Effects of Reflow Processing and Flux Residue on Ionic Migration of Lead-Free Solder Plating Using the Quartz Crystal Microbalance Method

抄録

To investigate the ionic migration, quite a new measurement method has been developed by the authors, which enables real time monitoring of the growth process of ionic migration using a QCM (Quartz Crystal Microbalance). This research has focused on the QCM method to study the growth process of ionic migration in various types of lead-free solder plating and the effects of the reflow processing and flux residue of soldering processes. In addition, we investigated the anode dissolution characteristics of the elements in each type of solder alloy by measuring the current-potential curve in 0.1 kmol m⁻³ KNO₃ solution. When using Sn–3.5 mass%Ag solder plating, reflow processing segregates the stable compound Ag₃Sn layer and Sn layer. The Sn layer selectively promotes the anode dissolution reaction, increasing the occurrence of migration. When using Sn–9 mass%Zn solder plating, the Sn effectively prevents the excessive dissolution reaction of Zn. However, since reflow processing causes each element to separate out, reflow processing lessens the effectiveness of Sn, thus promoting the occurrence of migration. The flux processing of lead-free solders suppresses anode dissolution and effectively prevents the occurrence of migration. However, with Sn–9 mass%Zn, the lowered adhesion between the flux film and the electrodes is a factor in speeding the growth of migration.