Effect of Annealing for Copper and Mild Steel Base Metals on Solderability

Abstract

The wettability of a molten tin-lead solder on copper and mild steel plates was investigated in relation to the effects of annealing for the base metals and discussed from the viewpoint of the surface energies on rolling or recrystallization textures of base metals. The wettability was evaluated in terms of the spreading area of solder on the base metals. The spreading test was made by the special designed apparatus, using eutectic tin-lead solder and ZnCl₂-NH₄Cl aqueous solution flux. The results obtained are summarized as follows.
(1) The wettability of a tin-lead solder on copper and mild steel plates tended to decrease with increasing annealing temperature of base metals. The spreading area on the copper base metal annealed at 1073 K was approximately 50% of that on the as-rolled copper.
(2) There was a close relation between the spreading area of solder and the microstructures of base metals. It is suggested that the spreading area of solder depends largely on the surface energies of base metals in the preferential orientation of textures.
(3) In the spreading process of molten solder it is important for tin of solder to diffuse on the base metal surface prior to spreading of the main solder drop.