Application of an asymmetrical four point bend shear test to solder joints

The asymmetrical four-point bend shear (AFPB) test method was used to measure the shear strength and creep properties through the stress relaxation experiments using three different Pb-free solder joint compositions in an assolidified condition. Since it was difficult to shear the uniform specimens and the local bending usually occurs at the inner loading points, the notches were introduced at the joint line to preferentially weaken this region. The stress analysis by finite element modeling showed that the straight notches transform the parabolic shear stress distribution in the uniform specimen into a relatively uniform shear distribution along the bond line in the notched specimens. Therefore, the shear strength results from the notched specimens are expected to be much more accurate. Experiments showed that both the Sn-3.6Ag-1Cu (wt.%) and Sn-3.6Ag-1Cu-0.45Co joints have superior strength and creep properties as compared to the Sn-3.5Ag joint. However, there was no statistical difference between the shear strength of the Sn-3.6Ag-1Cu and Sn-3.6Ag-1Cu-0.45Co joints. Moreover, the difference between the creep resistance of these two types of joints was small.