Liquid crystal polymer (Liquid Crystal Polymer, LCP for short) is an intermediate state (liquid crystal state) substance between isotropic liquid and fully ordered crystal, which has both good fluidity and liquid The crystal structure is more complete and ordered. According to different liquid crystal formation conditions, liquid crystals can be divided into lyotropic liquid crystals (LLCP) and thermotropic liquid crystals (TLCP). Liquid crystal polymer has both the properties of liquid crystal and the properties of polymer materials. These unique properties endow it with many excellent comprehensive properties, known as "super engineering materials for the 21st century".
LCP performance characteristics
LCP is an engineering plastic with excellent performance, the main features are as follows:
Excellent mechanical properties (high strength, high modulus)
Very small linear expansion coefficient
Outstanding heat resistance
Excellent electrical properties (stable low dielectric constant and dielectric loss factor)
Excellent flame retardancy
Strong chemical resistance
Excellent radiation resistance and aging resistance
Very low water absorption rate
Very environmentally friendly and halogen free
Strong molecular self-orientation and extremely difficult film formation
It can be seen from the comparison of the performance of LCP substrates for FCCL and the most widely used PI substrates:
The transmission speed that PI substrate adapts to is below 6Gbps, the higher the operating frequency, the greater the signal transmission attenuation loss. Therefore, it is only suitable for use at lower frequencies, and the performance degradation in the high-frequency field is very obvious.
The moisture absorption rate of the PI substrate is significantly higher than that of the LCP substrate. After the material absorbs moisture, the transmission loss of the LCP substrate only deteriorates slightly with the increase of the operating frequency, but the transmission loss of the PI substrate is not obvious when it does not absorb moisture. Greater than the LCP substrate, after moisture absorption, its signal transmission attenuation degree accelerates and expands as the operating frequency increases.
Obviously, PI film substrates can no longer meet the requirements of 5G high-frequency high-speed signal transmission. LCP film substrates are the best choice for high-frequency copper clad laminates in the 5G era. Under high-frequency conditions above 15GHz, LCP films show unparalleled The performance advantage has become a 5G commercial strategic support material, which has been included in China's new material "14th Five-Year Plan" key research system.
LCP film forming mechanism and process characteristics
Because LCP molecules have a strong orientation, it is easy to form a single orientation arrangement under the action of shear stress during flow. Therefore, it is difficult for LCP to form a film by traditional casting or blown film.
Schematic diagram of the influence of LCP molecular flow characteristics and arrangement direction on the film forming process
There are two existing mature processes: bidirectional rotating die head film blowing + heat treatment; casting + bidirectional stretching. The former process uses more. The following is a schematic diagram of a typical rotating die structure and a film blowing process, and a comparison between a common die and a bidirectional rotating die film blowing process.
Schematic diagram of key process deconstruction of blown film
Comparison diagram of film blowing process
It can be seen from this that the ordinary die can not be used for the film formation of LCP, and the bidirectional rotating die must be used.
LCP film blowing and post-processing integrated production line
The LCP special blown film production line independently developed by Shanghai Legion has a wide resin processing temperature and small product thickness fluctuations (can be controlled within ± 10%). After film blowing, the product can be heat-treated online to reduce the product thickness fluctuations to ± 2 ~ 4 % To ensure that the dielectric constant and dielectric loss factor of the finished film are stable. The product specifications are suitable for 5G product types with a film thickness below 75 μm.
The film produced by the LCP film blowing method must be subjected to subsequent high-temperature rolling and heat treatment to reduce the fluctuation of the film thickness, adjust the thermal expansion coefficient of the film, eliminate the internal stress of the film, and improve the uniformity of dielectric constant, dimensional stability and plasticity Processing performance.
If the customer already has a film blowing production line, then only need to configure a film heat treatment production line.
Main process parameters of production line:
Production line speed: 3 ~ 30m / min
LCP film width: 1100mm
LCP film thickness: 25μm, 50μm, 75μm
Film thickness deviation: ± 2 ~ 4%
Extruder diameter: φ75mm
Extrusion capacity: 120kg / hr (max)
Die head type: bidirectional rotating die head
Support carrier type: aluminum foil / copper foil
Support carrier thickness: 20 ~ 80μm
Mechanical accuracy of hot pressing roller: ± 0.001mm (@RT), ± 0.005mm (@PT)
LCP resin manufacturers:
Abroad: Celanese, Polyplastics, Sumitomo Chemical, Toray
Domestic: Taiwan South Asia, Split, Water Shares, Jinfa Technology, Changchun Group, Shanghai Legion