You will find different prices on the LED screen because of different raw materials. Today, I’d like to briefly introduce one of the raw materials—LED lamp, which is also the most important part in determining the price, after learning about LED lamp, I believe you can choose more professional LED suppliers
1.what is the led lamp?
LED is the abbreviation of the light-emitting diode. The basis part of the led lamp is led chip which is also called light-emitting semi-conductive. There are following processes from led chip to led lamp:
1.Curing the led chip to the substrate by silver plastic or white plastic
2.Connected with PCB board by gold wire or silver wire
3.Encapsulation by epoxy to protect the inner led chip and wire.
4.Installation of the bottom case
Led lamp is the most important part of the LED screen, it will influence the whole visual effect of the led screen.
We often see 2121,2727,3535 led lamps on the led market, but what is the meaning of those numbers? It’s the size of the led lamp. Such as 2121 means the size of led lamp at 2.1×2.1mm (w*h).Knowing this will help us to choose led lamp. When we know the pixel pitch of the screen, we can check whether the led lamp is suitable for the screen or not. Such as P2.5mm usually uses a 2121 led lamp but no 2727 on the market, because P2.5mm means the distance between two pixels is only 2.5mm. There will be no enough place to insert two led lamps if using 2727 lamp since one lamp size is 2.7mm. Same as that P1.875 will use 1515 but not 2121 etc. So if we see the configuration of the P2.5mm screens’ led lamp is 2727, we should recognize that it is the wrong specification.
But for the outdoor LED screen, it usually uses 2727,3535,3528 led lamp, etc. There is enough space to insert 2121 led lamp, but why not choose 2121? Because outdoor screen has high brightness requirement. The led lamp size also means the led chip size. For 2121 led lamp, it is hard to increase the brightness because led chip is too small to enlarge the current passing. So at this time, we will consider choosing big size led lamp to reach the high brightness requirement. That’s the reason why we choose a big size led lamp for outside application.
2. What will influence the led lamp’s lifespan?
1).The quality of the led chip. This is the most important factor.
2).The technology of encapsulation. Poor encapsulation technology will cause a heat dissipation problem.
3). Reasonable led lamp design: related to conductive, heat dissipation, etc.
4). Driving method. There are constant current and constant voltage driving method. The constant current driving method will lengthen the lifespan of led.
5).Acidic conditions. Under acidic conditions, LED will be easily affected, so when in acidic conditions we need to consider the high level of IP protection.
6).Heat. The temperature around the led.
7).Humidity.The performance of LED also depends on the ambient humidity. Because in humid environments, electronic components, metal parts, etc. tend to be quickly damaged and rust, so it’s very important to make the LED system avoid moisture.
Above we mentioned constant current will be good than constant voltage.
Here I would like to talk about why choosing a constant current driving method but not constant voltage driving method:
1). LED nonlinear device, a small change in forwarding voltage will cause big change at forwarding current.
Like: LED at 3.3V voltage the current is 20mA, but if the voltage changes into 4.5V, the current will be more than 100mA, expanded 5times, it’s easy to cause burning of led lamp.
2). Like 1W power consumption LED. if forward voltage change 10%(from 3.4V decreasing to 3.1V), which will cause forward currents changing from 350mA to 100mA, 3.5times change.
3). Led light output direct ratio with the forward current. like the following picture, if the forward current declines from 300mA to 100mA, the light output will decline more than 70%.
4). LED display is a semi-conductive diode, which has Volt-ampere characteristics. It means that the voltage and current change because of temperature. Like the following picture, if using constant voltage, when the temperature is up to 85degree, the forward current will change from 20mA up to 35-37mA, but the brightness will not increase. When temperature declines into-40degree, forward current declines from 20mA to 8-10mA, and brightness decrease. So we will choose constant current on led display.
That’s the reason why led screens usually adopt a constant current driving method.
