Papers by Keyword: Solder Microstructure

Abstract: In this study the possibility to apply electrochemical impedance spectroscopy as an alternative method for the characterisation of the intermetallic microstructures of Sn-3.5Ag lead free solder samples was investigated. The aim of the study is to compare the electrochemical impedance spectra of solder samples, reflowed with different heat profiles. A quenching technique was applied in order to solidify the solder samples in cylindrical crucibles. Differences in the microstructures of the solidified alloys were achieved by changing the temperature of the quenching media. The molded and cross sectioned specimens were observed using both optical microscopy and scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). The microstructure of the ingots was revealed by selective electrochemical etching. The electrochemical impedance spectrum (EIS) was measured before and also after the selective etching process. The complex impedance spectra contain information regarding the characterized microstructure. Our aim is to determine quantitative parameters which are identical to the characteristics of the microstructure.

Abstract: The microstructure of the commonly used SnAgCu (SAC) lead free solder alloy was investigated. SAC solder bumps were soldered by two different soldering techniques (Vapor Phase Soldering (VPS), Laser reflow). Since the soldering profile of the VPS method is considerably different from the temperature profile of the laser reflow soldering, the created microstructures are expected to be diverse. Selective electrochemical etching was applied on cross sectional samples in order to extract the tin from the cross sectioning plane. In this manner the spatial structure of Cu₆Sn₅ and the Ag₃Sn intermetllic compounds (IMCs) was highlighted. The microstructures of the samples were analyzed with optical microscopy and Scanning Electron Microscope (SEM) on cross-section samples. The composing elements were identified by SEM-EDS.

Abstract: A tin-lead solder is generally used to mount an electronic package on to a printed circuit board (PCB) of an electronic devices. In this study, we investigated the microstructure of the solder joint from a four years old used mobile phone. Microstructure and morphology of the joint was obtained using optical and scanning electron microscopy (OM and SEM) respectively. Cracks and voids can clearly be seen in the solder area for the most of the sample observed. Crack up to 10 μm wide appeared to be propagating along the solder line between Cu lead and Cu substrate. Energy dispersive X-ray (EDX) analysis revealed that cracks occurred at the richer tin content. It was not clear the exact mechanism that leads to the existence of the crack. However we believe that thermomechanical cause such as thermal fatigue, void formation and the thicker layer of intermetallic compound contributed to the failure of the solder joint.