LED display COB and SMD package dispute
LED display COB and SMD package dispute
For a long time, SMD encapsulation is the mainstream of LED full-color display, it is no exaggeration to say that SMD occupies 90% of the full-color screen on the market, but with the arrival of the era of small pitch, a new encapsulation - COB quietly arrived, so what are the advantages of this new encapsulation? Can shake the dominance of SMD?
What is COB
COB is the abbreviation of English ChipOnBoard, is a different from the existing commonly used three-in-one SMD packaging technology, a new type of packaging. Based on the solid crystal plane technology plus precise dispensing technology and developed a new process of LED full-color display, COB product process, the PCB board first patch IC and then fixed in the substrate appearance of the wafer, followed by wire soldering method in the wafer and the substrate between the establishment of an electrical connection, and in the detection of the qualified dispensing solid sealing, to become a piece of LED full-color module.
What is SMD
SMD package, SurfaceMountedDevic abbreviation, meaning surface mount device. (SMD surface mount technology) package of LED products, can be three different colors of RGB LED chip package SMT lights in accordance with a certain spacing package in the same gel. The production process usually consists of upstream lamp bead manufacturers packaging lamp cups, brackets, wafers, leads, epoxy resin and other materials into different specifications of lamp beads. Downstream display manufacturers with high-speed mounter, high-temperature reflow soldering lamp beads welded to the circuit board, made of different spacing LED full-color display display unit.
SMD defects
SMD small pitch LED full color display has many advantages such as bright color, high saturation, high brightness, no splicing seam, unlimited splicing, etc., and the industry chain is complete, so it is widely used at present and occupies the main share of the small pitch LED application market. However, due to the SMD packaging process can not avoid some of the defects, but also gradually show shortcomings.
First of all, the dead light phenomenon is also bad point. SMD small pitch LED production process, the lamp beads need to high temperature reflow soldering in the circuit board, and in the high temperature reflow soldering due to the lamp beads in the bracket, substrate, epoxy resin and other materials with different expansion coefficients, it is very easy to cause the bracket and the epoxy resin encapsulation shell falling off, there is a gap, the late use of the phenomenon is prone to dead light; at the same time the SMD encapsulation technology At the same time, the SMD packaging technology, LED foot pads exposed external easy to be oxidized, resulting in water vapor invasion of the LED internal chip, water and oxygen under the action of the temporary operation of the wick caused by the internal electrochemical reaction, dead; in addition to the bare foot pads are also susceptible to the impact of static electricity, resulting in dead. Of course, manufacturers will control the rate of bad points in the factory in the specification value, but with the use of time, bad points will continue to increase. Although the bad point can be replaced, but will still bring trouble to the customer, while increasing the service cost of LED display manufacturers, and if it is a different production batch of wicks, brightness and color will vary, resulting in the replacement of the picture of the non-consistency of the problem.
Second, heat dissipation. Surface-mounted LED products wafer fixed in the bowl cup, not in direct contact with the PCB board, mainly through the gel and the four pads heat dissipation, heat dissipation area is small, the heat will be more concentrated in the chip, for a long time will result in serious light attenuation phenomenon, or even dead light phenomenon, reducing the service life and quality of small pitch LED full color display.
Again, stability. SMD surface-mounted products lamp beads are not seamlessly connected to the PCB board, which makes the collision process is easy to cause pressure on a single lamp bead concentration. The transportation of large screen system, device, etc., there are inevitable vibration and collision, resulting in increased chances of small pitch led full color display bad light.
Fourth, viewing angle and viewing comfort. Compared with COB, SMD small pitch LED viewing angle has some limitations, only between 120~140 degrees. This is firstly because the LED chip is at the bottom of the lamp cup, and the mouth of the cup to form a certain drop between; Secondly, the encapsulated lamp in the patch process position of the precision error; Again, the unevenness of the locking mask, resulting in a reduced viewing angle and unevenness of the viewing angle. Secondly, SMD small pitch LED full-color screen is frequently refreshed, the human eye periodically accepts the light signal stimulation, long time viewing as well as close viewing will feel uncomfortable.
