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LCD Display--Chip-On-Glass (COG) -vs- Chip-On-Board (COB)

2023-12-14

When we talk about the lcd display, we will come up with two sealing processes, there are COB and COG. Let's talk about these two processes briefly.


Unlike typical LCD modules, COG displays are designed without a PCB. Instead, the LCD's driver/controller is directly bonded to the glass of the display. This allows COG displays to be smaller in size, more cost effective and a highly customizable display solution compared to typical LCD modules.


What is COG?

COG LCDs are composed of two pieces of polarized glass. On the non-polarized side of the glass, a special polymer is added to create grooves that run in the same direction as the polarizing film. Once this is done, a liquid crystal material is added to the grooved side of one of the polarized glasses. These grooves align the liquid crystal with the glass. The second piece of glass is placed on top with the grooved side in, aligned perpendicular to the first pieces of glass creating a row and column arrangement. The LCD driver/controller is then mounted directly to the LCD glass by bonding the gold bumps of the IC to the indium tin oxide (ITO) tracks on the glass.


COG Unique Features

1. 5x8 dot matrix characters or monochrome graphics with custom icons
2. Low power but high brightness
3. No bezel for profiles as thin as 2mm
4. Character COGs have 4 font tables
5. Particularly cost-effective


What is COB?

COB (Chip On Board) uses bonding to fix the bare IC chip onto the printed circuit board. This process involves directly attaching the bare chip to the designated position on the PCB board with adhesive, connecting the chip electrodes to the corresponding solder pads on the PCB board with aluminum wire through a soldering machine, and then sealing and solidifying the chip and aluminum wire with black glue to achieve electrical and mechanical connections between the chip and the circuit board electrodes. This process includes seven processes: adhesive bonding, curing, pressure welding, testing, sealing, curing, and testing. The COB process uses small bare chips with high equipment accuracy, which are used to process PCB boards with a large number of lines, small gaps, and small area requirements. After the chips are soldered and pressed, they are sealed with black glue to prevent external damage to the solder joints and wires, resulting in high reliability.


The feature of COB

1. Superior performance: Using COB technology, the bare die of the chip is directly bound to the PCB board, eliminating the requirement for wire bonding connections, increasing the input/output (I/O) connection density, and making the product performance more reliable and stability;
2. Higher integration: Using COB technology, the connection pins between the chip and the application circuit board are eliminated, improving the integration of the product;
3. Smaller volume: Using COB technology, since it can be bonded and mounted on both sides of the PCB, the size of the COB application module is correspondingly reduced and the application space of the COB module is expanded
4. Stronger ease of use and more simplified product process: using cluster bus technology, pins are used between the COB board and the application board to facilitate interconnection, eliminating the need for welding and other processes that must be used to use the chip, reducing the cost The difficulty of using the product simplifies the product process while making the product easier to replace and enhancing the ease of use of the product;
5. Lower cost: COB technology is directly bonded and packaged on the PCB board, eliminating the need for chip ball placement and welding.