METALLURGY OF FILLET WIPED SOLDERED JOINTS 77 



crucible is tilted sideways to a position shown in Fig. 5 a portion of the re- 

 maining eutectic may be poured out leaving spongy regions. This loss of 

 eutectic is observed frequently during the formation of the old massive type 

 joints which may lose several drops by drainage after the splicer has com- 

 pleted his shaping operations. It is also shown by the greater number of 

 pores in the top half of a joint compared to the bottom and the somewhat 

 grayer surface appearance of the top. 



Fig. 5 — An ingot of wiping solder which had been tilted while in the crucible before 

 completely solidified. The lower lip represents eutectic drainage from the partially 

 solidified mass (magnification I5 X). 



Although a solidification range in which quantities of liquid and solid 

 metal may exist at equilibrium is an essential feature of a wiping solder, 

 another factor of major importance is the nucleation rate of the alloy. Wip- 

 ing solders having high nucleation rates will develop quickly a myriad of 

 points or nuclei throughout the melt from which further crystallization will 

 proceed, while an alloy of low nucleation rate will develop relatively few of 

 these points in the same time and consequently grow fewer and larger 

 crystals. The former alloy will have a texture similar to fine clay while 

 the latter will behave like coarse sand and water when subjected to wiping 



