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Development of lead-free solders for hybrid microcircuits

Description: Extensive work has been conducted by industry to develop lead-free solders for electronics applications. The driving force behind this effort is pressure to ban or tax the use of lead-bearing solders. There has been further interest to reduce the use of hazardous chemical cleaners. Lead-free soldering and low-residue, ``no clean`` assembly processing are being considered as solutions to these environmental issues. Most of the work has been directed toward commercial and military printed wiring board (PWB) technology, although similar problems confront the hybrid microcircuit (HMC) industry, where the development of lead-free HMC solders is generally lagging. Sandia National Laboratories is responsible for designing a variety of critical, high reliability hybrid components for radars. Sandia has consequently initiated a project, as part of its Environmentally Conscious Manufacturing program, to develop low-residue, lead-free soldering for HMCs. This paper discusses the progress of that work.
Date: January 1, 1996
Creator: Hosking, F.M.; Vianco, P.T.; Frear, D.R. & Robinson, D.G.
Partner: UNT Libraries Government Documents Department

Challenges in the Packaging of MEMS

Description: The packaging of Micro-Electro-Mechanical Systems (MEMS) is a field of great importance to anyone using or manufacturing sensors, consumer products, or military applications. Currently much work has been done in the design and fabrication of MEMS devices but insufficient research and few publications have been completed on the packaging of these devices. This is despite the fact that packaging is a very large percentage of the total cost of MEMS devices. The main difference between IC packaging and MEMS packaging is that MEMS packaging is almost always application specific and greatly affected by its environment and packaging techniques such as die handling, die attach processes, and lid sealing. Many of these aspects are directly related to the materials used in the packaging processes. MEMS devices that are functional in wafer form can be rendered inoperable after packaging. MEMS dies must be handled only from the chip sides so features on the top surface are not damaged. This eliminates most current die pick-and-place fixtures. Die attach materials are key to MEMS packaging. Using hard die attach solders can create high stresses in the MEMS devices, which can affect their operation greatly. Low-stress epoxies can be high-outgassing, which can also affect device performance. Also, a low modulus die attach can allow the die to move during ultrasonic wirebonding resulting to low wirebond strength. Another source of residual stress is the lid sealing process. Most MEMS based sensors and devices require a hermetically sealed package. This can be done by parallel seam welding the package lid, but at the cost of further induced stress on the die. Another issue of MEMS packaging is the media compatibility of the packaged device. MEMS unlike ICS often interface with their environment, which could be high pressure or corrosive. The main conclusion we can draw about MEMS ...
Date: March 26, 1999
Creator: Malshe, A.P.; Singh, S.B.; Eaton, W.P.; O'Neal, C.; Brown, W.D. & Miller, W.M.
Partner: UNT Libraries Government Documents Department

Final Report: Free Standing Quantum Wells, August 15, 1996 - May 31, 1999

Description: Recent advances in microfabrication techniques in conjunction with the precise growth of layers of single crystalline materials by epitaxial growth techniques allow the creation of new electro-optic microstructures. We have selectively etched compositionally modulated 111-v heterostructures to produce quantum wells (QW's) which are confined on both sides by air or vacuum. The material is patterned so to have the QW's suspended horizontally between vertical support posts. This structure is ideal for probing the local properties of solids, e.g., the interaction of quantum confined states with surface or interface states.
Date: October 11, 1999
Creator: Williams, M.D.; Lee, H.W.H. & Collins, J.
Partner: UNT Libraries Government Documents Department

Meso-scale machining capabilities and issues

Description: Meso-scale manufacturing processes are bridging the gap between silicon-based MEMS processes and conventional miniature machining. These processes can fabricate two and three-dimensional parts having micron size features in traditional materials such as stainless steels, rare earth magnets, ceramics, and glass. Meso-scale processes that are currently available include, focused ion beam sputtering, micro-milling, micro-turning, excimer laser ablation, femto-second laser ablation, and micro electro discharge machining. These meso-scale processes employ subtractive machining technologies (i.e., material removal), unlike LIGA, which is an additive meso-scale process. Meso-scale processes have different material capabilities and machining performance specifications. Machining performance specifications of interest include minimum feature size, feature tolerance, feature location accuracy, surface finish, and material removal rate. Sandia National Laboratories is developing meso-scale electro-mechanical components, which require meso-scale parts that move relative to one another. The meso-scale parts fabricated by subtractive meso-scale manufacturing processes have unique tribology issues because of the variety of materials and the surface conditions produced by the different meso-scale manufacturing processes.
Date: May 15, 2000
Partner: UNT Libraries Government Documents Department

