Polyphenylene Sulfide: Toray Industries’ New Polymer Film for 5G Circuit BoardsDecember 25, 2019 by Gary Elinoff
A new polyphenylene sulfide (PPS) film from Toray Industries offers low dielectric losses as well as thermal and flame resistance.
Toray Industries has announced Torelina, a new type of polyphenylene sulfide (PPS) film highlighted for its dielectric characteristics, flame retardancy, and chemical robustness. The new, proprietary technology controls the crystal structure of PPS films while improving thermal resistance.
By controlling the orientation of film molecular chains, Torelina is said to attain a 98ppm/°C coefficient of thermal expansion in the thickness direction.
FPC cable using Toray’s new PPS film. Image from Toray Industries
Toray explains that the new film resists deformation and is dimensionally stable near its melting point of 280°C. The company also states that as a crystalline engineering plastic, PPS also offers excellent electrical insulation.
Toray expects that the high thermal dimensional stability and cost-competitiveness of Torelina, combined with its dielectric characteristics, will make the new material a useful choice for OEMs involved in the expanding universe of 5G applications—particularly smartphones.
What is PPS?
Polyphenylene sulfide (PPS) is a polymer made up of aromatic rings linked by sulfides with a melting point of 280°C. The polymer is mechanically and chemically strong and flame resistant. It also has a high degree of dimensional stability. Unless altered through oxidation or through the use of dopants, it is an electrical insulator.
Polyphenylene sulfide. Image from Wikimedia Commons
PPS is said to maintain its thermal resistance at a point 40°C higher than conventional counterparts. However, PPS film can deform in the presence of heat, and, predictably, doesn’t stand up well to the soldering process.
Toray asserts that its new PPS film does not deform at temperatures up to 250°C. This property would allow manufacturers to employ existing PCB manufacturing methods when working with Torelina. It would also enable OEMs to design smaller, multi-layered circuit boards with the new material.
Torelina resin and finished parts. Image (modified) used courtesy of Toray Industries
The company also expects that Torelina will also serve in a range of other applications. These include electrical components such as switches and connectors, automobile components, and even chassis parts and housings.
About Dielectric Constants
To better understand the implications of this new circuit board material, it may be important to discuss dialectic constants and how PPS will affect it.
Within a PCB, when a signal moves to a space with a higher dielectric constant, velocity, signal amplitude, and wavelength are all reduced.
The left side of the image below illustrates an electronic signal traveling in a region with a relatively low dielectric constant. The image on the right illustrates the same signal after it moves into a region with a higher dielectric constant.
Circuit with low Dk vs circuit with high Dk. Image source (modified) used courtesy of (PDF) Rogers Corporation
Toray asserts that this new material is a significant development for designers in the 5G industry because it allows for low dielectric losses of electrical energy and less data transmission losses at high speeds.
Important Implications for 5G
As Toray points out, 5G harnesses frequency bands below 6GHz and above 20GHz. Those higher frequencies deliver the magic of 5G—low latency, multi-connectivity, and blindingly fast data transmission rates.
The application of Torelina in flexible printed circuits offers two key advantages to OEMs developing 5G and other high-speed applications.
The new PPS film’s stability in temperature and humidity makes it possible for OEMs to more easily manufacture reliable mobile devices that operate at high frequencies.
Polymers Comparative to PPS
Liquid crystal polymers (LCP) have emerged as a flexible printed circuit substrate material for 5G applications. LCP’s dielectric properties reduce transmission losses in high-frequency bands. However, they are expensive and difficult to process.
PbS (lead sulfide) also exhibits better dielectric properties than LCP film does, and it is also less vulnerable to extreme temperature and humidity.
Toray states that PPS film offers better flame retardancy and chemical resistance than LCP.
What experiences have you had with 5G circuit boards? As a 5G future draws nearer, what design changes to boards have you seen?