Influence of Pretreatment Processes on Adhesion of Ni/Cu/Ni Multilayer on Polyetherimide Resin Reinforced with Glass Fibers
Round 1
Reviewer 1 Report
The authors investigate the influence of pretreatment processes of polyetherimide resin on the adhesion of Ni/Cu/Ni multilayer deposited by electroless plating. The following deficiencies must be corrected before publication:
1. “Modifyer A/B/C” agents used in pretreatment are quite undefined.
2. How was the layer thickness controlled in electroless plating? What were the deposition times? It should be defined for each layer. How did the authors determine the necessary deposition times?
3. Sputtering angle applied in XPS analysis should be given! Why did the authors mention that samples were analysed either at the surface or after sputter cleaning if they do not specify for XPS curves whether they were measured with or without surface sputter? They do not show any comparison with or without sputter clean spectra.
4. Eq.5: Gamma is only one surface energy! Which surface energy is gamma from the above three?
5. Figure4: The red illustration of contact angle is shifted compared to the image. In Figure9 put on a label to show which is the red and black line!
6. Figure7: The conclusions from SEM images are not acceptable: In plan-view images there are no sphere shaped particles. There is a continuous film. The globular shape of the top of columnar features can be observed. In cross sections the mentioned features cannot be identified due to bad quality cross section.
7. Regarding Figure8 they say “The chemical state of ions in the solution was changed by the observation of UV-vis spectra.” If they know that observation of UV spectra change the chemical state, why do they want to publish artefacts?
8. Line315:“The chemical composition of the initial Ni layer was composed of 71.6 wt% Ni, 18 wt% C, 315 5.9 wt% O and 4.5 wt% P (Fig. 6(d)).” Very high additive/contamination level. Can we still call it Ni layer? What is the source of the contamination? Especially the 18wt%C and 5.9wt%O. Due to low atomic weight of C and O, their concentration in at% is higher than 50at% together. It is unacceptable either as EDS composition measurement or as “Ni layer”
Based on these deficiencies the paper is not suitable for publication in the present form. Many other mistakes are pointed out in the attached pdf. Major review is necessary.
Comments for author File: 
Comments.pdf
Author Response
Reviewer #1
- “Modifyer A/B/C” agents used in pretreatment are quite undefined.
Answer: Because this is a commercial secret. These chemicals were purchased from the company.
- How was the layer thickness controlled in electroless plating? What were the deposition times? It should be defined for each layer. How did the authors determine the necessary deposition times?
Answer: The bath chemistry and deposition parameters were listed in Table 2. The thicken of the layer was controlled by the deposition time. The thickness of the initial electroless Ni layer was about 2 µm.
The thickness of the top-surface Ni layer was about 6 µm. In fact, the thickness of the top-layer was about 6.3 µm, observing by fracture of the samples. The necessary deposition time for electroless plating was dependable on the deposition rate.
- Sputtering angle applied in XPS analysis should be given! Why did the authors mention that samples were analysed either at the surface or after sputter cleaning if they do not specify for XPS curves whether they were measured with or without surface sputter? They do not show any comparison with or without sputter clean spectra.
Answer: We have asked Dr. Jun Jiang, who did help the XPS experiment. It should be 90o angle of the sputtering beam compared to the surface. However, we did not the sputter cleaning by Ar ions, these sentences have been deleted and improved.
- Eq.5: Gamma is only one surface energy! Which surface energy is gamma from the above three?
Answer: It should be the surface energy of the solid, the PEI substrate.
- Figure4: The red illustration of contact angle is shifted compared to the image. In Figure9 put on a label to show which is the red and black line!
Answer: Yes, all figures have been improved, and figure 9 is also improved according to the comment.
- Figure7: The conclusions from SEM images are not acceptable: In plan-view images there are no sphere shaped particles. There is a continuous film. The globular shape of the top of columnar features can be observed.In cross sections the mentioned features cannot be identified due to bad quality cross section.
Answer: Thanks! We have improved this sentence. At present, the characterization was limited due to the pandemics.
