Anisotropic conductive films (ACF) are important component used in LCD and LED screen packaging, utilized for many different electronic devices. To be effective, these films require highly conductive microparticles that can be arranged to connect the terminals of various LCD components. In this research, various novel double core shell particles were examined to help fulfill this role. Polystyrene cores were utilized with an inner shell composed of either copper or a nickel/cobalt/phosphorus alloy and the outer shells were composed of either silver or reduced graphene oxide(rGO). The Ni/Co/P layer functions to add magnetic properties to the particles whereas copper, silver and rGO all provide electrically conductive layers. Although many of these metals have been used previously...[ Read more ]

Anisotropic conductive films (ACF) are important component used in LCD and LED screen packaging, utilized for many different electronic devices. To be effective, these films require highly conductive microparticles that can be arranged to connect the terminals of various LCD components. In this research, various novel double core shell particles were examined to help fulfill this role. Polystyrene cores were utilized with an inner shell composed of either copper or a nickel/cobalt/phosphorus alloy and the outer shells were composed of either silver or reduced graphene oxide(rGO). The Ni/Co/P layer functions to add magnetic properties to the particles whereas copper, silver and rGO all provide electrically conductive layers. Although many of these metals have been used previously, the unique combination of Ni/Co and Ag and the utilization of rGO are newly examined for this purpose.

Here an electroless plating process was utilized to coat the microparticles. Each process was optimized for the specific metal and to maximize either its conductivity or magnetic sensitivity. Several parameters were optimized, including surface chemistry, plating solution composition, the timing of chemical additions and the pH, temperature, time, and mixing speed of the electroless plating bath. Graphene oxide was attached using either electrostatic interactions or covalent bonding, with the covalent bonding yielding a more consistent attachment. Several methods of graphene oxide reduction were attempted, including sodium borohydride, hydrazine, and ascorbic acid with the utilization of ascorbic acid removing the most functional groups and partially restoring of the SP2 graphene carbon network. By fabricating particles with a Ni/Co/P inner shell and rGO outer shell, sufficient properties were achieved but particles with a silver outer shell proved to have superior conductive properties with a resistance of 0.02Ω, while still maintaining an induced magnetic moment 0.06 EMU. These particles were combined with a UV curing polymer film to produce an ACF that meets or exceeds industrial specifications for conductivity(<0.1Ω), adhesion strength(>500g/cm), short circuit mitigation(XY Resistance > 1 MΩ) and are able to maintain this performance even after an extended period in a high temperature and humidity environment. This research marks the first time rGO has been successfully utilized for ACFs and can provide insight into the most important factors of maximizing the conductivity and magnetivity during the sequential electroless plating of dual layers of Ag on top of Ni/Co. With these innovations ACFs can be made cheaper, while still maintaining a superior performance suitable for the smaller pitch and higher conductivity requirement needed for the next new wave of electronic devices.