Saturation optical near-field

Dissolved base metal can potentially saturate the nearby molten Pb-Sn solder field. Upon solidification, the base metal, M, precipitates out as M cS% intermetallic compound particles located near to, and at, the interfece. For example, dissolved Cu will precipitate as Cu Sns particles, forming a zone of such particles adjacent to a contiguous intermetallic layer. This morphology is shown in Fig. 11. Optical micrographs were taken of the 37Pb-63Sn solder/Cu interface after the base metal had been exposed to molten solder (215°C) for 5, 60, 300, and 900 sec. 

---