- Regarding Figure8 they say “The chemical state of ions in the solution was changed by the observation of UV-vis spectra.” If they know that observation of UV spectra change the chemical state, why do they want to publish artefacts?
Answer: We just want to what it was changed in solution, resulting in the change and failure of solution color.
- Line315:“The chemical composition of the initial Ni layer was composed of 71.6 wt% Ni, 18 wt% C, 315 5.9 wt% O and 4.5 wt% P (Fig. 6(d)).” Very high additive/contamination level. Can we still call it Ni layer? What is the source of the contamination? Especially the 18wt%C and 5.9wt%O. Due to low atomic weight of C and O, their concentration in at% is higher than 50at% together. It is unacceptable either as EDS composition measurement or as “Ni layer”
Answer: It should be Ni film layer. The signal of carbon element was taken from the PEI substrate due to the thin film with some microcracks, however, the oxygen element was done from the passive film in the air environment. Therefore, the weak corrosion process was used to remove the passive film.
Based on these deficiencies the paper is not suitable for publication in the present form. Many other mistakes are pointed out in the attached pdf. Major review is necessary.
- In line 31, change ‘using’ to ‘used’.
Answer: We have modified it.
- In line 64, change ‘exposed’ to ‘exposed to etching’.
Answer: We have modified it.
- In line 128, ‘Modifier A/B/C’ is a rather undefined agent.
Answer: This is a commercial secret. These chemicals were purchased from the company.
- In line 165, probably the authors wanted to say: ‘the surrounded Pd nuclei’ rather than ‘Pd nuclei surrounded’.
Answer: We have modified it.
- From line 169-177 and line 185-190, the reviewer asked: How did you control the thickness? What is the layer thickness?
Answer: The bath chemistry and deposition parameters were listed in Table 2. The thicken of the layer was controlled by the deposition time. The thickness of the initial electroless Ni layer was about 2 µm.
- From line 192-193, the reviewer asked: What is the resulted layer thickness?
Answer: The thickness of the top-surface Ni layer was about 6 µm. In fact, the thickness of the top-layer was about 6.3 µm, observing by fracture of the samples.
- In line 200, change ‘place’ to ‘placing’.
Answer: We have modified it.
- In line 201, change ‘smooth’ to ‘smoothing’.
Answer: We have modified it.
- In line 214, change ‘wereperformed’ to ‘were performed’.
Answer: We have modified it.
- In line 219, the reviewer asked: what was the angle of the sputtering beam compared to the surface?
Answer: We have asked Dr. Jun Jiang, who did help the XPS experiment. It should be 90o angle of the sputtering beam compared to the surface.
- In line 229, change ‘were’ to ‘was’.
Answer: We have modified it.
- In line 230, change ‘measured’ to ‘dropped’.
Answer: We have modified it.
- In line 231, change ‘by three’ to ‘three’.
Answer: We have modified it.
- In line 242, the reviewer asked: gamma is only one surface energy! Which surface energy is gamma from the above three?
Answer: It should be the surface energy of the solid, the PEI substrate.
- In line 255, change ‘improving’ to ‘improve’.
Answer: We have modified it.
- In line 264, change ‘was increased’ to ‘increased’.
Answer: We have modified it.
- In Figure 4, the red illustration of contact angle is shifted compared to the image.
Answer: We have modified the red illustration of contact angle in Figure 4.
- In line 315, the reviewer asked: Very high additive/contamination level. Can we still call it Ni layer? What is the source of the contamination?
Answer: It should be Ni film layer. The signal of carbon element was taken from the PEI substrate due to the thin film, however, the oxygen element was done from the passive film in the air environment.
- In line 331, the reviewer believes that there is a continuous film. The globular shape of the top of columnar features can be observed.
Answer: Thanks! We have improved this sentence.
- From line 334 to 337, the reviewer believes that features cannot be identified due to bad quality cross section.
Answer: At present, the characterization was limited due to the pandemics.
- From line 346-347, the reviewer believe that there is a lack of references.
Answer: We have added reference [43] to the article.
- In line 361, change ‘the yellow color’ to ‘yellow’.
Answer: We have modified it.
