TABLE OF CONTENTS Contamination in the tin-lead solder system refers to metallic additions that are found in the material and have alloyed with it. These are usually present in the material for various reasons discussed below and are not artificial additions introduced to obtain certain properties. The impurities can result from the ores used as raw material or can come from contamination picked up during the soldering process. A solder pot, for example, can be contaminated by the work that is passed through it. Many contaminants, e.g., silver and bismuth, are not specifically detrimental in small quantities and therefore are only an indication of the purity of the solder. Other contaminants, e.g., aluminum and zinc, are very detrimental to the performance of the alloy and are definitely an indication of how well the material would perform in service. Nonmetallic impurities such as sulfur are also dangerous to the solders, since they can cause certain dewetting conditions of both the tool and the work. Other nonmetallic elements such as phosphorus affect the properties of the solder in ways we do not completely understand at this time. Finally, a class of contaminants has received more attention, namely, oxides and sulfides of tin and lead, which are present in the form of inclusions in the bulk of the material.
To protect the consumer, many government and industrial organizations have issued specifications to...
