Development of a Highly Densified Magnetic Sheet for Inductors and Advanced Processes through Silane Surface Treatment of Fe Nanopowder

Round 1

Reviewer 1 Report

Dear Authors,

I have found your manuscript quite readable with effort. The scientific content is quite ok, albeit you said you have used several methods of characterization but we see few measurements. The manuscript can be highly improved, due to the good experimental results in the pre-industrialization production of magnetic thin sheet.

I strongly suggest a second round of thinking on how to put together your results and to improve the text. A good, readable text will help to understand better your progress.

At the bottom you will find my most serious comments, for the moment I wish you to see you seen with an improved version of your manuscript.

Here my suggestions:

1. abstract: in 3 lines you repeat "improve" 3 times. Honestly I did not read beyond the third time.
2. Line 30: I do not believe that mobile phones and TV are miniaturing. I would say, the electronic components TV and phone are squeezing down the dimension to ... (complete as you wish)
3. Line 34, please, specify who is "the company".
4. Line 36, who/what is divided in ferrite and etc etc ?
5. Line 39, who/what high current stability deteriorates?
6. Lines 38-41, please reformulate, the use of "however" does not make sense.
7. Lines 48-51, I understand what you mean, but it is written very chaotically. Please, reformulate.
8. Here I stop with the english, sorry, It will be too huge revision. If you have an english colleague I suggest you to ask help from him/her. In the specifically, Dr Dong-Hyun Kim being in an international company can ask help from someone in USA to patch the english text.
9. You miss to say that the nanopowder is passivate with -OH. In Figure 1, the H does not give 2 bonds, indeed you claim you have hydrogen bonds, therefore make a correct figure. Chemistry does matter.
10. Lines 67-70: I do not understand how you did, what you did, and why it is the most accurate method.
11. Lines 82-87, I think I have understood what you mean, but other less-proficient English speakers will not understand.
12. Pag 4, top table, who is μ ?
13. Figure 4, subfigure e) and i) are identical.
14. Lines 103-104: where are the theoretical results?
15. How did you measure the demagnetization field?
16. figure 6. Are you sure the sizes are in inch? 3225 inches are approximately 82 m.
17. figure 7, μ is a relative measurement to what?
18. Can you specify which the total thickness of the film (substrate+magnetic thin film) ?
19. Do you notice cracks in the film to accomodate the large difference in density as one can see in table 2?
20. Conclusion? I find the conclusion too short to grab a minimal information of what you did. Readers read the abstract, introduction, and conclusion to estimate whether the manuscript is worth to be read. Please, extend it.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 1 Comments

 

The authors would like to express our wholehearted thanks to both the Editor and Reviewer for giving the valuable suggestions/comments regarding our paper. These reviews have been very helpful in enhancing our paper. Based on the comments and suggestions, the revised manuscript was prepared. Below is a detailed discussion of the changes we have made to address the reviewer comments. And the parts you mentioned are marked with red color words and gray highlights.

Point 1 abstract: in 3 lines you repeat "improve" 3 times. Honestly I did not read beyond the third time.

 

Response 1: We carefully checked the manuscript, and deleted repetitive words. Abstract are described concisely as shown in bellow sentences.

 Abstract: For developing subminiature and highly integrated multilayer inductors, soft magnetic powder has been used; however, its ferrite magnetic component is characterized by high resistivity and reduced direct current saturation, leading to the deterioration of the inductor under high currents. Therefore, herein, to improve the electromagnetic properties of thin-film inductors, Fe nanopowder was used to increase the volume fraction of magnetic sheets. Surface treatment was performed using silane coupling agents, which improved the bonding strength and dispersibility of the Fe nanopowder with a heterogeneous epoxy binder. For uniform surface treatment on the nanopowder, the silane-treated powder was aged for 24 h at a temperature of 3 °C. The surface-treated Fe nanopowder was used with a mixing ratio of the soft magnetic powder (coarse:fine:nano) of 7:2.5:0.5 wt%; this was successful in producing a flexible and highly densified magnetic sheet. As a result, the volume fraction of the magnetic sheet for thin-film inductors to which a low-temperature aging-treated nanopowder was applied was significantly improved.

 

Point 2: Line 30: I do not believe that mobile phones and TV are miniaturing. I would say, the electronic components TV and phone are squeezing down the dimension to ... (complete as you wish)

Response 2: As reviewer’s comment, we edit the sentence as below.

