What is the difference between the COF FPC carrier board for smartphones and TV panels

What is the difference between the COF FPC carrier board for smartphones and TV panels

What is the difference between producing a COF FPC carrier board that can be used in smartphones and a normal TV panel COF FPC? Where is the difficulty of processing?

The COF FPC traditionally used in the TV field is actually not much different from the ordinary FPC in production and processing. In addition to the finer line width and spacing of the FPC compared to the ordinary FPC, it is still produced by the standard subtractive etching method.

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

The processing technology of SAP semi-additive method mainly comes from SLP carrier PCB. But entering the smartphone industry application, Apple is the earliest to use this process on a large scale in the production of mobile phone motherboards.

 Before, 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, an atomic deposition production process called ALD in the semiconductor process was used to Encapsulation of OLED devices not only controls the thickness of the encapsulation layer to less than 0.1 microns, but also greatly improves the OLED device packaging yield, and the service life of OLED products has also increased by several times.

When the application of ALD technology in the packaging of OLED devices has matured, Apple has expanded this technology to the production of Apple ’s mobile phone PCBs. Apple ’s recent generations of iPhone mobile phone PCB motherboards all use the semi-additive method of ALD technology. produce

After the full-screen display technology began to be applied on smartphones, this semi-additive processing method of ALD process was also introduced into the production of COF FPC carrier boards. Except for Apple ’s iPhone XR LCD display, all of which used the COF process, Most of Samsung's full-screen OLEDs have also begun to import the COF process.

Compared with Japan, South Korea, and Taiwan, where the semiconductor industry chain is very complete, the COF industry chain in mainland China can basically only produce COF FPC substrates for TV panels, all of which are produced using standard subtractive etching methods. However, there are currently manufacturers and research institutes that have begun to introduce ALD machines to develop semi-additive production processes related to ALD processes.

On the COF bonding machine for smart phones, it is still dominated by Japanese manufacturers, and other manufacturers are basically still in the research and development stage. Therefore, when Japanese, Korean, and Taiwanese manufacturers did not intend to increase production capacity and increase production capacity in the COF process for smartphones, companies in mainland China want to open up the COF industry chain to increase production capacity. They also need panel factories, IC factories, and FPC factories. It is only possible to plan together with relevant production equipment manufacturers, work together, and make breakthroughs simultaneously.

Specific to the COF FPC substrate production, basically adopt the following methods.

First of all, COF FPC still needs to determine whether to punch holes in the substrate according to the design of the drawing. If necessary, first complete this step. Then, after necessary cleaning of the FPC substrate, it enters the ALD machine to process the coupling agent layer. After the processing is completed, a coupling material less than one nanometer thick is formed to cover the FPC substrate.

The subsequent process is basically similar to the traditional FPC production process. Electroless copper is deposited on the FPC substrate with "copper seeds" to control the thickness of the copper layer to about 0.1 microns. Shape the circuit pattern, then use the electrolytic copper plating process to form the final circuit, and finally strip the resist, and then perform the flash etching process to complete the entire COF FPC substrate production process.

It can be seen from the above that in addition to the introduction of the ALD semiconductor production process, the production process of the COF FPC substrate is the biggest difference from the traditional standard subtractive etching method, that is, instead of laminating rolled copper on the substrate as a conductive layer, chemical Copper plating is deposited to form the main conductive layer, so it can process very thin products and form finer circuits.