Taewon Yoo

Polyimide–Epoxy Composites with Superior Bendable Properties for Application in Flexible Electronics

The need for flexible electronics with outstanding bending properties is increasing due to the demand for wearable devices and next-generation flexible or rollable smartphones. In addition, the requirements for flexible or rigid–flexible electronics are sharply increasing to achieve the design of space-saving electronic devices. In this regard, coverlay (CL) film is a key material used in the bending area of flexible electronics, albeit infrequently. Because flexible electronics undergo folding and unfolding numerous times, CL films with superior mechanical and bending properties are required so that the bending area can endure such severe stress. However, because current CL films are only used for a designated bending area in the flexible electronics panel, their highly complicated and expensive manufacturing procedure is a disadvantage. In addition, the thickness of CL films must be decreased to satisfy the ongoing requirement for increasingly thin products. However, due to the limitations of the two-layer structure of existing CL films, the manufacturing process cannot be made more cost effective by simply applying more thin film onto the board. To address this problem, we have developed liquid coverlay inks (LCIs) with superior bendable properties, in comparison with CL films, when applied onto flexible electronics using a screen-printing method. The results show that LCIs have the potential to become one of the leading candidates to replace existing CL films because of their lower cost and faster manufacturing process.

Effects of nanoclay on the properties of low temperature cured polyimide system

Polyimide is a major polymer material in the electronics industry, and we conducted a study to cure polyimide at low temperatures in order to improve its thermal and mechanical properties. In this study, polyimide/clay nanocomposites were prepared by the reaction of 4,4’-(hexafluoro isopropylidene) diphthalic anhydride (6FDA) and 4,4’-oxydianiline (ODA) with the addition of 1,4-dizabicyclo[2.2.2]octane (DABCO) as a low-temperature catalyst and nanoclay (Cloisite 20A). The synthesis of polyimide at low temperatures and the dispersion of a nanoclay in the polymer matrix was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. Thermal stabilities of the nanocomposites were confirmed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The mechanical properties were measured by an universal testing machine. We demonstrated that when polyimide was cured at low temperatures and short curing times, it was possible to improve the thermal and mechanical properties via the addition of a catalyst and inorganic material. Polyimide with DABCO and 0.25 wt% nanoclay showed a 5 °C higher degradation temperature, 560.88 °C; a 6 °C higher glass transition temperature, 293.62 °C; and a 20 MPa greater tensile strength, 136.94 MPa. Therefore, the polyimide curing process was demonstrated to be successful at low temperatures.

Norbornene end-capped polyimide for low CTE and low residual stress with changes in the diamine linkages

AbstractThe effects of norbornene (NE) crosslinking and diamine bridge linkages (ether, sulfone, and trifluoromethyl) on polyimide films were investigated. The purpose of this study was to study the behavior of the NE endcapped polyimide with different diamine bridge linkage structure at elevated temperatures on residual stress and modulus change. 5-Norbornene-2,3-dicarboxylic acid was introduced as the end-capping agent in order to increase the ratio of crosslinking in the structure through reverse Diels-Alder reaction. Wide angle X-ray diffraction (WAXD) was measured to study the relation of d-spacing and structure change of the bridge linkage of polymers through NE crosslinking. Coefficient of thermal expansion (CTE) and residual stress were measured to confirm the loaded stress between the substrate and polymer film through a thin film stress analyzer (TFSA). Storage (ε′) and loss modulus (ε″) were studied at elevated temperatures to study the relation of bridge linkage mobility of the polyimide at elevated temperature.

Erratum to: Low dielectric transparent poly(amide-imide) thin film with nano scale porous structure

Page 1115, the Acknowledgments should be corrected as follows:This work was supported by the KIST Institutional Program (Project No. 2E26600-16-041) and National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2017R1D1A1B03033332).

Low dielectric transparent poly(amide-imide) thin film with nano scale porous structure

AbstractA transparent poly(amide-imide) (PAI) was synthesized with good thermal and optical properties and after that silica nano particles were introduced and removed for nano porous polymer matrix. The successful synthesis of PAI with nano scale porous structure was confirmed with FT-IR and FE-SEM measurement. The effects of free volume of polymer on thermal properties were measured with TGA and DSC. This physically modified polymer matrix showed increased thermal degradation and glass transition temperature over 250 °C. In the case of optical properties, UV-Vis and yellow index were measured and PAI with nano porous structure showed transparent colorless properties with light transmittance in the range of 80-40% and yellow index 2.1-1.1. The results also showed low dielectric constant in the range of 3.2-2.5 and contact angles that of 70-73°.