In Situ Study the Grooving Effect Induced by Ag Particles on Rapid Growth of Cu6Sn5 Grain at Sn-xAg/Cu Soldering Interface during the Heat Preservation Stage
Round 1
Reviewer 1 Report
Thanks for sharing your research. Although the experimental and characterization techniques were adequate for your research, I have some comments on the presentation of the experimental research as well on the analysis and discussion, as follows.
The main topic presented in the work title deals with the use of Ag nanoparticles during growth of Cu6Sn5 grain at Sn-xAg/Cu soldering interface.
However, there is no presentation of characterization of those nanoparticles, that could help in following the kinetics of phase transformations during solidification. I would like to see also photomicrographs of Ag nanoparticles, becuse I only see micron sizes Ag particles. This can be done at the beginning of the description of the experimental techniques.
During discussion of experimental results, it will be useful also to make a presentation of the sequence of formation of the intermetallics precipitating during solidification.
This will be helpful to understand precipitation kinetics
Author Response
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Reviewer 2 Report
In this paper, the authors studied the kinetics of intermetallic phase formation at the interface of lead-free solder alloys with a Cu substrate. The results of Sn-1Ag and Sn-3.5Ag solders have been compared with pure Sn. The rate constants were found to increase with increasing Ag addition. The paper is interesting; however, it requires a major revision before being reconsidered for possible publication in Metals.
1.The entire chapter 3.1 is introductory. As such, it should be integrated into the Introduction.
2.The authors claim that they observed Ag nanoparticles in the solder alloy (see the title). However, their presence has not been experimentally confirmed. The resolution of SEM is insufficient to confirm such a small particle size (Figs. 3, 5). You need to include an experimental proof of their existence, e.g., an HR TEM image. Otherwise, you cannot make such claims.
3.The IMC layer has a scallop shape (Figs. 3, 5). Therefore, the kinetic curves in Fig. 4 must include error bars.
4.The labeling of Fig. 5 must be improved. The letters a), b), c), etc. are very dark. It is difficult to read them on a dark background. Use white lettering instead.
5.The rate constants in Table 1 should be rounded to two decimals.
6.The experimentally determined activation energies for the growth of Cu6Sn5 (Table 1) seem to be very low. They should be compared with previous reports, for example, http://dx.doi.org/10.1007/s11664-997-0268-4, http://dx.doi.org/10.1007/s11661-010-0592-9, http://dx.doi.org/10.1016/j.jallcom.2011.03.164. Any difference should be sufficiently discussed.
7.A thin Cu3Sn interlayer is usually observed between the Cu substrate and Cu6Sn5, see the above papers. Have you observed any Cu3Sn in the present study?
8.The identity of the intermetallic phases should be experimentally verified. You should provide an XRD pattern. Furthermore, the specimen should be inspected via EDS. Please provide an EDS line-scan for Cu and Sn across the interface.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thanks for your response about my main observation on your paper. I hope you can give a brief explanation about the necessity for future wor. in the revised version of your paper.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
The authors answered most of my previous comments. The paper has been greatly improved. However, one major issue remains to be addressed sufficiently. If this issue (the size of Ag particles) is resolved, the paper can be accepted for publication. The following comments should be considered:
1.The authors continue claiming that they observed Ag nanoparticles in their solders (see lines 200, 299, schematic figures 9, 10, etc.). However, the particle size has not been experimentally verified. In the cover letter to the revised version, they even claim that they observed Ag atoms (!) in the solder and estimate their size to be 0.144 nm (!). Such claims are not supported by any experimental evidence. You must provide solid experimental evidence that such a small particle size has been observed. You must inspect the specimen by HR TEM to confirm such a small particle size. If you don’t have any experimental evidence, you cannot claim that nanoparticles have been observed. You may use the term “Ag microparticles” or simply “Ag particles” instead. For such statements, the presented XRD results and SEM/EDS analyses are sufficient. Please correct your statements or provide a solid experimental proof of the nanometer size.
2.Include the powder diffraction file numbers of the identified phases in X-ray diffractograms (Fig. 3).
Author Response
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Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
The paper is acceptable for publication.
