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A lead-free solder paste suitable for reflow soldering includes a plurality of different types of metal powder mixed with a flux. One of the metal powders is a Sn alloy powder. Another of the metal powders is selected from a Sn alloy powder, elemental Ag powder, elemental Cu powder, and elemental Sn

A lead-free solder paste suitable for reflow soldering includes a plurality of different types of metal powder mixed with a flux. One of the metal powders is a Sn alloy powder. Another of the metal powders is selected from a Sn alloy powder, elemental Ag powder, elemental Cu powder, and elemental Sn powder. Each Sn alloy powder includes 0-8 mass % of Ag, 0-5 mass % of Cu, and at least 80 mass % of Sn. The plurality of metal powders have a composition when melted of 1-5 mass % Ag, 0.5-3 mass % Cu, and a remainder of Sn.

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1. A method of soldering a surface mounted device comprising performing reflow soldering using a lead-free solder paste including a plurality of different types of metal powder mixed with a flux, one of the metal powders being a Sn alloy powder, another of the metal powders being selected from a Sn

1. A method of soldering a surface mounted device comprising performing reflow soldering using a lead-free solder paste including a plurality of different types of metal powder mixed with a flux, one of the metal powders being a Sn alloy powder, another of the metal powders being selected from a Sn alloy powder, elemental Ag powder, elemental Cu powder, and elemental Sn powder,each Sn alloy powder including 0-8 mass % of Ag, 0-5 mass % of Cu, and at least 80 mass % of Sn, the plurality of metal powders having a composition when melted of 1-5 mass % Ag, at least 0.5 and less than 3 mass % Cu, and a remainder of Sn, the reflow soldering including melting the plurality of metal powders in the solder paste. 2. A method as claimed in claim 1 wherein one of the metal powders comprises an elemental metal powder of Ag, Cu or Sn.3. A method as claimed in claim 1 wherein the plurality of metal powders have a composition when melted containing at most 1.0 mass % of Cu.4. A method as claimed in claim 1 including completely melting the plurality of metal powders in the reflow soldering.5. A method as claimed in claim 1 including completely melting the plurality of metal powders in a single reflow step.6. A method as claimed in claim 1, wherein the plurality of metal powders include two different Sn alloy powders.7. A method as claimed in claim 6 wherein the two Sn alloy powders contain the same components as each other in different proportions.8. A method as claimed in claim 6 wherein the plurality of metal powders include two different Sn?Ag?Cu alloy powders.9. A method as claimed in claim 6 wherein one of the metal powders is a Sn?Ag alloy powder and another of the metal powders is a Sn?Cu alloy powder.10. A method as claimed in claim 6 wherein the plurality of metal powders include a Sn?Ag alloy powder, a Sn?Cu alloy powder, and a Sn?Ag?Cu alloy powder.11. A method as claimed in claim 6 including performing the reflow soldering at a reflow temperature of at most 250° C.12. A method as claimed in claim 11 wherein the reflow temperature is at most 240° C.13. A method as claimed in claim 6 wherein the surface mounted device comprises a chip component.14. A method as claimed in claim 6 including printing the solder paste on a printed circuit board.15. A method as claimed in claim 6 wherein the plurality of metal powders have a composition when melted containing at most 1.0 mass % of Cu.16. A method as claimed in claim 6 including completely melting the plurality of metal powders in the reflow soldering.17. A method as claimed in claim 16 including completely melting the plurality of metal powders in a single reflow step.