3. What factors affect the reliability of LED packaging?
LED devices account for about 40% to 70% of the cost of LED display screens. The significant reduction in the cost of LED display screens benefits from the cost reduction of LED devices. The quality of the LED package has a greater impact on the quality of the LED display. The key to package reliability includes the selection of chip materials, the selection of packaging materials, and process control. As the LED display screen gradually penetrates into the high-end market, the quality requirements for LED display devices are becoming higher and higher.
The main materials used in the packaging of LED display devices include brackets, chips, solid-state adhesives, bonding wires, and packaging adhesives. SMD (Surface Mounted Devices) refers to surface-mount package structure LEDs, which mainly include PCB board structure LEDs (ChipLED) and PLCC structure LEDs (TOP LED)
LED bracket
(1) The role of the stent. The PLCC (Plastic Leaded Chip Carrier) bracket is the carrier of SMD LED devices and plays a key role in the reliability and light performance of LEDs.
(2) The production process of the stent. The production process of the PLCC stent mainly includes the steps of die-cutting, plating, PPA injection molding, bending, and five-sided three-dimensional inkjet. Among them, plating, metal substrates, plastic materials, etc. occupy the main cost of the bracket.
(3) Improved design of the support structure. The PLCC bracket is a physical combination of PPA and metal, and the gap will become larger after the high-temperature reflow furnace, which will cause water vapor to easily enter the device along the metal channel and affect the reliability.
In order to improve the reliability of the product to meet the high-end market demand for high-quality LED display devices, some packaging factories have improved the structural design of the bracket. For example, a certain Foshan nationstar Optoelectronics Co., Ltd. uses advanced waterproof structure design, bending and stretching methods In order to extend the water vapor entry path of the bracket, at the same time, multiple waterproof measures such as waterproof grooves, waterproof steps, and drainage holes are added inside the bracket.
This design not only saves the packaging cost but also improves the reliability of the product. It has been widely used in outdoor led display products. SAM (Scanning Acoustic Microscope) was used to test the airtightness of the LED bracket with the folded structure design and the normal bracket after the package was designed.
Chip
LED chips are the core of LED devices, and their reliability determines the life and luminous performance of LED devices and even LED displays. The cost of LED chips accounts for the total cost of LED devices. With the cost reduction, LED chip size cutting is getting smaller and smaller, and it also brings a series of reliability problems.
With the reduction in size, the pads of the P electrode and the N electrode also shrink. The reduction of the electrode pad directly affects the quality of the bonding wire, and it is easy to cause the gold balls to detach or even the electrodes to detach during the packaging process and use, and eventually fail.
At the same time, the distance between the two pads will also be reduced. This will cause the current density at the electrodes to increase excessively, and the current will locally collect at the electrodes. The unevenly distributed current will seriously affect the performance of the chip, causing the chip to have a local temperature. Problems such as too high brightness, uneven brightness, easy leakage, electrode loss, and even low luminous efficiency eventually lead to reduced reliability of the LED display.
Bonding wire
The bonding wire is one of the key materials for LED packaging. Its function is to achieve the electrical connection between the chip and the pins, and it plays the role of the current introduction and export of the chip and the outside. Common bonding wires for LED device packaging include gold wires, copper wires, palladium-plated copper wires, and alloy wires.
The bonding wire is one of the key materials for LED packaging. Its function is to achieve the electrical connection between the chip and the pins, and it plays the role of the current introduction and export of the chip and the outside. Common bonding wires for LED device packaging include gold wires, copper wires, palladium-plated copper wires, and alloy wires.
(1) The gold thread. Gold wire is widely used and the process is mature, but the price is expensive, which leads to excessive packaging cost of LED.
(2) Copper wires. Copper wire instead of gold wire has the advantages of low cost, good heat dissipation effect, and slow growth of intermetallic compounds during the wire bonding process. The disadvantages are that copper is susceptible to oxidation, high hardness, and high strain strength. Especially in the heating environment of the copper-copper sintering process, the copper surface is easily oxidized, and the formed oxide film reduces the bonding performance of the copper wire, which places higher requirements on the process control in the actual production process.
