Improving the Dimensional Stability of Polyphenylene Oxide without Reducing Its Dielectric Properties for High-Frequency Communication Applications

Abstract

The 5th generation mobile communication technology (5G) requires materials with high reliability, high dimensional stabilities, and low dielectric constant (D k) and low loss factor (D f). However, achieving both high dimensional stabilities and low dielectric is difficult. In this work, we propose a strategy to improve dimensional stabilities of printed circuit board (PCB) substrates without reducing their dielectric properties by introducing crosslinking agents with trifluoromethyl groups and allyl groups to polymers. Polyphenylene oxide (PPO) was selected as the representative research object, and a series of cured PPO-Allyl-F with varying contents of trifluoromethyl and allyl side chains were designed and synthesized. The molecular structures of the thermosetting PPO were characterized using 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. The isothermal curing kinetics of the thermosetting PPO were monitored with in situ FTIR. The thermal stability, mechanical properties, glass transition temperature (T g), coefficient of thermal expansion (CTE), and dielectric properties of the cured PPO-Allyl-F materials were investigated in detail. The results show that the obtained thermosetting PPO with improved dimensional stabilities and low dielectrics has great potential for the application in high-frequency electronic circuits. This work provides a new approach for developing high-performance polymers that can address the contradiction between dielectric properties and dimensional stability.

Recent Progress in Modification of Polyphenylene Oxide for Application in High-Frequency Communication

“…Considering the contradiction between improving the dielectric properties and thermosetting of polymer materials, our research group proposed a method to balance thermosetting and dielectric properties by introducing a crosslinking agent with both trifluoromethyl groups and allyl groups to PPO. In situ Fourier transform infrared spectra indicated the resulting PPO with different contents of trifluoromethyl groups was cured at 250 °C to obtain the cured PPO-allyl-F ( Figure 15 b) [ 46 ]. These cured PPO-allyl-F materials exhibited a D k value in the range of 2.56–2.67 at 10 GHz and a D k value in the range of 2.57~2.68 at 1 MHz, which were lower than the above-mentioned thermosetting PPO.…”

“…Therefore, researchers seldom consider anisotropy in the CTE of PPO. In the previous literature reports, P(APO-co-PO) and PPO-allyl-F exhibit a lower CTE as the crosslinking density increases [ 45 , 46 ]. This indicates that covalent connections between polymer chains are beneficial for restricting segment movement and free volume expansion.…”

“… ( a ) DSC traces of PPO and P(APO-co-PO) at a heating rate of 5 °C min −1 [ 45 ]. ( b ) In situ FTIR spectra of PPO-Allyl-F cured at 250 °C for different curing times [ 46 ]. …”

Graft Architectured Poly(phenylene oxide)-Based Flexible Films with Superior Dielectric Properties for High-Frequency Communication Above 100 GHz

“…Furthermore, the thermal stability of pristine PPO should be enhanced when considering the microelectronics manufacturing process . Recently, several groups modulated the structures of PPO and developed PPO-based flexible dielectric film with enhanced processability and excellent thermal and dielectric properties. ,− For example, Chen et al synthesized cross-linkable PPO by copolymerizing 2,6-dimethylphenol and 2,6-diphenylphenol and fabricated cross-linked PPO films with desired balance of flexibility and thermal resistance . Fang et al modified PPO by introducing anethole as cross-linkable side chains, allowing the fabrication of PPO films with improved thermomechanical properties and good dielectric performance at a moderate frequency (3 MHz) .…”

“…Poly­(phenylene oxide) (PPO), which is one of the popular polymers used in the electronics industry, shows great potential to be used as a promising material in the field of high-frequency communication owing to its fascinating properties, including low water uptake and low dielectric characteristics at high frequency. − However, the limited solubility and the high molecular rigidity of PPO result in high viscosity in its melt state, often imposing limitations on the processing of pristine PPO for versatile applications . Furthermore, the thermal stability of pristine PPO should be enhanced when considering the microelectronics manufacturing process .…”