Abstract
It is well known on Pb-Sn solders that the maximum spreading on a copper plate is obtained at near eutectic composition of the solder, and the maximum equilibrium rising height in vertical capillary copper joints or the maximum penetration coefficient in horizontal capillary copper joints are obtained respectively at pure tin component of the solder. But, the adequate cause of difference in these phenomena is not known at presentn.
This investigation was made to clear the cause. The results obtained are as follows;
1) The maximum wetting between the solder and copper is obtained at the intermediate (near eutectic) composition of solder, and the shape of wetting curve is mountainous in each case described above. The solder of eutectic composition, accordingly, gave both properties of a good wetting and spreading.
2) The discrepancy in both spreading and penetration can be attributed to the tact that the surface (or interfacial) tension of pure tin is larger than that of the solder of the intermediate composition.
3) The flow of solder in contact with copper solid surface is controlled by factors such as the wetting between solder and copper, the density and viscosity of solder and flux used. A good flowing, therefore, is not always a good wetting and the converse holds good.
4) In the calculation of immersional wetting, it is a mistake to taking the "ideal" wetting condition into account.
