A comparative study of silver-epoxy and tin-lead solder in their joints with copper was made through simultaneous mechanical and electrical measurements during debonding. Silver-epoxy joints to copper abruptly increased in contact electrical resistivity upon completion of shear debonding, whereas tin-lead soldered joints to copper did not, due to the higher ductility of solder compared to silver-epoxy. The contact resistivity before debonding was higher for silver-epoxy than solder. Cleansing of the copper surface was essential for silver-epoxy, but not for solder. Acetone washing of copper surface helped silver-epoxy joints, but not soldered joints. Acid washing helped soldered joints more than acetone washing, but helped silver-epoxy joints to the same extent as acetone washing.