Hermetic Properties Research Articles

Analytical microscopy techniques using coaxial and oblique illuminations to detect thin glass particulates generated from glass vials for parenteral drug products

Glass vials are the most widely used primary containers for the packaging of parenteral products due to their optical clarity, general inertness, and hermetic properties, but under certain circumstances, they can pose safety concerns. Most of these issues are related to the potential formation of glass particulates through delamination or precipitation, resulting from the chemical interaction between the drug product and the inner surface of the glass vial. Hence, it is imperative for pharmaceutical companies to conduct product-vial compatibility studies to determine the appropriate packaging/container closure system. To support this development activity, scientists need to develop analytical methods to detect subvisible glass particulates in parenteral products, along with the appropriate positive controls, to facilitate detection and identification. This paper outlines the utilization of coaxial/episcopic and oblique illumination microscopy, combined with spectroscopic techniques, to detect thin glass particulates generated from a modified procedure. It also showcases the importance of angle-dependent lighting in visualizing positive control samples containing thin glass particulates. The analytical microscopy techniques discussed in this paper can assist scientists in selecting suitable container closure systems for developing parenteral products.

Hoop Strain Measurement During a SiC/SiC Ceramic Composite Tube Burst Test by Digital Volume Correlation of X-Ray Computed Tomographs

BackgroundSilicon carbide-fibre/silicon carbide matrix (SiC/SiC) composites are candidate materials for accident tolerant fuel cladding in light water and advanced gas cooled nuclear fission reactors. The mechanical and damage behaviour of ceramic composites is sensitive to the composite geometry, the microstructure and the loading state. Reliable test methods are needed to investigate the subcritical damage that affects hermetic properties and strength, and this requires precise measurements under loading states that are representative of operating conditions.ObjectiveThe objective was a novel methodology to measure the deformation of an internally pressurised ceramic composite tube.MethodsA burst test of an internally ground SiC/SiC (filament wound and braided) ceramic composite tube, pressurized by radial expansion of a compressed elastomer insert, was observed in situ by high resolution (synchrotron) X-ray tomography. The full field three-dimensional displacements were measured by digital volume correlation, with a precise rotation correction applied to obtain the relative radial and circumferential displacements of the tube wall for the first time.ResultsThe hoop strain, and its spatial variations, were determined as a function of the applied hoop stress and showed ovalisation and barreling of the tube. The quantity of subcritical matrix cracking increased with the tensile hoop strain, but the critical crack that caused rupture was not at the location of maximum tensile strain.ConclusionPrecise measurements of the deformation during the burst test found non-uniform hoop strains that caused a non-uniform distribution of subcritical cracking, which could influence the hermetic properties and strength.

Analysis of the marginal adaptation of temporary filling materials to tooth tissues

Aim. To evaluate the marginal fit of temporary filling materials used in practice of a dentist-therapist.Materials and methods. The analysis of the degree of marginal fit of temporary sealing materials was carried out: light polymerization-«Tempofot liquid-flowing» (VladMiVa), «Restorin liquid-flowing (Technodent)», «Tempofot packable» (VladMiVa) and chemical curing – «Parasept» (VladMiVa), «Dentin paste» (Vladmiva), «Tempodent» (Technodent). The study was conducted on 120 removed teeth.Results. After 1 day of exposure, the materials «Dentin paste», «Tempodent» and «Tempofot packable» were penetrated by the hyposalix solution along the filling-tooth border. It can be stated that these materials have no hermetic properties. Thematerial «Parasept» and the materials «Tempofot liquid-flowing», «Restorin liquid-flowing» retained their hermetic properties, there was no staining of the filling-wall border of the tooth. After 3 days, the materials «Parasept» and «Tempofot liquid-flowing» staining was not detected, the material «Restorin liquid-flowing», the penetration of the dye to the mouth of the root canals was noted.Conclusions. The study found that temporary sealing materials of chemical and light polymerization have various hermetic properties.

