Effect of Conformal Coating on Electrochemical Migration Behavior of Multi-Layer Ceramic Capacitor for Automotives Based on Water Drop Test

Round 1

Reviewer 1 Report

The current manuscript presents intriguing findings pertaining to the behavior of multi-layer ceramic capacitors (MLCCs) in automotive applications, specifically focusing on the impact of conformal coating on electrochemical migration. The study investigates this phenomenon through the utilization of water drop testing. These results hold significance for the Journal of Coatings, given its emphasis on surface protection and material performance. Anyhow, the reviewer would like to make the following comments.

1.      How has the utilization of Multi-Layer Ceramic Capacitors (MLCCs) evolved within automotive applications, and what are the key areas where MLCCs are predominantly employed?

2.      What is the relationship between applied voltage and failure time in solder pad patterns undergoing WDT, and how does this relationship inform our understanding of ECM behavior?

3.      How does the migration of Sn components from the anode to the cathode contribute to the observed spherical particle formation?

4.      What is the role of Sn coating on the cathode electrode in preventing the formation of dendrites during WDT?

5.      How does the applied voltage and electrode distance affect the surface morphology of MLCC specimens after WDT?

6.      How does the distance between electrodes influence the migration and adherence of damaged material from the anode to the cathode during water drop testing?

7.       How does the presence of metallic dendrites, rather than Sn-O compounds, contribute to electrical short circuits and reliability issues in solder pad patterns subjected to WDT?

Author Response

We attached the comments and answers file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript discusses the effects of voltage, NaCl concentration, and distance between electrodes on non-mount multilayer ceramic capacitors, surface mount multilayer ceramic capacitors, and solder pad patterns, which were evaluated by means of a water drop test. Based on the analysis of the effects of the presence of conformal coating, applied voltage, concentration of NaCl, and the distance between electrodes, a mechanism model for electrochemical migration behavior in multilayer ceramic capacitors is proposed in this manuscript.

Overall, the manuscript exhibits average originality, primarily due to the absence of references that could substantiate the topic's relevance and current state-of-the-art in the field. Moreover, the lack of certain experimental results within the manuscript raises questions regarding why these experiments were not conducted earlier by other groups or why the authors did not obtain these results previously. It remains unclear whether exposing the Sn layer on the surface provides protection against electrochemical migration or if the method utilizing water drops for investigation constitutes the original and most crucial aspect of the manuscript. Additionally, there is ambiguity regarding whether Sn is the most effective material for surface exposure as protector against electromigration, despite the authors' statements in the conclusions suggesting otherwise.

Furthermore, the manuscript lacks arguments explaining the rationale behind the authors' research and their expectations regarding the research outcomes. It is important to ascertain whether these results have met the authors' expectations or not.

Additionally, the conclusions lack authors’ recommendations or some kind of summary on the potential practical applications of the research results.

In summary, the manuscript would benefit from clearer explanations, more comprehensive referencing, and a deeper exploration of the motivations and expectations underlying the research.    

There are also some English and typographical error that need to be specified in the referee report:

1. In the Abstract the definite article is missing (see lines 17-18): <…>…occur, with cathode… <…> should be …occur, with the cathode… (add "the" before "cathode") and also in <…> …In this study, effects of voltage...<...> should be …In this study, the effects of voltage...; (add "the" before "effects");

2. The definite article is missing in part of Introduction (see line 29): <…>…increased due to the adoption of the latest technologies…<…> should be “…increased due to the adoption of the latest technologies…” (add "the" before "adoption");

3. The same issue is present in line 90: “…and analyzed the ECM behavior…” should be “…and analyzed the ECM behavior…” (add "the" before "ECM");

4. There is a typographical error in the sentence in line 91: “…NaCl solution to simulates the…” should be “…NaCl solution to simulate the…”;

5. There are the specific lines where spaces are missing between numerical values and symbols '%' (percent), 'V' (volts), and 'um' (micrometers): see lines 106, 114, 137-138, 148, 152-153, 161, 183-185, 188, 190, 194, 196, 209, 212, 217, 219, 222, 225, 233, 236, 248, 254, 260, 262, 268, 273, 276, 287, 295, 297, 310, 321, 326, 329, 338, 341, 349, 353, 259-360, 362, 364, and 395;

6. Figure 3, particularly Figure 3a, is of too low resolution. It might not effectively convey the intended information. Consider removing Figure 3 from the manuscript if it does not add significant value, or if the information it contains can be adequately described in the text;

7. In Figure 4, the objects, particularly in the Cl Ka1 component, are difficult to discern. Considering this limitation, it may be more beneficial to exclude Figure 4 from the manuscript and instead describe the information it presents in detail within the text. This ensures clarity and comprehension for readers;

8. For Figure 5, where the current vs. time dependencies are shown, the measurements at 2 V, 3 V, and partially at 5 V are difficult to discern. To address this issue, consider either presenting Figure 5 in semi-log scale to better visualize the data at lower voltages, or alternatively, exclude the measurements at lower voltages and provide detailed information about them in the manuscript text;

9. In Figure 6, while it is labeled as "Cathode," the boundary of the cathode and specific locations in Figure 6b are not sufficiently clear. To improve clarity, consider enhancing the labeling or providing additional annotations to clearly indicate the boundary of the cathode and specific locations within Figure 6b. This will help readers better understand the information presented in the figure;