MEMS Packaging - Current Issues and Approaches

Description: The assembly and packaging of MEMS (Microelectromechanical Systems) devices raise a number of issues over and above those normally associated with the assembly of standard microelectronic circuits. MEMS components include a variety of sensors, microengines, optical components, and other devices. They often have exposed mechanical structures which during assembly require particulate control, space in the package, non-contact handling procedures, low-stress die attach, precision die placement, unique process schedules, hermetic sealing in controlled environments (including vacuum), and other special constraints. These constraints force changes in the techniques used to separate die on a wafer, in the types of packages which can be used in the assembly processes and materials, and in the sealing environment and process. This paper discusses a number of these issues and provides information on approaches being taken or proposed to address them.
Date: January 19, 2000
Partner: UNT Libraries Government Documents Department

The Impact of Emerging MEMS-Based Microsystems on US Defense Applications

Description: This paper examines the impact of inserting Micro-Electro-Mechanical Systems (MEMS) into US defense applications. As specific examples, the impacts of micro Inertial Measurement Units (IMUs), radio frequency MEMS (RF MEMS), and Micro-Opto-Electro-Mechanical Systems (MOEMS) to provide integrated intelligence, communication, and control to the defense infrastructure with increased affordability, functionality, and performance are highlighted.
Date: January 20, 2000
Partner: UNT Libraries Government Documents Department

Infrastructure, Technology and Applications of Micro-Electro-Mechanical Systems (MEMS)

Description: A review is made of the infrastructure, technology and capabilities of Sandia National Laboratories for the development of micromechanical systems. By incorporating advanced fabrication processes, such as chemical mechanical polishing, and several mechanical polysilicon levels, the range of micromechanical systems that can be fabricated in these technologies is virtually limitless. Representative applications include a micro-engine driven mirror, and a micromachined lock. Using a novel integrated MEMS/CMOS technology, a six degree-of-freedom accelerometer/gyroscope system has been designed by researchers at U.C. Berkeley and fabricated on the same silicon chip as the CMOS control circuits to produce an integrated micro-navigational unit.
Date: July 9, 1999
Creator: Allen, J.J.; Jakubczak, J.F.; Krygowski, T.W.; Miller, S.L.; Montague, S.; Rodgers, M.S. et al.
Partner: UNT Libraries Government Documents Department

Intelligent Microsystems: Keys to the Next Silicon Revolution

Description: Paul McWhorter, Deputy Director for of the Microsystems Center at Sandia National Laboratories, discusses the potential of surface micromachining. A vision of the possibilities of intelligent Microsystems for the future is presented along with descriptions of several possible applications. Applications that are just around the corner and some that maybe quite a ways down the road but have a clear development path to their realization. Microsystems will drive the next silicon revolution.
Date: October 20, 1999
Partner: UNT Libraries Government Documents Department

Conveyorized Photoresist Stripping Replacement for Flex Circuit Fabrication

Description: A replacement conveyorized photoresist stripping system was characterized to replace the ASI photoresist stripping system. This system uses the qualified ADF-25c chemistry for the fabrication of flex circuits, while the ASI uses the qualified potassium hydroxide chemistry. The stripping process removes photoresist, which is used to protect the copper traces being formed during the etch process.
Date: February 24, 2009
Creator: Donahue, Megan
Partner: UNT Libraries Government Documents Department

Laser tabbed die: A repairable, high-speed die-interconnection technology. 1994 LDRD final report 93-SR-089

