Hermeticity Test Research Articles

PARTICULAR FEATURES OF ROOT CANAL FILLING IN TEETH WITH RESORBED APICAL OPENING NEAR THE MANDIBULAR CANAL

When filling root canals of teeth with apical resorption near the mandibular canal, there is a risk that the material will go beyond the apex into the region of mandibular canal, which can lead to serious damage to the innervation of this area. In most cases, modern approaches and technologies in endodontics allow to achieve the formation of dentinal plug in the resorption area, thus minimizing the risk of traumatization of the patient.
 Background. Improving efficiency of endodontic treatment of teeth with apical resorption in the region of mandibular canal.
 Materials and methods. 56 patients aged between 18 and 45 years were examined. All patients had clinical signs of mandibular endodontic treatment failure with a dark radiolucent focus in the region of the apex, which bordered the mandibular canal. Radiological indicators and quality of obturation were assessed on the basis of CBCT, the presence of dentinal bridge was assessed visually using a dental microscope and an apical hermetic test. The results were evaluated after 4, 6, 12, and 24 months.
 Results. After 16 weeks of treatment, more than 70% of apical barrier formation occurred in groups 1 and 2, which allowed us to perform a quality permanent obturation without excessive risks of complications.
 Conclusion. The use of a dental microscope in conjunction with modern endodontic techniques in the treatment of teeth with apical resorption can significantly reduce the treatment time, thereby improving the quality of treatment of patients with this pathology.

Low-Temperature Parylene-Based Adhesive Bonding Technology for 150 and 200 mm Wafers for Fully Biocompatible and Highly Reliable Microsystems

Wafer bonding is a crucial process for fabricating microsystems. Within this study, the polymer parylene was used to establish a low-temperature adhesive wafer bonding process for wafers of 150 and 200 mm diameters. The bonding process was investigated for silicon and glass wafers with different additional coatings including silicon dioxide, silicon nitride, aluminum, and parylene C. Important process parameters such as bonding temperature and time were also investigated and the parylene adhesive was analyzed in detail with respect to its dimensions and type. The performance of the parylene bonding was characterized in different aspects, including mechanical tests, cross-sectional scanning electron microscopy, infrared light transmission, and different hermeticity tests. The reliability of the parylene bonded compounds was also investigated with respect to constant loading, mechanical shocking, and thermal cycling. As a result, the parylene bonding is feasible with various materials and shows high tensile and shear strengths of up to 35 MPa and 80 MPa, respectively. Hermeticity was excellent, with a helium leakage rate lower than 10‒7 mbar∙l s−1. The parylene bonded compounds were proven to feature high reliability. Finally, application of the superior properties of the parylene bonding was demonstrated with respect to the fabrication of different three-dimensional structures.

Review of the Techniques to Measure the Hermeticity of Glass Frit Encapsulated Solar Cells

Emerging 3rd generation photovoltaic technologies such as perovskite and dye-sensitized solar cells are very attractive for commercialization mainly due to their low-cost materials and fabrication processes. The main drawback of these devices is their poor long-term stability. To increase the long-term stability of these devices, a hermetic encapsulation is required. The hermeticity of encapsulated devices are measured and characterized using hermeticity tests according to standard test procedures. A review of the several techniques to measure the hermeticity is presented, addressing the test methods, limitations and applicability to perovskite and dye-sensitized solar cells glass frit encapsulated devices.

(Invited) Parylene C Based Adhesive Bonding on 6” and 8” Wafer Level for the Realization of Highly Reliable and Fully Biocompatible Microsystems

The ongoing miniaturization and implementation of new functionalities into micro-electro-mechanical systems (MEMS) demand the development and application of new wafer bonding and encapsulation technologies with a high performance. Requirements are low process temperatures, high mechanical strengths of the bonded interface, as well as the applicability on large wafer sizes. Within the presented study, the polymer Parylene C was used as an adhesive for the bonding of 6” and 8” wafers. Doing so, the material combinations of the wafers, the Parylene thicknesses and geometries as well as the bonding parameters were varied. The properties of the wafer compounds were characterized with various methods, including mechanical tests, infrared imaging, cross-sections, hermeticity tests and the investigation of the thermal reliability. Using the Parylene C bonding process, tensile strengths of up to 35 MPa, and shear strengths of up to 80 MPa were realized. The determined helium leakage rate was lower than 1 ∙ 10-7 mbar ∙ l/s and the thermal reliability was verified to be excellent.

