Propagation of adhesives in joints during capillary adhesive bonding of microcomponents

 Capillary adhesive bonding is used successfully to integrate microsystems. To ensure high reliability and quality of the interconnection technique, it is imperative that the propagation of adhesives in the joints be controlled. Two adhesives frequently used in capillary adhesive bonding were examined: a one-component, UV-curing methacrylate adhesive (Dymax 191-M), and a two-component epoxy resin bonding adhesive curing at room temperature (Epo-tek 302-3M). The propagation of these adhesives in joints with different gap heights of 2–20 μm between two PMMA surfaces and between one PMMA and one PI surface was measured and compared with the theoretical adhesive propagation in accordance with the Hagen–Poiseuille equation for a gap flow, with the capillary pressure taken into account. Once the dynamic viscosity, the wetting angle and the surface tension of the adhesive have been determined as a function of the measuring time, the measured propagation of the Epo-tek 302-3M and Dymax 191-M adhesives can be described in good agreement with the theory for all the gap heights under study. Received: 30 March 1999 / Accepted: 12 April 1999     

Device-level hermetic packaging of microresonators by RTP aluminum-to-nitride bonding

This paper presents a device-level microelectromechanical systems (MEMS) packaging process with accelerated tests and reliability analysis. Surface-micromachined microresonators are sealed inside microcavities by a rapid thermal processing (RTP) aluminum-to-silicon nitride bonding and packaging technique. Chip-to-chip bonding is used to form packages both under atmospheric pressure and in vacuum. The hermeticity of the package seals are evaluated by IPA (isopropyl alcohol) leak tests. The vacuum seal is evaluated by measuring the Q-factor (quality factor) of the packaged microresonators. The measured Q-factor of a vacuum-packaged comb-resonator is 1800/spl plusmn/200, corresponding to a 200 motor vacuum inside the micro cavity, and has not degraded over 37 weeks of shelf-life. The reliability information is evaluated by combining accelerated testing of the packages in a harsh environment (an autoclave chamber, 130/spl deg/C, 2.7 atm and 100% RH) and statistical analysis. The mean-time-to-failure (MTTF) of the packaged device is estimated as 29.7 weeks in an autoclave chamber, and tests on vacuum-packaged devices have confirmed the estimation.     

Reliability study of hermetic wafer level MEMS packaging with through-wafer interconnect

In this paper, we developed a hermetic wafer level packaging for MEMS devices. Au–Sn eutectic bonding technology in a relatively low temperature is used to achieve hermetic sealing, and the vertical through-hole via filled with electroplated copper for the electrical connection is also used. The MEMS package has the size of 1 mm × 1 mm × 700 μm, and a square loop Au–Sn metallization of 70 μm in width for hermetic sealing. The robustness of the package is confirmed by several tests such as shear strength test, reliability tests, and hermeticity test. The reliability issues of Au–Sn bonding technology, and copper through-wafer interconnection are discussed, and design considerations to improve the reliability are also presented. By applying O₂ plasma ashing and fabrication process optimization, we can achieve the void-free structure within the bonding interface. The mechanical effects of copper through-vias are also investigated numerically and experimentally. Several factors which could induce via hole cracking failure are investigated such as thermal expansion mismatch, via etch profile, copper diffusion phenomenon, and cleaning process. Alternative electroplating process is suggested for preventing Cu diffusion and increasing the adhesion performance of the electroplating process.     

Development of near hermetic silicon/glass cavities for packaging of integrated lithium micro batteries

A technology was developed for fabrication of very thin, chip-sized lithium secondary micro batteries. With help of wafer level processing the batteries can be directly integrated into silicon chips or MEMS devices. The batteries were packaged in 200 μm deep cavities of the silicon wafer and encapsulated with a glass substrate. Battery demonstrators were realized with 7 and 12 mm square and round foot prints. Near hermetic packaging was accomplished with the help of a UV curable epoxy seal that should ensure several years of battery lifetime. Bonding parameters, shear force and the water permeation rate of the adhesive were investigated. A capacity of 3 mAh/cm² and an energy density of 10 mWh/cm² were achieved. The electrical contact between the battery and the contact pads of the housing was investigated in detail. Electrical tests were made with encapsulated micro batteries and compared with macroscopic lithium polymer batteries. A reduction in capacity of approximately 10% was measured after 100 cycles.     