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

For the realization of advanced bio-microsystems for medical applications such as implants, fabrication processes require the usage of biocompatible materials only. Especially for the encapsulation and hermetic sealing, e. g. of microfluidic structures, a biocompatible wafer bonding process is necessary. Additionally, the ongoing integration of new and temperature sensitive materials in micro systems, such as biomolecules, requires bonding processes with low bonding temperatures only.However, when choosing the wafer bonding process, additional criteria are a high reliability, since the bonding is critical for the operation of the chip, as well as the applicability on 6” and 8” wafer level in order to fabricate a high number of devices at low costs.In order to fulfill all these requirements, we propose an adhesive bonding process, which uses Parylene C as intermediate layer. Parylene C is a thermoplastic polymer, which is ISO 10993 certified as biocompatible and biostable, chemically inert against all common acids, bases and solvents, as well as a low permeable and optical transparent. In addition and in contrast to other established bond adhesives, such as SU8, the Parylene layers are deposited by CVD, and offer a very high three dimensional conformity as well as a very high homogeneity without any pinholes. Furthermore, due to its chemical inertness, Paryleneis compatible with a variety of established microtechnologies.Previous studies prove that adhesive bonding using Parylene C is feasible. However, these works are limited to 4” wafer level and the bonding provides only low tensile strengths, e. g. 10 MPa. [1-7]Our presented Parylene based adhesive bonding technology uses a 0.5 µm to 10 µm Parylene C layer, which is deposited on 6” and 8” wafers and can be patterned optionally by an oxygen plasma without leaving residues. A subsequent thermal and adhesive bonding process at temperatures of 280°C to 300°C as well as moderate wafer contact pressures are performed to successfully bond the wafers. Within our study, different materials combinations for the bond interface, e. g. silicon - silicon, silicon - silicon dioxide, silicon – glass, silicon – silicon nitride, and silicon – aluminum were investigated. Doing so, only one wafer was coated with Parylene. Additionally, bonding processes were performed with two Parylene coated wafers, and hence, a Parylene - Parylene bond interface. Since almost all materials, established in microsystem technologies can be coated with Parylene, this enables the usage of this bonding process for a high variety of material combinations and particularly materials, which were not investigated by our study. The focus of the experiments was the investigation and optimization of a feasible parameter range in respect of the bonding time, bonding temperature, wafer contact pressure, and Parylene thickness.The characterization of the bonding process was performed using Parylene test structures of squared geometry and different width. The bonding process was analyzed by IR imaging to determine voids and defects. Afterwards the wafers were diced into chips, centering the Parylene frame. The investigation of tensile and shear strengths proved a high reliability of the bonding but also a strong dependency on the bonding parameters. The tensile strength reached up to 35 MPa was improved by a factor of 3 compared to previous studies, the shear strength reached up to 80 MPa Furthermore, the impact of thermal and mechanical shocks as well as long-time load on the tensile strength was investigated. Finally, cross-sections of the bonded chips were analyzed by SEM. The results prove that the Parylene frame structure was still intact after bonding and not flattened due to bonding. Furthermore, the hermetic properties of the Parylene bonds were investigated. Doing so, the Helium leakage rate was determined to < 1∙10-7 mbar ∙ l/s. The study was completed by the investigation of the bonding process on three dimensional structures, which refers to bonding over patterned metal but also bonding of cavities without previous pattern of the Parylene. Finally, after successfully bonding the test frames, the established bonding process was applied on a real microsystem.