Towards CMOS Bulk Sensing for In-Situ Evaluation of ALD Coatings for Millimeter Sized Implants.

To meet the dimensional requirements for bioelectronic medicine, new packaging solutions are needed that could enable small, light-weight and flexible implants. For protecting the implantable electronics against biofluids, recently various atomic layer deposited (ALD) coatings have been proposed with high barrier properties. Before implantation, however, the protective coating should be evaluated for any defects which could otherwise lead to leakage and device failure. In these cases, the conventional helium leak test method can no longer be used due to the millimeter size of the implant. Therefore, an in-situ sensing platform is needed that could evaluate the coating and justify the implantation of the final device. In this work, we explore the possibility of using the CMOS bulk for such a platform. Towards this aim, as a proof of concept, test chips were made in a standard 6-metal 0.18 µm CMOS process and for the connection to the bulk, a p+ diffusion was used. A group of samples was then coated with an ALD multilayer. For coating evaluation, off-chip DC current leakage and impedance measurements were carried out in saline between the CMOS bulk and a platinum reference electrode. Results were compared between non-coated and coated chips that clearly demonstrated the potential of using the bulk as a sensing platform for coating evaluations. This novel approach could pave the way towards an all integrated in-situ hermeticity test, currently missing in mm-size implants.

ReStore: A wireless peripheral nerve stimulation system

BackgroundThe growing use of neuromodulation techniques to treat neurological disorders has motivated efforts to improve on the safety and reliability of implantable nerve stimulators. New methodThe present study describes the ReStore system, a miniature, implantable wireless nerve stimulator system that has no battery or leads and is constructed using commercial components and processes. The implant can be programmed wirelessly to deliver charge-balanced, biphasic current pulses of varying amplitudes, pulse widths, frequencies, and train durations. Here, we describe bench and in vivo testing to evaluate the operational performance and efficacy of nerve recruitment. Additionally, we also provide results from a large-animal chronic active stimulation study assessing the long-term biocompatibility of the device. ResultsThe results show that the system can reliably deliver accurate stimulation pulses through a range of different loads. Tests of nerve recruitment demonstrate that the implant can effectively activate peripheral nerves, even after accelerated aging and post-chronic implantation. Biocompatibility and hermeticity tests provide an initial indication that the implant will be safe for use in humans. Comparison with existing method(s)Most commercially available nerve stimulators include a battery and wire leads which often require subsequent surgeries to address failures in these components. Though miniaturized battery-less stimulators have been prototyped in academic labs, they are often constructed using custom components and processes that hinder clinical translation. ConclusionsThe results from testing the performance and safety of the ReStore system establish its potential to advance the field of peripheral neuromodulation.

Graphite Foil-Incorporated PAN/Pitch/Phenolic-Derived Carbon/Carbon Composite and Preliminary Hermetic Sealing Test in Molten Fluoride Salt

Graphite Foil-Incorporated PAN/Pitch/Phenolic-Derived Carbon/Carbon Composite and Preliminary Hermetic Sealing Test in Molten Fluoride Salt

Wafer-level packaging for ultra-thin glasses using hermetic room temperature welding technology

