The Interface Microstructure and Shear Strength of Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints under Thermal-Cycle Loading

Round  1

Reviewer 1 Report

This paper is one of the better ones that summarize recent findings for SAC+Ni solders.  That said, lines 88-89 are very awkward and likely need revising.  Perhaps break the thought up into more than one sentence.  In Methods, the solder strip used was 0.1mm thick, how parallel was the seam after soldering?  Were measurements made to ensure the substrates surfaces were parallel after soldering?  This would have an effect on the shear force values.  It seems the Abstract & Conclusions don't match:  many times 0.05% Ni is indicated as the maximum concentration to see the Ni effect, but clearly data shows 0.1% has a similar effect.  In the Abstract and Conclusion section should agree on this point.  

Author Response

Response to Reviewer 1 Comments

Point 1: This paper is one of the better ones that summarize recent findings for SAC+Ni solders. That said, lines 88-89 are very awkward and likely need revising. Perhaps break the thought up into more than one sentence.

Response 1: Thank you for your high comments of this manuscript. The long sentence in lines 88-89 contains two different meanings, we have change it into two sentences.

Point 2: In Methods, the solder strip used was 0.1 mm thick, how parallel was the seam after soldering? Were measurements made to ensure the substrates surfaces were parallel after soldering? This would have an effect on the shear force values. It seems the Abstract & Conclusions don't match: many times 0.05% Ni is indicated as the maximum concentration to see the Ni effect, but clearly data shows 0.1% has a similar effect. In the Abstract and Conclusion section should agree on this point.

Response 2: In Methods, in order to keep the solder matrix parallel to the Cu substrates surfaces after soldering, special design and measurement for substrates and solder matrix were as follows: firstly, the thickness of the Cu substrate is 4 mm, and the thickness of soldering area is 2 mm, as shown in Figure 1 (a). The substrate surface for soldering was sanded with abrasive paper (#800, #1200, and #1500) and cleaned with acetone. Secondly, the final solder produced was rolled into 10 mm×20 mm×0.12 mm strips, then they were sanded with abrasive paper (1500 mesh), the final thick of the solder strips is 0.1 mm, it should be noted that the solder strip was always flat without fold during the process. Thirdly, the 0.1 mm thick solder strip was fixed between two Cu substrates, the solder strip was pressed by upper Cu substrate during soldering. The solder joint is flat as shown in figure 1(b), and the solder matrix surfaces were parallel to the substrate surfaces after soldering, eliminating the adverse effect on the shear force values of the solder joints.

Figure 1. Details of Cu substrate sample (a) and solder joint (b).

Point 3: It seems the Abstract & Conclusions don't match: many times 0.05% Ni is indicated as the maximum concentration to see the Ni effect, but clearly data shows 0.1% has a similar effect. In the Abstract and Conclusion section should agree on this point.

Response 3: We are agree with the opinion about the optimum Ni content, the optimum Ni content is 0.05 wt.%. Hence, Abstract and Conclusion section have been revised.

All the changes were colored in red which can be found in the revised manuscript.

Reviewer 2 Report

Dear Editor:           I would like to express my deep thanks for inviting me to review the manuscript ID: Metals- 488883

Title:                       The Interface Microstructure and Properties of  Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints under  Thermal Cycle Loading

Authors:                Congcong Cao, Keke Zhang, Baojin Shi, Huigai Wang, Di Zhao, Mengmeng Sun, Chao Zhang

Comments:

 Title

The Interface Microstructure and Properties of  Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints under  Thermal Cycle Loading

Replaced by

The Interface Microstructure and shear strength of Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints under Thermal Cycle Loading

Abstract:

“The interface microstructure and properties of Sn2.5Ag0.7Cu0.1RExNi/Cu solder----”.

Replaced by

“The interface microstructure and shear strength of Sn2.5Ag0.7Cu0.1RExNi/Cu solder----”.

