SUPERPLASTIC CREEP OF LOW MELTING-POINT SOLDER JOINTS

In prior work, we showed that eutectic Sn-Pb solder joints exhibit superplastic behavior after rapid solidification. Further examples of superplasticity in nominally air-cooled solder joints are reported in this study of three low-melting point alloys: 40In-40Sn-20Pb (wt. %), eutectic 52In-48Sn, and 43Sn-43Pb-14Bi, which were creep-tested in shear at 20-degrees, 65-degrees, and 90-degrees-C. The test results indicate that above 65-degrees-C, the indium-containing solders have stress exponents between 2.4 to 2.9, a possible overall shear strains of 500%, and an absence of primary creep; at 90-degrees-C, 43Sn-43Pb-14Bi solder has a stress exponent close to 2.3. Optical microstructures of the three solders are presented; they help to explain the superplastic behavior.