The Interphases Formed During the Very Early Stage Liquid Solder/Metal Substrate Interaction of the Soldering Process

The initial step of the soldering process may consist of dissolution of metal substrate and the subsequent counterdiffusion between substrate atoms and solder elements. The counterdiffusion gives rise to the formation of the various interphases (phases at the interfacial region). A close investigation of the interphases formed at the very early stage of soldering will provide the root understanding to the soldering process. No in situ observation at the liquid/solid interaction was possible thus far. A number of studies attempted to adopt rapid quench of the soldered specimen at the very early stage of interaction, around 10 s or less after solder melts, so as to freeze the occurrences. The current article provides a review of the achievements of these studies, although not many, and the interphases formed during the very early stage of the soldering process for various solder systems.