COG is the abbreviation of chip on glass, that is, the chip is directly bonded to the glass. This installation method can greatly reduce the volume of the LCD module, and is easy to mass-produce. It is suitable for LCD of consumer electronic products, such as: mobile phones, PAD and other portable products. This installation method, under the promotion of IC manufacturers, It will be the main connection method between IC and LCD in the future.

COG process/process technology

The COG process uses the flip chip (Flip Chip) conduction method to directly align the wafer with the electrodes on the glass substrate, and uses the Anisotropic Conductive Film (hereinafter referred to as ACF) material as the interface material for bonding, so that the two The electrodes in the vertical direction of the binding object are turned on. The production process of the current COG bonding process is carried out in an automated way. The COG bonding operation consists of three operations: anisotropic conductive film attachment, IC pre-bonding and IC bonding

1. Attachment of anisotropic conductive film conductive film

First of all, the first step in the COG production process is to attach the ACF to the LCD electrode part, and then tear off the ACF release paper, leaving only the ACF attached to the LCD electrode part to complete the ACF attaching operation.

2. IC pre-binding

Transfer the LCD that has completed the ACF attachment operation to the IC pre-bonding project for IC pre-bonding operation. This project needs to align the IC on the opposite electrode of the LCD, so it is necessary to carry out CCD image reading and identification, and use computer image processing. The system recognizes the preset recognition positions on the IC and the LCD respectively. After the computer automatically calculates the relative coordinates, the IC can be accurately pasted on the LCD electrodes to complete the IC pre-binding operation.

3. IC book binding work

Finally, the completed IC pre-binding operation LCD will be transported to the IC binding project for the IC binding operation. This project is the key to the quality of the COG process. The pressing temperature, pressing pressure and pressing time are the three elements of ACF curing. The following A separate description of it:

(1) Pressing temperature: ACF adhesive materials are mainly polymer resins, which can be mainly divided into two types: thermosetting (Thermal-Setting) and thermoplastic (Thermal Plastic) resins. Generally, ACF manufacturers will provide technical information on the characteristics of ACF. The biggest impact is that too low temperature will cause the resin to not dissolve, and too high temperature will cause the loss of conductive particles, so the pressing temperature must be controlled in the optimal range to ensure the reliability of the product.

(2) Crimping pressure: It has the greatest impact on the on-resistance. Too small pressure will lead to insufficient contact area between the conductive particles and the electrode, resulting in poor conduction, while too much pressure will crush the conductive particles and reduce the conduction. resistance, so the crimping pressure must be controlled in the optimal range to maintain good conductivity.

(3) Crimping time: Due to the flow characteristics of the conductive particles in ACF, the crimping time must be matched with the crimping temperature, and there will be mutual influence between the two. Increasing the crimping temperature can shorten the crimping time. Increasing the pressing time, the combination of these two parameters will increase the number of conductive instances captured by the Bump. But the increase in pressing time will reduce the production capacity.

To sum up, the formulation of the IC binding operation parameters is the most important. The operation parameters are the crimping temperature, the crimping pressure and the crimping time, which have interactive effects, and are the most important in the process quality and productivity.

COB process/process technology

The (abbreviation of Chip On Board, COB) process is first to cover the placement point of the silicon wafer with thermally conductive epoxy resin (generally epoxy resin doped with silver particles) on the surface of the substrate, and then place the silicon wafer directly on the surface of the substrate, heat treatment to The silicon wafer is firmly fixed to the substrate, and then the electrical connection is established directly between the silicon wafer and the substrate by wire bonding. There are two main forms of bare chip technology: one is COB technology, and the other is flip chip technology (Flip Chip). Chip-on-Board Package (COB), the semiconductor chip is handed over and mounted on the printed circuit board, the electrical connection between the chip and the substrate is realized by the wire stitching method, the electrical connection between the chip and the substrate is realizstitching method, and covered with resin to ensure reliability . Although COB is the simplest bare die attach technology, it is far less dense than TAB and flip-chip bonding.

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