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Article
Peer-Review Record

Effectiveness of Critical-Strain-Based Methodology Considering Elastic Mode Vibration of Mechanical Housing of Electronics

Aerospace 2023, 10(11), 974; https://doi.org/10.3390/aerospace10110974
by Jae-Hyeon Park 1, Seong-Keun Jeong 2 and Hyun-Ung Oh 1,3,*
Reviewer 1:
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Aerospace 2023, 10(11), 974; https://doi.org/10.3390/aerospace10110974
Submission received: 18 October 2023 / Revised: 14 November 2023 / Accepted: 17 November 2023 / Published: 20 November 2023
(This article belongs to the Special Issue Advanced Spacecraft/Satellite Technologies)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The test results in Table 8 must be reevaluated by performing the experimental procedures again. 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English language level is moderate. 

Author Response

RESPONSES TO REVIEWER’S COMMENTS

We greatly appreciate the reviewer’s positive comments on our manuscript. We tried our best to properly answer the reviewer’s comments and address his concerns. Please, let us know whether additional revisions are required.

 

  • The test results in Table 8 must be reevaluated by performing the experimental procedures again.

To experimentally validate the electronics structural design technique based on critical strain theory, we performed a fatigue life test on specimens comprising electronic packages comprehensively mounted on PCBs in various mounting configurations and combined with mechanical housing. As a result of the test, all packages except U5 and U7 failed. Here, failure means damage to the solder joint that physically connects the electronic package and the PCB. Fatigue destruction of the solder joint occurred owing to the periodic bending mode of the PCB in an extreme vibration environment. During the test, 20 grms of random vibration was continuously excited until the solder joint was ‘intentionally’ broken (Page 7, Lines 240-242), and the failure times are summarized in Table 4 in the manuscript.

After performing the fatigue life test, structural analysis was performed on the specimen using a simplified FE modeling technique to evaluate the analytical effectiveness of the proposed critical strain theory-based structural design technique. In addition, structural safety evaluation using Steinberg’s theory was performed to determine the consistency between test and analysis results for each theory.

As a result of analysis and evaluation, it was confirmed that although all packages except U5 and U7 were damaged in the test, positive margins were derived in all of them when evaluating structural safety by applying Steinberg’s theory. On the other hand, when applying the structural design technique based on critical strain theory, negative margins were derived in all cases, demonstrating that the test results were validly represented. Here, the U5 and U7 packages showed a negative margin although no damage occurred, which implies that as the damage of the solder joint gradually progresses owing to continuous random vibration excitation in the actual test, the strain response propagated to the surrounding package is gradually alleviated. It is believed that this is due to limitations in considering the situation in the analysis.

What should be noted in this verification process is the MoS calculation result according to whether the solder joint of the electronic package is damaged, and it was analytically and experimentally proven that compared to the Steinberg’s theory, the critical strain theory-based structural design technique reasonably represented the test results.

 

  • The English language level is moderate.

Following your comment, the manuscript has been proofread by a professional editor to improve its language level.

 

[End of author’s response]

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study examines the reliability of the Oh-Park methodology, a PCB strain-based structural design approach for spaceborne electronic units. The objective is to evaluate whether the methodology can effectively ensure structural safety for a comprehensive specimen with multiple mounted packages under various boundary conditions. The study also considers the effects of complex elastic mode vibrations of a mechanical housing structure on the PCBs.

The study is well written, and the following comments can improve the readability:

Add more about the problem background in the abstract.

Add a schematic diagram explaining the experimental work and fatigue test setup.

Remove package manufacturer labels from Table 1 images.

 

Comments on the Quality of English Language

Re-edit long sentences like this one in lines 403-407. 

"In this study, the effectiveness of the PCB strain-based structural design methodology for spaceborne electronic units, called the Oh-Park methodology, was investigated to validate whether it is reliable for evaluating the structural safety of a comprehensive PCB specimen with multiple packages mounted under various boundary conditions and under the condition that the elastic mode vibration of a mechanical housing structure acts complexly on the PCBs.

