Low cost copper-based electrically conductive adhesives

One of the main drawbacks of silver-filled isotropically conductive adhesives (ICAs) is the high cost of silver fillers, while low cost copper-filled ICAs are not reliable due to the oxidation of copper fillers. In this paper, we develop highly conductive, highly reliable, and low cost ICAs filled with silver-coated copper (Ag-coated Cu) flakes, i.e. an anhydride-cured ICA filled with Ag-coated Cu flakes modified with an amine-based silane coupling agent and an amine-cured ICA filled with untreated Ag-coated Cu flakes. Compared with anhydride-cured ICAs filled with untreated Ag-coated Cu flakes (1.3 × 10^-3 Ω cm), the two ICAs developed showed a much lower resistivity (about 2 × 10^-4 Ω cm). The resistivity of the two ICAs developed is comparable to that of commercial Ag-filled conductive adhesives. The amine-cured ICAs filled with untreated Ag-coated Cu flakes showed stable bulk resistivity during 85°C/85% RH aging for more than 1000 h. Anhydride-cured ICAs filled with modified Ag-coated Cu flakes showed a stable contact resistance on a Ni/Au surface during 85°C/85% RH aging for more than 1000 h. The causes leading to the much lower resistivity and better reliability of the developed ICAs have been discussed.