목차
Quick takeaway
Common cathode Flip COB is currently the most stable and advance technology in LED display, especially for fine and micro pixel pitch led display. Not only it can make a wide range pixel pitch from 0.3mm – 1.875mm, but also it offers a wide color gamut, wide viewing angle, less heat, and a longer life span.
But why it has adjectives of “Common cathode” and “ Flip”, Actually it two technologies.
Brief review of SMD led display technology?
There are two kinds of COB technology,
one is wire bonding COB, the other is flip COB. COB means “Chip on boards” which means that the chip is fixed on the PCB boards directly. In comparison with SMD that the “chip” is fixed in a “package”. Then the “package” soldering on the PCB boards.
The SMD package works very well before the led display’s pixel pitch is smaller than 1mm. As you can see in the picture ( this is Top structure SMD）, the SMD lamp has
Soldering pad : for soldering with PCB
PPA bracket : Protect the led chip
led chip
Wire : Connecting the led chip with the soldering pad
Epoxy cover: Protecting the led chip
The PPA bracket has a size limit, hence the led factory come up with “chip” structure. Which does not have the PPA bracket. 
Though the “chip” structure can make smaller led lamp, but it also means smaller soldering pad which means the led lamp has less adhesive force on the PCB, which means the led lamp is easy to loose on the PCB.
Drawback of Normal SMD LED display technology
- Can not make pixel pitch smaller than 1mm (4 in one led lamp use to solve this problem)
- Soldering pads are exposed to air, which would get oxidized and fragile to moist. (GOB solution to solve this problem)
- Wire might be fragile during the bonding process
- Small pixel pitch led lamp has small adhesive force on the PCB (4 in one led lamp used to solve this problem)
- Bad heat dissipation, as the led chip pass the heat to air
Wire bonding COB LED display
The market tends smaller pixel pitch. So how do we get it?
When you take a look of the “chip” structure led lamp, it already does not have the bracket, why not take away the soldering pad and substrate, and directly fixed the led chip on PCB board, then do the wire bonding on the PCB board directly. With this, it can make smaller pixel pitch. and boom, the application of COB technology in led display started.
The main production process of Wire bonding COB technology is as below:
Step 1: Mass transfer, take the led chip and Fixed the led chip on the led board
Step 2: Wire bonding the P electrode and N electrode to the PCB
Step 3: Testing
Step 4: Cover the whole PCB with Epoxy
Wire bonding COB Technology Benefits:
1: Less investment, as the bonding machine is the same as the SMD’s bonding machine, which saves a lot of investment
2: Better heat dissipation than SMD, as the led chip is directly attached on the PCB, hence the heat would pass to the PCB board to spread the heat faster
3: As PCB is covered with Epoxy, which means it is waterproof and shockproof, and also not afraid of scratches.
4: Easy to clean
5: working in wide environment
Wire bonding COB technology Drawbacks:
1: Still need to use Wire
2: Consistency of the Epoxy would affect the visual effect a lot
3: Color consistency is also a problem
4: viewing angles like SMD
5:Hard to repair
Notice: Consistency is always a big problem in COB led display, (Due to mass transfer technology, and the Epoxy) Though calibration can improve the color consistency of the led display, but we do need to check the led display’s visual effect when the led display’s calibration is turned off.
Flip COB technology
In the Wire bonding COB technology, we have already removed the bracket,
and soldering pad of the SMD lamp, while we also thought why not flip the LED chip, to make the P electrode and N electrode directly connected with PCB, then we can also save the wire. And boom, Flip COB technology appeared. This “Flip” actually is because in the chip business, the wire bonding technology is the main stream, hence we take the wire bonding led chip direction as the normal direction. Below is its production process
Step1: Mass transfer, take the led chip, and fix it on the PCB board
Step2: Light up testing
Step3: Cover the whole PCB with Epoxy
Flip COB Technology Benefits:
1: Without Wire
2: Better heat dissipation than SMD, as the led chip is directly attached on the PCB, hence the heat would pass to the PCB board to spread the heat faster
3: As PCB is covered with Epoxy, which means it is waterproof, and shockproof, and also not afraid of scratches.
4: Wide viewing angle
5: Easy to clean
Flip COB technology Drawbacks:
1: Huge investment on the machines, as many machines is not compatible with old SMD production machine
2: Consistency of the Epoxy would affect the visual effect a lot
3: Color consistency is also a problem
4: Hard to repair
Notice: Consistency is always a big problem in COB led display, (Due to mass transfer technology, and the Epoxy) Though calibration can improve the color consistency of the led display, but we do need to check the led display’s visual effect when the led display’s calibration is turned off.
Mix COB technology
Due to the Red lamp is a little different, and hard to make it flip, hence it also have a solution, that the red lamp still use wire bonding, while green and blue lamp is using flip chip technology, While now few factory is using this now. 
