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Eutectic Sn-Bi solder has attracted a great deal of interest since it offers good reliability comparable to that of Sn-Pb solders. Additionally, the increasing need for low cost manufacturing processes, particularly in consumer electronics, has made it an interesting alternative. This paper presents reliability and microstructural studies of eutectic 42%Sn-58%Bi (wt.%) lead-free solder alloy. The reliability was investigated using two different accelerated environmental tests. The first test series was subjected to isothermal aging at 100°C, the second series was subjected to salt spray test to analyze corrosion resistance, and the last test series was exposed to a combination of both tests. To study the effect of salt spray and isothermal aging on the mechanical reliability shear test and drop test were performed on the samples. A failure analysis was conducted and different types of failure modes were extracted. In addition, the effect of IMC types and growth on the mechanical strength of the solder joints was investigated.

Φ Abstract --This article describes observations about power MOSFET failures and degradation experienced during accelerated testing involving high temperature and high humidity stresses. The examined power MOSFETs were operated in commercial variable speed drives in flyback transformer topology as power switches. Known power MOSFET failure mechanisms are summarized and electrical stresses typical for the flyback topology are reviewed. In addition, effects of electrical stresses due to power interruptions were studied. The power MOSFET failure analysis results are presented. The visual appearance of the samples with catastrophic damage was examined with such analysis methods as X-ray, acoustic microscopy (SAM) and optical microscopy. The samples with no obvious failures were also analyzed in research for electrically measurable failure precursor parameters to characterize the physical degradation of the devices. Under these test circumstances, the power MOSFET channel off-resistance R DS-off was discovered to have degraded. This resistive leakage phenomenon was also visualized with backside OBIRCH technique.

Low-cost manufacturing in the electronics industry is becoming more demanding, particularly in the production of consumer electronics. Such manufacturing processes require reliable and low-cost lead-free solders. Among the low-temperature lead-free solders, eutectic Sn-Bi solder attracts a great deal of interest as it offers good reliability compared with that of Sn-Pb solders. In this paper, the reliability of eutectic 42%Sn-58%Bi (wt.%) lead-free solder is studied using combinations of environmental tests such as thermal aging (TA) at 100°C, salt spray test (SST), and a sequential combination of TA and SST. Microstructural studies on the samples are performed at different time intervals. To study the effect of salt spray and TA on the mechanical reliability, drop testing is performed on the samples. Failure analysis is conducted after different tests. Marked corrosion is seen after the SST. This also has a considerable effect on the impact strength of the solder interconnections. TA increases the thickness of the intermetallic layers, which is found to affect the drop performance.Index Terms-Corrosion, drop performance, microstructure, Sn-58Bi lead-free solder.

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