Newly developed real time monitoring system for ionic migration of lead-free solder by means of quartz crystal microbalance

To investigate the ionic migration, quite a new measurement method has been developed by the authors, which enables real timemonitoring of the growth process of ionic migration using a QCM (Quartz Crystal Microbalance). This research has focused on the QCM method to study the process of ion 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-/sup 3/ KNO/sub 3/ solution. When using Sn-3.5 mass%Ag solder plating reflow processing segregate the stable compound Ag /sub 3/Sn 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. In the end of this report the ionic migration of lead free solder in severe NOx circumstance will be commented.