COB advantages
Compared with SMD package these lack, COB technology has a good indication, mainly reflected in
First, good stability. As COB packaging technology in the processing technology does not exist in the reflow soldering sticker lamps, it avoids the problem of high-temperature soldering within the welder caused by the lamp bead bracket and the epoxy resin gap between the problems, so the COB products are not easy to appear after the factory is not a dead lamp phenomenon. In addition COB package due to the use of a more integrated overall process, making the crystal selection can be selected on the power area density is lower, the crystal particles of some of the larger wafers, which reduces the core light-emitting point of the intensity of work. At the same time, COB package realizes the epoxy resin full package under the whole solid seamless heat dissipation, make the working state of the LED crystal heat concentration decreases, is conducive to prolong the life of small pitch LED full color display, enhance system stability.
Second, strong durability, COB encapsulation technology, no bare feet, smooth appearance without gaps, with moisture, anti-static, anti-knock, dust and other functions, the front protection level reaches IP65 to prevent SMD encapsulation of small spacing LED due to moisture, static electricity, dust, knocking and other environmental or man-made factors caused by the dead lamp, bad light problem. Lamp point appearance raised into a spherical surface, smooth and hard, impact resistance and wear resistance. Bad point, can be repaired point by point, because there is no mask, the appearance of flat and smooth, water or cloth can clean the appearance of stains.
Third, can be bent, COB package no bracket welding, LED chip sealed by epoxy resin glue in the light bit, so it can be bent at will bending ability with the size of the small pitch LED full color display module size and thickness of the PCB board and decide. SMD bending may cause the chip pin desoldering, and the cost is higher than COB.
Fourth, more comfortable to watch. As the COB package using the shallow well spherical light-emitting, so a wider viewing angle, greater than 175 degrees, close to 180 degrees, and has a better optical diffuse color than SMD muddy light effect. In addition, the light emitting uniformity, similar to the “surface light source” can effectively eliminate moiré.
Its matte coating technology. Its matte coating technology, but also significantly improve contrast, reduce glare and blinding feeling, not easy to occur visual fatigue.
What is COB
COB is the abbreviation of English ChipOnBoard, is a different from the existing commonly used three-in-one SMD packaging technology, a new type of packaging. Based on the solid crystal plane technology plus precise dispensing technology and developed a new process of LED full-color display, COB product process, the PCB board first patch IC and then fixed in the substrate appearance of the wafer, followed by wire soldering method in the wafer and the substrate between the establishment of an electrical connection, and in the detection of the qualified dispensing solid sealing, to become a piece of LED full-color module.
What is SMD
SMD package, SurfaceMountedDevic abbreviation, meaning surface mount device. (SMD surface mount technology) package of LED products, can be three different colors of RGB LED chip package SMT lights in accordance with a certain spacing package in the same gel. The production process usually consists of upstream lamp bead manufacturers packaging lamp cups, brackets, wafers, leads, epoxy resin and other materials into different specifications of lamp beads. Downstream display manufacturers with high-speed mounter, high-temperature reflow soldering lamp beads welded to the circuit board, made of different spacing LED full-color display display unit.
SMD defects
SMD small pitch LED full color display has many advantages such as bright color, high saturation, high brightness, no splicing seam, unlimited splicing, etc., and the industry chain is complete, so it is widely used at present and occupies the main share of the small pitch LED application market. However, due to the SMD packaging process can not avoid some of the defects, but also gradually show shortcomings.