Introduction part:

Please modify the first paragraph “Because of environmental concerns, the use of -------------- use has high Ag-content, and the joints reliability need to be improved. The micro alloying has been used to reduce the Ag-content and improve the joints reliability. Trace amounts of rare earth (RE)-------”

Replaced by

Because of environmental concerns, the use of Sn-Pb alloy has been gradually restricted for its toxicity, various types of environmental-friendly Sn-based alloys for example, Sn-3.0Ag-0.5Cu [1], Sn-35Bi-1Ag [2], Sn-14Bi-5In [3], Sn-0.7Cu [4], Sn-9Zn [5], Sn-8Zn-3Bi [6] and Sn-58Bi [7] have been introduced for the application of green electronic packaging systems. Among them, SnAgCu solder has been proposed as the most promising substitute for lead-containing solders because of its relatively low melting temperature, its superior mechanical properties. SnAgCu solder for commercial use has high Ag-content, and the joints reliability need to be improved [1]. Further, as the trend of electronic products is towards increased power, density, and reliability while being more functional, the quality and reliability of solder joints is facing challenges in the field of electronic packaging, where the joints have to endure extremely high temperature and stress generated by high current density in the complex circuitry [8]. In order to meet these needs, the development of environment-friendly, highly reliable lead-free solder has become one of the hot research topics in the field of micro-joining. To Improve the mechanical reliability Now a days, various types of nanoparticles such as Al, Rare earth (RE), Ni, Ag, Al₂O₃ TiO₂, ZrO₂, SiC, CeO₂ etc. were incorporated into solder materials to develop a composite solder for modification the solder material structure that influence on the physical and material properties [1,6, 9-11]. Trace amounts of rare earth (RE)----

1.        AK Gain, L. Zhang, Y. C. Chan, “Microstructure, elastic modulus and shear strength of alumina (Al₂O₃) nanoparticles-doped tin-silver-copper (Sn-Ag-Cu) solders on copper (Cu) and gold/nickel (Au/Ni)-plated Cu substrates” J Mater Sci: Mater Electron (2015) 26:7039-7048

2.        A.K. Gain, L. Zhang, Interfacial microstructure, wettability and material properties of nickel (Ni) nanoparticle doped tin-bismuth-silver (Sn-Bi-Ag) solder on copper (Cu) substrate, J. Mater. Sci.: Mater. Electron. 27, (2016) 3982-3994.

3.        F. Gnecco, E. Ricci, S. Amore, G. Borzone, R. Novakovic Wetting behaviour and reactivity of lead free Au–In–Sn and Bi–In–Sn alloys on copper substrates, International Journal of Adhesion and Adhesives 27(5) 2007, 409-416.

4.        AK Gain, L. Zhang, M.Z. Quadir Thermal aging effects on microstructures and mechanical properties of an environmentally friendly eutectic tin-copper solder alloy, Mater. Des. 110(15) 2016, 275-283

5.        H.R. Kotadia, P.D. Howes, S.H. Mannan, A review: On the development of low melting temperature Pb-free solders, Microelectron. Reliab., 54, 1253 (2014)

6.        AK Gain, L Zhang, Microstructure, thermal analysis and damping properties of Ag and Ni nano-particles doped Sn-8Zn-3Bi solder on OSP-Cu substrate, J. Alloys Compd. 617, (2014)779-786.

7.        AK Gain, L Zhang, Growth mechanism of intermetallic compound and mechanical properties of nickel (Ni) nanoparticle doped low melting temperature tin–bismuth (Sn–Bi) solder, Journal of Materials Science: Materials in Electronics, 27 (1), 2016, 781-794.

8.        Y.C. Chan, D. Yang, Failure mechanisms of solder interconnects under current stressing in advanced electronic packages, Prog. Mater Sci. 55, 428 (2010).

9.        A.K. Gain, L Zhang, Microstructure, mechanical and electrical performances of zirconia nanoparticles-doped tin-silver-copper solder alloys, J. Mater. Sci.: Mater. Electron. 27(7), (2016) 7524-7533.

10.     L Zhang, KN Tu “Structure and properties of lead-free solders bearing micro and nano particles” Mater. Sci.Eng.R 82,  (2014)1-32

11.     A.K. Gain, L. Zhang, Harsh service environment effects on the microstructure and mechanical properties of Sn-Ag-Cu-1 wt% nano-Al solder alloy, J. Mater. Sci.: Mater. Electron. 27(11), (2016) 11273-11283.

