Flux Action Based on Electrical Conductivities of Molten Fluxes for Soldering (Report 2)

Abstract

The phase diagram and specific electrical conductivity of fused salt systems ZnCl₂-SnCl₂, ZnCl₂-NH₄ Cl and ZnCl₂-SnCl₂⋅2H₂O, which are used generally as flux in soldering, were measured to clear a relation between the structures of these mixed salts and the spread area of Pb-Sn eutectic solder on copper base plate.
The results obtained were as follows:
1) The diagram of ZnCl₂-SnCl⋅₂ system is a simple eutectic with no solid solution, and ZnCl₂-NH₄Cl system forms a intermediate compound formation with two simple eutectics. It seems the diagram of ZnCl₂-SnCl₂⋅2H₂O system is a intermediate compound formation type.
2) The dissociation of ZnCl₂-SnCl₂ system was presumed as follows from the basis of J.D. Mackenzie theory on single zinc-chloride;
3ZnCl₂→ZnCl₆^4-+2Zn, ²⁺, SnCl₂→Sn₂²⁺+2Cl^-
3) Isotherms of specific conductivity of ZnCl₂-SnCl₂ system deviate negatively from additivity when plotted against composition, and three partial negative deviations were found near the compositions of two eutectics and a intermediate compound in ZnCl₂-NH₄Cl system at just above liquidus temperature for each.
4) The transition temperature obtained from temperature.dependence of activation energy for electrical conductivity of ZnCl₂-SnCl₂ or ZnCl₂-NH₄Cl systems coincided with the temperature required for good spreading of the solder on copper plate, using these systems as flux. This result showed that an effective action temperature range of flux is from the liquidus to the transition temperature of itself and, therefore, a recommendable soldering temperature is limitted by these temperatures of flux to be used generally.
5) Th flux action of ZnCl₂-SnCl₂⋅S2H₂O system could be explained as follows;
SnC-l₂⋅2H₂O→SnCl₂+2H₂O
ZnCl₂+H₂O→Zn(OH)Cl+HCl
CuO+2HCl→CuCl₂+H₂O
Although two equations of the latter were presented by H.H.Manko, the H₂O produced by the dissociation of SnCl₂⋅2H₂O during heating reacts with ZnCl₂ and forms HC1. The HO and SnCl₂ act as flux in soldering of the range 180-350°C, and no SnCl₂⋅2H₂O acts as flux in the form of itself.