Abstracts Engineering

The use of electrochemical micromachining for making a microfloat valve

by Sang-Bin Park

Micromanufacturing consists of processes for producing structures, devices or systems with feature sizes measured in micrometers. Micromanufacturing began in the mid-1960's with microelectronics fabrication technology. In the 1980's, Micro-Electro-Mechanical Systems (MEMS) began to be developed, in which electrical and mechanical subsystems were integrated at small scales. More recently, Microtechnology-based Energy and Chemical Systems (MECS) have been developed that have led to improved heat and mass transfer in energy and chemical systems. At Oregon State University, new methods to fabricate MECS have been developed. One of the new methods involves microlamination – bonding thin strips of different materials together. This method has generated a high volume and low-cost approach to the production of high-aspect-ratio (height-to-width) structures. Past efforts to make microfloat valves using microlamination methods resulted in an 11:1 diodicity ratio. It was hypothesized that the valve had a ridge of redeposited material around the valve seat caused by the condensation and deposition of ablation ejecta during laser machining. The contribution of this thesis is the creation of a microfloat valve using an Electrochemical Micromachining (EMM) method. EMM methods are known to produce smooth surfaces, free of burrs or any other types of aspirates. Therefore, it was hypothesized that float valves made with EMM methods would improve valve performance. Four steps were involved in the creation of the microfloat valve: lamina formation, laminae registration, laminae bonding and component dissociation. A total of 9 laminae-some of which were made with 304 stainless steel 76.2 μm thick, others of which were made with 50.8 μm thick polyimide-made up the microfloat valve. Photolithography and EMM were used to form the lamina. Even though the laminae created by EMM were smaller in size than desired, the machined areas did not have redeposited material, and some areas had straight walls. In laminae registration, a two edge registration method was used. In the laminae bonding step, laminae were bonded by the adhesive method at 248°C under 135 kPa pressure for 13.5 minutes. In the component dissociation step, a capacitor dissociation method that was designed at OSU was used. Upon performance testing, the average diodicity ratio for the EMM valve was 12.45 over the range 0 kPa-450 kPa, indicating improved performance when compared to the Laser Ablation valve-which had an average 11.17 over the range 0 kPa-100 kPa. Microscope examination of valves revealed that statistically significant improvement in valve performance would require refinement of component dissociation methods.