Construction of silver-epoxy adhesive with suppressed silver migration rate based on thiol-silver interaction

Abstract

The silver migration limits the application of silver based conductive adhesives in wet environment. The existing methods for inhibiting silver migration in epoxy conductive silver adhesives involve one or more issues such as cost, complexity, and inhibition of conductivity. Moreover, there is currently a lack of strategies that can suppress the silver migration effect while ensuring good dispersion of silver fillers in the matrix and constructing a good filler matrix interface. Herein, a facile method was reported suppressing the silver migration in silver-epoxy conductive adhesive. Tetrafunctional thiopentaerythritol tetramercaptoacetate (PERTMA) was introduced into 1,4-cyclohexanedimethanol diglycidyl ether (CHDMGE) epoxy resin as the curing agent. This method utilized the strong interaction between silver and thiols, including coordination and covalent bonding, to achieve good compatibility between filler and matrix. By tightly combining silver with the resin system, the content of free silver atoms was reduced, capturing and inhibiting the hydrolysis of silver atoms and their migration with current, and the conductivity of the conductive silver adhesive was not greatly degraded due to the silver-thiol interaction. At the same time, the introducing of PERTMA was able to reduce the surface hydrophilicity of epoxy resin, which also helped suppressing the silver migration effect under humid circumstances. The interaction between silver and thiol was characterized, and the influence of silver content on the curing behavior, material mechanical performance, conductivity, resistivity on silver migration and flexibility was explored. The CHDMGE/PERTMA/Ag conductive adhesive based on strong thiol-silver interaction had excellent resistance to silver migration, which occurred after 3500s, which was 10.67 times longer than the control group. In addition, the silver filler enhanced the tensile strength of the matrix resin by this thiol-silver interaction. This study will provide new ideas for the design and development of silver migration resistant conductive adhesives based on matrix filler interaction.