Lead-free solder alloy, connecting member and a method for its manufacture, and electronic part

Abstract

A lead-free solder which can reduce the occurrence of voids and a connecting member which uses the solder and has excellent adhesion, bonding strength, and workability are provided. The lead-free solder alloy has a composition consisting essentially of Sn: 0.1-3% and/or Bi: 0.1-2%, and a remainder of In and unavoidable impurities and has the effect of suppressing the occurrence of voids at the time of soldering. The connecting member is prepared by melting the lead-free solder alloy, immersing a metal substrate in the melt, and applying ultrasonic vibrations to the molten lead-free solder alloy and the metal substrate to form a lead-free solder alloy layer on the surface of the metal substrate. A heat sink and a package are soldered to each other through this connecting member by reflow heating in the presence of flux.

1 - 6 . (canceled) 
     
     
         7 . A lead-free solder alloy consisting essentially of (A) at least one of Sn: 0.1-3 mass % and Bi: 0.1-2 mass %, and (B) a remainder of In and unavoidable impurities. 
     
     
         8 . A connecting member comprising a metal substrate and a layer of a lead-free solder alloy as claimed in  claim 7  formed on at least connection regions of the metal substrate. 
     
     
         9 . A connecting member as claimed in  claim 8  wherein the metal substrate has a chemical composition with a Cu content of at least 95 mass %. 
     
     
         10 . A manufacturing method for a connecting member comprising immersing a metal substrate in a molten lead-free solder alloy as claimed in  claim 7  to form a lead-free solder alloy layer on at least connection regions of the metal substrate. 
     
     
         11 . An electronic part comprising a connecting member as claimed in  claim 8 , and a first member and a second member each contacting a connecting region of the connecting member, wherein the first member and the second member are connected through the connecting member by reflow heating of the connecting member, the first member, and the second member in the presence of a flux. 
     
     
         12 . An electronic part as claimed in  claim 11  wherein the connecting member is connected to the first member and to the second member by joints having a voids rate as defined below of at most 33.0%.
 Voids rate: A solder alloy sheet to be tested having a thickness of 100 μm and measuring 5 mm×5 mm which is sandwiched between electroless nickel and gold plated lands each measuring 5 mm×5 mm after flux is applied to the lands is subjected to reflow heating with a reflow profile having a peak temperature of 160° C. and then the proportion of the area of voids with respect to the area of the lands is measured 3 times using an X-ray inspection apparatus (TOSMICRON 6090 FP made by Toshiba IT & Control Systems Corporation), the average of 3 measurements being made the voids rate.