Electronic Components and Technology Conference (ECTC), 2016 IEEE 66th

Effect of Epoxy Flux Underfill on Thermal Cycling Reliability of Sn-8Zn-3Bi LeadFree Solder in a Sensor Application

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


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.

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