- From line 365-366, the reviewer asked: If you know that observation of UV spectra change the chemical state, why do you want to publish artefacts?
Answer: We just want to what it was changed in solution, resulting in the change and failure of solution color.
- In Figure 8, the reviewer asked why we called one of the sample ‘failed ’?
Answer: After a period, the function of the solution was disappeared, so we call the solution was failed.
- In Figure 9, the reviewer asked to put on a label to show which is the red and black line.
Answer: We have marked the legend in Figure 9.
Reviewer 2 Report
In my opinion, the manuscript entitled “Influence of pretreatment processes on the adhesion of Ni/Cu/Ni multilayer on polyetherimide resin reinforced with glass fibers” done by Xiaodong Xu, Dingkai Xie, Jiaqi Huang, Kunming Liu, Guang He, Yi Zhang, Peng Jiang, Lixin Tang, and Wangping Wu is publication worthy in Metals as it meets journal’s goals. The authors have presented an original investigation on metal coatings' development of polyetherimide substrates. And they have presented sufficient arguments that their technology works. However, before publication, some major corrections to the manuscript content have to be done.
Firstly, a logical layout of the manuscript, in a subsection of experimental is presented point by points steps, how to prepare the surface of a substrate for Ni/Cu/Ni coatings development. In my opinion, similarly can be presented characterization results in the subsection result and discussion that in the end a proper coating with good adhesion has been developed. In the present version of the manuscript, the subsection results and discussion starts with surface characterization probably by atomic force microscopy, technic that hasn’t been mentioned in the experiment, disclosing sandblasting's influence on surface roughness, and ends with a type peeling test. In this section, the same order of steps can be conserved, and finally in the end will be presented the main authors' finding on the coating adhesion strength. All used characterization technic have to be mentioned in the experimental section. It seems like the authors missed mentioning one point from the steps of the surface treatment as well. Presenting the EDS results, they refer to P content between lines 315 and 317. The question is on which of the stages the surface has been contaminated by P? And why it isn’t contaminated by Si at all after sandblasting? It has to be clarified.
The edition of Figures has to be improved. Many of them have moved layers and they are illegible! On some of them, a legend has to be introduced e.g., in Figure 5 are seen some polygons with any explanation! In Figures 10 b and d are seen two peaks from the Sn0 state in different energy. How it is possible to assign two different energies to one electronic state. They need to be distinguished. Between different Figures can be conserved lines color for the same states. In Figure 10a two of the peak are without explanation. Due to lack of peak consideration, the spectrum fit is poor in Figure 10c.
With any explanation of what is a modifier A, B, or C and corresponding conditions in Table1, this Table doesn’t introduce any valuable information!
In lines 102, 294 and 297 are mentioned grades of the adhesion scale. The experimental section should be introduced information, which allows readers to be more familiar with this scale. In this way, a reader can easily follow the authors’ ideas.
In line 101, what is the meaning of Ni/7.54μm Cu/Ni and Ni/58.6μm Cu/Ni
The meaning of sentences in line 180, between lines 269 and 272, from 275 to 269 and from 301 to 304, and many others are unclear. the English of the manuscript needs to be corrected by a native speaker.
Author Response
Reviewer #1
In my opinion, the manuscript entitled “Influence of pretreatment processes on the adhesion of Ni/Cu/Ni multilayer on polyetherimide resin reinforced with glass fibers” done by Xiaodong Xu, Dingkai Xie, Jiaqi Huang, Kunming Liu, Guang He, Yi Zhang, Peng Jiang, Lixin Tang, and Wangping Wu is publication worthy in Metals as it meets journal’s goals. The authors have presented an original investigation on metal coatings' development of polyetherimide substrates. And they have presented sufficient arguments that their technology works. However, before publication, some major corrections to the manuscript content have to be done.
