Process control in a high-noise environment using a limited number of measurements
ABSTRACT In this paper, we develop a hybrid control algorithm that produces control values for processes where only a limited number of function evaluations are available for the control law generation. This situation arises, for example, in stencil printing processes in printed circuit board manufacturing, where the cost associated with multiple function evaluations is prohibitive: The proposed control algorithm is given by a modified version of a constrained conjugated-gradient method, transitioned into a windowed-smoothed block-form of the least-squares affine estimator.
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ABSTRACT: A physical model of the screen printing process is described. Interrupted printing tests provided guiding information on the flow pattern in the paste during the deposition process. The paste flow region ahead of the squeegee was divided into three regions: the pressurization region (region I), the downward screen cross-flow region (region II), and the paste accumulation region (region III). During printing, the squeegee tip becomes deformed and its angle of attack decreases. Region I extends from the leading edge of the deformed squeegee tip to the beginning of the deformation region. As a result of pressure buildup in region I ahead of the squeegee, there is a flow of paste under the squeegee. The paste deposition process depends mainly on the flow process in region I. Analysis of experiments indicates that the squeegees used deform so that their fronts can be approximated by a wedge. The angles of hard squeegees decrease by approximately 20° from the undeformed angle of 45°. The corresponding angle decrease for soft squeegees is on the order of 30-40°. The vertical forces acting on the squeegees were estimated to be between 60 and 47 lbf. The average speed of the paste under the squeegee, caused by the developed hydrodynamic pressure, was found to be between 0.1 and 0.2 of the squeegee speedIEEE Transactions on Components Hybrids and Manufacturing Technology 07/1990;
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ABSTRACT: A generic study involving solder paste characterization, stencil configuration, printed wiring board layout, and printing parameters was performed. The authors summarize findings in the following areas: solder paste-powder particle size distribution, rheology, slump, and solder ball formation; stencils-single versus dual thickness, brass or other materials, opening sizes, vendor capabilities; printed wiring boards-pad geometry, dimensional tolerance, pad surface finish; printing process-setup and alignment, squeegee materials, printing speed downward pressure; and, component placement-handling, placement accuracy, force limitations. Some practical concerns, including the current process operating window and future fineness of print limitations, are discussedIEEE Transactions on Components Hybrids and Manufacturing Technology 10/1991;
Conference Proceeding: Solder joint design optimization for fine pitch component applications[show abstract] [hide abstract]
ABSTRACT: Fine pitch leaded components, such as TSOP/QFP, have been widely used in portable electronics in recent years. One of the most critical issues in the electronic packaging industry is to find effective ways to reduce manufacturing related solder joint defects in these electronic components. During the fine pitch component reflow process, major failure mechanisms include solder bridging, solder opens, insufficient soldering, etc. This research aims to develop a physics-based validated modeling methodology, allowing for effective simulation of the solder joint formation process and prediction of the above solder defects. The goal of the methodology is to determine the optimal solder joint configuration (i.e. bond pad size, stencil aperture design, solder volume, etc.) in a cost-effective manner. The solder joint formation process during the solder solidification stage has been simulated using the Surface Evolver software tool. This paper consists of three integral parts: (1) simulation of the 3D solder joint formation process for the final solder joint geometry configurations; (2) determination of the optimal pad/stencil aperture; and (3) determination of the optimal solder paste volume and material. The methodology can also enable one to analyze the safety margin for a given pad/stencil aperture design. Finally, the simulation models were used to accurately pinpoint the deficiencies in certain pad/stencil aperture designs, which can cause solder bridging, opens or insufficient solderingThermal and Thermomechanical Phenomena in Electronic Systems, 1998. ITHERM '98. The Sixth Intersociety Conference on; 06/1998
PROCESS CONTROL IN HIGH-NOISE ENVIRONMENTS
USING A LIMITED NUMBER OF MEASUREMENTS
The Academic Faculty
Leandro G. Barajas
In Partial Fulfillment
Of the Requirements for the Degree of
Doctor of Philosophy
School of Electrical and Computer Engineering
Georgia Institute of Technology
Copyright © 2003 by Leandro G. Barajas
S T I TUTE • OF • TECHNO LOGY •
S ERV I CE
Process Control in High-Noise Environments
Using a Limited Number of Measurements
Dr. Magnus Egerstedt, Advisor
Dr. David Taylor
Dr. George Vachtsevanos
Date Approved: 03/28/2003
This work is dedicated to my parents Edgar and Alba,
who gave me life and strength of character to become what I am…
… to my brothers Mauricio and Nicolas,
for always believing in and trusting me…
… to my Family,
who surrounded with love as I was growing up…
…and to my wife Elizabeth for a life of happiness.
I would like to express my deepest and sincerest gratitude towards my thesis advisors,
Dr. Magnus B. Egerstedt and Dr. Edward W. Kamen for instructing me in the paths of
knowledge and professional integrity, for their constant support and encouragement and
for giving me the highest standards to live up to as a researcher. Having a mentor of the
stature and trajectory of Professor Kamen provided me with the guidance, support, and
right mentality to be successful in my research career; somehow, he was always able to
foresee problem outcomes in ways I never even imagined; our different points of view
often originated very interesting and constructive practical and theoretical discussions.
With his enthusiasm, drive, and directed thinking, Professor Egerstedt provided
invaluable advice and contributions to this work. I am grateful to him for initiating me
into the field of hybrid systems, and for being able to focus my research in the overall
picture (rather than expending too much time in minute details as I used to). His
continual support, encouragement, and feedback always kept me going, especially during
the exhausting writing process of the papers generated by this work.
I am grateful to Professors David G. Taylor, George J. Vachtsevanos, Aaron D.
Lanterman, and Amy R. Ward for serving as committee members in the proposal
examination and the final dissertation defense, and for their extensive and constructive
comments and suggestions.
I would also like to express my gratitude to Dr. Allen R. Tannenbaum for introducing
me to the world of the computer vision and to the wonders of mathematical morphology.
In addition, for their dedication, help, and inspiration, I want to thank all my graduate
school professors but specially the following: Phillip E. Allen, John F. Dorsey, Paul E.
Hasler, Mark J.T. Smith, Erick I. Verriest, and Yorai Y. Wardi. Furthermore, I want to
express my gratitude to the Universidad Distrital Francisco José de Caldas Professors
Jaime Angulo, Edgar Betancourt, Rodrigo Herrera, and Jorge Pedraza that during my
undergraduate years encouraged and oriented me in the pursuit of a research career that
lead me to this point.
Special thanks to Alex Goldstein for his constant advisement and support during the
implementation and development of this research project; especially for always keeping
the laboratory facilities running smoothly and for managing the projects developed with
all different companies that were involved in this work.
My profound thanks and love to my family, for giving me their constant moral,
emotional, and economical support during these years. Finally, yet importantly, I thank
my wife, Elizabeth for showing me and giving me happiness in life.
This research was supported in part by Siemens Dematic EAS, Norcross, GA, USA,
and by The Julian T. Hightower Chair Professorship in Manufacturing Engineering.
I also give my sincere gratitude to the Center for Board Assembly Research (CBAR) at
the Manufacturing Research Center (MARC) for providing all facilities, equipment,
parts, and supplies and as well as human and technical resources for the successful
culmination of this research project.