Please modify the third paragraph of introduction part (In practice, electronic products are usually------------------- compared with the commercial SAC305 solders

Please introduce novelty and aims of this section “RE and Ni are ----------------- and high reliability with lead-free solder”.

Therefore, we have chosen In–xBi as an alternative low-temperature

Replaced by

Therefore, in the present study, environment-friendly In–xBi solder alloys have been chosen as an alternative low-temperature

Experimental procedure part:

Please check this sentence “In and Bi used in this study were a commercially available pure metal sheet and shot, respectively”

Results and discussion:

(i)      Please add solder matrix SEM image in Figure 4.

(ii)     Please add EDS spectra in Figure 5.

(iii)   Please use different colour for each composition in Figure 9(a)

Conclusion part:

Please include interfacial IMC’s name in the conclusion part

RECOMMENDATION

After reviewing the enclosed manuscript for “Metals”, the present manuscript contains some kinds of scientific analysis but it is mandatory required to modify according to the preceding remarks. So, the manuscript can be accepted for publication after major mandatory revisions have been made.

Author Response

     Thanks very much for your comments, we have revised the manuscript  carefully. Detail are in the word.

Reviewer 3 Report

Please find the comments below.

 “... and the roughness and average thickness of the interfacial IMC layer reduced.”

Reading the abstract, it is a little bit confusing when you characterize the interfacial layers of a solder by the "roughness", because the roughness refers typically to the properties of a surface. You define the term in “Materials and Methods”, but maybe it is better to use other term to avoid such confusion. Please consider it.

“Figure 9. Relationship between shear strength and number of thermal cycles (a) and the IMC thickness and roughness (b). (a) Thermal cycles effect;(b) IMC d and IMC R effect”

Comment: There is no reason to double the information

Author Response

   Thanks very much for your comments, we have revised the manuscripts carefully. Detail are in the word.

Round  2

Reviewer 2 Report

Authors address all of my comments in the revised version manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round  1

Reviewer 1 Report

The manuscripts entitled “The Interface Microstructure and Properties of Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints under Thermal Cycle Loading” contains interesting results on microstructure and mechanical properties for thermo-physical properties for Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints with x=0-3.0 at.% under a various number of thermal cycles. There are, however, several major comments:

- Page 4, Line 134: an equation is not numbered and contains variable “Z_i” which is not identified.

- Figure legend for Figure 3 refers to an average thickness d and a roughness R, which are not presented in Figure 3.

- Figure 4 should contain SEM micrographs with higher magnification to show that the interface IMC layer consists of Cu6Sn5, Ni3Sn4 and Cu3Sn IMCs.

- Page 8, Line 250: for the first time it was mentioned that Cu atoms replace by Ni atoms in the Cu6Sn5 IMC forming (Cu,Ni)6Sn5 IMC; while XRD analysis provided for this sample has shown the formation of Cu6Sn5 and Ni3Sn4 IMCs.

Furthermore, authors published investigations of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints with x=0-1.0 at.% in the following papers:

(lit1) Zhang Keke, Guo Xingdong, Wang Huigai, Interfacial microstructure and mechanical properties of Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joint under thermal shock, Rare Metal Materials and Engineering, 46 (5) 2017 1353-1358.

(lit2) GUO Xing-dong, ZHANG Ke-ke, QIU Ran-feng, SHI Hong-xin, WANG Yao-li, MA Ning, Effect on interface and property of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints in severe thermal cycling, The Chinese Journal of Nonferrous Metals, 26(12) 2016 2573-2579.

These papers are not mentioned in the manuscript; while data published previously are in disagreement with the present results. For instance

-       according to (lit1) the average thickness of the interfacial IMC layer of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joint is about 2.25 mm, while is equal to about 3.8 mm in the present manuscript;

-       according to (lit2) the average thickness of the interfacial IMC layer of the Sn2.5Ag0.7Cu0.1RE/Cu solder joint after 100 thermal cycling is about 5.4 mm, while is equal to about 4.8 mm in the present manuscript

Therefore, it seems to be better to rewrite and resubmit the manuscript afterward.