Firstly, a logical layout of the manuscript, in a subsection of experimental is presented point by points steps, how to prepare the surface of a substrate for Ni/Cu/Ni coatings development. In my opinion, similarly can be presented characterization results in the subsection result and discussion that in the end a proper coating with good adhesion has been developed. In the present version of the manuscript, the subsection results and discussion starts with surface characterization probably by atomic force microscopy, technic that hasn’t been mentioned in the experiment, disclosing sandblasting's influence on surface roughness, and ends with a type peeling test. In this section, the same order of steps can be conserved, and finally in the end will be presented the main authors' finding on the coating adhesion strength.
Answer: Thanks for your comments. It is difficult to measure the surface roughness using AFM technique for the rough surface of PEI substrate, we just studied the effects of sandblasting and accelerations pretreatment processes on the adhesion of the Ni/Cu/Ni multilayer on PEI composite substrates, therefore in the subsection of results and discussion, a logical layout of the manuscript, we presented the effect of sandblasting, and then the effect of accelerator on the adhesion of the coating on PEI substrate. This logical layout also presented in the end of the introduction. Therefore, we want to keep the previous state.
All used characterization technic have to be mentioned in the experimental section. It seems like the authors missed mentioning one point from the steps of the surface treatment as well.
Answer: We have added all used characterization techniques in sub-section of experiments.
Presenting the EDS results, they refer to P content between lines 315 and 317. The question is on which of the stages the surface has been contaminated by P? And why it isn’t contaminated by Si at all after sandblasting? It has to be clarified.
Answer: Thanks! The signal of carbon element was taken from the PEI substrate due to the thin film, however, the oxygen element was done from the passive film in the air environment.
The edition of Figures has to be improved. Many of them have moved layers and they are illegible! On some of them, a legend has to be introduced e.g., in Figure 5 are seen some polygons with any explanation! In Figures 10 b and d are seen two peaks from the Sn0 state in different energy. How it is possible to assign two different energies to one electronic state. They need to be distinguished. Between different Figures can be conserved lines color for the same states. In Figure 10a two of the peak are without explanation. Due to lack of peak consideration, the spectrum fit is poor in Figure 10c.
Answer: Figures have improved, and figure 10 has been updated according to the comments.
With any explanation of what is a modifier A, B, or C and corresponding conditions in Table1, this Table doesn’t introduce any valuable information!
Answer: this is a commercial secret. These chemicals were purchased from the company.
In lines 102, 294 and 297 are mentioned grades of the adhesion scale. The experimental section should be introduced information, which allows readers to be more familiar with this scale. In this way, a reader can easily follow the authors’ ideas.
Answer: We have added table 3 in the experimental.
In line 101, what is the meaning of Ni/7.54μm Cu/Ni and Ni/58.6μm Cu/Ni
Answer: we have published one paper about the influences of copper interlayer thickness and heat treatment on the adhesion state of the multilayer coatings on the PEI substrate. Ni/7.54μm Cu/Ni and Ni/58.6μm Cu/Ni represent that two multilayer coatings were composed of nickel layer, copper interlayer with thickness of 7.54μm and 58.6μm Cu, and initial electroless nickel layer.
The meaning of sentences in line 180, between lines 269 and 272, from 275 to 269 and from 301 to 304, and many others are unclear. the English of the manuscript needs to be corrected by a native speaker.
Answer: we have carefully revised these sentences and the English in the manuscript.
Round 2
Reviewer 1 Report
The authors made some minor modifications, but ignored some major points. The paper is still not suitable for publication:
1. “Modifyer A/B/C” agents used in pre-treatment are quite undefined. The difference in their composition should be specified!
6. Figure7: In cross sections the mentioned features cannot be identified due to bad quality cross section. Fig7c was improved by relocation of the labels, but it is still not possible to recognize the deposited Ni/Cu/Ni triple structure. The meaning of the black line with arrows on both end is not clear. There should be a label. It is still not possible to recognize the deposited Ni/Cu/Ni triple structure in Figure 7d either. Nor possible to identify which part of Fig7c is magnified and the message from the higher magnification image is not specified.
7. Regarding Figure8 they say in line 366: “The chemical state of ions in the solution was changed by the observation of UV-vis spectra.” If they know that observation of UV spectra change the chemical state, why do they want to publish artefacts? To avoid this misunderstanding, the authors could write: “According to the observation of UV-vis spectra, the chemical state of ions in the solution was changed after 10 days in the air.” - If the authors mean that.