First of all, the dead light phenomenon is also bad point. SMD small pitch LED production process, the lamp beads need to high temperature reflow soldering in the circuit board, and in the high temperature reflow soldering due to the lamp beads in the bracket, substrate, epoxy resin and other materials with different expansion coefficients, it is very easy to cause the bracket and the epoxy resin encapsulation shell falling off, there is a gap, the late use of the phenomenon is prone to dead light; at the same time the SMD encapsulation technology At the same time, the SMD packaging technology, LED foot pads exposed external easy to be oxidized, resulting in water vapor invasion of the LED internal chip, water and oxygen under the action of the temporary operation of the wick caused by the internal electrochemical reaction, dead; in addition to the bare foot pads are also susceptible to the impact of static electricity, resulting in dead. Of course, manufacturers will control the rate of bad points in the factory in the specification value, but with the use of time, bad points will continue to increase. Although the bad point can be replaced, but will still bring trouble to the customer, while increasing the service cost of LED display manufacturers, and if it is a different production batch of wicks, brightness and color will vary, resulting in the replacement of the picture of the non-consistency of the problem.
Second, heat dissipation. Surface-mounted LED products wafer fixed in the bowl cup, not in direct contact with the PCB board, mainly through the gel and the four pads heat dissipation, heat dissipation area is small, the heat will be more concentrated in the chip, for a long time will result in serious light attenuation phenomenon, or even dead light phenomenon, reducing the service life and quality of small pitch LED full color display.
Again, stability. SMD surface-mounted products lamp beads are not seamlessly connected to the PCB board, which makes the collision process is easy to cause pressure on a single lamp bead concentration. The transportation of large screen system, device, etc., there are inevitable vibration and collision, resulting in increased chances of small pitch led full color display bad light.
Fourth, viewing angle and viewing comfort. Compared with COB, SMD small pitch LED viewing angle has some limitations, only between 120~140 degrees. This is firstly because the LED chip is at the bottom of the lamp cup, and the mouth of the cup to form a certain drop between; Secondly, the encapsulated lamp in the patch process position of the precision error; Again, the unevenness of the locking mask, resulting in a reduced viewing angle and unevenness of the viewing angle. Secondly, SMD small pitch LED full-color screen is frequently refreshed, the human eye periodically accepts the light signal stimulation, long time viewing as well as close viewing will feel uncomfortable.
COB advantages
Compared with SMD package these lack, COB technology has a good indication, mainly reflected in
First, good stability. As COB packaging technology in the processing technology does not exist in the reflow soldering sticker lamps, it avoids the problem of high-temperature soldering within the welder caused by the lamp bead bracket and the epoxy resin gap between the problems, so the COB products are not easy to appear after the factory is not a dead lamp phenomenon. In addition COB package due to the use of a more integrated overall process, making the crystal selection can be selected on the power area density is lower, the crystal particles of some of the larger wafers, which reduces the core light-emitting point of the intensity of work. At the same time, COB package realizes the epoxy resin full package under the whole solid seamless heat dissipation, make the working state of the LED crystal heat concentration decreases, is conducive to prolong the life of small pitch LED full color display, enhance system stability.
Second, strong durability, COB encapsulation technology, no bare feet, smooth appearance without gaps, with moisture, anti-static, anti-knock, dust and other functions, the front protection level reaches IP65 to prevent SMD encapsulation of small spacing LED due to moisture, static electricity, dust, knocking and other environmental or man-made factors caused by the dead lamp, bad light problem. Lamp point appearance raised into a spherical surface, smooth and hard, impact resistance and wear resistance. Bad point, can be repaired point by point, because there is no mask, the appearance of flat and smooth, water or cloth can clean the appearance of stains.
Third, can be bent, COB package no bracket welding, LED chip sealed by epoxy resin glue in the light bit, so it can be bent at will bending ability with the size of the small pitch LED full color display module size and thickness of the PCB board and decide. SMD bending may cause the chip pin desoldering, and the cost is higher than COB.
Fourth, more comfortable to watch. As the COB package using the shallow well spherical light-emitting, so a wider viewing angle, greater than 175 degrees, close to 180 degrees, and has a better optical diffuse color than SMD muddy light effect. In addition, the light emitting uniformity, similar to the “surface light source” can effectively eliminate moiré.
Its matte coating technology. Its matte coating technology, but also significantly improve contrast, reduce glare and blinding feeling, not easy to occur visual fatigue.