The aim of the study was to develop a hermetic package using ultra-thin glass wafers. A novel glass welding technology, with a minimal heat load, was used to construct the encapsulations. Industry requirements of the miniaturization of the electronic components, for example in medical implants and consumer electronics and opto-electronics, challenge the conventional manufacturing technologies and package materials [1]. Low-cost glass interposers and packages have been research by GeorgiaTech at their PRC industry program. Glass packaging can offer even ten times affordable option than using silicon [2]. During the last few years, the advancements in the glass manufacturing technologies have enabled a cost effective production of the ultra-thin glass wafers and panels. Laborious glass grinding process from thick material to ultra-thin is no longer necessary since the fusion forming process can be used. Ultra-thin glass makes it possible to reduce the package size and weight [3]. Typically, glasses thickness of 300 μm or less are considered as ultra-thin material. However, even as thin as 25 μm glass is commercially available [4]. Several methods are used for glass joining including: anodic, fusion, and adhesive bonding [5]. During the recent years increasing number of laser based techniques are applied to glass packaging. Numerous studies have concentrated on frit bonding [6, 7]. Elementary study of the direct laser joining without any additive layers has been demonstrated by Miyamoto et al. [8]. Glass welding method has been further investigated in several researches [9, 10]. The package is constructed of three ultra-thin glass wafers: base and lid, thicknesses of 200 μm and spacer, thickness of 100 μm. Commercially available 6” borosilicate, D263T, wafers are used which were welded together by using novel laser welding technology. Welding is implemented on material interface without using any additive materials or coating layers. Glass surfaces are left untouched and optical quality is retained. Welding was performed on a wafer level and the single packages were cut after the final welding. Hermeticity test was performed to ensure the welding quality. Radioisotope leak test with krypton 85 was performed at Oneida Research Services. The results showed an excellent hermeticity: leak rate less than 6,0×10–12 atmcm3/s Kr-85 was achieved. Limits set in the MIL-standard are easily reached. The study proves that novel glass welding technology can be applied to wafer-level packaging with ultra-thin glasses. Technique eliminates the need of additive materials, and due to the minimal heat load bending and warping of the material can be avoided. Also, glass offers effortless visual inspection through the entire lifetime of the device.

Hermetic package for optical devices using room temperature welding technology and transparent lid, for space applications

The objective of the study was to develop a hermetic package for optical devices, with a transparent lid. A novel room temperature glass welding technology was used for the construction of the packages. The design solution and technology must be robust enough for use in space flight applications. Environmental and hermeticity tests were performed to evaluate the package capability & quality. Whilst initially targeted on a specific requirement, there are several industrial sectors that require hermetic encapsulation including; space, military, biotechnology, and telecoms etc. It is common for the space industry for packages, assemblies or even space craft, to be stored before use, driving the stringent hermeticity requirements, to prevent degradation issues when ground testing, integrating or operating in a space environment. The design and technology of the glass package proved to be robust: environmental tests had no influence on the functionality or properties. Other benefits of the laser welded glass package were also discovered: hermeticity, easy failure analysis and inspection due to the lid and package transparency, and mountable design onto a PCB (printed circuit board). Welding technique offers a quick, one-step, room temperature process without any additive materials.

Low-temperature anodic bonding using thin films of lithium-niobate-phosphate glass

This paper reports on the investigation of a low-temperature anodic bonding process with layers of a lithium-niobate-phosphate glass on chip level. The glass layers are deposited by means of rf sputtering. The applied glass is characterised by its high ion conductivity, enabling anodic bonding at room temperature. Results of the optimisation process concerning the intrinsic stress of the glass layers and the thermal exposure of the substrates through the deposition process are presented. The stoichiometry of the glass layers is verified through Rutherford backscattering spectroscopy (RBS). The bonding strength is measured by tensile tests. Microfabricated atomic vapour cells are used for hermeticity tests of the bonding by absorption measurements of the caesium D1 line.

Wafer-level reliability characterization for wafer-level-packaged microbolometer with ultrasmall array size

For the development of a small and low-cost microbolometer, wafer-level reliability characterization techniques for vacuum-level packaged wafers are introduced. Amorphous-silicon-based microbolometer-type vacuum sensors fabricated on an 8-inch wafer are bonded with a cap wafer by using an Au–Sn eutectic solder. Membrane deflection and integrated vacuum sensor techniques are independently used to characterize the hermeticity at the wafer level. For a packaged wafer with a membrane thickness below 100 μm, it is possible to determine the hermeticity via a screening test performed using an optical detector. An integrated vacuum sensor having the same structure as a bolometer pixel shows a vacuum level below 100 mTorr. All steps from the packaging process to the fine hermeticity test are implemented at the wafer level to verify that high-volume and low-cost production of the microbolometer is possible.

