INVESTIGATING TESTING CONDITIONS FOR ELECTROMIGRATION EVALUATION AND EFFECT OF ADDITIVE ELEMENTS ON ELECTROMIGRATION RESISTANCE OF Sn58Bi SOLDER

摘要

The present research systematically investigates the testing conditions for electromigration (EM) tests and compares the EM resistances of Sn58Bi (SB, in weight percent)-based solders including SB, Sn58Bi0.5Ag (SBA), and Sn58Bi0.5Ag0.1Cu0.07Ni0.01Ge (SBACNG) solders. With the contribution of a 2D Cu/solder/Cu interconnected-test structure which has been developed in our previous work, a quantity of EM tests are conducted on SB solder under various combinations of current density and temperature. The testing conditions are classified into three groups depending on three cases of experimental results, which are that the samples melted just after the current stressing beginning; that the morphological change (hillock formation) occurred after the sample being subjected to a current stressing for 10 h; and that there was no morphological change after 10 h, respectively. These results are plotted with the corresponding current density and temperature to investigate the appropriate testing conditions for EM tests. In addition, based on the melting temperature of SB solder and the investigated testing conditions under which the sample melted, the variation of temperature increase due to Joule heating with current density is estimated. Finally, we compare the EM resistances of SB, SBA and SBACNG solders under an average current density of 23 kA/cm2 and at 333 K for total of 20 hours. The EM resistances are compared via the morphological changes of the solders after current stressing. The morphological change is quantitatively investigated by measuring the ratio of the total EM-induced hillock volume to the current stressing time. As a result, SBACNG solder shows a higher EM resistance than those of SB and SBA solders. The effect of adding microelements on the EM resistance of SB solder is discussed.