Impact of the Formation of Intermetallic Compounds in Current-Carrying Connections

In electrical power engineering a number of different metallic materials are applied. At interfaces of current-carrying connections, these materials meet. Depending on the combination, intermetallic compounds (IMC) can form between the different metals. Interdiffusion and the resulting formation of IMC has been considered an important aging mechanism for such interfaces affecting their long-term reliability. This paper aims to compile the physical characteristics and the impact of IMC that can occur in the electrical power system. The material combinations Al-Cu, Ag-Al, Ni-Sn, and Ag-Sn were investigated. The specific electrical resistance of the IMC, its temperature coefficient and the growth constants were determined. Electrical long-term tests and metallographic investigations were conducted on components in which IMC occur such as bolted joints with busbars and fuse elements. The measurements were compared to calculations of the resistance based on aging only by formation of IMC. The results suggest that the growth of IMC in current-carrying connections is not as critical as it has been assumed in the past. IMC grow less than expected and are not solely responsible for electrical failures in the investigated systems. Based on the findings, the standardized maximum allowed temperatures for the connections are evaluated.