As Micro ElectroMechanical Systems become more complicated, building them asintegrated systems may not be possible and exploring new microassembly technologies becomes necessary. Capillary-based fluidic microassembly is of interest because of its many advantages over serial pick-and-place assembly techniques. The capillary-based process is capable of providing sub-micron alignment accuracy; it can be applied to various microcomponent and substrate material combinations, and it is an economical non-contact parallel assembly technique.
In this work, the capillary-based technique has been extended to obtain single to multiple electrical between and the interconnects microcomponents substrate. Applications for both single and multiple electrical interconnects have been implemented. Commercial JFETs, with a single electrical interconnect, were assembled with a micromachined variable capacitor to create a high-resolution electrometer. The MEMS1electrometer, with 1.5 fC resolution, out performs the best commercial instruments by anorder of magnitude. Micromachined inductors, with two electrical interconnects, we reassembled onto standard 10 ohm-cm substrates. The maximum Q of the assembled inductor was 60 at 5 GHz.
Critical issues related to the capillary-based fluidic microassembly process are binding site material selection and treatments, coating control and surface issues, and equilibrium microcomponent positioning. Various materials and treatments have been explored, and the necessary criteria for applications identified. Three surfaces that preferentially wet with hexadecane in water most effectively are SAM-coated gold, parylene, and Freon treated i-line resist with corresponding interfacial energy differences of 41.3, 40.2, and 32.4 mJ/m^2, respectively. Coating control and surface issues associated with dip coating have been characterized in order to control the volume of capillary liquid coated onto the binding sites. Dip coating of the capillary fluid gives thicknesses according to h~ = WCa^l/ll, where Ca is the capillary number and W is the binding site half-width. It has been determined that tilted microcomponent positioning is caused by trapping of the assembly fluid inside the capillary fluid, caused by binding site defects.
December 31, 2003
Scott, K. L. (2003). Electrical Interconnect of Components Transferred by Fluidic Microassembly Using Capillary Forces. United States: University of California, Berkeley.