When is a solder joint considered an "intermetallic" junction?

A solder joint is regarded as an "intermetallic" junction when it consists of two or more metals that have reacted during soldering. This reaction typically occurs at the interface of the solder and the base metals, resulting in the formation of intermetallic compounds. These compounds can enhance the mechanical strength and thermal properties of the joint, leading to improved performance under certain conditions.

The formation of intermetallics is crucial in soldering processes, particularly in electronics, where the reliability of connections is essential. The intermetallic junction signifies a chemical bond beyond mere physical contact, ensuring better electrical and thermal conductivity. Recognizing this criterion helps ensure proper quality control and assessment of solder joints in the manufacturing and assembly of electronic components.