| MEMS (Micro-electromechanical systems) are integrated micro-devices or systems which combine electrical and mechanical components. They are fabricated using integrated circuit (IC) batch processing techniques and can range in size from micrometers to millimeters. MEMS technology is an enabling technology and current applications include accelerometers, pressure, chemical and flow sensors, micro-optics, optical scanners, and fluid pumps. One of the most common methods for manufacturing MEMS devices is to use surface micro-machining. Due to the nature of thin film deposition technology, a fundamental problem with surface micro-machining is its inability to produce highly three-dimensional structures. Traditionally, achieving highly three-dimensional MEMS structures using surface micro-machining requires the use of hinged structures that are rotated and assembled into functioning devices. In the initial development of this technology, the methods of assembly were ineffective and inadequate for mass manufacturing. The recent development of surface tension driven self-assembly has potentially alleviated this problem. Surface tension self-assembly of MEMS has been shown to be an excellent approach for assembling three-dimensional MEMS structures by allowing more precise alignments, vastly increased complexity, and the cost/alignment reduced by orders of magnitude. As a result, this focus of work on self-assembly has changed from whether hinged MEMS can be assembled, to how accurately they can be assembled? The answer lies in the management of process-induced stresses and tolerances through optimal design. The main purpose of this thesis work was to increase the angle control precision of solder self-assembled structures. To increase the angle control precision of solder self-assembly, it was necessary to understand the effects of inter-metallic reactions and reduce deformation of the structure by optimizing various design element effects. To deal with inter-metallic and scaling related problems, various pertinent inter-metallic reactions is researched and their effects on solder self-assembly are analyzed. An optimization method was developed in order to optimize the solder self-assembly structure. This optimization method was used in combination with modeling and experimental data to find the optimum shape and gain an understanding of reduction of deformation and curvature in a basic, partially covered MEMS plate and a Basic building block MEMS structure. Based on the knowledge resulting from the optimization and design study, it was demonstrated that the angle precision could be increased from one and 0.5 degrees in previous work. Measurements of a set of experimental samples showed that the angle variation could be reduced to at least 0.9 degrees, and that a typical building block structure could be designed to have an angle precision of 0.5 degrees. |
