Highly Reliable Copper-Based Conductive Adhesives Using an Amine Curing Agent for in Situ Oxidation/Corrosion Prevention

Abstract

One critical obstacle to preparing highly reliable isotropically conductive adhesives (ICAs) filled with Ag-coated Cu flakes is the oxidation and corrosion of Ag-coated Cu fillers, which cause the degradation of electrical properties of the ICAs at elevated temperatures and relative humidity (RH) during long-term reliability tests. Various organic compounds could be used for corrosion prevention of the exposed Cu surface of Ag-coated Cu fillers, however, with poor thermal stability at elevated temperatures. In this paper, we report a novel approach for the preparation of highly reliable, highly conductive, and low-cost ICAs filled with Ag-coated Cu flakes by using an amine curing agent for in situ oxidation/corrosion prevention. The coordination of the amine curing agent to the exposed Cu of Ag-coated Cu flakes prevents the oxidation of the exposed Cu during the ICA curing at 150°C. After curing, the formed ample secondary and tertiary amine groups could further protect the exposed Cu surface from oxidation/corrosion effectively in harsh environments. In comparison with an anhydride-cured ICA (resistivity: ~1.3 × 10-3 Ω-cm), an amine-cured ICA exhibits a much lower bulk resistivity (~2 × 10-4 Ω-cm). This resistivity is comparable to that of commercially available Ag filled ICAs. Moreover, the amine-cured ICA shows very stable bulk resistivity during 85°C/85 % RH aging for more than 1000 h and triple reflow tests with a peak reflow temperature at 255°C. We discuss the reasons why the amine-cured ICA provides lower bulk resistivity and better reliability than the anhydride-cured ICA. The novel approach of in situ Cu oxidation/corrosion prevention paves the way towards highly reliable, highly conductive, and low cost ICAs for electronic packaging applications.