Miniaturization of electronic components

Point 3: Line 34, please, specify who is "the company"

Response 3: As reviewer’s comment, we edit the sentence correctly.

electronics component companies

Point 4: Line 39, who/what high current stability deteriorates?

Response 4: As reviewer’s comment, we edit the sentence correctly.

For this reason, the high current stability of the multilayer power inductor is deteriorated.

Point 5: Line 36, who/what is divided in ferrite and etc etc ?

Response 5: As reviewer’s comment, we edit the sentence as below.

Soft magnetic powder used as a material for multilayer power inductors is divided into ferrite and metal composites.

Point 6: Lines 38-41, please reformulate, the use of "however" does not make sense.

Response 6: As reviewer’s comment, we edit the sentence correctly.

In addition, the DC saturation characteristics are reduced due to its low saturation magnetization properties. For this reason, the high current stability of the multilayer power inductor is deteriorated. However, metal composites show low hysteresis losses with low coercive force and high stability at high currents.

Point 7: Lines 48-51, I understand what you mean, but it is written very chaotically. Please, reformulate.

Response 7: As reviewer’s kindly comment, we edited the sentence concise and factually.

Three kinds of powders were used to prepare a magnetic sheet. Fe-6.5 wt% Si powder (average particle size = 40 µm) manufactured by Atmix Inc. and fine iron powder (average particle size = 3 µm) were used as raw materials, and Fe nanopowders (average particle size = 100 nm) were used to effectively fill the void space between the coarse Fe-6.5 wt% Si powder and fine iron powder.

Point 8: Here I stop with the english, sorry, It will be too huge revision. If you have an english colleague I suggest you to ask help from him/her. In the specifically, Dr Dong-Hyun Kim being in an international company can ask help from someone in USA to patch the english text.

Response 8: As reviewer’s kindly comment, the manuscripts are huge revision. And we are enclosed the "CERTIFICATE OF ENGLISH EDITING"

Point 9: You miss to say that the nanopowder is passivate with -OH. In Figure 1, the H does not give 2 bonds, indeed you claim you have hydrogen bonds, therefore make a correct figure. Chemistry does matter.

Response 9: We carefully checked the manuscript, and corrected the part of the picture you pointed out. For more information, please check the attached file.

Point 10: Lines 67-70: I do not understand how you did, what you did, and why it is the most accurate method.

Response 10: We carefully checked the manuscript, deleted sentences that are difficult to understand.

The most accurate method is to prepare the magnetic sheet, print the internal electrodes, and then analyze the electromagnetic characteristics of the power inductor through lamination and sintering.

Point 11: Lines 82-87, I think I have understood what you mean, but other less-proficient English speakers will not understand.

Response 11: As reviewer’s kindly comment, we edited the sentence concise and factually.

At this time, the molding pressure was increased from 1.8 to 6.25 ton/cm² to test its effect on permeability and volume fraction. When only Fe-6.5 wt% Si powder was used, many voids were created between the coarse powders, resulting in low volume fraction and permeability. When bulk magnetic composites were prepared with the addition of 20% by weight of fine iron powder, the permeability and volume fraction were greatly improved. This testing confirmed that the volume fraction and permeability increase with increasing molding pressure (Table 1).

Point 12: Pag 4, top table, who is μ ?

Response 12: As reviewer’s kindly comment, we edited the symbol to word.

For more information, please check the attached file.

Point 13: Figure 4, subfigure e) and i) are identical.

Response 13: As reviewer’s comment, we edit the figure correctly.

For more information, please check the attached file.

Point 14: Lines 103-104: where are the theoretical results?

 Response 14: We have identified "theoretical results" as references using Ollendorf's equation. Then, the result was plotted. References “[18]” have been inserted into sentences.

Mathematical calculation methods and theories are specified in this reference.

 Point 15: How did you measure the demagnetization field?

Response 15: Actually we measured the demagnetization field using by VSM.

Point 16: figure 6. Are you sure the sizes are in inch? 3225 inches are approximately 82 m.

Response 16: As reviewer’s comment, we edit the length unit correctly.

For more information, please check the attached file.

Point 17: figure 7, μ is a relative measurement to what?

Response 17: As reviewer’s comment, we edit the symbol to word.

