Abstract
Soldering processes involving the use of Pb have been known and practiced for more than 5000 years. In 2000, the European Union imposed a ban on the use of Pb because of the fact that Pb is poisonous to humans. Consequently, attempts are being made worldwide to develop a Pb-free solder. Among the various Pb-free solders, the Sn–0.75wt%Cu (Sn-0.75Cu) solder is the suitable one from the viewpoint of cost. Moreover, its acoustic properties are superior to those of the other Pb-free solders. However, the Sn-0.75Cu solder has a few disadvantages: its joining strength is lower than that of the other solders, and its melting temperature is higher than that of the Sn-37wt%Pb (Sn–Pb) solder. Therefore, we have attempted to decrease the melting temperature and improve the joining strength of Sn-0.75Cu to match those of the Sn–Pb solder. It is well known that when Ga is added to a Sn-based alloy, the melting temperature of the alloy decreases. Moreover, Ga has superior wettability. Therefore, we added Ga to the Sn-0.75Cu solder in order to improve the joining strength and decrease the melting temperature of the solder. We observed that the melting temperature of Sn95.3Cu0.7Ga4 reduced to less than that of the Sn–Pb solder. We also investigated the joining strength between the Ga-added solder and a Cu wire. We observed that the joining strength increased with an increase in Ga content, was the highest for Sn97.3Cu0.7Ga2, and then decreased with an increase in Ga content. The peak joining strength of the Ga-added solder was almost 1.5 times that of the Sn-0.75Cu solder. However, the brittleness of the solder increased with an increase in the Ga content. This is a disadvantage of the addition of Ga to Sn.
Published Version
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