A solder paste using a Sn-Ag base, Sn-Cu base, or similar alloy powder has a high melting point, so it causes thermal damage to electronic devices. Sn-Ag-In base lead-free solder alloys having a low melting temperature have been studied, but they are difficult to use because they cause much occurrence of chips standing up during reflow.
The present invention forms a solder paste by separating a Sn-Ag-In base lead-free solder into first and second solder alloy powders for which the difference in their peak temperatures measured by differential thermal analysis is at least 10°C and blends the mixed powders with a flux.