For more information, please check the attached file.

Point 18: Can you specify which the total thickness of the film (substrate+magnetic thin film) ?

Response 18: The total thickness of the film (substrate+magnetic thin film) are about 40um.

Point 19: Do you notice cracks in the film to accomodate the large difference in density as one can see in table 2?

Response 19: The film cracking due to the large difference in density could not be identified.

Point 20: Conclusion? I find the conclusion too short to grab a minimal information of what you did. Readers read the abstract, introduction, and conclusion to estimate whether the manuscript is worth to be read. Please, extend it.

Response 20: As reviewer’s kindly comment, the conclusion of the manuscript was extended. Please check the text below and the attached file.

4. Conclusions

In order to manufacture a high-densification magnetic sheet, it is necessary to apply a nanopowder process that improves the coarse powder-fine powder filling method currently used. In this research, a highly densified magnetic sheet for a power inductor was successfully fabricated by a magnetic sheet casting process using Fe-6.5 wt% Si coarse powder, fine iron powder, and nano iron powder. Using a surface treatment with a silane coupling agent, Fe nanopowder with a high specific surface area was effectively implemented with the binding system used in the current mass production process. Magnetic properties of the sheet fabricated by using trimodal powder was highly improved compared to the magnetic sheet fabricated by using bimodal powder. The optimum conditions for the manufacture of high-filled magnetic sheets were determined through the experiments presented here and culminated in the study outcomes as follows.

1. Nanopowder is receptive to surface treatment by epoxy-based silane coupling agents.
2. The surface treatment condition of the nanopowder involves mixing the nanopowder with 1% silane coupling agent followed by aging for 24 h at 3 °C.
3. An effective dispersion process for effective dispersion of nanopowders was developed.
4. A press sheet casting process to fill powder effectively when forming a sheet was developed.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript by Lee et al. describes the synthesis of magnetic Fe sheets enhanced through silane coupling agents surface treatment. The magnetic sheets and toroidal bulk magnetic composites were characterized by electron microscopy and permeability measurements. The synthesis was carried out clearly, and the characterization of the magnetic sheets is missing some technical details. I recommend this paper to be published in Applied Sciences after addressing a few minor points listed below.

(1)  Introduction is poorly written and additional literature reports related to highly densified magnetic sheet for power inductors should be mentioned. Also, when discussing their results comparison to other similar systems would be appreciated.

(2)  Experimental section is missing the method paragraph. In particular, the information of electromagnetic characteristics and density measurements used in this experiment is missing. Also, the authors used TEM measurements (Fig. 8).

(3)  Ollendorf's equation symbols are not displayed correctly (page 5).

(4)  Low magnification SEM images of magnetic sheets should be shown.

Author Response

Response to Reviewer 2 Comments

The authors would like to express our wholehearted thanks to both the Editor and Reviewer for giving the valuable suggestions/comments regarding our paper. These reviews have been very helpful in enhancing our paper. Based on the comments and suggestions, the revised manuscript was prepared. Below is a detailed discussion of the changes we have made to address the reviewer comments.

Point 1: Introduction is poorly written and additional literature reports related to highly densified magnetic sheet for power inductors should be mentioned. Also, when discussing their results comparison to other similar systems would be appreciated.


 Response 1: Thanks for the kind comment. As review’s comment, we add manuscript related to highly densified magnetic sheet for power inductors.

 

Point 2: Experimental section is missing the method paragraph. In particular, the information of electromagnetic characteristics and density measurements used in this experiment is missing. Also, the authors used TEM measurements (Fig. 8).

 

Response 2: Thanks for the insightful comment. As reviewer’s comment, we edit experimental section as shown in bellow sentences.

 

The microstructures of magnetic sheets were analyzed by scanning electron microscope (SEM, JSM-7100F, JEOL Ltd., Japan). The surface characteristics of magnetic sheet were analyzed by surface profiler (Dektak 150, Veeco Tucsom Inc.). Density and volume fraction of magnetic sheets were evaluated by electric balance (OHAUSS Adventure, Mettler Toledo Inc.) with Archimedes method. TEM images were taken on a JEOL 4010 (JEOL Ltd., Japan). Permeability of toroidal was evaluated by LCR meter (Agilent E4980A, Agilent Inc.)

 

Point 3: Ollendorf's equation symbols are not displayed correctly (page 5).

