When soldering a package having an electrode on which Ni/Au or Ag—Pd alloy is plated, to a printed circuit board having a Cu electrode or an electrode on which Cu is plated, a solid-phase diffusion layer is formed within a layered solder material for bonding different species of electrodes. The layered solder material is composed of a solder material of Sn—Ag—Cu series or Sn—Sb series and a solder material of Sn—Ag—Cu—Ni series or Sn—Pb series. The electrode on which Ni/Au or Ag—Pd alloy is plated and the Cu electrode or the electrode on which Cu is plated are soldered with the solder material of Sn—Ag—Cu series or Sn—Sb series being attached to the Cu electrode and the solder material of Sn—Ag—Cu—Ni series or Sn—Cu series being attached to the electrode on which Ni/Au or Ag—Pd alloy is plated. This restrains formation of intermetallic compounds and provides high bonding reliability.