(3) Palladium-plated copper wire. In order to prevent oxidation of copper wires, palladium-plated bonded copper wires have gradually attracted attention from the packaging industry. The palladium-plated bonded copper wire has the advantages of high mechanical strength, moderate hardness, and good soldering properties, and is very suitable for high-density, multi-pin integrated circuit packaging.
Glue
At present, the glue for LED display device packaging mainly includes epoxy resin and silicone.
(1)Epoxy resin. Epoxy resin is easy to age, easy to be wet, and has poor heat resistance. It is easy to change color under short-wave light and high temperature. It has certain toxicity in the gel state. The thermal stress does not match the LED well, which will affect the reliability and life of the LED. Therefore, epoxy resin is usually attacked.
(2)Silicone. Compared with epoxy resin, silicone has higher cost performance, excellent insulation, dielectric properties, and adhesion. However, the disadvantage is that the airtightness is poor and it is easy to absorb moisture. Therefore, it is rarely used in packaging applications of LED display devices.
In addition, high-quality LED displays have special requirements for display effects. Some packaging factories use additives to improve the stress of the glue while achieving the effect of matte. No appearance damage and mark damage. Soak in IPA solvent for 5 ± 0.5 minutes, dry at room temperature for 5 minutes, and then wipe 10 times.
4. What factors affect the reliability of LED packaging?
(1). Viewing Angle
The viewing angle of the screen depends on the viewing angle of the LED lamp. At present, when for the outdoor screen, we usually choose DIP LED lamp which is 100°（H）/50°（V）; when for the indoor screen, we usually choose SMD LED lamp which is 110°（H）/110°（V）. The viewing angle and brightness can’t coexist because a big viewing angle will lower brightness absolutely. The choice of viewing angle depends on the concrete application.
(2). Brightness
The brightness of the LED lamp is an important factor in the screen’s brightness. The higher brightness of the LED, the more remain of current, which is beneficial to power saving and keep LED stable. LED has different viewing angle values, under the certain circumstances of LED’s brightness, the smaller viewing angle, the brighter LED lamp. So the recommended LED lamp’s viewing angle is 100°to ensure enough viewing angle of the screen.
(3).Failure Rate
Due to the full color LED screen is consist of tens of thousands or even hundreds of thousands of led lamps, which is consist of red, green, and blue LED chips, the failure of any color of LED chips will influence the overall visual performance. In general, the failure rate before shipment not more than five over ten thousand.
(4).Anti-static Ability
LED is a semiconductor device, which is sensitive to static and causes failure once incurred static, thus anti-static ability is vital for the lifespan of the screen.
(5).Lifespan
Theoretically, the lifespan of the LED device is 100,000 hours, which largely exceeds the lifespan of others’ devices on the screen. If we can guarantee the LED device in excellent quality, suitable working current, reasonable PCB thermal dissipation design, strict production workmanship, LED device will be one of the most durable devices on the screen.
(6).Degradation Feature
When the screen works for a long time, it will have the brightness degradation phenomenon. The brightness degradation of LED will lower the brightness of the overall screen. What’s more, the brightness degradation range nonconformity of RGB will cause the color nonconformity of the LED screen. The LED devices in superior quality control bright degradation range nicely.
(7).LED Device Size
On the basis of certain pixel pitch, the increased LED device size, which can increase the showing square meter and decrease granular sensation, but it will lower contrast and vice versa.
(8).Consistency
The full-color screen is consists of countless LED lamps that contain an RGB LED chip. The consistency of brightness, white balance, and chromaticity depend on the consistency of the brightness of each color in LED and wavelength.
Due to LED has a viewing angle, thus screen has an angle orientation feature similarly, to put it simply, the brightness will have a progressive increase or decrease when viewing at different angles. In this way, the angle consistency of the RGB LED chip will influence the consistency of white balance at different angles seriously, which will affect the chromatic fidelity directly.
Do you think the introduction of the above LED lamp is helpful to you?
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