In the development of epoxy materials for the printed wiring boards of high-speed communication devices, we have developed a curing agent with a low dielectric constant and low dielectric loss tangent. By developing the basic technology of the active-ester type epoxy resin curing agent announced, we have succeeded in developing a new polyfunctional oligomer type active-ester type epoxy resin curing agent which can be used as a material for electronics. Compared with the widely used phenol novolac curing system, a significantly lower dielectric constant and lower dielectric loss tangent have been achieved whilst maintaining a high glass transition temperature. It is considered that the centrally-located dicyclopentadiene skeleton exhibits an excellent low dielectric constant and low dielectric dissipation factor whilst maintaining heat resistance due to its rigidity, small molar polarisability and large molar volume.

To prepare for the application of communication standard of 5G and the upcoming 6G, internet data center (DC) as a core of the cloud computing is built more, and many edge servers are used for the communication with the terminal equipment such as smartphone and personal computer. These electronic equipments have been developed in the direction further large-capacity data processing in real time. In these electronics equipment, state-of-the-art semiconductor chips with 5 nm wiring rule are used. In addition, the high-density LSI packaging technologies including high performance network polymers play a very important role. I clarified material characteristics required for multilayered wiring board, package substrate, redistribution layer (RDL) of interposer and mold resin, respectively. Moreover, I explained recent technology and trend about the network polymer which had low dielectric properties to be required from the viewpoint of high frequency and high-speed signal transmission.

As the core technologies to support recent high-capacity and high-speed data communication systems, the importance of flexible printed circuit boards (FPCs) used in mobile communication devices has significantly increased. To obtain FPCs compatible to 5G-communication technologies, novel high-temperature dielectric substrate materials with low dissipation factors (tan δ) at high operating frequencies (≥ 3.6 GHz) are strongly required. This review paper proposes the molecular design for novel heat-resistant dielectrics consisting of modified polyimides, poly(ester imide)s, and exhibits their excellent combined properties, including significantly reduced tan δ values at 10 GHz, extremely low linear coefficients of thermal expansion, suppressed water uptake, and very high glass transition temperatures.

In 5G and advanced driver-assistance systems, transmission loss imposes a challenge for their use in high-frequency regions. The insulating materials in semiconductor packages for high-frequency applications thus require low dielectric properties. We report the technological trends in low dielectric resin, low-loss molded underfill (MUF) and low-loss copper clad laminate (CCL) in high-frequency semiconductor packages.For the next generation low dielectric resin, the target dissipation factor (Df) would be ≦ less than 0.001. A simulation on the transmission loss of MUF assuming an antenna in package (AiP) showed that the reduction of Df has a significant influence on the transmission loss. Furthermore, we developed CCL that satisfy both low coefficient of thermal expansion (CTE) and low dielectric properties by improving the compatibility of low CTE and low polarity resins. Low-loss MUF and low-loss CCL are expected as semiconductor packaging materials for millimeter-wave-compatible AiP and RF front-end (RFFE) modules.

Today, wireless network systems are one of the most important types of social infrastructure because of development of the Internet of Things (IoT). In IoT era, the next-generation communications, 5th generation (5G) or 6th generation (6G) communications are attracting attention because of high-speed, highcapacity, and low-latency communications. In 5G and 6G communications, the frequency of signals much higher, so transmission loss is a major problem. Thus, a material with low-loss is required. In this review, we focus on polyphenylene ether (PPE) and introduce its features and applications. PPE is an excellent low-dielectric polymer, so it is suitable for low-loss materials. However, PPE has low processability as a substrate material because it is a thermoplastic polymer and has low solubility in organic solvents. Therefore, thermosetting PPE and soluble PPE are developed and applied as substrate materials. PPE-based materials showed excellent low-loss properties and the broad development is expected in the future.