A new COP bonding using non-conductive adhesives for LCDs driver IC packaging

In this study, attempts were made to develop a reliable and low cost chip on plastic (COP) bonding process by using electroplated Sn bump and non-conductive adhesives. Results showed that the bumped chip was successfully bonded with PES, and the initial average contact resistance was less than 30 mΩ, which is much lower than that of ACF bonding. Thermal cycling (TC) test was performed to study the reliability of the COP assembly. The joints passed over 1000 thermal cycles without failure. The contact resistance decreased and leveled off during the TC test. 30 μm fine pitch joints were fabricated and electrically tested. Microstructure observation disclosed that interfacial intermetallic compound formed at the Sn/pad interface, indicating a chemical bonding was achieved. EDS analysis showed that its average composition was very close to (Cu, Au)₆Sn₅. During thermal cycling, the interfacial IMC layers were observed to gain dramatic growth.     

A new generic surface micromachining module for MEMS hermetic packaging at temperatures below 200 °C

This paper presents the different processing steps of a new generic surface micromachining module for MEMS hermetic packaging at temperatures around 180 °C based on nickel plating and photoresist sacrificial layers. The advantages of thin film caps are the reduced thickness and area consumption and the promise of being a low-cost batch process. Moreover, sealing happens by a reflow technique, giving the freedom of choosing the pressure and atmosphere inside the cavity. Sacrificial etch holes are situated above the device allowing shorter release times compared to the state-of-the-art. With the so-called over-plating process, small etch holes can be created in the membrane without the need of expensive lithography tools. The etch holes in the membrane have been shown to be sufficiently small to block the sealing material to pass through, but still large enough to enable an efficient release.     

Production processes and applications for the passive alignment of microcomponents

Research into structural elements for the passive alignment of microcomponents is an essential part of the framework of the collaborative research center 440 (SFB 440). For this purpose, V-groove structures for the passive alignment of cylindrical microcomponents are in a first step examined theoretically. The theoretical results are then validated by experimental testing. The use of ultra precision engineering processes, such as diamond machining, for the production of passive alignment structures is then introduced and the alignment precision of these structures is measured by the use of glass fibres representing the cylindrical microcomponents and acting as light sources for the optical observation of the alignment accuracy. In addition, these structures are compared with alignment structures which are fabricated through lithographic and micro-electroplating processes.     

Modeling of hermetic transitions for microwave packages

Two numerical techniques, the finite difference in time domain (FDTD) and the finite element method (FEM) in frequency domain, are employed to characterize microstrip hermetic transition geometries in an effort to investigate high-frequency effects. Measurements performed on these transitions compare favorably with theory. Two different types of transitions have been analyzed from 10 to 25 GHz and have been found to be limited in performance by higher return loss as frequency increases. It is shown that microstrip-through-CPW hermetic transitions in the shielded environment may suffer from parasitic waveguide modes which, however, can be eliminated with the use of vias at appropriate locations. The hermetic wall on top of the CPW section shows a relatively small (≤ 2 dB) effect on the original circuit performance. Similarly, the hermetic bead transition shows good performance at a lower frequency region while it degrades as frequency increases. This indicates the need for very careful characterization of transitions intended for use in microwave and millimeter-wave applications. © 1996 John Wiley & Sons, Inc.     

Fabrication of ceramic microcomponents and microreactor for the steam reforming of ethanol

Ceramics have several advantages over other materials in MEMS, such as heat resistance, hardness, corrosion resistivity even in harsh environments, chemical inertness for biological applications and catalytic activity of surfaces and so on. For these advantages ceramic microstructures will be very potentially useful in microsystem, especially in microreactor. A novel method for the high aspect ratio micro ceramic structures fabrication based on deep X-ray lithography and lost-mold technique is developed. By using this method, ceramic microreactors have been successfully fabricated. The ceramic microreactor consists of 14 identical microchannels in parallel, each with typical dimensions of approximately 300 μm in width, 400 μm in height and 20 mm in length. The Ni film catalyst with thickness of 300 nm is uniformly coated through sputtering process. The steam reforming of Ethanol into hydrogen on the ceramics microreactor was studied at temperatures between 500 and 700°C. The microreactors have been characterized by studying of C₂H₆O conversion, H₂ selectivity, and product stream composition.     

Manufacturing and packaging of sensors for their integration in avertical MCM microsystem for biomedical applications

Demonstrates the feasibility of integrating fragile micromachined chips into a complex three-dimensional (3-D) multichip module (MCM) microsystem for a biomedical application. The system is based on the vertical integration of the different parts: micropumps and valves, a multisensor chip for on-line control of the system and a signal-processing chip. In this paper, packaging of the microsystem is studied in order to minimize the induced stress that can affect the integrity of the different micromachined parts of the system. Standard commercially available components and materials were used so as to minimize costs for the case of high volume packaging. For testing the approach, a multisensor chip which includes thin silicon membrane-based devices has been used as the main test structure to compare different packaging materials. In addition, for the fabrication of such a sensor chip in an efficient mode, technological modules needed to fabricate sensors on complementary metal-oxide-semiconductor (CMOS) wafers are discussed. The definition of standardized add-on sensor modules to the CMOS process of a foundry is intended to limit the development cost of smart sensors     

