The demands of using In-Vehicle Information System (IVIS) have been increasing in the 5G & AIoT ecosystem. A Center Information Display (CID) with touch panel has become very popular in new luxury vehicles. Many reports have raised safety concerns about touchscreens in cars, sosome groups of people still prefer physical switches/buttons. More and more people accept the automotive touch human-machine interface nowadays. Considering the huge market for autonomous/electric vehicles in China, it will lead to a greater increase in the interaction between the drivers/passengers and the cars. As a result, the development of IVIS is also expected to contribute in the growth of panel fabrication, and enable the panel manufacturers to shift their focus from consumer market.
Increasing demand for narrow-bezel automotive display panels
According to the existing CID models in automotive industry, the method of splicing integrating dashboard with CID into a single screen is widely used. Since splicing screen is limited by the bezel thickness of each display panel, the narrow-bezel technology provides a superior solution for such application. In recent years, the emergence of COG (chip-on-glass) and COF (chip-on-film) has made more breakthroughs for larger splicing display panel on CID. The traditional display panel required source and gate ICs to drive the thin film transistor (TFT), and the COG or COF integrate the gate IC with the FPC or glass substrate separately by using a Flip Chip Bonding method. It can save the space of PCB to narrow the bezel. In addition, the GOA (Gate On Array) technology which has been widely applied to TVs allows the display panel to control the TFT switch. This feature makes the gate IC is no longer required and can reduce the left and right bezel width.
Electrostatic discharge problems on narrow-bezel display panels
Electrostatic discharge (ESD) is a natural phenomenon that cannot be completely prevented in our daily life. Panel fabrication requires multiple manufacturing processes to create a final product. There is a very high chance that different components contact each other during alignment and coating. The film should also be attached and detached during assembly. All above processes lead to the appearance of static electricity by friction. In addition, the glass substrate of the LCD panel is an insulating material with low dissipation of static electricity which is easy to accumulate a significant amount of electric charges on it. Due to the equivalent inductance of COG/COF’s signal lines on the FPC and glass substrate, it can easily absorb the ESD as exposed antennas. Besides, unlike conventional PCBs, the FPC and glass substrates used in the COG/COF are insulating that lack for conductor shield, and make the accumulated static charges even more difficult to dissipate.
In addition to material characteristics, the reduced bezel width of display panel by using COG or COF method allows the gate IC to be closer to the panel bezel. When the user’s finger touches the screen, there would be a discharge event from human body and increase the likelihood of ESD damage to gate IC. Besides, it should be also noted that the T-Con board and COG/COF need to be assembled with other components such as LCD panel, backlight panel in the assembly process. It is most likely that ESD occurs in the processes of assembly and functional test (FT) of finished product due to hot-plugging during the test or the ESD generated by the friction of gloves and jackets. The process requirements of GOA are more critical than COG/COF, that the gate circuit is integrated directly into the TFT array. The TFT is extremely fragile and can be damaged by the ESD while doing hot-plugging, or even cause to burn out.
ESD protection solution for narrow-bezel automotive display panels
With the accumulated R&D capacities from the NCTU (National Chiao Tung University) and the Industrial Technology Research Institute over the past decades, the Amazing Microelectronic Corp. has developed its own patented technology for the transient voltage suppressor (TVS) suitable for high-speed-signal ESD protection. As shown in Figure 1: for the COG/COF and GOA, the TVS can be installed on PMIC’s power and signal routing. This 60V 4-channel TVS AZ4260-04F can be used on four high-voltage power and signal lines to protect the back-end gate IC. As the AZ111S-08F in Figure 2, the circuit design gives it an extremely low parasitic capacitance as Cp~0.1 pF and can be applied to high-speed interfaces such as V-by-One to ensure the high quality of 8K resolution images while providing excellent ESD protection. In addition, its tiny size (3.8 mm x 1.0 mm) for 8 channels can effectively reduce the cost of PCB’s board size. Amazing Microelectronic Corp. will continue to develop relevant countermeasures to meet the newest IVIS market demand as well as reduce the return rates.
Figure 1. (a) Schematic diagram of ESD protection on GOA (b) AZ4260-04F application circuit diagram