 

Response 3: Thanks for the kind comment. It seems to be a problem caused by the difference of the software version. So, I replaced it with an image.

 

Point 4: Low magnification SEM images of magnetic sheets should be shown.

 

Response 4: Thanks for the kind comment. Previously, we tried to compare the microstructure of magnetic sheets having different magnetic powders using SEM at low resolution. However, we couldn’t compare the microstructures of the magnetic sheets due to the different particle size distribution and high packing density. As shown in Figure 9, it was possible to compare the microstructure of the three magnetic sheets at a resolution of about 1000 times using the SEM. As you can see the photographs of the three magnetic sheets (Fig. 9), the magnetic powders were uniformly distributed throughout the film macroscopically.

Author Response File: Author Response.docx

Reviewer 3 Report

Extensive editing of English language and style is required.

This research simply blends nanoparticles to fill the voids between coarse and fine particles, which is nothing new to the magnetic sheet fabrication.

The introduction part should include more background information about current research status of magnetic inductors, the challenges faced by the industry and what is the novelty of this research.

Experimental part should include details of the instruments and procedures used to allow people to repeat the experiment.

 

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 3 Comments

 

The authors would like to express our wholehearted thanks to both the Editor and Reviewer for giving the valuable suggestions/comments regarding our paper. These reviews have been very helpful in enhancing our paper. Based on the comments and suggestions, the revised manuscript was prepared. Below is a detailed discussion of the changes we have made to address the reviewer comments.

 

Point 1: Extensive editing of English language and style is required.

 

Response 1: As reviewer’s kindly comment, the manuscripts are huge revision. And we are enclosed the "CERTIFICATE OF ENGLISH EDITING"

Please check the attached answer (1).

Point 2: This research simply blends nanoparticles to fill the voids between coarse and fine particles, which is nothing new to the magnetic sheet fabrication. The introduction part should include more background information about current research status of magnetic inductors, the challenges faced by the industry and what is the novelty of this research.

Response 2: Thanks for the insightful comment. As reviewer’s comment, we edit/add the sentences as below.

To improve electromagnetic properties of inductor, many researchers have an effort to develop new composition of magnetic powders, change inductor design, and optimize internal electrode design[8,9].

Point 3: Experimental part should include details of the instruments and procedures used to allow people to repeat the experiment.

Response 3: Thanks for the kind comment. As reviewer’s comment, we include details of the instruments and procedures as below sentences.

Three kinds of powders were used to prepare a magnetic sheet. Fe-6.5 wt% Si powder (average particle size = 40 µm) manufactured by Atmix Inc. and fine iron powder (average particle size = 3 µm) were used as raw materials, and Fe nanopowders (average particle size = 100 nm) were used to effectively fill the void space between the coarse Fe-6.5 wt% Si powder and fine iron powder. Nanopowders were surface-treated using an epoxy-based silane coupling agent from Shinetsu Inc. To achieve uniform surface treatment, a silane solution using ethanol and distilled water was prepared (Figure 1). The prepared silane solution was added to the nanopowder for a mixture of 1% silane solution, which was then mixed with a pre-mixer for 1 hour. The surface-treated nanopowders were subjected to dehydration condensation at 3 °C for 24 h, thereby preparing surface-treated nanopowders for producing a magnetic sheet [18]. After mixing each powder at a constant mixing ratio, a magnetic slurry was prepared using an epoxy binder and a dispersant. The prepared slurry was dispersed and mixed at a frequency of 64 Hz for 3 min using a resonance acoustic mixer. The magnetic slurry produced was made of a magnetic sheet using a tape casting process (Figure 2). The microstructures of magnetic sheets were analyzed by scanning electron microscope (SEM, JSM-7100F, JEOL Ltd., Japan). The surface characteristics of magnetic sheet were analyzed by surface profiler (Dektak 150, Veeco Tucsom Inc.). Density and volume fraction of magnetic sheets were evaluated by electric balance (OHAUSS Adventure, Mettler Toledo Inc.) with Archimedes method. Transmission electron microscope images were taken on a JEOL 4010 (TEM, JEOL Ltd., Japan). Permeability of toroidal was evaluated by LCR meter (Agilent E4980A, Agilent Inc.)

Round 2

Reviewer 1 Report

I have anything to say about this improved version.

It is acceptable in the present form.