Description: A unique technology for multichip module production is presented. The technology, called Laser Tabbed Die (L-TAB), consists of a method for forming surface-mount-type {open_quotes}gull wing{close_quotes} interconnects on bare dice. The dice are temporarily bonded to a sacrificial substrate which has a polymer thin film coated onto it. The gull wings are formed on the side of the die with a direct-write laser patterning process which allows vertical as well as horizontal image formation. Using the laser patterning system, trenches are formed in a positive electrodeposited photoresist (EDPR) which is plated onto a metal seed layer, allowing copper to be electroplated through the resultant mask. After stripping the resist and the metal seed layer, the polymer film on the substrate is dissolved, releasing the chip with the {open_quotes}gull wings{close_quotes} intact. The chips are then bonded onto a circuit board or permanent substrate with solder or conductive adhesive.
Date: September 1, 1995
Creator: Malba, V. & Bernhardt, A.F.
Partner: UNT Libraries Government Documents Department

Microelectronics plastic molded packaging

Description: The use of commercial off-the-shelf (COTS) microelectronics for nuclear weapon applications will soon be reality rather than hearsay. The use of COTS for new technologies for uniquely military applications is being driven by the so-called Perry Initiative that requires the U.S. Department of Defense (DoD) to accept and utilize commercial standards for procurement of military systems. Based on this philosophy, coupled with several practical considerations, new weapons systems as well as future upgrades will contain plastic encapsulated microelectronics. However, a conservative Department of Energy (DOE) approach requires lifetime predictive models. Thus, the focus of the current project is on accelerated testing to advance current aging models as well as on the development of the methodology to be used during WR qualification of plastic encapsulated microelectronics. An additional focal point involves achieving awareness of commercial capabilities, materials, and processes. One of the major outcomes of the project has been the definition of proper techniques for handling and evaluation of modern surface mount parts which might be used in future systems. This program is also raising the familiarity level of plastic within the weapons complex, allowing subsystem design rules accommodating COTS to evolve. A two year program plan is presented along with test results and commercial interactions during this first year.
Date: February 1, 1997
Creator: Johnson, D.R.; Palmer, D.W. & Peterson, D.W.
Partner: UNT Libraries Government Documents Department

Modeling and Simulation of Microelectrode-Retina Interactions

Description: The goal of the retinal prosthesis project is the development of an implantable microelectrode array that can be used to supply visually-driven electrical input to cells in the retina, bypassing nonfunctional rod and cone cells, thereby restoring vision to blind individuals. This goal will be achieved through the study of the fundamentals of electrical engineering, vision research, and biomedical engineering with the aim of acquiring the knowledge needed to engineer a high-density microelectrode-tissue hybrid sensor that will restore vision to millions of blind persons. The modeling and simulation task within this project is intended to address the question how best to stimulate, and communicate with, cells in the retina using implanted microelectrodes.
Date: November 30, 2002
Creator: Beckerman, M
Partner: UNT Libraries Government Documents Department

Molecular Dynamics Simulation of Polymer Dissolution

Description: In the LIGA process for manufacturing microcomponents, a polymer film is exposed to an x-ray beam passed through a gold pattern. This is followed by the development stage, in which a selective solvent is used to remove the exposed polymer, reproducing the gold pattern in the polymer film. Development is essentially polymer dissolution, a physical process which is not well understood. We have used coarse-grained molecular dynamics simulation to study the early stage of polymer dissolution. In each simulation a film of non-glassy polymer was brought into contact with a layer of solvent. The mutual penetration of the two phases was tracked as a function of time. Several film thicknesses and two different chain lengths were simulated. In all cases, the penetration process conformed to ideal Fickian diffusion. We did not see the formation of a gel layer or other non-ideal effects. Variations in the Fickian diffusivities appeared to be caused primarily by differences in the bulk polymer film density.
Date: February 1, 2003
Partner: UNT Libraries Government Documents Department

Deep x-ray lithography based processing for micromechanics

Description: Deep x-ray lithography based fabrication provides a means to fabricate microactuators with useful output forces. High energy x-ray exposure provides a tool for fabrication of the next generation of precision engineered components. Device characterization, materials science, an metrology continue to pose challenges at this scale.
Date: October 1995
Creator: Christenson, T. R.
Partner: UNT Libraries Government Documents Department

