M. Mostofizadeha, M. Najaria, L. Friska, D. Dasb and M. Pechtb
a Department of Electrical Engineering
Tampere University of Technology
Tampere, Finland
b CALCE, Center for Advanced Life Cycle Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20740, USA
Abstract:
The use of sensors has significantly increased in both
domestic and industrial applications. In some applications, the
sensor component is used along with a heat-sensitive
component; therefore, the attachment process using common
lead-free solders that have high melting temperature (e.g., SnAg-Cu,
Tm = 217 °C) may be challenging. Among lead-free
solders with low melting temperature, Sn-8%Zn-3%Bi (wt.%),
lead-free solder has a rather similar melting temperature to
that of typical Sn-Pb solders. In addition, it offers good
mechanical properties. However, the presence of Zn makes it
prone to oxidation especially at high temperatures. In this
paper, the reliability of sensor attachments using Sn-8%Zn-
3%Bi solder and epoxy flux underfill was studied under
thermal cycling. Thermal cycling results showed that the
lifetime of the lead-free solder joint was lower than that of the
Sn-Pb-2Ag solder joints. Failure analysis revealed that the
dominant failure mode in lead-free samples was delamination
of the sensor pad. In contrast, the failure mode of Sn-36%Pb-
2%Ag samples was fatigue crack inside the solder.
Additionally, it was found that Sn-Zn-Bi lead-free solder was
compatible with epoxy flux underfill.
This article is available online here and to CALCE Consortium Members for personal review.