Glass–Glass Laser-Assisted Glass Frit Bonding

A novel sealing method is proposed for encapsulating devices comprised of glass substrates. This sealing method is based on applying a glass frit paste cord onto the substrate and then using a laser beam to locally supply the necessary energy to allow the formation of a hermetic bonding layer. A detailed description of the laser bonding technique, the necessary equipment and method, and a preliminary study is carried out. The need to apply mechanical pressure during the bonding step is averted, thus facilitating the manufacturing process. The glass bonding cord obtained by the laser-assisted process was found to have an excellent contact with both substrates and no gas inclusions or voids were detected, indicating that an effective sealing was achieved. Preliminary hermeticity tests of the laser-bonded cells yielded encouraging results. The developed laser-assisted glass frit bonding process is a promising technique for obtaining hermetic sealing of photoelectronic and electrochemical devices, as it allows temperature-sensitive materials to be used inside them.

Review of test methods used for the measurement of hermeticity in packages containing small cavities

This paper presents a critical review of the traditional and newly proposed test methods used for the measurement of hermeticity in packages with very small cavity volumes. Closed-form expressions of the minimum and maximum true leak rates achievable are provided for the helium fine leak test method. These expressions are shown to provide practical guidelines for the accurate testing of hermeticity for ultrasmall packages. A portfolio of hermeticity test methods is also presented outlining the limitations and advantages of each method.

Polymer-Based Hermetic Packaging for Flexible Micro Devices

In recent years, polymers have been widely adopted as a low-cost, light-weight and high-flexibility alternative to traditional silicon materials for MEMS. However, the majority of polymers do not provide hermetic protection because of their high moisture- and gas permeation rates. Yet, hermetic packaging is critical for many applications such as medical devices [1], RF MEMS [2] and micro heat pipes [3]. In particular, our group has been developing flexible thermal ground planes based on heat pipe technology [3] for advanced electronics cooling applications. Heat pipes require hermetic sealing, while flexibility requires the structural material to be polymer-based. Hermetic packaging methods for MEMS typically include welding, soldering [4], and various epoxies and polymers [1, 2, 5] to bond the parts in a package together. The bond interface is a major potential source of gas and moisture leakage. Although welds and solder joints offer effective hermetic seals, the bond interface is mechanically rigid. On the other hand, flexible bond materials like epoxies typically possess high moisture absorption rate and bonding strength degradation at high temperature [6] while polymers such as BCB [2] or LCP [7] either provide only semi-hermetic sealing or degrade at high temperature. We report a polymer-based hermetic packaging approach using fluorinated ethylene propylene (FEP), which possesses flexibility, high operating temperature compatibility (204°C), chemical resistance, and low water absorption rate. We report results of hermeticity tests in which FEP, solder, and epoxy were used to bond a copper-clad kapton “lid” onto a water-containing copper vessel which is then kept in an oven at 100 °C. The only path for water loss is through the bond interface. We show that the FEP-bonded test vehicles result in negligible water loss comparable to the solder-bonded containers, and far outperforming the epoxy-bonded containers.

The Limits of Hermeticity Test Methods for Micropackages

Hermeticity is crucial for the long-term implantation of electronic packages. Pushed by advances in micromachining, package volumes are decreasing and current leak detection methods are no longer sensitive enough. This article reviews the limits of the most common methods and exposes their inadequateness for medical electronic applications where the device's life is 50 years or longer.

Low-Temperature Wafer Bonding for MEMS Hermetic Packaging Using Sub-micron Au Particles

A study of wafer-level hermetic bonding using sub-micron gold particles with a mean diameter of 0.3 μm was conducted at bonding temperatures of 150–200°C with varying bonding pressures in the range of 50–100 MPa. 4.5 mm-square, 10 μm–100 μm-wide sealing line patterns of sub-micron Au particles were formed on glass wafers by means of waferlevel processing using photolithography and a slurry-filling technique. The tensile bond strength was measured with a stud-pull method using 5 mm × 5 mm chips and exhibited as > 20 MPa. A preliminary hermeticity test was performed by immersing the bonded wafer pairs into a low-viscosity liquid and it was confirmed that the sealing lines with widths as thin as 20 μm showed a good sealing property against the liquid. The result demonstrated the feasibility of this lowtemperature wafer bonding process using sub-micron Au particles, which could achieve hermetic sealing with absorbing a micron-level surface roughness and/or topography.

