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Copyright © 2011, Emerald Group Publishing Limited
Article Type: Editorial From: Soldering & Surface Mount Technology, Volume 23, Issue 3
As highlighted in my editorial for the last issue of Soldering & Surface Mount Technology, there is much work being undertaken globally to address the performance of lead-free alloys via the addition of nanoparticles and, in this issue of the journal, there are two papers detailing research in this important area. Molybdenum has one of the highest melting points of all the elements and is normally found in applications that take advantage of its high thermal stability. However, in the paper by M.M. Arafat, A.S.M.A. Haseeb and Mohd Rafie Johan, the results of a study to investigate the influence of molybdenum nanoparticles on the dissolution of copper and the formation of interfacial intermetallic compounds are reported. The findings indicated that the presence of molybdenum nanoparticles had an influence in slowing the rate of copper dissolution and the growth of the IMC layer.
One of the key issues often raised when traditional lead-based solders were being replaced by SAC alloys was their inferior wetting properties compared to tin-lead. Again, there has been much work over the years to improve the wetting properties of SAC alloys by a variety of means and, in the second paper of the issue, K. Bukat, M. Kościelski, J. Sitek, M. Jakubowska and A. Młożniak report the effects of adding silver nanoparticles on the wettability of SAC solder pastes and the subsequent solder joint microstructure on copper. Perhaps, not surprisingly, the use of silver nanoparticles in SAC solder paste resulted in better wetting properties on copper. The results also indicated that, by using SAC solder paste with added silver nanoparticles, it might be possible to improve the reflow soldering process and to lower soldering temperatures.
There are still many reliability concerns and questions to be answered regarding the use of lead-free alloys, particularly in applications requiring the assembly of BGAs. The paper by Jue Li, Hongbo Xu, Jussi Hokka, Toni T. Mattila, Hongtao Chen and Mervi Paulasto-Kröckel details an investigation into the reliability of SAC solder interconnections under different thermal shock loading conditions. Stress-strain analyses were performed to study the differences between different loading conditions. Crack growth correlations and lifetime predictions were performed. Using finite element analysis, the authors were able to make lifetime predictions for the solder interconnections exposed to thermal shock test conditions.
The fourth paper also has a focus on accelerated testing and, in this case, it is the well-established temperature humidity test at 85 °C and 85 per cent relative humidity that receives attention. This test has been widely used for several decades but, as components have become more reliable, there has also been a growth in the use of harsher test conditions that can cause failures on a shorter time scale. Nevertheless, the 85/85 test can still provide valuable information and, in the work reported by Johanna Virkki, Lauri Sydänheimo and Pasi Raumonen, modifications of the standard 85/85 test and the temperature cycling test have been investigated and suitable new test conditions proposed that are more suitable for the testing of tantalum capacitors. The 85/85 test was modified by adding a ripple voltage followed by a voltage off-period, while the temperature cycling test was modified by using an applied voltage during the test and then by shortening the testing time. Using these modified test conditions, it was possible to detect the failure mechanisms of tantalum capacitors faster and more accurately than when using standard accelerated test conditions.
When one considers surface mount technology, it is normal to assume that the solder joints between the components and the substrate will have been formed using a conventional reflow process. However, there are other soldering techniques that can be used and one such process makes use of lasers. In the fifth paper of this issue, Peng Xue, Song-bai Xue, Liang Zhang, Yi-fu Shen, Li-li Gao, Sheng-lin Yu, Hong Zhu, Zongjie Han and Yan Chen report the results of an investigation into the reliability during thermal cycling of fine pitch QFP lead-free solder joints formed by laser soldering.
The final paper of the issue is on tin pest, a subject that is still a concern for many people and especially those working on the production of lead-free electronics for use in harsh environments. Tin pest can be a real issue with the tin-rich lead-free solders that are now widely used in much of the world’s electronics production. Tin undergoes an allotropic transformation at temperatures below 13 °C and the resulting product has an increased volume that can have serious implications for solder joint reliability. Agata Skwarek, Marcin Sroda, Mariusz Pluska, Andrzej Czerwinski, Jacek Ratajczak and Krzysztof Witek report the results of a study into the occurrence of tin pest on the surface of tin-rich lead-free alloys.
I began this editorial by reiterating some comments from the previous issue and I am concluding in the same way by repeating my invitation for researchers to join our team of reviewers. The journal is always looking to add new expert reviewers and I would like to hear from readers with an interest in reviewing the papers submitted to Soldering & Surface Mount Technology. The journal now uses the online “ScholarOne Manuscripts” system for both paper submissions and their subsequent reviewing. Please visit the web site: http://mc.manuscriptcentral.com/ssmt for further information and to create a user account. As always, I welcome comments and feedback and can be contacted at: email@example.com