Abstract
Sn-Ag-Cu solders doped with rare-earth elements were reported to exhibit beneficial mechanical properties; however, rapid whisker growth could be induced. In order to retain the advantageous effects of rare-earth doping without causing the formation of tin whiskers, a Sn-3Ag-0.5Cu-0.05Ce alloy was suggested. In the present study, metallographic observations indicate that whisker growth is indeed prevented in this alloy. However, tensile tests with the bulk materials show that the ultimate tensile strength and Young’s modulus of this Sn-3Ag-0.5Cu-0.05Ce alloy are only slightly higher than those of undoped Sn-3Ag-0.5Cu. Further reliability tests with actual ball grid array packages indicate that the Sn-3Ag-0.5Cu-0.05Ce solder joints have fatigue lives similar to those of undoped Sn-3Ag-0.5Cu specimens regardless of the various surface finishes, such as electroless nickel/immersion gold (ENIG), immersion tin (ImSn), and organic solderability preservatives (OSP). The results suggest that, although lowering the content of rare-earth elements in solders can inhibit the occurrence of rapid whisker growth, it cannot ensure the improvement of the tensile properties of bulk solders and the fatigue reliability of solder joints in actual packages.
Published Version
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