Lithographic, Galvanoformung, Abformung (LIGA) component fabrication is a process in which structural material is deposited into a patterned polymethyl-methacrylate (PMMA) mold realized through deep X-ray lithography. The process permits fabrication of metal microelectromechanical systems (MEMS) components with representative dimensions that range from a few microns to several millimeters. This investigation characterizes the microstructure and mechanical properties of LIGAfabricated nickel (LIGA Ni), electrodeposited using Watts bath and sulfamate bath chemistries. As a prelude to studying high-temperature joining processes in LIGA Ni components, an annealing investigation was conducted on samples fabricated from both bath chemistries. Mechanical properties and microstructural analyses on as-deposited and annealed samples were conducted using a mini servohydraulic load frame and the electron backscatter diffraction (EBSD) microtexture measurement technique. The deposits were found to have fine-grain, highly textured microstructures oriented with an acicular or columnar morphology relative to the plating direction. Previously uncharacterized, anomalous, local spatial variations in the crystallographic texture of the as-deposited microstructures were identified by EBSD analyses. Microstructural evolution during annealing seemed to follow a recovery, recrystallization, rapid grain-growth microstructural-evolution mechanism in LIGA Ni deposited from the sulfamate bath chemistry and simply a recovery and grain-growth microstructural-evolution mechanism in LIGA Ni deposited from the Watts bath chemistry. The evolution of microstructure in the annealed samples corresponded with a dramatic drop in their strength and determined the limiting diffusion-bonding temperature for LIGA Ni components.
The characteristics of a nickel sulfamate/iron chloride plating bath suitable for high rate electrodeposition of NiFe alloys are described. The effects of current density, electrolyte agitation, and Ni ϩ2 /Fe ϩ2 content on deposit composition and plating current efficiency are explored via stripping voltammetry using a rotating ring-disk electrode. Specific plating bath formulations and operating conditions for depositing a wide range of alloy compositions at a variety of growth rates are illustrated. Special attention is given to determination of polarization and electrolyte mixing conditions for plating Permalloy and Invar. X-ray diffraction studies are used to investigate relationships between alloy composition and crystal structure. The implications for using the plating bath to electroplate composition-modulated alloys and 3D microstructures are discussed.
This paper describes the development of a fabrication and etching process for the in-situ formation of sacrificial layers in electrodeposited NiFe magnetic alloys. Sacrificial layers consist of iron-rich material electrodeposited in a nickel-rich matrix. The iron-rich layers are formed using a pulsed electrolyte agitation scheme. The removal of sacrificial layers is investigated using a concentrated acid etching procedure as well as a potentialenhanced etching technique. The formation of sacrificial layers in electrodeposited microgears and planar films is demonstrated. We find that glacial acetic acid preferentially removes the sacrificial layers at a rate of 0.5 µm hr −1 while leaving the remaining nickel-rich structure unaffected. An applied potential is used to accelerate the etch rate of sacrificial material in dilute acetic acid as well as in a chloride-based etching solution. Under potential control, sacrificial layers are etched at rates approaching 80 µm hr −1 . The remaining nickel-rich matrix is not significantly affected during etching and retains its structural fidelity. NiFe sacrificial layers of varying compositions are shown to etch at rates that depend on the iron content. The implications for using these techniques in conventional through-mold plating applications are discussed.
Flow-induced NiFe composition-modulated alloys (CMAs) are plated onto the disk of a rotating ring-disk electrode (RRDE) by oscillating the RRDE rotation rate during galvanostatic deposition. The relationships between processing and compositional structure in the electrodeposited CMAs are explored using an optimized potentiostatic stripping voltammetry technique, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Results show that the CMA wavelength scales as the inverse of the flow oscillation frequency and the composition modulation amplitude are strongly affected by variations in both electrolyte flow oscillation frequency and amplitude. Fast Fourier transform analysis is used to probe the dynamic time scales of NiFe electrodeposition and to investigate the sensitivity of NiFe deposition to the oscillating electrolyte flow field. Results indicate that critical deposition chemistries occur over time scales much slower than those governing typical mass-transfer processes.
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