SOME PHYSICAL PROPERTIES OF WIPING SOLDERS 



115 



Photographs were taken with a magnification of 25 X , which allowed 

 0.5 cm. of the sample to be photographed at one time. Three photo- 

 graphs were taken along the radius of each sample, one bordered by the 

 axis of the sample, one by the edge, and one mid-way between these 

 two. 



These photomicrographs were placed in a beam of light of constant 

 intensity. Since the eutectic appears as a light background, while the 

 particles which separate out as solid above the eutectic temperature 

 appear dark, the light transmitted through the plate is a comparative 

 measure of the relative amount of eutectic present in different parts 

 of the sample. The variation in light transmitted as the picture is 

 passed before the beam therefore indicates the amount of segregation. 

 The transmitted light was directed on a caesium photo-cell and the 

 amplified photo-electric current measured, four measurements being 

 required to span each plate, making twelve measurements on each 

 sample. 



Table III gives the results of these measurements. In this table, 

 only the averages of the four measurements of each photomicrograph 

 are given. 



TABLE III 



Segregation Measurements 

 Light Transmitted Measured in Milliamperes of Amplified Photo-electric Current 



Results — Comparison with Porosity 



The only conclusion that can be drawn from this tabulation of 

 results is that segregation is not an important factor in porosity. 

 Among solders Nos. 1, 2 and 3, good and poor solders alike show 



