A Study on Low-melting-point-alloy incorporated Epoxy-based Conductive Polymer Composites for Direct-write Printing Technology

In recent years, the development of printed electronics technologies, using printing techniques for conductive patterning, has been increasingly attractive. Direct-write printing is an effective way to form various patterns, electrical circuits and conformal structures on a substrate with great softy and flexibility. Compared to the traditional methods such as microcontact printing, direct-write printing is an affordable method that offers flexibility and efficiency for the printing of conductive patterns on the substrate. With excellent conductivity and good flexibility, conductive polymer composites are well-suited for use in direct-write printing. To achieve composite materials with appropriate viscosity and high conductivity, the selection of both the insulting polymer matrix and conductive fillers is crucial. As a promising conductive filler, low-melting-point alloys (LMPAs) can be employed to achieve high conductivity under low load conditions. Due to their good biocompatibility and excellent thermal/electrical conductivity, these LMPAs have shown promising practical value in electronics circuits and thermal management. Recently, our group has designed a promising metal particle of Bi-In-Sn LMPA particles with standard spherical shape and adjustable size, which can be used for solder interconnection and conductive fillers.In this work, we obtained the bulk Bi-In-Sn alloy that has a weight ratio of 45% In, 28% Bi, and 27% Sn. Based on our previous research, we prepared uniform and small-sized spherical LMPA particles, and the morphology, structure, and electrical/thermal properties of the prepared particles were investigated. Compared to bulk alloys, the prepared submicrometer LMPA particles have a uniform elemental distribution, controllable particle size, and standard spherical structure, which helps achieve a uniform dispersion of the particles and their blending with larger conductive fillers. Subsequently, LMPA particles were incorporated as conductive fillers to create a polymer conductive material with lower viscosity and enhanced conductivity, using epoxy resin as the matrix. Micro-electronic printer was used to generate various types of conductive patterns on the substrate, allowing us to investigate the electrical capability and processability of polymer composites. In addition, scanning electron microscopy (SEM) is utilized to observe the morphology of LMPA particles, and X-ray diffraction (XRD) is used to prove that the prepared LMPA particles had good crystallinity and to analysis the phase information. Differential scanning calorimetry (DSC) is utilized to study the thermal stability behaviors of the prepared LMPA particle fillers under a nitrogen atmosphere, and electrical measurement is employed to test the resistance of the electrical patterns. This work provides a preparation method and performance study of spherical LMPA particles as promising conductive fillers, offering a feasible approach for future research on conductive interconnection materials.