Patent ID: 9301403
Filing Date: 2016-03-29
CPC Classification: B23K,C22C,H01L,H05K

Claim Text:
1. A method of soldering an electronic part by two steps of high- and low-temperature soldering in a reflow process employing at least two kinds of solders having different reflow temperatures, characterized in that; high-temperature soldering as the former step is carried out by employing a solder cream obtained by kneading an Sn—Ag—Cu alloy with a flux, wherein the Sn—Ag—Cu alloy comprises a mixture of a first powder alloy for a high melting point and a second powder alloy for a low melting point, the first powder alloy comprises 10 to 30% by weight of Ag and 2 to 20% by weight of Cu with a balance consisting of Sn and unavoidable impurities, the second powder alloy comprises smaller compositions (% by weight) of Ag and Cu than the first powder alloy and having a melting point lower than that of the first powder alloy and, the mixture contains a total of not more than 35% by weight of Ag and Cu, and further, the total amount of Ag component in the alloy composition of the mixture after melting is more than 10% by weight, and whereafter low-temperature soldering as the latter step is carried out by employing a solder cream obtained by kneading the second powder alloy with a flux.