The traditional COF FPC used in the television industry is not much different from ordinary FPC in the production and processing process. In addition to the finer line width and spacing compared to ordinary FPC, FPC is still produced using standard reduction etching method.

The COF FPC carrier board used in smartphones is produced using a completely different method from the standard subtractive etching method, using an additive method for semiconductor chips. The industry calls this process the SAP semi additive method. Because the minimum line width and line spacing of FPC produced by standard reduction etching method are generally above 15 microns, it is basically powerless for COF production processes with finer lines.

The processing technology of SAP semi additive method mainly comes from SLP type carrier PCB. However, when it entered the smartphone industry, Apple was the first to use this technology on a large scale in the production of mobile phone motherboards.

Earlier, when Apple, Samsung, and LG developed new OLED display devices, in order to improve the device packaging yield and product performance of flexible OLED products, they used an atomic deposition production process called ALD in semiconductor technology to package OLED devices. This not only controlled the thickness of the packaging layer to below 0.1 micrometers, but also significantly improved the device packaging yield of OLED, The device lifespan of OLED products has also increased by several times.

As the ALD process became increasingly mature in OLED device packaging, Apple also expanded the production of iPhone PCBs using this process. In recent generations, Apple's iPhone PCB motherboards have all been produced using the half addition method of the ALD process

After the application of full screen display technology on smartphones, this semi additive processing method of ALD technology was also introduced into the production of COF FPC carrier boards. Apart from Apple's iPhone XR LCD display screen all adopting COF technology, most of Samsung's full screen OLEDs also began to import COF technology.

Compared to Japan, South Korea, and Taiwan, which have a very complete semiconductor industry chain, the COF industry chain in mainland China can only produce COF FPC substrates for television panels, all of which use standard reduction etching production processes. However, currently there are also manufacturers and research institutions that are introducing ALD machines and developing semi additive production processes related to ALD processes.

On the COF bonding machine used for smartphones, it is still dominated by Japanese manufacturers, while other manufacturers are still in the research and development stage. Therefore, on that day, Korean and Taiwanese manufacturers were not willing to increase production capacity in the COF process related links for smartphones. In order for mainland Chinese enterprises to connect the COF industry chain to increase production capacity, they still need panel factories, IC factories, FPC factories, and relevant production equipment manufacturers to jointly plan and work together, and achieve breakthroughs simultaneously before it is possible to achieve this.