Materials Selection and Processing Techniques for Small Spacecraft Solar Cell Arrays

University of Kentucky UKnowledge Theses and Dissertations--Electrical and Computer Engineering Electrical and Computer Engineering 2013 Materials Selection and Processing Techniques for Small Spacecraft Solar Cell Arrays Naseem M. Torabi University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Torabi, Naseem M., "Materials Selection and Processing Techniques for Small Spacecraft Solar Cell Arrays" (2013). Theses and Dissertations--Electrical and Computer Engineering. 22. https://uknowledge.uky.edu/ece_etds/22 This Master's Thesis is brought to you for free and open access by the Electrical and Computer Engineering at UKnowledge. It has been accepted for inclusion in Theses and Dissertations--Electrical and Computer Engineering by an authorized administrator of UKnowledge. For more information, please contact [email protected]. STUDENT AGREEMENT: I represent that my thesis or dissertation and abstract are my original work. Proper attribution has been given to all outside sources. I understand that I am solely responsible for obtaining any needed copyright permissions. I have obtained and attached hereto needed written permission statements(s) from the owner(s) of each third-party copyrighted matter to be included in my work, allowing electronic distribution (if such use is not permitted by the fair use doctrine). I hereby grant to The University of Kentucky and its agents the non-exclusive license to archive and make accessible my work in whole or in part in all forms of media, now or hereafter known. I agree that the document mentioned above may be made available immediately for worldwide access unless a preapproved embargo applies. I retain all other ownership rights to the copyright of my work. I also retain the right to use in future works (such as articles or books) all or part of my work. I understand that I am free to register the copyright to my work. REVIEW, APPROVAL AND ACCEPTANCE The document mentioned above has been reviewed and accepted by the student’s advisor, on behalf of the advisory committee, and by the Director of Graduate Studies (DGS), on behalf of the program; we verify that this is the final, approved version of the student’s dissertation including all changes required by the advisory committee. The undersigned agree to abide by the statements above. Naseem M. Torabi, Student Dr. Janet K. Lumpp, Major Professor Dr. Zhi David Chen, Director of Graduate Studies MATERIALS SELECTION AND PROCESSING TECHNIQUES FOR SMALL SPACECRAFT SOLAR CELL ARRAYS THESIS A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering in the College of Engineering at the University of Kentucky By Naseem Meetra Torabi Lexington, KY Director: Janet K. Lumpp, Ph.D., Professor of Electrical Engineering Lexington, Kentucky 2013 ABSTRACT OF THESIS MATERIALS SELECTION AND PROCESSING TECHNIQUES OF SMALL SPACECRAFT SOLAR CELL ARRAYS Body mounted germanium substrate solar cell arrays form the faces of many small satellite designs to provide the primary power source on orbit. High efficiency solar cells are made affordable for university satellite programs as triangular devices trimmed from wafer scale solar cells. The smaller cells allow array designs to pack tightly around antenna mounts and payload instruments, giving the board design flexibility. One objective of this work is to investigate the reliability of solar cells attached to FR‐4 printed circuit boards. FR‐4 circuit boards have significantly higher thermal expansion coefficients and lower thermal conductivities than germanium. This thermal expansion coefficient mismatch between the FR‐4 board and the components causes concern for the power system in terms of failures seen by the solar cells. These failures are most likely to occur with a longer orbital lifetime and an extended exposure to harsh environments. This work compares various methods of attaching solar cells to printed circuit boards, using solder paste alone and with a silicone adhesive, and considering the application of these adhesives by comparing the solder joints when printed by screen versus a stencil. An environmental test plan was used to compare the survivability and performance of the solar arrays. KEYWORDS: Solar Cells, Solar Cell Arrays, Circuit Board Assembly, Material Testing, Small Satellites Naseem M Torabi May 3, 2013 MATERIALS SELECTIONS AND PROCESSING TECHNIQUES FOR SMALL SPACECRAFT SOLAR CELL ARRAYS By Naseem Meetra Torabi Janet K. Lumpp Director of Thesis Zhi David Chen Director of Graduate Studies May 3, 2013 ACKNOWLEDGMENTS I would first like to thank my mentor and thesis advisor Dr. Janet K. Lumpp, for her endless encouragement and guidance throughout this work as well as my entire graduate school experience. I greatly appreciate all of the time and effort she put into ensuring my educational progress and advancement. Additionally, I would like to thank Dr. James E Lumpp, Jr. for his support in making my research possible and for all of the invaluable opportunities he provided for me and my fellow lab colleagues. I also wish to thank my friends at Kentucky Space and Space Systems Laboratory for their technical assistance throughout my experimentation. Next, I wish to thank my family for helping me get through the challenges I have faced throughout college and graduate school. Their continual support has given me the confidence to pursue and accomplish my educational goals. Finally, a very special thanks to all three of my committee members: Dr. Janet Lummp, Dr. James Lumpp, Jr., and Dr. Todd Hastings for their time and challenging comments and questions during my thesis defense. iii TABLE OF CONTENTS Acknowledgments. iii List of Tables. vi List of Figures. viii List of Images. .ix Chapter One: Introduction. .1 Kentucky Space. .1 Cube Satellite Standard. 1 Kentucky Satellite‐1: Research Background. .4 Chapter Two: Experimental. 10 Screens and Stencils. .10 Materials. .13 Board Fabrication. .13 Testing Equipment. .16 Testing Cycles. .17 Board X‐Ray Analysis. 17 Thermal Aging. 18 Vacuum Exposure. .18 Thermal Cycling. .18 Vibration Testing. 19 Validation. .20 Chapter Three: Results. 21 Discussion. 21 iv Board 1a/b: Stencil Printed Silicone Adhesive, Manually Dispensed Solder Paste. .21 Board 2a/b: Stencil Printed Solder Paste Only. 29 Board 3a/b: Manually Dispensed Silicone Adhesive, Stencil Printed Solder Paste. .37 Board 4a/b: Screen Printed Solder Paste Only. 45 Chapter Four: Conclusions. .53 General Observations. 53 Future Work. 55 References. .56 Vita. 58 v LIST OF TABLES 1.1, Common solder metal alloys and their application. 6 1.2, Common flux types. .6 2.1, Durometer ratings for polyurethane squeegees. .12 2.2, The solar board adhesive materials and application combinations tested in this experiment. 14 2.3, Kester solder paste suggested reflow profile. .15 2.4, NASA GEVS random vibration. 20 3.1, Initial functional test results‐board A. .24 3.2, Functional test results post vacuum chamber‐board A. 24 3.3, Functional test results post thermal cycling‐board A. .25 3.4, Functional test results post vibration testing‐board A. .25 3.5, Initial functional test results‐board B. .26 3.6, Functional test results post extreme thermal cycling‐board B. 27 3.7, Functional test results post vacuum chamber‐board B. 27 3.8, Functional test results post thermal cycling‐board B. 28 3.9, Functional test results post vibration testing‐board B. .28 3.10, Initial functional test results‐board A. .31 3.11, Functional test results post vacuum chamber‐board A. .32 3.12, Functional test results post thermal cycling‐board A. .32 3.13, Functional test results post vibration testing‐board A. .33 3.14, Initial functional test results‐board B. .34 3.15, Functional test results post extreme thermal cycling‐board B. .35 3.16, Functional test results post vacuum chamber‐board B. .35 vi 3.17, Functional test results post thermal cycling‐board B. .36 3.18, Functional test results.

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