SOME PHYSICAL PROPERTIES OF WIPING SOLDERS 113 



As the value of b can be determined in a single test with the plastom- 

 eter, its relation to workability should permit of the rapid e\'al nation 

 of the latter property, provided the relation holds in general. Apply- 

 ing this criterion to the solders tested, No. 4, showing virtually a 

 viscous type of flow, {b ^ 5), would be at once thrown out. Solder 

 No. 3 would be classed as a superior solder from the standpoint of 

 workability. Nos. 1 and 2 could be classed as satisfactory. The use 

 of Nos. 5 and 6 would be questionable, with No. 6 having the best 

 chance for success. Practical tests on these last two solders are insuf- 

 ficient to completely confirm this classification, but general indications 

 are that it is correct. Practice has completely confirmed the classi- 

 fication of the other four. 



Usefidness of Plastometer in Research and Control Testing 



It is believed that the work which has been done on these six solders 

 has furnished information which justifies the use of the plastometer in 

 the future when any group of alloys is to be investigated as to working 

 properties. It appears that the principal demand upon a workable 

 solder is a wide temperature range in which it can be worked. Whether 

 or not a solder is suitable in this respect can very well be determined 

 by the plastometer either by making runs at several temperatures or 

 by determining b at some temperature representative of the wiping 

 range. 



A further possible use of the plastometer is in testing solders manu- 

 factured or purchased subject to requirements as to their composition. 

 As a rule, the sample height after a given time of compression is quite 

 different for alloys differing in composition. This is illustrated by 

 the curves of Fig. 6, which represent the data obtained with the 

 plastometer on a number of alloys. These show that such a test of 

 composition would not be infallible in a wide application, as the quite 

 dissimilar alloys C and F give quite similar curves. In distinguishing 

 an excess or deficiency of one component in any given series of alloys, 

 however, the test should be quite sensitive. 



If the plastometer were used for this purpose, the allowable limits 

 of composition would correspond to limits of sample height in satis- 

 factory samples. Consider, for example, the case of a lead-tin solder 

 of a composition between that of solders Nos. 1 and 2. A convenient 

 temperature of test would be 195° C. At this temperature, the 

 sample height after ten minutes would be 110 mils for a solder of com- 

 position 65 per cent Pb, 35 per cent Sn, and 137 mils for one of com- 

 position 60 per cent Pb, 40 per cent Sn. Since the plastometer results 

 are reproducible within 2 mils, the accuracy in detecting variation in 