Micro-machined heat pipes in silicon MCM substrates

Description: Multichip modules (MCMs) containing power components need a substrate with excellent heat spreading capability to both avoid hot spots and to move dissipation heat toward the system heat sinks. Polycrystalline diamond is an excellent MCM heat spreading substrate but remains several orders of magnitude too expensive and somewhat more difficult to process than conventional mother-board materials. Today`s power MCMs concentrate on moderately priced silicon wafers and aluminum nitride ceramic with their improved thermal conductivity and good thermal expansion match to power semiconductor components in comparison to traditional alumina and printed wiring board materials. However, even silicon and AlN substrates are thermally challenged by designers needs. The authors report on the integral fabrication of micro-heat pipes embedded in silicon MCM substrates (5 x 5 cm) by the use of micromachined capillary wick structures and hermetic micro-cavities. This passive microstructure results in more than a 5 times improvement in heat spreading capability of the silicon MCM substrate over a large range of power densities and operating temperatures. Thus diamond-like cooling is possible at silicon prices.
Date: January 1, 1997
Creator: Benson, D.A.; Mitchell, R.T. & Tuck, M.R.
Partner: UNT Libraries Government Documents Department

The Effect of Humidity on the Reliability of a Surface Micromachined Microengine

Description: Humidity is shown to be a strong factor in the wear of rubbing surfaces in polysilicon micromachines. We demonstrate that very low humidity can lead to very high wear without a significant change in reliability. We show that the volume of wear debris generated is a function of the humidity in an air environment. As the humidity decreases, the wear debris generated increases. For the higher humidity levels, the formation of surface hydroxides may act as a lubricant. The dominant failure mechanism has been identified as wear. The wear debris has been identified as amorphous oxidized silicon. Large slivers (approximately 1 micron in length) of debris observed at the low humidity level were also amorphous oxidized silicon. Using transmission electron microscopy, we observed that the wear debris forms spherical and rod-like shapes. We compared two surface treatment processes: a fluorinated si- lane chain, (FITl) and supercritical C02 dried (SCC02). The microengines using the SCC02 process were found to be less reliable than those released with the FIX process under two humidity levels.
Date: February 2, 1999
Creator: Dugger, M.T.; Eaton, W.P.; Irwin, L.W.; Miller, S.L.; Miller, W.M.; Smith, N.F. et al.
Partner: UNT Libraries Government Documents Department

End-point process development for low-volume, high reliability tungsten CMP

Description: A temperature end point method was developed for tungsten CMP (WCMP) processing in the Sandia Microelectronics Development Laboratory (MDL), a facility which develops and prototypes a variety of silicon based devices including ASIC, memory, radiation hardened CMOS and microelectromechanical systems. A large product variety and small production lot size prevents process recipe optimization or standardization for each mask level and product. Rigorous product reliability requirements and prohibitively expensive hardware qualifications essentially require that a single process and consumable set be established for all products, with minimal opportunity for adjustment. A timed process was not suitable without significant potential for manual inspections and rework. Over several weeks of processing on an IPEC 472, the temperature end point method gave a 7.7% 1-sigma end point time distribution. This enabled a 50% reduction in daily process qualification wafers, and allowed minimization of yield loss, rework, and oxide erosion.
Date: December 1, 1997
Creator: Merkle, P.B. & Myers, T.L.
Partner: UNT Libraries Government Documents Department

Performance of a two-mirror, four-reflection, ring-field optical system at {lambda}=13 nm

Description: Performance of an Extreme Ultraviolet Lithography (EUVL) imaging optic was characterized by printing resolution test images in resist. While features as small as 0.137 {mu}m were successfully printed, a resolution of 0.175 {mu}m better represents the performance of the system over the full 0.9 mm{sup 2} image field. The contrast of the aerial image was estimated to be about 40% or less for the fine features printed. This low contrast value is attributed to a degradation of the modulation transfer function due to presence of scattered light in the image.
Date: May 24, 1996
Creator: La Fontaine, B.; Gaines, D.P.; Kania, D.R.; Sommargren, G.E.; Baker, S.L. & Ciarlo, D.
Partner: UNT Libraries Government Documents Department