A mold and transfer technique for lead-free fluxless soldering and application to MEMS packaging

This paper demonstrates a technique to premold and transfer lead-free solder balls for microelectrocmechanical systems (MEMS)/electronics packaging applications. A reusable bulk micromachined silicon wafer is used to mold a solder paste and remove excess flux prior to transfer to a host wafer that may contain released MEMS. This technique has been used to fabricate low temperature thin film MEMS vacuum packages. Long term (>5 months) reliability of these packages at room temperature and pressure is demonstrated through integrated Pirani gauges. These packages have survived over 600 hours in an autoclave (130/spl deg/C, 85% RH, 2 atm) and more than 1300 temperature cycles (55/spl deg/C to 125/spl deg/C).     

A hermetic glass-silicon micropackage with high-density on-chipfeedthroughs for sensors and actuators

This paper describes the development of a hermetic micropackage with high-density on-chip feedthroughs for sensor and actuator applications. The packaging technique uses low-temperature (320°C) electrostatic bonding of a custom-made glass capsule (Corning 7740, 2×2×8 mm³) to fine grain polysilicon in order to form a hermetically sealed cavity. High-density on-chip multiple polysilicon feedthroughs (200 per millimeter) are used for connecting external sensors and actuators to the electronic circuitry inside the package. A high degree of planarity over feedthrough areas is obtained by using grid-shaped polysilicon feedthrough lines that are covered with phosphosilicate glass (PSG), which is subsequently reflown at 1100°C in steam for 2 h. Saline and DI water soak tests at elevated temperatures (85 and 95°C) were performed to determine the reliability of the package. Preliminary results have shown a mean time to failure (MTTF) of 284 days and 118 days at 85 and 95°C, respectively, in DI water. An Arrhenius diffusion model for moisture penetration yields an expected lifetime of 116 years at body temperature (37°C) for these packages. In vivo tests in guinea pigs and rats for periods ranging from one to two months have shown no sign of infection, inflammation, or tissue abnormality around the implanted package     

包装防伪中信息技术的应用研究

在现代包装中应用信息防伪技术,可提高防伪质量、增强客户便利性、增加客户与商品之间的互动。同时,因启用信息防伪技术具有一定的难度与成本,进而让相关厂家难以仿造出假冒伪劣制品,可以为商品安全提供保障。     

Galvanic deposition in partially conductive plastic molds for manufacture of finely detailed microcomponents

Combining multicomponent injection molding and electroforming processes, a method for manufacturing medium and large quantities of high-quality metallic parts had been developed. Since the process steps involved are based on two technologies suitable for series production, low product costs per unit will be realistic. The high quality of the metallic microparts was verified, among other things, by means of demonstrator surface and dimensional measurements. Compared with competing methods (MicroPIM), significantly better or at least equal values were obtained. In addition, multi-material micro components containing e.g., ceramic inserts were manufactured successfully. There are certain potentials for optimizing the dimensional accuracy or scatter of the finished galvanic parts. Besides, 2C film injection molding, which allows replication of very fine exposed structures, has been examined successfully and will be developed further.     

Reliability of thermo-setting anisotropically conductive adhesives in Chip on Glass application

Thermo-setting type anisotropically conductive adhesives have been identified to possess key properties suitable for interconnection of bare chip directly to glass substrate (CoG). The coG technology offers higher electric performance, shorter signal delays and further miniaturisation compared to the conventional heat seal interconnecting technology. This paper summarizes reliability testing results using thermo-setting anisotropically conductive for CoG interconnection. Anisotropically conductive adhesives in paste and film are used for interconnection on the following bumping surfaces: chemical plated Ni and electrolytically plated Au. Mechanical and electric measurements were performed before and after environmental tests in terms of temperature cycling between −40 and +85°C for 1000 cycles and in terms of different constant humidity conditions at 60°C, 95% RH and at 85°C, 85% RH, each for 1000 hours. The results show that high-reliable anisotropically conductive adhesive joints can be obtained for the CoG application. This work is sponsored by NUTEK (the National Swedish Board for Industrial and Technical Development) with Grant No 92-9258 and supported by the following companies: DA Elektronik AB, Ericsson Components AB, Ericsson Microwave Systems AB, Esselte Meto Electronic Display Systems, ICL AB, Loctite Ltd, Nokia Mobile Phones OY, Planar International Ltd, Propoint Electronics AB, Combitech Electronics AB, Touch Display Systems AB and Victor Hasselblab AB. This work is also a result of a collaboration between VTT Electronics Laboratory, Finland and IVF, Sweden.     

