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In the numerical evaluation system described in this paper, the nominal diameter of a sphere formed by a standardized solder specimen provides the zero per cent mark; the infinite thinness of the same solder mass spread as a film provides the 100 per cent mark, on a percentage scale. Intermediate values are determined by measurement of the height or thickness of the solder spots, obtained after melting, by means of a hand micrometer. The empirical spread-factor values thus obtained provide a simple, reproducible, visually significant numerical system. A general relationship to cos ϑ, where ϑ is the contact angle between liquid solder and solid base, is shown. Applications of this system for the evaluation of solders, fluxes, and metallic surfaces with respect to solderability are given.
Components Div., Radio Corporation of America, Camden, N. J.