Method for step-soldering

A method for step-soldering, the method comprising:

• applying a first solder alloy having a melting point in a temperature range from 160 to 210° C. to a jointed portion of a first electronic component and a substrate, and heating them in the temperature range from 160 to 210° C.;
• and
• applying a second solder alloy having the melting point in a temperature range lower than 160° C. to a joint portion of a second electronic component and the substrate to which the first electronic component is joined, and heating them in the temperature range lower than 160° C.,
• wherein, the heating of the temperature range from 160 to 210° C., the first solder alloy, the first electronic component and the substrate is heated 5 to 20° C. higher than a liquidus temperature of the first solder alloy,
• wherein, in the heating of the temperature range lower than 160° C., the second solder alloy, the second electronic component and the substrate is heated 5 to 20° C. higher than a liquidus temperature of the second solder alloy,
• wherein the method further comprising cooling at 2-3° C./sec the first solder alloy, the first electronic component and the substrate after the heating of the temperature range from 160 to 210° C. and before the heating of the temperature range lower than 160° C., and
• wherein the first solder alloy consists of 13-22 mass % of In, 0.5-2.8 mass % of Ag, 0.5-5.0 mass % of Bi, 0.002-0.05 mass % of Ni, optionally at least one selected from P, Ge and Ga in total of 0.09 mass % or less, optionally 0.005-0.1 mass % of Sb and a balance Sn.