Toray Develops Game-Changing PPS Film for 5G Flexible Printed Circuit Boards

Japan’s Toray Industries (U.S. office in New York, N.Y.) Tokyo,   has created what appears to be the first of its kind PPS  (polyphenylene sulfide) film specifically for 5G flexible printed circuit boards. Said to be a revolutionary film, Torelina is a biaxially-oriented PPS product that maintains the outstanding dielectric characteristics—or low dielectric losses of electrical energy—flame retardancy, and chemical robustness of that polymer while remaining thermally resistant at 40C /104 F higher than conventional counterparts. The new film resists deformation and is dimensionally stable near its melting point. PPS is a super engineering plastic that also offers excellent electrical insulation. It is crystalline, with a melting point of 280C/536F.

Toray has already finalized testing of the new film’s technology on a pilot basis, and looks to have a mass production setup in place during 2020 that would help swiftly popularize devices in the fast-expanding 5G arena. 5G is commanding attention as an advanced platform for delivering outstanding speed capacity, multi-connectivity, and low latency. It harnesses frequency bands below 6 GHz and above 20 GHz.

Employing Torelina in flexible printed circuits offering 5G and other fast data rates would offer two key benefits. First, the film would cut the transmission losses of communication devices at high frequencies. Second, it would help stabilize high-speed communication across the temperature and humidity spectrums. Flexible printed circuits are film-like wiring boards in which electrical circuits are formed on base materials from bonding thin, soft insulating base films with copper foil or other conductive metals.

Development efforts have seen the emergence of practical LCP (liquid crystal polymer) films as flexible printed circuit substrate materials needed for 5G. The dielectric properties of such films reduce transmission losses in high-frequency bands. These films also offer thermal resistance when soldering circuit boards. However, the high cost and processing issues of LCP films fueled the exploration of other materials that could overcome those shortcomings.

Generally, PPS film offers superior flame retardancy and chemical resistance while matching or exceeding the dielectric properties of LCP film, and is far less vulnerable to temperature and humidity extremes. On the downside, however, PPS film deforms easily at high temperatures and provides insufficient resistance to heat when soldering circuit boards. These considerations drove Toray to blaze a new trail in film design. In the course of that effort, the company developed a proprietary technology that controls the crystal structure of PPS films. It thereby maintained the outstanding properties of PPS polymer while dramatically increasing thermal resistance.

Testing to 250C/482F confirmed that Toray’s new PPS film does not deform. Increasing thermal resistance should make it possible to employ existing processing facilities of circuit boards. Toray attained a low coefficient of thermal expansion in the thickness direction of 98 ppm/C by employing technology it has amassed over many years to control the orientation of film molecular chains. The diverse applications leveraging those features, including 5G transmission cables and antennas, should enable the design of smaller, multi-layered circuit boards.