Preliminary results from solderability studies are used to elucidate the physicochemical aspects of solderability, in particular the relationship between liquid composition and wetting. Spreading front morphology is discussed and a possible mechanism for observed rapid spreading sequences is advanced. That mechanism is based on solubility of metallization in one of the solder components (Sn). A composition study of a spreading sequence exhibiting a precursor film is presented along with a discussion of the role of the film in the overall wetting process. Segregation of the Pb and Sn alloy components during the spreading is discussed in terms of surface energy concepts, and the microscopic features of the substrate.

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