Effect of heat treatment on the electrical resistivity of near-eutectic Sn-Ag-CuPb-free solder alloys

The electrical resistivity of solder joints prepared from Sn-Ag, Sn-Ag-Cu, and Sn-Ag-Cu-X alloys (where X = Co, Fe, or Bi) was characterized by a four-point probe technique and interpreted in terms of microstructure and composition. The resistivity is also reported of drawn solid wires of these alloys. The solder-joint samples were prepared by hand soldering to copper substrates and were electrically characterized over a temperature range from 293-423 K, covering the anticipated range of elevated-temperature operation for Pb-free solders. Selected joint specimens were measured before and after a 72-h heat treatment at 423 K. Metallographic inspection of the solder joints was performed to characterize coarsening effects and to determine the degree to which these changes affected electrical conduction.