SOME PHYSICAL PROPERTIES OF WIPING SOLDERS 103 



4. Porosity: At the start of the investigation it was thought that the 

 porosity of the joint might be related to the plasticity of the solder. 

 As this was not found to be the case, other factors which might be 

 responsible for this condition were investigated. In particular, 

 experiments were performed to determine if porosity is dependent 

 upon segregation, or if it is related to the particle size of the solid phase 

 at wiping temperatures. Porosity and segregation were found to be 

 quite independent, but a relation between porosity and particle size 

 was found in the two tests made in this connection. 



Experimental work directed toward these objects has in\olved the 

 following groups of experiments: 



1. Plasticity studies. 



2. Segregation studies. 



3. Investigation of particle size. 



The first of these groups was planned to cover the first three objects 

 enumerated above, while the other two groups are of interest in con- 

 nection with porosity. 



Alloys Ixvestigated 



Six different alloys were tested as described in Table I. In this 

 table, the compositions sought in preparing the samples are given, 

 together with the composition found by analysis at the top and bottom 

 of the cast (T & B), except for solders Nos. 5 and 6, of which no 

 analyses were made. 



Nos. 2 and 3 are good, workable solders giving non-porous joints, 

 with No. 3 possibly being given preference in ease of handling while 

 the joint is being wiped. No. 1 is also satisfactory from the standpoint 

 of workability, but the joints formed from it are often porous, while 

 the splicers described it as being somewhat " coarse." No. 4 is un- 

 satisfactory in all respects. Some tests on No. 5 showed it to be good, 

 but in recent tests the workability has been poor and a number of 

 porous joints have been found. Solder No. 6 seemed to be fair both 

 in workability and porosity, but the number of tests has been alto- 

 gether too limited for definite conclusions to be drawn. The work- 

 ability of neither of these last two solders is as good as that of the 

 lead-tin and lead-tin-cadmium alloys. The results of wiping and 

 porosity tests are summarized to the right of Table I. 



A point which the authors wish to stress is that they are interested 

 here only in two of a number of factors which may affect the utility 

 of solders; namely, workability and porosity. Therefore, that a 

 solder is good in those respects does not necessarily imply that it is a 

 good solder in a general sense, and leaves open the question as to 