10. The caption for Figure 9 should include an explanation of the meaning of the dashed red line and specify how the authors defined the position of that boundary. Additionally, the caption for the figure should appear on the same page as the figure itself. The definite article is missing in line 248: <…>… Figure 9. Surface appearance of … <…> should be … Figure 9. The surface appearance of… (add "the" before "Surface"); The Figure caption does not sound;

11. The caption for Figure 11 should appear on the same page as the figure itself;

12. Figure 12, composed of parts a, b, and c, is of low quality. The magnification scale is hardly visible, and the meaning of the red dashed line is unclear. Additionally, it appears that Figures 12a and b do not provide any extra valuable information compared to Figure 12c;

13. The definite article is missing in lines 308-309 of the manuscript: <…>…To determine effects of …<…> should be “…To determine the effects of …<…>  (add "the" before "effects"); Same in <…> … Figure 14 shows effects of applied…<…> should be …Figure 14 shows the effects of applied… (add "the" before "effects");

14 The article an is missing in line 309: <…>…with electrode distance…<…> should be “with an electrode distance…” (add "an" before "electrode");

15. Experimental data given in Figure 14b is missing error bars. A dot is missing at the end of the figure caption;

16. The manuscript text in lines 384-388 needs to revise and to check English. There are definite articles missing in the text and also a typographical error in line 388: <…>…coating failed die to a strong…<…> most probably should be ‘…coating failed due to a strong…” (replace “die” with “due”);

17. In the part of Conclusions the definite article is missing (see line 438): <…>…in ECM phenomenon…<…> should be “…in the ECM phenomenon… (add “the” before “ECM”) and same in line 439: “…coating, the ECM phenomenon…”. Skip the article an in line 444: “…with electrical insulation…”;

18. Correct the text in Reference No. 29 (see line 528): The name of the author should end with a dot, not with a semicolon.

Several English and typographical errors have been identified and outlined in the referee report section titled "Comments and suggestions for authors".  

Author Response

We attached the comments and answers file.

Author Response File: Author Response.pdf

Reviewer 3 Report

This study evaluated how voltage, NaCl concentration, and electrode spacing affect non-mounted MLCCs, surface-mounted MLCCs, and solder pad patterns using a water drop test (WDT). Some suggestions are as follows:

(1) The challenge described in the introduction requires further elaboration, and it would be beneficial to discuss the progress made in previous research.

(2）The text in Fig.1 is small. The figures in fig. 2/5/8/11 can be enlarged. 

(3) If conditions permit, please supplement with XRD or XPS to strengthen the explanation of the mechanism.

(4) "Figure 3a is an image observed at x500 magnification of the area .." This is SEM image, and its magnification level is different from the actual magnification. Please be careful in your description. It is recommended to describe the changes in the dimensions of the surface-produced material structure according to the scale of the SEM.

(5) In EDS results, the element atom % percentages should be recorded and analysed. 

(6) In Fig. 16, lots of Si appear in the surfaces, Why? 

(7) Please add the description of conformal coating in the article. The description of the coating in the text is very limited.

(8) The logical structure of the article needs further improvement.

(9) Some grammar and typo errors were found, need to check the whole paper carefully.

The language needs polishing.

Author Response

We attached the comments and answers file.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The manuscript discusses the effects of voltage, NaCl concentration, and distance between electrodes of non-mount multilayer ceramic capacitors, surface-mount multilayer ceramic capacitors, and solder pad patterns, which were evaluated by means of a water drop test. Based on the analysis of the effects of the presence of conformal coating, applied voltage, concentration of NaCl, and the distance between electrodes, a model for electrochemical migration behavior in multilayer ceramic capacitors is proposed in this manuscript. After the authors' revisions, the conclusions still lack a summary addressing the potential practical applications of the research results or assessing their quality or importance in the context of results obtained by other authors. The conclusion presented in the manuscript is a restate of the results already presented in the original section of the paper.

There are also some English and text formatting error that need to be specified. They are as follows:

1. Dashes are missing in line 92: <…>… fluxes such as Rosin based flux, water soluble flux, and… <…> should be … fluxes such as Rosin-based flux, water-soluble flux, and… (add dashes in “Rosin-based” and “water-soluble”);

2. Same in line 133: here should be … mechanism in surface-mount MLCCs and non-mount… add dash in “surface-mount”);

3. There are the specific lines where spaces are missing between numerical values and symbols 'um' (micrometers): see Figure 4 (line 222), Figure 7, Figure 10 (line 299), Figure 13 (line 335), Figure 16 (line 391), Figure 18 (line 404),

4. Spaces are missing between numerical values and symbols 'V' (volts) in Figure 14a;

5. Inappropriate formatting of text at the end of page 6: Figure 5 and its caption should appear on the same page. Inappropriate formatting of text at the end of page 6: Figure 5 and its caption should appear on the same page. The same error occurs in the cases of Figure 7, Figure 9, and Figure 16;

6. The caption of Figure 14 lacks an explanation for the dashed red color line.

The comments are provided in the section "Comments and Suggestions for Authors".

Author Response

We attached the file.

Author Response File: Author Response.pdf