Author Response

Responses to Reviewer #2’s Comments

COMMENTS TO THE AUTHOR(S)

This study examines the reliability of the Oh-Park methodology, a PCB strain-based structural design approach for spaceborne electronic units. The objective is to evaluate whether the methodology can effectively ensure structural safety for a comprehensive specimen with multiple mounted packages under various boundary conditions. The study also considers the effects of complex elastic mode vibrations of a mechanical housing structure on the PCBs.

The study is well written, and the following comments can improve the readability:

 

RESPONSES TO REVIEWER’S COMMENTS

We greatly appreciate the reviewer’s positive comments on our manuscript. We tried our best to properly answer the reviewer’s comments and address his concerns. Please, let us know whether additional revisions are required.

 

  • Add more about the problem background in the abstract.

We fully agree with the reviewer's opinion that the problem background has been insufficiently described in the abstract of the manuscript. Following the reviewer’s comment, the abstract has been augmented with additional sentences as follows:

These verifications were performed only at the PCB unit with a single electronic package mounted. However, in actual industrial fields, electronics with various types of electronic packages mounted comprehensively are mainly applied to electronics combined in a mechanical housing structure. Therefore, the verification of the corresponding methodology for the above actual conditions is essential.” (Page 1, Lines 14–18)

 

  • Add a schematic diagram explaining the experimental work and fatigue test setup.

Based on the reviewer's comments, the following schematic diagram has been added to the revised manuscript. (Page 8, Figure 3)

 

  • Remove package manufacturer labels from Table 1 images.

Thank you for pointing out this oversight. Following your comment, the electronic package manufacturer label has been removed, and the figure has been modified. (Page 4–5, Table 1)

 

[End of author’s response]

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I have read the manuscript. It does not need a long review as it is clear that the topic is new and the content is practical. However, this reviewer has a problem with the work. We all know that the FEM technique, in general, is not an exact method to consider mechanical and stress analysis. Thus, everytime a validation with experiment or other techniques are essential. So, how can these results be credible with lack of a comparison?

Author Response

Responses to Reviewer #3’s Comments

 

RESPONSES TO REVIEWER’S COMMENTS

We greatly appreciate the reviewer’s positive comments on our manuscript. We tried our best to properly answer the reviewer’s comments and address his concerns. Please, let us know whether additional revisions are required.

 

  • I have read the manuscript. It does not need a long review as it is clear that the topic is new and the content is practical. However, this reviewer has a problem with the work. We all know that the FEM technique, in general, is not an exact method to consider mechanical and stress analysis. Thus, everytime a validation with experiment or other techniques are essential. So, how can these results be credible with lack of a comparison?

This manuscript is mainly concerned with a structural design technique based on critical strain theory that can overcome the limitations of the existing Steinberg’s theory and which is called the ‘Oh-Park methodology’. This methodology not only includes a technique to evaluate the structural safety of electronic package solder joints based on ‘PCB strain rate’ but also includes a ‘simplified FE modeling technique’ that is efficient in terms of time and effort when performing structural analysis.

Previous studies on critical strain-based structural design techniques have proven their effectiveness analytically and experimentally for various electronic packages such as BGA, CGA, and SOP. In addition, in this study, fatigue life tests were performed on PCB specimens with mechanical housing in which the electronic packages verified in previous studies were mounted, and structural analysis was performed to evaluate the structural safety of the solder joints. As a result, reasonable results were demonstrated when applying the methodology even under conditions where the electronic package was comprehensively mounted in various mounting configurations and the PCB was affected by the mechanical housing bending mode.

Accordingly, because the effectiveness of this methodology has been proven analytically and experimentally under the various conditions described above, it is expected that highly reliable prediction results will be derived when evaluating the structural safety of electronic package solder joints under extreme vibration environments.

 

 

[End of author’s response]

Author Response File: Author Response.pdf

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