The application and challenge of polyimide film in mobile phones!

Components and applications of polyimide film in mobile phones

  1. Soft board and reinforcement

Flexible circuit board, also known as “soft board”, namely FPC board, is a printed circuit made of flexible insulating substrate. The traditional flexible board has a multi-layer structure composed of copper foil, insulating substrate, cover film, etc. Generally, copper foil is used as the conductor circuit material, and PI film is used as the circuit insulating substrate.

iPhone processing scheme in high frequency communication

If the black LCP antenna is black, a reinforcing material is also required below, and the thickness is required to be about 0.225-0.25MM, and PI is generally used. But it is very difficult for PI to make such thick, dielectric constant.

Later, some manufacturers used the compounding process to compound them with epoxy resin or acrylic hot melt adhesive, which was easy to delaminate and had low rigidity. After die-cutting, the glue overflow phenomenon is serious.

  1. Graphite sheet

High thermal conductivity graphite film: It is obtained by carbonizing polyimide film and graphitizing it at 2800~3200℃. Also known as artificial graphite film, corresponding to natural graphite film.

Since artificial or natural graphite is prone to delamination, the surface is covered with PI or PET protective film (acrylic system tape). However, with the progress of time and use temperature, the glue system is easy to age, which greatly reduces the life of graphite and the risk of conductive short circuit caused by graphite exfoliation. We first coat the graphite surface with PI liquid and then carry out the imidization film forming process. On the one hand, the imine will penetrate into the graphite gap a little bit, and the bonding force will be better after the film is formed. The service life will be greatly increased, and the ten-year life will not be a problem. The use temperature of graphite can also be around 80 degrees (the problem of acrylic glue), and it can rise to more than 260 degrees at once.

Graphite can be turned into a base material of a tape, which can be specially treated, glued or compounded, or PVD magnetron sputtering conductive or chemical electroplating can be used for application development in special fields. We also combine the new PPCVD technology (plasma polymerization chemical vapor product) to make a protective layer on the metal layer, which makes the metal less prone to oxidation and scratches, and does not affect its conductivity.

  1. Cover film and lithium battery wrapping

Covering film: It is used to cover and protect the flexible circuit to play a “three-proof” protection function under heat (high temperature), humidity, pollutants and corrosive gases and harsh environments. FPC black PI film The main requirement is 12.5μm, and a certain CTE value is required.

Why choose black matte cover film and tape for the inside of your phone.

The main purpose of black is aesthetic simplicity, to prevent the internal design of the product from being copied by opponents, to reduce the damage of light to the internal metal during the production process, and to reduce the error of optical inspection equipment caused by reflection of matte black. At the same time, black also combines the simple and beautiful design concept to improve the appearance and texture of the product.

Since the aluminum-plastic composite film is a thin film, it is bound to leave a seal when wrapping the battery. In order to increase safety, a special high temperature resistant tape is required to cover the seal to prevent leakage of electrolyte or gas. These harmful substances will damage the mobile phone, and will also burn and explode when exposed to electricity.

At this time, polyimide (PI) tape, also known as KAPTON tape, has room to play. PI itself has the functions of temperature resistance, chemical resistance and mechanical strength, flame retardant and halogen-free, so it is the material of choice for sealing and edging with glue.

PET is a biaxially stretched material with a certain degree of rigidity, so when it is made into tape, it is easy to warp when it is wrapped in a particularly narrow edge.

NOMEX aramid paper is suitable for thick areas and deep grooves on the surface. The wrapping property of the paper is good, but the pressure resistance value is average. The cost of dyeing black is relatively high and it is easy to absorb moisture. Generally, it is only used for the parts of the positive and negative interfaces.

  1. Shield

The traditional shielding process is to paste a layer of insulating glue on the inner surface of a single PCS product after stamping and forming, commonly known as “sticking”. Disadvantages such as low production yield and difficulty in controlling flatness.

Application method of late polyimide film

  1. CPI changes mobile phone design

The successful development of transparent PI film (CPI) will bring revolutionary changes to curved display screens, and even the entire TV industry and mobile phone products. When CPI is used as a replacement glass screen, attention must be paid to the hardening problem.

Superior thermal stability, dimensional stability, mechanical properties, flexibility and surface hardness compared to conventional optical films

  1. New application of transparent PI

The transparent PI film uses the principle of magnetron sputtering to perform mirror treatment on the surface to make it semi-transparent or fully transparent, and can be made into various colors. Then use a mask method, or etching reduction, or laser micro-engraving technology to texture the metal layer. When there is no light, it can be like a mirror, and when the backlight is on, it can have special lines. It can also be used as a substrate for high-end diffuser films in the LED field. The high temperature resistance and flame retardancy of PI itself are used in high-level LED high-power light box advertisements, etc., and it has obvious advantages to replace PET or PC.

It can also be used in fully transparent FPC as a high-end transparent substrate. But pay attention to the influence of different CPI structures on the UV yellowing phenomenon. It is also necessary to combine PPCVD & R-R technology to achieve mass production and reduce manufacturing costs.

  1. Research and development of conductive PI plastic film

Development of conductive plastic films to replace metals. Conductive PI, also using magnetron sputtering, and then thickening by water plating. The conductive PI film produced in this way has the characteristics of lightness and softness, and can replace copper foil in many occasions.