8. Line315:“The chemical composition of the initial Ni layer was composed of 71.6 wt% Ni, 18 wt% C, 315 5.9 wt% O and 4.5 wt% P (Fig. 6(d)).” Very high additive/contamination level. Can we still call it Ni layer? What is the source of the contamination? Especially the 18wt%C and 5.9wt%O. Due to low atomic weight of C and O, their concentration in at% is higher than 50at% together. It is unacceptable either as EDS composition measurement or as “Ni layer”
For this question the authors write in Line 315-316: “The signal of carbon element was taken from the PEI substrate due to the thin film, however, the oxygen element was done from the passive film in the air environment.” The second part of the sentence is not clear in English: “the oxygen element was done from the passive film in the air environment.” I suppose that he authors mean that the oxygen signal comes from surface oxide, and carbon signal from the substrate due to thin film. The surface oxide cannot give so high contribution. The nominal 2 micrometer film thickness is not very small compared to the excited volume. The excited volume can be decreased by decrease of acceleration voltage to avoid artefact. By the way, the acceleration voltage in SEM is not defined! Without avoiding the artefact, there is no sense publishing the EDS spectrum.
The high P content also should be explained: the P content is more than 10at% compared to Ni.
Based on these deficiencies the paper is not suitable for publication in the present form. Major review is necessary.
Author Response
- “Modifyer A/B/C” agents used in pre-treatment are quite undefined. The difference in their composition should be specified!
Answer: We have inquired some guys from Arf. Company, who used these chemicals to manufacture the electroless plating. Modifyer A/B/C, the pH value of the mixed solution was about 9-10. We could assess that this solution could modify the surface of the PEI substrate after etching, and might supply a positively charged group, which could be helpful to absorb the negatively charged Pd group. The difference in their composition is that Modifyer A is an alkaline solution, Modifyer B is a solution contained stabilizer, and Modifyer C is the complexing agent. For some special polymer composite materials, such as PEI and PI composite polymer materials, this step has to be done after etching process, to obtain much more Pd species for the next step-activation process. However, for metallization of ABS polymer materials after etching process, this step does not been done, directly to do the activation process. We can just support this information.
- Figure7: In cross sections the mentioned features cannot be identified due to bad quality cross section. Fig7c was improved by relocation of the labels, but it is still not possible to recognize the deposited Ni/Cu/Ni triple structure. The meaning of the black line with arrows on both end is not clear. There should be a label. It is still not possible to recognize the deposited Ni/Cu/Ni triple structure in Figure 7d either. Nor possible to identify which part of Fig7c is magnified and the message from the higher magnification image is not specified.
Answer: Thanks very much. It is clear that the fracture of the sample by mechanical machine was relatively rough, causing that it is difficult to observe the SEM images. Figure 7b and 7d in the previous manuscript has been deleted. At present, the SEM images are better.
- Regarding Figure 8 they say in line 366: “The chemical state of ions in the solution was changed by the observation of UV-vis spectra.” If they know that observation of UV spectra change the chemical state, why do they want to publish artefacts? To avoid this misunderstanding, the authors could write: “According to the observation of UV-vis spectra, the chemical state of ions in the solution was changed after 10 days in the air.” - If the authors mean that.
Answer: Yes, thanks! We have revised this sentence according to the comments of reviewer.
- Line315:“The chemical composition of the initial Ni layer was composed of 71.6 wt% Ni, 18 wt% C, 315 5.9 wt% O and 4.5 wt% P (Fig. 6(d)).” Very high additive/contamination level. Can we still call it Ni layer? What is the source of the contamination? Especially the 18wt%C and 5.9wt%O. Due to low atomic weight of C and O, their concentration in at% is higher than 50at% together. It is unacceptable either as EDS composition measurement or as “Ni layer”.
