Solder paste

摘要

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.

主权项

1. A lead-free solder paste comprising a first solder alloy powder of a first solder alloy, a second solder alloy powder of a second solder alloy, and a flux mixed with the first and second solder alloy powders, wherein the main peak temperature of the first solder alloy measured by differential thermal analysis is at least 10° C. lower than the main peak temperature of the second solder alloy measured by differential thermal analysis, the first solder alloy has a composition consisting of 3-4 mass % of Ag, 12-20 mass % of In, 0-1 mass % of Bi, and a balance of Sn, the second solder alloy has a composition consisting of 3-4 mass % of Ag, 0-1 mass % of Cu, 0-1 mass % of Bi, and a balance of Sn, and the overall composition after melting of the first and second solder alloy powders consists of 3-4 mass % of Ag, 3-10 mass % of In, 0-1 mass % of Bi, 0-1 mass % of Cu, and a balance of Sn.