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Degradation Mechanism of Conductive Adhesive/Sn Interface under High Humidity
Keywords: Conductive adhesive, Degradation mechanism, Galvanic corrosion
Ag-epoxy conductive adhesives have been proposed as one of the ecological alternatives to lead-bearing solders in electronic industries. Although Ag-epoxy conductive adhesives possess many advantages as the alternative, they have still several drawbacks to be clarified. One of the drawbacks is the poor compatibility with Sn-plated components in a humid atmosphere. The humid environment sometimes brings the interfacial degradation of Ag-epoxy conductive adhesive on Sn surface. This degradation has been reported to be attributed to one sort of corrosion, i.e., Galvanic corrosion, however, neither definitive explanation nor proof has been achieved yet. The present study focuses on the degradation mechanism of the joint interface between Ag-epoxy conductive adhesive and Sn plating under high humidity condition. The degradation characteristics of the joint interface were examined in detail by use of transmission electron microscope (TEM). As a result of TEM analyses, two different types of oxide layers, SnO and SnO2 phases, were found at the interface, which caused increase of the interfacial electrical resistance. The Sn-oxides were mainly formed at the interface where the surface of Sn plating was close to Ag particles in the conductive adhesive and they became thicker and larger with exposure time. Many voids were also found at the Sn-oxide layers. In the present study, the formation of Sn-oxides and voids at the joint interface is the root cause of the interfacial degradation. The formation of these defects can be attributed to Galvanic corrosion in a humid atmosphere. The detailed degradation mechanisms of the Ag-epoxy conductive adhesive joints are to be discussed.
Sun Sik Kim,
ISIR, Osaka University
Ibaraki, Osaka 567-0047,

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