For this question the authors write in Line 315-316: “The signal of carbon element was taken from the PEI substrate due to the thin film, however, the oxygen element was done from the passive film in the air environment.” The second part of the sentence is not clear in English: “the oxygen element was done from the passive film in the air environment.” I suppose that he authors mean that the oxygen signal comes from surface oxide, and carbon signal from the substrate due to thin film. The surface oxide cannot give so high contribution. The nominal 2 micrometer film thickness is not very small compared to the excited volume. The excited volume can be decreased by decrease of acceleration voltage to avoid artefact. By the way, the acceleration voltage in SEM is not defined! Without avoiding the artefact, there is no sense publishing the EDS spectrum.
The high P content also should be explained: the P content is more than 10at% compared to Ni.
Answer: we have deleted this EDS spectrum in the manuscript. We think some impurity on the surface of the deposits. The P content is more than 10wt% compared to Ni, it is not at%. Electroless nickel alloy coatings. Acid bath: Ni–P alloy, 3–5% P (L), 6–9% P (M), 10–14% P (H).
Reference: Jothi Sudagar Jianshe Lian, Wei Sha.Electroless nickel, alloy, composite and nano coatings – A critical review. Journal of Alloys and Compounds, 571, 2013, 183-204.
Reviewer 2 Report
After reconsideration of the authors' corrections, there are two issues, which have to be solved before the publication of the article. The first is the unknown technique of surface imaging, presented in Figure 1. I had guessed that it was AFM, but it isn't. So, what was the technique used for surface imaging? It still needs an explanation. And the second question concerns the content of table 1 and surface modification by secret modifiers A, B, or C after each step of the process presented in Figure 2. Due to the authors' explanation, these modifications are crucial from the viewpoint of the success of the developed coating technology, and they must remain a secret of the company. Ok, I can understand that. However, from the viewpoint of the manuscript publication goals, this article says completely nothing as the secret modifications haven't been included even in the technological steps presented in Figure 2. Table 1 presents the percentage of fulfilling conditions, but it hasn't been said what kind of conditions have to be done. The authors should judge what can be said and what cannot. However, in my opinion, the presented compromise is not a good one.
Author Response
The first is the unknown technique of surface imaging, presented in Figure 1. I had guessed that it was AFM, but it isn't. So, what was the technique used for surface imaging? It still needs an explanation.
Answer: The two-dimensional drawing of figure 1 about PEI composite substrate was figured by auto-CAD software. I think that reviewer means figure 3, which is measured by a surface profilometer (BRUKER ContourGT K0) with a 12.5 µm radius tip, in order to obtain the surface roughness. It is not AFM technique.
And the second question concerns the content of table 1 and surface modification by secret modifiers A, B, or C after each step of the process presented in Figure 2. Due to the authors' explanation, these modifications are crucial from the viewpoint of the success of the developed coating technology, and they must remain a secret of the company. Ok, I can understand that. However, from the viewpoint of the manuscript publication goals, this article says completely nothing as the secret modifications haven't been included even in the technological steps presented in Figure 2. Table 1 presents the percentage of fulfilling conditions, but it hasn't been said what kind of conditions have to be done. The authors should judge what can be said and what cannot. However, in my opinion, the presented compromise is not a good one.
Answer: This step has been included in the process step in Figure 2, surface neutralizing. This mixed solution could modify the surface of the PEI substrate after etching, and might supply a positively charged group, which could be helpful to absorb the negatively charged Pd group. Modifyer A/B/C, the pH value of the mixed solution was about 9-10. For some special polymer composite materials, such as PEI and PI composite polymer materials, this step has to be done after etching process, to obtain much more Pd species for the next step-activation process. However, for metallization of ABS polymer materials after etching process, this step does not been done, directly to do the activation process.
Round 3
Reviewer 1 Report
I acknowledge the changes and explanations that the authors made.
I recommend to specify the applied acceleration voltage in SEM.
Author Response
Thanks for your reviewer.
The microstructure and morphology of the surface and cross-section of the deposits were observed by a scanning electron microscopy (SEM, Zeiss-Supra55), the scanning rate was set to 40 s at an operating voltage of 10 kV.Reviewer 2 Report
Due to changes done by the authors, I accept the manuscript at present form.
Author Response
Thanks for the reviewer.
