Classification of LCD Module
LCD Module(LCM) has 4 parts: LCD screen, LED backlight, IC and PCB (maybe a plastic shell). We can simply consider that it has two parts: LCD screen and LED backlight because we can see from the appearance and they are the main constituents. LCM can be divided into COB(chip on board), COG(chip on glass) and COF(chip on film) by the position of chip. It can also be divided into segment LCD and dot matrix LCD by the content they are going to display.
COB is the abbreviation for Chip On Board, which is a most common way of processing the drive circuit board of LCM. The IC is attached directly to a specified location on the PCB with a sticky piece of plastic. See the picture below and the IC is under the black plastic. The electrodes of the chip are connected to the corresponding pads of PCB board with aluminum wire by a soldering machine. And they are covered by a sticky piece of plastic on the surface.
COB is the most common, reliable and cheapest technology which requires high precision equipments and a complicated processing procedure. It uses PINs to connect and fasten the LCD screen, LED backlight and PCB all together, so it can’t be disconnected. It is very reliable and it can’t be damaged under normal circumstances. But if it is damaged, unfortunately, it can’t be repaired. I think this is the main defect that COB has. If our customers don’t have any special requirements, we would suggest that we use COB technology.
COG is the abbreviation for Chip On Glass, where IC is bound to the ITO glass directly. Please see the picture below. It can greatly reduce the size of the LCD module and be easy for mass production for consumer electronics products, such as: mobile phones, PDAs and other portable products.
COG doesn’t need PCB. It is cheaper, isn’t it? I am sorry to tell you that on the contrary, it is not. COG is going to need a dedicated glass mold and a dedicated LCD FPC mold which COB doesn’t need. Maybe it needs a dedicated light guide plate mold and a dedicated backlight FPC mold because of its special structure. So the tooling fee of COG is the most expensive among the three of them. If the quantity you want is only 1000 pieces, the unit price will be incredibly high because of the tooling fee. At the same time, the tooling fee can be almost negligible if the order quantity is very large, say like 100 thousand, 1 million.
Is it safer? Of course, it is not. COB is the most reliable one. The only reason I think why COG is popular is that it can save a lot of space by concentrating all the functions on a single IC. It is extremely important for the modern portable electronic products which require small volumes.
COF is the abbreviation for Chip On Film, where IC is bound to a flexible film conveyor belt directly. Please see the picture below. It can greatly reduce the size of the LCD module too.
The tooling fee of COF is less than COG’s, but it is more than COB’s. It needs a dedicated FPC mold, compared to COB. But I think it is the most unreliable one because the IC is bound to a flexible film which is moving all the time. So if you really want to save the space, I strongly suggest that you choose COG instead of COF.
Segment LCD only shows the fixed pattern. Take the 7 segment LCD panel for example. See the picture below. Figure 0 has six segments are turning red; figure 9 has five segments which are turning red; figure 8 has seven segments which are turning red and so on.
Segment LCD can’t show any graphic unless you have pre-designed it.
Post time: Apr-20-2017