Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Electrical and Computer Engineering
The monitoring of solder paste characteristics during surface mount circuit assembly procedures is ultimately concerned with obtaining a high yield of reliable solder joints. The process control of solder paste systems under manufacturing conditions is, at present, not derived from on-line measurements of the paste. Because these tests are not performed in-process, they cannot detect critical changes in paste behavior caused by varying process conditions, environmental factors, or the loss of rheological characteristics induced by prolonged shear stress on a screen printer. AC impedance spectroscopy can be a valuable tool in characterizing the properties of materials that possess measurable dielectric behavior. Recent advances in impedance measurement instrumentation ( and the evolution of the personal computer) have yielded improved data acquisition and analysis capabilities. This has precipitated efforts to utilize this methodology for the evaluation of more complex materials systems ( such as solder paste). The primary focus of this investigation was the implementation of AC impedance techniques as a means of characterizing the behavior of a broad range of solder paste formulations. In the course of this work, it has been determined that it is possible to represent both the dielectric and the electro-chemical nature of these materials in the form of an electrical equivalent circuit model. This modeling yields significant detail concerning the microscopic attributes of these materials, unobtainable from other forms of study. As a result, it forms the basis for a process control methodology in the manufacturing realm.