Enhancement of the electrical and thermal conductivity of epoxy-based composite films through the construction of the multi-scale conductive bridge structure

Electrically conductive adhesive films (ECAFs), a novel electrically and thermally adhesive material, have been widely used in the large-area bonding of microelectronics packaging. However, it is still a challenge to optimize the silver micro-flakes (Ag-MFs) dispersion, and build a more effective electrically and thermally conductive network. In this study, we improved the dispersion of Ag-MFs in epoxy matrix through the intermolecular hydrogen bonding, and proposed a new multi-scale conductive bridge structure. Specifically, poly (3,4-ethyl-enedioxythiophene)/poly (styrene sulfonate) (PEDOT/PSS or P/P for short) can form the intermolecular hydrogen bonding with Ag-MFs based on the sulfonic groups of PSS chain and the carboxyl group located on the surface of Ag-MFs, resulting in improving dispersion of Ag-MFs. Besides, PEDOT can occur conformation change from benzoid conformation to quinone conformation and form PEDOT conductive crystalline nanofibril, and then multi-scale conductive bridge structure with Ag-MFs were constructed. Moreover, the initial viscosity of epoxy-based composite is maintained within 106 mPa s, which means Ag-MFs is uniformly dispersed after the addition of P/P. Scanning electron microscopy (SEM) and oscillating viscoelastic measurement were used to demonstrate the improved dispersion of Ag-MFs after the addition of P/P. In addition, atomic force microscope (AFM) and Raman spectroscopy were used to verify the conformation change of PEDOT. Compared with ECAF without P/P, the electrical and thermal conductivity of ECAF with 6 wt% P/P was enhanced by 73.1% and 166.3%, respectively. Meanwhile, scattering parameter (S-parameter) measurements demonstrated that ECAF with 6 wt% P/P had excellent radio-frequency behavior at 2-4 GHz, indicating high-performance in the mi-croelectronics packaging industry.