Effects of oxide film on solderability of copper alloy for lead-frames

摘要

Factors affecting the growth of copper oxide film on the surface of a copper strip, and the effect of this film on solderability were investigated using an optimized cathodic reduction technique that permits easy measurement of thickness of copper oxide film. Humidity was found to be the most important factor affecting the growth of copper oxide film. At room temperature, copper oxide film grew slowly under low humidity conditions, but grew quickly as relative humidity increased. The resultingcopper oxide film adversely effected the solderability of the copper strip, especially when non-flux soldering was used. When the thickness of the copper oxide film exceeded 6nm, solderability was severely lowered. Good solderability of the coppersurface can be maintained by limiting the growth of the copper oxide film to 6 nm. The thickness of the oxide film obtained by the present cathodic reduction method was in good agreement with that determined by AF~ analysis, especially when the oxidethickness is less than 10nm.