| In this work, fundamental studies of reliability issues of current conductive adhesives technology are conducted and, based on the resulted understanding, conductive adhesives with improved performance are developed. To begin with, chemical nature and thermal behaviors of the organic lubricants of silver flakes are investigated. The roles of silver flake lubricant layer and resin cure shrinkage on conductivity establishment of an ECA are also studied. It is found that silver flake lubricant layer is not strongly related to the initiation of conductivity of ECAs but resin cure shrinkage is one of the factors that initiates electrical conductivity of ECAs. Several approaches are discovered to improve electrical conductivity of an ECA. To clarify the dominant mechanisms underlying the unstable contact resistance of current commercial ECAs on non-noble metals, a series of experiments are designed. The results clearly indicate that metal oxide formation resulting from galvanic corrosion of the non-noble metallization is the main mechanism. Several approaches are identified to stabilize contact resistance. In order to improve impact strength of an ECA, many modified resins including rubber-modified epoxy resins and epoxide-terminated epoxy resins are introduced into ECA formulations. Based this study, effective resins are identified. By combining effective resins for improving impact strength, effective additives for stabilizing contact resistance and effective approaches to improve electrical conductivity, conductive adhesives with high performance are developed. These developed ECAs meet all the National Center for Manufacturing Science (NCMS) requirements for solder replacements. |
