structural improvement planning of the bracket. The PLCC bracket is physically combined because of the combination of PPA and metal. After the over-temperature reflow oven, the gap will become larger, and then the water vapor will simply enter the interior of the equipment along the metal channel and affect the reliability.
In order to meet the high-quality LED flashing equipment for the reliability of the products to meet the needs of high-end shopping malls, some of the packaged factories have improved the structural planning of the brackets. For example, Foshan Guoxing Optoelectronics Co., Ltd. selects advanced waterproof structure planning, bending and stretching, etc. The method is to extend the water vapor entry path of the bracket, and add a waterproof method such as a waterproof groove, a waterproof step, a water discharge hole, and the like inside the bracket. The plan not only saves the cost of packaging, but also travels to product reliability, and is now widely used in outdoor led display products. After the SAM (Scanning Acoustic Microscope) test of the bending structure of the LED bracket package and the airtightness of the normal bracket, it can be found that the product designed by using the bending structure is more airtight.
chip
LED chip is the center of LED equipment, and its reliability selects the life of LED equipment and even led display, lighting function and so on. The cost of LED chips accounts for the total cost of LED devices. With the decline in cost, LED chip standards are getting smaller and smaller, and together they bring a series of reliability problems.
As can be seen from the above figure, following the standard reduction, the pad of the P electrode and the N electrode is also reduced, and the reduction of the electrode pad directly affects the quality of the wire. In the process of packaging and application, the gold ball is detached and the electrode itself is detached. Invalid. Together, the interval a between the two pads will also shrink, which will cause the current density at the electrode to increase excessively, and the current is partially concentrated at the electrode, and the uneven current is seriously affected by the function of the chip, so that the chip has a partial temperature. Excessively high, uneven brightness, simple leakage, off-electrode, and even low-level lighting power, after all, led to decreased reliability of led display.
Bond wire
The bonding wire is one of the key data of the LED package. Its function is to end the electrical connection between the chip and the pin, and play the role of current introduction and derivation of the chip and the outside. Common bonding wires for LED equipment packages include gold wires, copper wires, palladium-plated copper wires, and alloy wires.
(1) Gold wire. The gold wire is the most widely used, the oldest process, but the price is expensive, resulting in excessive packaging cost of LED.
(2) Copper wire. The replacement of gold wire by copper wire has the advantages of low cost, good heat dissipation, and slow growth of intermetallic compounds in the process of wire bonding. The defect is that copper is susceptible to oxidation, high hardness and strain strength*. Especially in the heating environment of the bonding copper ball burning process, the copper surface is easily oxidized, and the formed oxide film reduces the bonding function of the copper wire, which puts higher requirements on the process control in the process of production.
(3) Palladium-plated copper wire. In order to prevent copper wire oxidation, palladium-bonded copper wire has gradually attracted the attention of the packaging industry. Palladium-bonded copper wire has the advantages of high mechanical strength, moderate hardness, good soldering and ball bonding, and is very suitable for high-density, multi-pin integrated circuit packages.
glue
Nowadays, the glue of the LED display device package mainly includes epoxy resin and silicone.
(1) Epoxy resin. Epoxy resin is easy to age, easy to be wet, and has poor heat resistance. Short-wave illumination and simple discoloration at high temperature have certain toxicity in the case of colloid. Thermal stress does not match LED well, which will affect the reliability and life of LED. number. Therefore, the epoxy resin is generally attacked.
(2) Silicone. Compared with silicone, epoxy resin has high cost performance, excellent insulation, dielectric properties and adhesion. However, the defect is that the airtightness is poor and it is easy to absorb moisture. Therefore, it is rarely used in the packaging application of led display equipment.
In addition, high-quality led displays also require flashing effects. Some packaging plants use additives to improve the stress of the glue and reach the matte matte side together.
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