Abstract
The differences in electrical characteristics of solder joints are so small that they are undetectable without the use of special methods. In this study, a simpler way of assessing solder paste functionality is proposed. ln place of the electrical characteristics that are generally used to evaluate solder functionality,the proposed method uses mechanical characteristics. Ten different solder compositions (solders A to J) were tested by finding their toughness values from load-displacement curves under shearing force obtained before and after the application of noise factors (high temperature and high humidity, thermal shock, corrosive gas, and electric current). The toughness of a solder joint means the amount of energy that must be applied to fracture it. The results of S/N ratio and sensitivity calculations using these relationships showed that the new type F solder (Sn-Ag-Cu-X) was superior by 3.9 db in its S/N ratio and 1.7 db in sensitivity to the conventional type B solder (Sn-3.0mass% Ag-0.5mass% Cu). After calculation of total loss values for all ten types, type F was finally selected as entailing the smallest loss (56% less than that of type B). Use of the proposed method enabled a solder paste to be selected that was satisfactory in all regards: quality, reliability, and cost.
