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. It 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 graphic LCD module and character LCD module by the resolution and Character Count.
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 LCD module is the most reliable technology which requires high precision equipments and a complicated processing procedure. It uses PINs or conductive rubber strip 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. it is an obsolete technology since it is too big and it is being replacd by COG LCD module.
COG is the abbreviation for Chip On Glass, where IC is bound to the ITO glassdirectly. 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 LCD module doesn’t need PCB. It is cheaper, isn’t it? I am sorry to tell you that it is not true. 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 reliable? Of course, it is very reliable. COB is the most reliable one. The reasons I think why COG is popular are it can save a lot of space by concentrating all the functions on a single IC and cost-saving if the quantity is large. 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.
We can barely see COF LCD module. Since no one makes it, I think it is best that we just follow the insdustry tradition. It is really expensive if you want to make some special. So if you really want to save the space, I strongly suggest that you choose COG instead of COF.