Application and status quo of PI film

Polyimide Film (PIF) has excellent durability and mechanical properties. Depending on the application, it can be divided into electrical-grade PI films for heat-resistant and insulating purposes, and electronic-grade PI films with requirements such as low expansion coefficient and high flexibility. Among them, electronic PI film is the largest and fastest application field in the current PI market as the core raw material of flexible copper clad laminate (FCCL) and packaging substrate (COF).

Applications for electronic grade polyimide films

PI film is used for flexible copper clad laminate Flexible printed circuit board (FPC) is a kind of flexible printed circuit board made of flexible copper clad laminate (FCCL) as the substrate, which itself is a kind of PCB, also known as "flexible board".

The flexible substrate used makes it have the advantages of high wiring density, light weight, thin thickness, bendability, high flexibility, etc., can withstand millions of times of dynamic bending without damaging the wire, move and expand arbitrarily according to the requirements of spatial layout, realize three-dimensional assembly, achieve the effect of component assembly and wire connection integration, and have incomparable advantages of other types of circuit boards, and are widely used in electronic products such as mobile phones, laptops, navigation equipment, aerospace equipment, etc. Among them, flexible copper clad laminate (FCCL) accounts for 40% of the entire raw material, and PI film can be made into flexible copper clad laminate (FCCL) substrate and overlay film to achieve FPC flexibility. The PI base film and cover film used in FCCL must not only have good thermal and mechanical properties, but also have excellent flexibility, dimensional stability, and dielectric insulation properties.

PI film is used for OLED flexible display

In recent years, OLED flexible display technology is developing in the direction of folding and rolling, and the key material to achieve flexibility is polyimide film. The units that require the use of polyimide film for flexible display include: display substrate, display packaging substrate, touch screen substrate, touch screen cover plate, display cover plate, etc. The polyimide film used in OLED display needs to have both high temperature resistance and colorless transparency. Low temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) are processed at temperatures of no less than 450 °C during the processing of flexible OLED devices, so polyimide films as flexible substrates also require extremely high heat resistance (Tg>450 °C). Polyimide films are also required to have an ultra-low coefficient of thermal expansion CTE<4 ppm/°C at room temperature ~400 °C to ensure dimensional stability in high-temperature processes. Compared to the low CTE of the polyimide film in FCCL, the flexible display substrate has lower requirements. In terms of structural design, the polyimide used in the flexible display substrate can use rigid rods, intermolecular hydrogen bonds or chemical cross-linking groups and other structural units to achieve ultra-high heat resistance and ultra-low thermal expansion coefficient. In addition, the traditional PI transparent film is usually yellow or brown, in order to improve the transparency of the PI film, large substituents, fluorine-containing groups or aliphatic ring structure diohydride or diamine can be introduced in the design of the PI molecular structure, which can effectively inhibit the formation of light-transmitting substances in the PI molecular chain, and then obtain a colorless and transparent PI film.

Summary of the current market status and research progress

Electronic grade polyimide film has broad market application prospects in the fields of flexible printed circuits, flexible electronic displays, and 5G communication thermal conductive films in China, but there is a gap between the overall level of the domestic PI film industry and foreign countries, and the field of electronic grade PI film is mainly occupied by foreign giants, and the products are heavily dependent on imports. In the context of China's industrial structure upgrading and localization of key materials, the market space for import substitution of electronic grade PI film is huge. Enterprises with independent and complete core technology systems represented by Ruihuatai are expected to gain more market share and promote the localization process of electronic-grade PI films. Polyimide films in different application fields have different requirements for performance, and researchers at home and abroad have carried out a lot of research on polyimide films with high dimensional stability, low dielectric properties, high temperature resistance, colorless transparency, and high thermal conductivity. The above properties of polyimide film are effectively improved by means of molecular structure design, improvement of film-forming process or addition of thermal conductive fillers, but the performance requirements of polymer materials in practical applications are multifaceted, such as when a large number of thermal conductive fillers are added to meet the high thermal conductivity of the thermal conductive film for 5G communication, the mechanical properties of the composite film will be affected, the flexibility and preparation processability will deteriorate, and there is still a big gap from the commercial application. It has always been a challenge for the scientific community and industry. Scientific research institutes should actively cooperate with enterprises to jointly develop PI film products with market demand and excellent comprehensive performance, so as to help enterprises occupy a place in market competition.