| 摘要 |
The invention relates to a lead-free soft solder, especially for use in electronic and electrical engineering. The aim of the invention is to provide a lead-free soft solder which does not tend to form coarse tin dentrides, has a smooth and homogeneous surface once melted and is suitable for the use as BGA balls. This aim is achieved by using a lead-free Sn-Ag-Cu solder alloy which comprises a base alloy composed of 5.0 to 20% by weight silver, 0.8 to 1.2 %lt by weight copper, remainder tin and usual impurities. To this base alloy, 0.8 to 1.2% by weight indium and 0.01 to 0.2% by weight nickel, or instead of nickel either 0.01 to 0.2% by weight germanium or 0.01 to 0.2% by weight of one of the elements of the lanthanoids such as for example lanthane or neodym are added. The last-mentioned three variants may be combined with one another or each other in the form of a prealloy in such a manner that the sum thereof is 0.01 to 0.2% by weight.
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