As flip chip COB technology does not need the wire which would save a procedure which would save cost. And without the wire also decreases the dead lamp rate. Hence fewer factory is using wire-bonding COB technology now.
With the cost of the flip chip COB continue to decrease, and the people’s desire for smaller pixel pitch led display. Flip chip COB technology would be the main product in the small and micro pixel pitch led display market in near future. As of June 2024, the price of pixel pitch 1.25mm flip COB led display already has a cheaper price than normal pixel pitch 1.25mm SMD led display.
Before we talk about Common Cathode, We need to discuss some history. As we know that RGB lamp actually has three led lamps, Red led lamp, Green led lamp and Blue led lamp.
Hence when we try to control those 3 led lamps, we need to have 6 electrodes. To decrease connecting electrodes in the SMD package, It has two solutions,
First is connecting those 3 led lamps’ anode electrode together, then it only has four electrode pad left, and this is Common anode led lamp
Second is connecting those 3 led lamps’ Common Cathode electrode together, then it only has four electrode pad left, and this is Common Cathode led lamp
Common anode To common Cathode
Common Cathode is not a new thing in led lamp application, but it did not exist in led display industry before 2011.
Early stage of led display industry:
Before 2005, The technology development of the led display is based on what the market have and the total led display is also not as big as it is today. In the beginning of the led display, it did not have driving IC that designed for led display, and the led lamp used was also in DIP package. Based on the driving IC and the DIP package at that time, common anode is a good solution.
SMD led display era:
Before 2011, With the development of the led display industry, special designed IC for led display is coming out, and to make it compatible with the DIP package, the driving IC is designed for common anode use. Which in return make the design of the RGB SMD lamp to be common anode too. And with the bigger quantities of common anode technology used, the price of the common anode led lamp and driving IC decrease very fast which stimulates this market to grow bigger
Heat dissipation and power consumption Problem
Before 2018, the led display is not what it is as today, especially for outdoor led display. LED displays generate a lot of heat, and also consume a lot of energy. Normally for a LED display, we would need to install an AC to cool it down, And the led display cabinet would have fan to ventilate. Of course, the design of the LED display do a lot of help, but so does the common Cathode.
As we mentioned above, in order to make the common cathode, you need to customize common cathode RGB led lamp, and also customize common cathode IC. The beginning of the Common cathode technology begins in 2011 when siliconcore designed their own driving IC, and their own common cathode RGB led lamps. This takes a lot of courage, and it also did pay off.
By using Common cathode, it generate less heat, and then use less power.
How much energy does common cathode save comparing with Common anode
It has R,G,B three lamp in 1 pixel, but the conducting voltage of the Red lamp is around 1.8v, while the conducting voltage of the Green lamp and Blue lamp is around 2.6V. And the white balance brightness R:G:B ratio is 3:6:1. Hence to reach the same brightness,
In common anode design, as R,G,B lamp is using the same voltage, normally it is 3.6V. The wattage would be (assume the current is I)
3.6*0.3*I + 3.6*0.6*I + 3.6*0.1*I = 3.6I
In common anode design, as R lamp is using 2.6V, ,G and B lamp are using the same voltage, normally it is 3.6V. The wattage would be (assume the current is I)
2.6*0.3*I + 3.6*0.6*I + 3.6*0.1*I = 3.3I
We would know it can save around (3.6I-3.3I)/3.6I = 8.3% in theory. But in truth, it can save around 20%, Why the difference?
This is because the led lamp’s brightness is strongly affected by temperature, if do not use common cathode, the 8.3% power saved would all be used in the form of heat, and that would be a lot of heat. Then the heat would affect the brightness a lot. Hence in real testing, the common cathode would have around 20% wattage less than the common anode.
And now due to the mass production of the common cathode led lamp, and IC, the price of the common cathode also has decreased a lot.
All major IC manufacturers have common Cathode driving ICs. For example,
Chipone has ICND1069, ICND2069, ICND3069
Mblock has MBI5754, MBI5759, MBI5762 and MBI5789
Unlike the SMD that need special common cathode lamps, COB process can make the COB pixels to be common cathode naturally, as for the COB, make it common anode or common cathode is the same process. Hence now many flip COB led display is using common cathode.
But why there also have common anode led display in the market. This is because if using common anode, you have a very wide driving IC selection, and as currently the common cathode driving IC’s performance is still not as good as common anode Driving IC. For example, Based on the LED boards’s original design, if it is the common anode design, the default driving IC is ICND1065ap with refresh rate of 3840Hz, if I do not like its performance, then I can change its IC to ICND2165 to reach a better greyscale visual effect, or even upgrade to ICND3065 to reach 7680Hz. But if you are using common cathode, the Driving IC’s selection is very narrow. And sometimes it can not meet the customer’s requirements.
