H. Tanaka et al., Effects of reflow processing and flux residue on ionic migration of lead-free solder plating using the quartz crystal microbalance method, MATER TRANS, 42(9), 2001, pp. 2003-2007
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 ioni
c 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 k
mol m(-3) KNO3 solution. When using Sn-3.5 mass%Ag solder plating, reflow p
rocessing segregates the stable compound Ag3Sn layer and Sn layer. The Sn l
ayer selectively promotes the anode dissolution reaction, increasing the oc
currence of migration. When using Sn-9 mass%Zn solder plating, the Sn effec
tively prevents the excessive dissolution reaction of Zn, However, since re
flow processing causes each element to separate out, reflow processing less
ens the effectiveness of Sn, thus promoting the occurrence of migration. Th
e flux processing of lead-free solders suppresses anode dissolution and eff
ectively prevents the occurrence of migration. However, with Sn-9 mass%Zn,
the lowered adhesion between the flux film and the electrodes is a factor i
n speeding the growth of migration.