Analyze the LED display SMD packaging related technology
With the full-color LED display gradually to the high-end market penetration, the quality of the full-color LED display device requirements are increasingly high. This article on the high quality LED display device packaging practical experience, to explore the realization of high quality full-color LED display device key technologies.
The key to package reliability includes the selection of chip materials, the selection of packaging materials and process control. In addition, strict reliability standards are also the key to test the high quality of LED devices.LED devices account for about 40% to 70% of the cost of full-color LED display, LED display cost has dropped significantly thanks to the cost reduction of LED devices.The quality of the LED package has a greater impact on the quality of the LED display.
LED display device packaging status
SMD (Surface Mounted Devices) refers to the surface mounted package structure LED, mainly PCB board structure LED (ChipLED) and PLCC structure LED (TOP LED). This paper focuses on TOP LEDs, SMD LEDs mentioned in the following text are referred to as TOP LEDs.
The main materials used in the packaging of LED display devices include stents, chips, solid crystal adhesive, bonding wire and encapsulation adhesive. The following from the packaging materials to introduce some of the basic development of the current domestic situation.
Chip
LED chip is the core of the LED device, its reliability determines the LED device and even the life of the LED display, luminous performance, etc. The cost of the LED chip accounted for the total cost of the LED device is also the largest. With the reduction of cost, LED chip size cutting smaller and smaller, but also brings a series of reliability problems.
With the size reduction, the P electrode and N electrode pad is also reduced, the electrode pad shrinkage directly affects the quality of the weld line, easily in the encapsulation process and the use of the process leads to the gold ball detachment or even the electrode itself detachment, and ultimately failure. At the same time, the distance a between the two pads will also be reduced, which will make the current density at the electrode
This will make the current density at the electrode increase excessively, the current in the electrode at the local aggregation, and the uneven distribution of the current seriously affects the performance of the chip, so that the chip has a local temperature is too high, the brightness is not uniform, easy to leakage, off the electrode, and even light-emitting efficiency and other problems, ultimately leading to the reduction of the reliability of the LED display.
LED bracket
(1) the stent production process. PLCC stent production process mainly includes metal strip punching, plating, PPA (polyphthalamide) injection molding, bending, five-sided three-dimensional inkjet process. Among them, plating, metal substrate, plastic materials, etc. occupy the main cost of the stent.
(2) Structural improvement of the design of the bracket. PLCC bracket due to the PPA and metal bonding is a physical combination, in the high temperature reflow oven after the gap will become larger, which leads to water vapor can easily enter the device along the metal channel inside thus affecting the reliability.
(3) the role of the bracket. PLCC (Plastic Leaded Chip Carrier) bracket is the carrier of the SMD LED device, the reliability of the LED, light and other properties play a key role.
Through the SAM (Scanning Acoustic Microscope) test bending structure design of the LED bracket encapsulation and normal bracket airtightness, the results can be found using the bending structure design of the product airtightness is better. In order to improve product reliability to meet the high-end market demand for high-quality full-color LED display devices, part of the encapsulation into the factory to improve the structural design of the bracket, the use of advanced waterproof structural design, bending and stretching methods to extend the bracket's path of water vapor into the bracket, and at the same time in the bracket to increase the waterproof groove inside the bracket, the waterproof steps, water release holes and other multiple waterproofing measures.
