LEAD-TIN-ARSENIC WIPING SOLDER 265 



mended percentage the difificulties in producing a satisfactory joint 

 increase. There is the possibility, however, that a lower tin content 

 can be tolerated but definite conclusions await further substantiation 

 in subsequent investigation. 



Although the percentage of arsenic in the new solder is relatively 

 small it has two important beneficial efifects. The amount of dross 

 formed on the arsenic-bearing solder is but a fraction of that ex- 











4l# 













Fig. 2 — Same as Fig. 1, except for an addition of 0.1% arsenic. Note the finer grain. 



perienced in the ordinary lead-tin solders. The practical advantage 

 is that less time need be spent in skimming the molten solder in the 

 melting pot, and there is less possibility for the inclusion of dross in 

 the finished joints. The presence of dross in the wiped joints is to be 

 avoided because of its possible contribution to porosity. 



The second beneficial effect of arsenic is related to the grain size in 

 the solidified alloy. This is illustrated by the photomacrographs shown 

 in Figs. 1 and 2 which compare the grain structure of a lead-tin solder 



