Product
As the small-pitch display market continues to expand, more and more companies are launching small-pitch device packaging. At present, small-pitch packaging mainly adopts SMD or COB technology, and the market acceptance of COB packaging is getting higher and higher. So what are the characteristics of COB packaging technology and what are the differences between each process? This article compares the mainstream COB packaging technology on the market.
COB process introduction
COB (chip-on-board) is a board-mounted package. It is a new full-color product developed based on the planar technology of dispensing and solid crystal and the traditional SMD precise dispensing technology. The process of this product is first to cover the silicon wafer placement point on the surface of the substrate with thermal conductive epoxy resin (generally epoxy resin doped with silver particles), and then directly place the silicon wafer on the surface of the substrate, heat treat until the silicon wafer is firmly fixed on the substrate, and then use wire welding to directly establish an electrical connection between the silicon wafer and the substrate. This process is simpler than the dot matrix module full color and SMD full color, so it is easy to mass produce. The picture shows the mainstream COB board-mounted three-in-one product and the "integrated three-in-one" product. Through the comparison of COB technology, the image & video performance, anti-collision and pressure resistance, maintenance cost, refresh rate, raw materials and other aspects are explained in depth, so that the industry and the market can have a more rational understanding of the small-pitch LED COB packaging process.
1. Image & Video Performance
After field investigation, the "light crosstalk" problem of the integrated three-in-one COB is very serious. The reason is because of an important physical characteristic of the process: the integrated three-in-one is to directly place the chip on the PCB board for crystal bonding, which is "convex". Since the integrated three-in-one certain color lamp beads have no PPA bracket to block, the light emitted by any lamp bead will directly affect the light emission of all adjacent lamp beads, and the colors are interspersed, resulting in serious light crosstalk and serious lack of display clarity.
The board-mounted three-in-one COB is to "dig" out "holes" on the PCB board to fix the crystal, which is "concave"; each lamp emits light independently, and the light will not have any effect on nearby lamp beads.
After the integrated three-in-one COB product is packaged, a film is pasted on the entire box to cover the inconsistency of the module group. After the film is pasted, the display is blurred, the color reproduction is poor, and the display is blurred.
2. Maintenance cost
The assembly process of the integrated three-in-one screen is to make 80?80mm small blocks first, assemble them into 240?240mm and seal them, and then assemble the 480?480mm box and paste the film on the whole box. Therefore, front maintenance is impossible.
In this way, there is a big hidden danger - that is, if there is an out-of-control point (that is, abnormal conditions such as dead lights, constant light, constant dark, etc.), even if it is just a small light or even a certain color in a light, the whole box must be torn off the film, repaired and re-pasted, resulting in a huge maintenance cost.
The board-pasted three-in-one always maintains the independence of the 120?60mm small board. In case of failure, it only needs to be replaced with a spare board. There is no technical threshold, maintenance is simple, and the cost is very low.
3. Anti-collision and pressure resistance
The finished product of the integrated three-in-one screen has a soft film on the outside; the soft glue is inside (as shown in the previous figure). This can be clearly felt when we press the integrated three-in-one screen. Therefore, when they are hit or pressed by external forces, their protection of the lamp beads is extremely limited, and a little force can separate the welding wires and cause dead lights.
The lamp beads of the board-mounted three-in-one COB screen (as shown in the previous figure) are slightly embedded, so the PCB becomes the best protection for the lamp beads. In view of the excellent physical properties of PCB, the anti-collision and pressure resistance of the board-mounted three-in-one COB screen is obviously stronger.
4. Refresh rate
The board-mounted three-in-one manufacturer uses FPGA patented technology to significantly improve the refresh rate of the COB display. Especially when the LED display is low-brightness or low-light, the refresh rate is at least doubled.
5. Raw materials
It is understood that the welding wire used by a company to integrate the three-in-one COB lamp core is aluminum wire, the plane welding process is complex, the crystal damage is very large, and it is easy to leak and die during the later use; while the board-mounted three-in-one manufacturer uses 99.9% pure gold wire. As we all know, the electrical and thermal conductivity of gold far exceeds that of aluminum, so at this point, it is obvious that the heat dissipation performance of the board-mounted three-in-one screen manufacturer COB is better and the light decay is smaller.
Good heat dissipation characteristics play a very important role in further maintaining the low bad pixel rate of COB.
In addition, the board-mounted three-in-one screen COB always uses large chips of at least 6?8μ to increase the heat dissipation area, improve the luminous efficiency, and ensure the excellent performance of the product.
6. Others
In other aspects, such as chromaticity and brightness correction, dual-channel hot backup, anti-glare, etc., both sides can achieve it.