Moisture and aging effects of solder wettability of copper surfaces

Description: Solderability is a critical property of electronic assembly that affects both manufacturing efficiency and product reliability. There is often a considerable time interval between initial fabrication of a circuit board or component and its use at the assembly level. Parts are often stored under a variety of conditions, usually not controlled. Solder wettability can soon deteriorate during storage, especially in extreme environments. This paper describes ongoing efforts at Sandia to quantify solder wettability on bare and aged Cu surfaces. In addition, organic solderability preservatives (OSPs) were applied to the bare Cu to retard solderability loss due to aging. The OSPs generally performed well, although wetting did decrease with exposure time.
Date: December 1, 1996
Creator: Hernandez, C.L.; Sorensen, N.R. & Lucero, S.J.
Partner: UNT Libraries Government Documents Department

Failure modes in surface micromachined microelectromechanical actuators

Description: In order for the rapidly emerging field of MicroElectroMechanical Systems (MEMS) to meet its extraordinary expectations regarding commercial impact, issues pertaining to how they fail must be understood. The authors identify failure modes common to a broad range of MEMS actuators, including adhesion (stiction) and friction induced failures caused by improper operational methods, mechanical instabilities, and electrical instabilities. Demonstrated methods to mitigate these failure modes include implementing optimized designs, model based operational methods, and chemical surface treatments.
Date: March 1, 1998
Creator: Miller, S.L.; Rodgers, M.S.; LaVigne, G.; Sniegowski, J.J.; Clews, P.; Tanner, D.M. et al.
Partner: UNT Libraries Government Documents Department

Fabrication and testing of optics for EUV projection lithography

Description: Extreme Ultraviolet Lithography (EUVL) is a leading candidate as a stepper technology for fabricating the next generation of microelectronic circuits. EUVL is an optical printing technique qualitatively similar to Deep UV Lithography (DUVL), except that 11-13nm wavelength light is used instead of 193-248nm. The feasibility of creating 0.1µm features has been well-established using small- field EUVL printing tools, and development efforts are currently underway to demonstrate that cost- effective production equipment can be engineered to perform full-width ring-field imaging consistent with high wafer throughput rates. Ensuring that an industrial supplier base will be available for key components and subsystems is crucial to the success of EUVL. In particular, the projection optics are the heart of the EUVL imaging system, yet they have figure and finish specifications that are beyond the state-of-the-art in optics manufacturing. Thus it is important to demonstrate that industry will be able to fabricate and certify these optics commensurate with EUVL requirements. The goal of this paper is to demonstrate that procuring EUVL projection optical substrates is feasible.
Date: September 16, 1998
Creator: Hudyma, R M; Sommargren, G E; Sweeney, D W & Taylor, J S
Partner: UNT Libraries Government Documents Department

Ultra-Precise Assembly of Micro-Electromechanical Systems (MEMS) Components

Description: This report summarizes a three year effort to develop an automated microassembly workcell for the assembly of LIGA (Lithography Galvonoforming Abforming) parts. Over the last several years, Sandia has developed processes for producing surface machined silicon and LIGA parts for use in weapons surety devices. Some of these parts have outside dimensions as small as 100 micron, and most all have submicron tolerances. Parts this small and precise are extremely difficult to assembly by hand. Therefore, in this project, we investigated the technologies required to develop a robotic workcell to assembly these parts. In particular, we concentrated on micro-grippers, visual servoing, micro-assembly planning, and parallel assembly. Three different micro-grippers were tested: a pneumatic probe, a thermally actuated polysilicon tweezer, and a LIGA fabricated tweezer. Visual servoing was used to accuracy position two parts relative to one another. Fourier optics methods were used to generate synthetic microscope images from CAD drawings. These synthetic images are used off-line to test image processing routines under varying magnifications and depths of field. They also provide reference image features which are used to visually servo the part to the desired position. We also investigated a new aspect of fine motion planning for the micro-domain. As parts approach 1-10 {micro}m or less in outside dimensions, interactive forces such as van der Waals and electrostatic forces become major factors which greatly change the assembly sequence and path plans. We developed the mathematics required to determine the goal regions for pick up, holding, and release of a micro-sphere being handled by a rectangular tool. Finally, we implemented and tested the ability to assemble an array of LIGA parts attached to two 3 inch diameter wafers. In this way, hundreds of parts can be assembled in parallel rather than assembling each part individually.
Date: April 1, 1999
Creator: Feddema, J.T.; Simon, R.; Polosky, M. & Christenson, T.
Partner: UNT Libraries Government Documents Department