Solder, solder paste and soldering method

Abstract

Disclosed are a solder and a solder paste used for soldering an electronic part to a circuit board. This solder comprises 2.0 to 3.5 wt % of Ag, 5 to 18 wt % of Bi and Sn for the rest. Alternatively, it further contains at least one element selected from the group consisting of 0.1 to 1.5 wt % of In, 0.1 to 0.7 wt % of Cu and 0.1 to 10 wt % of Zn.

1 . A solder comprising 2.0 to 3.5 wt % of Ag, 5 to 18 wt % of Bi and Sn for the rest.  
     
     
         2 . A solder comprising 2.0 to 3.5 wt % of Ag, 5 to 18 wt % of Bi and further comprising at least one element selected from the group consisting of 0.1 to 1.5 wt % of In, 0.1 to 0.7 wt % of Cu and 0.1 to 10 wt % of Zn, along with Sn for the rest.  
     
     
         3 . A solder paste comprising a flux composed of at least rosin, an activator, a thixotropic agent and a solvent, and a powder of a solder, characterized in that said solder comprises 2.0 to 3.5 wt % of Ag, 5 to 18 wt % of Bi and Sn for the rest.  
     
     
         4 . The solder paste in accordance with    claim 3   , wherein said solder further comprises at least one element selected from the group consisting of 0.1 to 1.5 wt % of In, 0.1 to 0.7 wt % of Cu and 0.1 to 10 wt % of Zn.  
     
     
         5 . A soldering method by a reflow soldering technique using the solder paste in accordance with    claim 3   , characterized in that immediately after a passage of a soldering object with said solder paste through an area showing a peak temperature in a reflow furnace, it is cooled at a cooling rate of about 10° C./sec or more.  
     
     
         6 . A soldering method by a reflow soldering technique using the solder paste in accordance with    claim 4   , characterized in that immediately after a passage of a soldering object with said solder paste through an area showing a peak temperature in a reflow furnace, it is cooled at a cooling rate of about 10° C./sec or more.