MEMS器件气密性封装的低温共晶键合工艺研究

介绍了一种采用Pb-Sn共晶合金作为中间层的键合封装技术,通过电镀的方法在芯片与基片上形成Cr/N i/Cu/Pb-Sn多金属层,在温度为190℃、压强为150 Pa的真空中进行键合,键合过程不需使用助焊剂,避免了助焊剂对微器件的污染。试验表明:这种键合工艺具有较好的气密性,键合区合金分布均匀、无缝隙、气泡等脱焊区,键合强度较高,能够满足电子元器件和微机电系统(MEMS)可动部件低温气密性封装的要求。     

Tactile displays: guidance for their design and application

OBJECTIVE: This article provides an overview of tactile displays. Its goal is to assist human factors practitioners in deciding when and how to employ the sense of touch for the purpose of information representation. The article also identifies important research needs in this area. BACKGROUND: First attempts to utilize the sense of touch as a medium for communication date back to the late 1950s. For the next 35 years progress in this area was relatively slow, but recent years have seen a surge in the interest and development of tactile displays and the integration of tactile signals in multimodal interfaces. A thorough understanding of the properties of this sensory channel and its interaction with other modalities is needed to ensure the effective and robust use of tactile displays. METHODS: First, an overview of vibrotactile perception is provided. Next, the design of tactile displays is discussed with respect to available technologies. The potential benefit of including tactile cues in multimodal interfaces is discussed. Finally, research needs in the area of tactile information presentation are highlighted. RESULTS: This review provides human factors researchers and interface designers with the requisite knowledge for creating effective tactile interfaces. It describes both potential benefits and limitations of this approach to information presentation. CONCLUSION: The sense of touch represents a promising means of supporting communication and coordination in human-human and human-machine systems. APPLICATION: Tactile interfaces can support numerous functions, including spatial orientation and guidance, attention management, and sensory substitution, in a wide range of domains.     

Tribological characterization and numerical wear simulation of microcomponents under sliding and rolling conditions

Increasing requirements for higher power densities and further miniaturisation in microsystem technology result in highly loaded micromechanical systems. Regarding these applications, the friction and wear behaviour of self-mated Si₃N₄ ceramic and WC-Co hardmetal has been characterized in laboratory micro tribometers. Experiments under unidirectional sliding and rolling conditions were carried out in air of 50% relative humidity as well as lubricated with water. Results from the model tests were used as input dataset for a numerical simulation tool Global Incremental Wear Model (GIWM) to predict volumetric wear as a function of operating conditions. The laboratory tests indicated that WC-Co as well as Si₃N₄ are applicable for microsystems running in water, due to their high wear resistance and low friction coefficient. Furthermore it was shown, that the numerical simulation can help to reduce the experimental effort by reliable predicting wear under different operating conditions, provided that the active wear mechanisms are comparable.     

Dispensing and hermetic sealing Rb in a miniature reference cell for integrated atomic clocks

An innovative method for fabricating the reference cell for a Rubidium (Rb) integrated atomic clock is presented. This method uses low-temperature solder sealing technique for producing mini-cells of the size of 14 mm × 10 mm × 3 mm, suitable for Rb miniature atomic clocks. Top and bottom of the cell consists of two glass slides. An LTCC (low-temperature cofired ceramic) module of 2 mm thickness, equipped with a small reservoir for confining the Rb is placed in between the two walls, acting as a spacer, increasing the total volume of the cell. A solder ring joins together the LTCC and the top of the cell. This paper also presents a new technique for handling the Rb, which allows its safe handling and long storage. The alkali metal is stored inside a pool of dodecane, which protects it from oxidation. Pure liquid Rb is then dispensed inside the adjacent reservoir using a glass micropipette; finally, the cell is heated in vacuum, in order to carry out the sealing. The achieved sealing hermeticity was tested, without Rb, by sealing N₂O gas and monitoring its pressure through absorbance measurements using FTIR spectroscopy. Hermeticity was also tested with Rb by integrating a pressure sensor in the LTCC module.     

Laser micromaching and light induced reaction injection molding as suitable process sequence for the rapid fabrication of microcomponents

 For the last years different “rapid”-technologies like Rapid Prototyping, Rapid Manufacturing or Rapid Tooling have been developed in the macro world for a fast prototype or molding tool generation in case of e.g. form visualisation or small scale production. Commercially available equipment allows smallest structural details of at least 100 μm and a position accuracy of 25 μm. Due to the poor achievable precision of the mentioned systems in comparison to the necessities in MST only a few attempts for the realisation of “micro-rapid” technologies have been investigated. In this work an approach which combines Rapid Tooling (mold insert fabrication via laser micromaching) with Rapid Prototyping (replication via light induced reaction injection molding) will be introduced and different examples for application e.g. in microfluidics will be given. Received: 30 May 2001 / Accepted: 3 August 2001