We used advanced electron microscopy techniques to study the microstructure of Ag-based conductive adhesives, which are promising alternatives to Pb-free solders. Systematic microscopy observations revealed the development of connections between Ag agglomerates, when the weight density of Ag (Ag content) was increased up to 92mass%. However, in a sample containing 94mass% Ag, disconnection between well-defined Ag agglomerates and/or formation of voids between Ag-filler particles were observed. These results appeared to be consistent with the plot of resistivity versus Ag content: the resistivity decreased to a minimum value at 92 mass% Ag. We also demonstrated the formation of very small Ag particles in a thin-foil specimen subjected to electrical breakdown. This microscopic observation may be useful for understanding the process of electric breakdown in thin-foil specimens.
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