LG Innotek (CEO Jeong Cheol-dong) announced on February 27 that it had introduced 2-Metal Chip on Film(COF), an essential product for XR devices, to strengthen its market targeting. The product attracted visitors' attention as it was exhibited at LG Innotek's metaverse zone. COF is a semiconductor package substrate that connects displays and flexible Printed Circuit Board(PCB)s. It minimizes display bezels of devices such as TVs, notebook PCs, monitors, and smartphones and helps to reduce modules' form factor. It requires advanced technology because it forms microcircuits on a very thin film. It is also called the ultra-thin flexible PCB (FPCB) that replaces existing FPCB. 2-Metal COF technically upgrades conventional single-side COF. While a conventional COF implements circuits on only one side, the biggest advantage of 2-Metal COF is that this is super integrated by forming circuits on both sides. This product finely perforates micro-via holes on a thin film and implements an ultra-micro circuit on both sides, transmitting signals between electronic devices more quickly and enabling ultra-high definition screens. According to LG Innotek, the via hole size of this product is 25 m (micrometer). Considering that the thickness of
the hair is 100 m, it makes holes one-quarter as thick as the hair. The smaller via holes create more channels connecting the product's top and bottom and the more pattern circuits that electrical signals can pass through. As the metaverse era has recently been in full swing, demand for curved or folding displays has increased, and flexibility is also required for the attached components. It is also why 2-Metal COF, which can be freely bent, is considered one of the products in line with current trends in the display industry. -- Supporting high-resolution display. Expected to increase user concentration levelLG Innotek's 2-Metal COF can form a total of more than 4,000 circuits (pattern circuits, also called channels, through which a signal passes per display pixel) on a film (1 unit), which is limited space. Generally, more pattern circuits result in enhanced pixels. And XR devices require higher levels of immersion that only enhanced pixels can deliver. If the resolution of the virtual image displayed through an XR device is low, the users may feel like viewing the image through a mosquito net which is said a screen door effect. LG Innotek has continuously improved the specifications of the 2-Metal COF since 2016 to minimize the screen door effect and support the ultra-high resolution. In particular, LG Innotek applied new engineering technology to reduce the circuit width from 18 to 16 m pitch, representing the narrowest level in the industry. Since the number of pattern circuits that can fit on the COF surface increases as the circuit width is reduced, users can view images with better quality, even on a display of the same size. IT manufacturers are increasingly adopting displays with high definition and minimal bezels to enhance the competitiveness of their devices. In the past, manufacturers used chip-on-glass (COG) technology to support display operations. However, as COG places a chip on a display, it does not meet current display industry trends of no bezel and flexible since it cannot support flexibility. It has forced the manufacturers to look for alternative technology that stably supports high pixels while the display's bezels continued to be reduced, leading to the wide demand for 2-Metal COF. -- Flexibility and unbounded design with thin filmsLG Innotek's 2-Metal COF is a thin, flexible film type that can be smoothly folded or rolled. Moreover, it bends more smoothly than conventional single-sided COF. It reduces the required mounting space for the display, and the set makers can secure more space for other parts. It even helps with designing and engineering more advanced XR devices.LG Innotek applied unique ultra-micro circuit forming technology to double the circuit integration of the 2-Metal COF while minimizing the thickness. The product's film thickness is only 70 m, the thinnest of semiconductor substrates, and clearly offers many advantages compared to the thickness of 150 m or more for conventional semiconductor
packaging substrates.