Fundamental study of electrically conductive adhesives (ECAs)

Variations of volume resistivity of three electrically conductive adhesives (Ag-filled epoxy, Ag-filled cyanate ester, and Ni-filled epoxy) during 85°C/85%RH aging were studied. Volume resistivity of the two Ag-filled ECAs decreased slightly at the beginning of aging and then remained stable. However, the volume resistivity of the Ni-filled epoxy increased substantially. Joint resistance variations of these conductive adhesives with different metals (Ag, Cu, and Sn) were also studied by using a specially designed test vehicle. The Ag-filled epoxy with Ag and Cu wires did not show appreciable joint resistance increase during 1000-hour 85°C/85%RH aging. However, dramatic joint resistance increase with Sn wire was observed. The joint resistance of the Ag-filled cyanate ester ECA with all the metal wires increased, slightly with Ag and Cu wires and more dramatically with Sn wire. The Ni-filled epoxy showed significant joint resistance increase with both Ag and Cu wires. The electrical conductivity development of an ECA and the Ag flake used in this adhesive was studied. It was found that under heating, electrical conduction was achieved above certain temperatures. The Ag flake achieved electrical conduction at higher temperature than the ECA. The effect of curing temperature on ECA resistivity and shrinkage was investigated. Samples cured at higher temperatures exhibited higher shrinkage and lower resistivity