Wafer-Level Hermetic Bonding Using Sn/In and Cu/Ti/Au Metallization

Low-temperature hermetic wafer bonding using In/Sn interlayer and Cu/Ti/Au metallization was investigated for microelectromechanical systems packaging application. In this case, the thin Ti layer was used as a buffer layer to prevent the diffusion between solder interlayer and Cu after deposition and to save more solders for diffusion bonding process. Bonding was performed in a wafer bonder at 180 and 150degC for 20 min with a pressure of 5.5 MPa. It was found that bonding at 180degC voids free seal joints composed of high-temperature intermetallic compounds were obtained with good hermeticity. However, with bonding at 150degC, voids were generated along the seal joint, which caused poor hermeticity compared with that bonded at 180degC. After four types of reliability tests-pressure cooker test, high humidity storage, high-temperature storage, and temperature cycling test-dies bonded at 180degC showed good reliability properties evidenced by hermeticity test and shear tests. Results presented here prove that high-yield and low-temperature hermetic bonding using Sn/In/Cu metallization with thin Ti buffer layer can be achieved.

MEMS ultra low leak detection methods: a review

PurposeThe purpose of this paper is to review traditional hermeticity test methods when applied to typical micro‐electro‐mechanical systems (MEMS) cavity volumes and to propose potential solutions.Design/methodology/approachStandards for traditional testing have been applied to typical MEMS cavity volumes and the resulting issues of range and sensitivity discussed. In situ test structures have been designed and fabricated with access to the internal cavities to allow characterisation of the structures as a function of pressure.FindingsThe ultra low leak rates necessary to guarantee hermeticity of MEMS cannot be measured using traditional methods. Optical test methods are possible although in situ test structures currently provide the greatest sensitivity. A portfolio of test techniques is required to allow accurate hermeticity testing of MEMS.Research limitations/implicationsThis paper provides a starting point for further investigation into several methods of MEMS hermeticity testing.Originality/valueThis paper provides a review of the limitations of traditional testing and proposals for future testing as the trend towards smaller volume packaging continues.

A Cost-Effective MEMS Cavity Packaging Technology for Mass Production

Cost effective microelectromechanical system (MEMS) packaging methods have been required, because the cost portion of the MEMS package is more than 80% of the manufacturing cost of a MEMS device. For this reason, cost-effective MEMS packaging is proposed in this paper for mass production using copper (Cu) lead frames (L/F) as a preplated frame (PPF). Package types include an epoxy molding compound (EMC) cavity wall and an on-frame type. The EMC-cavity package consists of a substrate, a cavity wall and a flat lid on top of the cavity. The on-frame package has a folded lid without a cavity wall. Finite element method (FEM) numerical modeling is performed to anticipate the mechanical warpage and stress of the packages. Assembled MEMS cavity packages were tested for wire pulling, lid pulling, hermetic test, and reliability tests in order to prove the feasibility of this packaging. The wire bonding strength was improved by 40% using plasma cleaning before wire bonding. Through a lid pulling test, a lid bonding strength of 2.40 kgf on average was obtained using an epoxy adhesive. Finally, all samples of the packages passed the reliability tests of the TC, HAST, and HTST, standardized by Joint Electron Device Engineering Council (JEDEC). Also, this cavity package showed excellent hermeticity through leak tests.

Fabrication and Testing of a Wafer-Level Vacuum Package for MEMS Device

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A wafer-level vacuum package with getters deposited on the cap wafer is developed for an accelerometer device. An accelerometer wafer and cap wafer is bonded together in a vacuum of 1 mtorr and is characterized using a micro-electro-mechanical systems (MEMS) motion analyzer (MMA). Vacuum inside the package is measured indirectly by measuring the <emphasis emphasistype="boldital">Q</emphasis>-factor response of the accelerometer structure inside the package. The obtained results indicated that there is variation from the center to the edge of the wafer. This may be due to difference in the outgassing of the package. Different reliability tests on the wafer-level package showed the package is robust to the reliability conditions. A progressive test on the <emphasis emphasistype="boldital">Q</emphasis>-factor for different cycles of reliability test proved that there is no shift in the measurement value. A 3-D wafer-level package for accelerometer device is also developed to meet the requirements of vacuum packaging. Hermeticity and CV test showed no degradation in the device performance when subjected to reliability tests. </para>