Aging Characteristics of Sn-Ag Eutectic Solder Alloy with the Addition of Cu, In, and Mn

In the present investigation, three types of solder alloy, i.e., Sn-Ag-Cu, Sn-Ag-In, and
Sn-Ag-Cu-Mn, have been prepared and joined with Cu substrate. In the reflowed condition, the
joint interface is decorated with Cu6Sn5 intermetallic in all cases. During aging at 100 C for 50
to 200 hours, Cu3Sn formation took place in the diffusion zone of the Sn-Ag-Cu and Sn-Ag-In
vs Cu assembly, which was not observed for the Sn-Ag-Cu-Mn vs Cu joint. Aging also leads to
enhancement in the width of reaction layers; however, the growth is sluggish (~134 KJ/mol) for
the Sn-Ag-Cu-Mn vs Cu transition joint. In the reflowed condition, the highest shear strength is
obtained for the Sn-Ag-Cu-Mn vs Cu joint. Increment in aging time results in decrement in
shear strength of the assemblies; yet small reduction is observed for the Sn-Ag-Cu-Mn vs Cu
joint. The presence of Mn in the solder alloy is responsible for the difference in microstructure
of the Sn-Ag-Cu-Mn solder alloy vs Cu assembly in the reflowed condition, which in turn
influences the microstructure of the same after aging with respect to others.