Highly reliable, low cost, isotropically conductive adhesives filled with Ag-coated Cu flakes for electronic packaging applications

One of the main hurdles for the wide use of current Ag-filled, isotropically conductive adhesives (ICAs) is the high cost of Ag fillers, while the challenge for low cost copper-filled ICAs is their poor reliability. In this paper, highly reliable, low cost ICAs in which the copper flakes used as filler are coated with silver (Ag-coated Cu flakes) have been developed. With Ag-coated Cu flakes modified by an amine-based silane coupling agent (SCA), the ICAs with the resistivity (2.4×10−4 Ω cm) comparable to that of commercially available Ag-filled ICAs have been achieved. Moreover, the contact resistance of the ICAs filled with the modified Ag-coated Cu flakes on a Ni/Au surface can be stabilized (less than 10% increase) for more than 1000 h of aging at 85 °C and 85% RH and after three reflows with a peak reflow temperature of 255 °C. The causes leading to the higher conductivity and the better reliability of the ICAs filled with Ag-coated Cu flakes modified by amine-based silane coupling agent are discussed.