Publications

Similar to other refractory metals, commercially pure niobium is difficult attach using soldering processes without first plating with nickel-gold, nickel-tin or similar materials that are directly solderable. Currently used procedures require the aforementioned plating process or a step-brazing process in which copper substrates are brazed at a lower temperature onto the niobium surfaces eliminating the plating requirements. A solder-dipping process is then used to pre-tin the exposed copper surfaces, preparing them for next-assembly soldering steps. As part of a product development effort to reduce or eliminate entire processes or processing steps, a project was initiated to replace commercially pure niobium sheet material with explosively bonded niobium-copper sheet. The exposed copper surfaces could then be subsequently coated using a solder dipping procedure. To simulate the component brazement geometry, explosively bonded niobium and copper metal sheets were actively brazed to 94% alumina ceramic test specimens. The thickness of the explosively bonded substrates was 0.5 mm and the thickness of the niobium metal approximately twice that of the copper. ASTM F19 tensile buttons were fabricated using the explosively bonded niobium-copper material as the interlayers. The test samples were active brazed using a commercially available gold-based active brazing filler metal of the composition 35Au-62Cu-2Ti-1Ni (wt %). Brazing peak temperatures and soak times at peak temperatures were varied to assess the process robustness. Finite element analysis (FEA) simulations were performed to determine the theoretical residual stresses in the braze samples. Helium mass spectrometer leak detection data, brazed sample tensile strengths and scanning electron microscope image analysis of the niobium-copper, niobium-alumina and copper-alumina interfaces will be presented. Copyright 2012 ASM International® All rights reserved.

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Many microfabrication techniques are being developed for applications in microelectronics, microsensors, and micro-optics. Since the advent of microcomponents, designers have been forced to modify their designs to include limitations of current technology, such as the inability to make three-dimensional structures and the need for piece-part assembly. Many groups have successfully transferred a wide variety of patterns to both two-dimensional and three-dimensional substrates using microcontact printing. Microcontact printing is a technique in which a self-assembled monolayer (SAM) is patterned onto a substrate by transfer printing. The patterned layer can act as an etch resist or a foundation upon which to build new types of microstructures. We created a gold pattern with features as small as 1.2 {micro}m using microcontact printing and subsequent processing. This approach looks promising for constructing single-level structures such as microelectrode arrays and sensors. It can be a viable technique for creating three-dimensional structures such as microcoils and microsprings if the right equipment is available to achieve proper alignment, and if a means is available to connect the final parts to other components in subsequent assembly operations. Microcontact printing provides a wide variety of new opportunities in the fabrication of microcomponents, and increases the options of designers.

Ceramic interconnect technology has been adapted to new structures. In particular, the ability to customize processing order and material choices in Low Temperature Cofired Ceramic (LTCC) has enabled new features to be constructed, which address needs in MEMS packaging as well as other novel structures. Unique shapes in LTCC permit the simplification of complete systems, as in the case of a miniature ion mobility spectrometer (IMS). In this case, a rolled tube has been employed to provide hermetic external contacts to electrodes and structures internal to the tube. Integral windows in LTCC have been fabricated for use in both lids and circuits where either a short term need for observation or a long-term need for functionality exists. These windows are fabricated without adhesive, are fully compatible with LTCC processing, and remain optically clear. Both vented and encapsulated functional volumes have been fabricated using a sacrificial material technique. These hold promise for self-assembly of systems, as well as complex internal structures in cavities, micro fluidic and optical channels, and multilevel integration techniques. Separation of the burnout and firing cycles has permitted custom internal environments to be established. Existing commercial High Temperature Cofired Ceramic (HTCC) and LTCC systems can also be rendered to have improved properties. A rapid prototyping technique for patterned HTCC packages has permitted prototypes to be realized in a few days, and has further applications to micro fluidics, heat pipes, and MEMS, among others. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.