Advances in Hermetic Projection Weld Sealing

Abstract In this article, we describe a novel process for hermetic projection weld sealing of semiconductor devices, considered by many to be an important legacy technology from decades gone bye, but not particularly relevant in today's arsenal of sealing technologies. We will demonstrate that with appropriate modifications to be described, this technology can used to seal various high power devices as well as high reliability semiconductors, crystals, hybrid packages, medical electronics, photonic devices, automotive electronics, etc. Its features primarily stem from the fact that it can be used to quickly and efficiently produce true hermetic seals in components. The welding is so rapid, that it is essentially a room temperature technology and the equipment is small enough that it can be housed in an atmosphere controlled chamber filled with any gas that is not explosive. Air, Nitrogen, Argon, Helium and their mixtures are the most commonly utilized gasses. The process is so adiabatic that it can be used to seal many liquids also. In some applications the technology competes against pulsed laser welding, but unlike laser welding the entire seal takes place in a few milliseconds because it is a single discharge, component-shaped spot/projection weld, which means that the entire seam is made in a single high speed discharge. So, in the same time that it takes a laser welding machine to make one of the many small overlapping spot welds required to make a seal, the projection welder has completed the entire operation. This process results in minimal stress and distortion, and maximum hermetic properties, strength and reliability, without requiring electroplating or preforms. Because the weld involves the localized high speed melting of metals, it among the highest energy density processes. A concern with the earlier resistance welding technologies has been the expulsion of particulates, both out of, and into the seal. This expulsion has been systemic and becomes progressively worse as the package size increases. In the course of this presentation we will demonstrate how this concern has been dealt with and corrected. Internal dew points can be held to −40 degrees, or lower if required. Other common applications for this technology include sealing and welding of nuts and studs for hermetic applications and sealing of devices for medical applications that must endure autoclave sterilization. In the course of this presentation, we will take you back to the roots of the original resistance welding process as taught by the early process developers so that you will understand how things have changed, and the reasons for the changes.

Post-harvest cereal structures and climate change resilience in rural Zimbabwe: a review

Farmers in Sub-Saharan Africa use storage structures that help maintain grain quality and safety. This study reviewed the use of different grain storage structures used by smallholder farmers in Zimbabwe namely granaries, metal silos, supergrain bags, polypropylene bags and cribs. Metal silos and supergrain bags, however costly, have hermetic properties that kill pests while granaries dilapidate with time. Cribs are susceptible to moisture entry, while polypropylene bags are prone to perforations by sharp objects. This review discussed the impact of climate change on preservation of grain quality during storage. Moulds, insect pest infestations and rodent attacks are major challenges that cause storage losses. Knowledge barriers, cost, fear of the unknown, effectiveness of storage structure and security of grain are factors that affect the diversity of storage structure use. Proper use of storage structures contributes towards achieving sustainable development goals and increases farmer resilience to the impacts of climate change.

Environmental Stress Testing of Wafer-Level Al-Al Thermocompression Bonds: Strength and Hermeticity

Hermeticity, reliability and strength of Al-Al thermocompression bonds realized by applying different bonding parameters have been investigated. Laminates of diameter 150 mm were realized by bonding wafers containing membrane structures to wafers with patterned bonding frames. The laminates were bonded applying a bond force of 36 or 60 kN at temperatures ranging from 300 to 400°C for 15, 30 or 60 minutes. The hermetic properties were estimated by membrane deflection measurements with white-light interferometry after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Bond strength was measured by shear test and pull tests. Laminates bonded applying a bond force of 60 kN at temperatures of 350 or 400°C resulted in hermetic bonds. No significant change in membrane deflection was observed after the steady-state life test or the thermal shock test. However, a gross leakage was observed in 1–11% of the dies after exposure to the moisture resistance test. The maximum leakage rate (MLR) estimated from membrane deflection measurements was below 10−11 mbar·l·s−1 for all laminates. The measured average bond strength of dies from selected laminates ranged from 28 to 190 MPa.

Environmental Stress Testing of Wafer-Level Au-Au Thermocompression Bonds Realized at Low Temperature: Strength and Hermeticity

Hermeticity, reliability and strength of four laminates bonded at different temperatures by Au-Au thermocompression bonding have been investigated. Laminates with a diameter of 150 mm were realized by bonding a wafer containing membrane structures to a Si wafer with patterned bond frames. A bond tool pressure of 2266 mbar was applied for 15 minutes at temperatures ranging from 150–300°C. The hermetic properties were estimated by membrane deflection measurements applying white-light interferometry after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Bond strength was estimated by pull test measurements. A dicing yield above 90% was obtained for all laminates. Laminates bonded at 200°C and above had significantly higher hermetic yield than the laminate bonded at 150°C. No degradation in hermeticity was observed after the reliability tests. The maximum leakage rate (MLR) was estimated from two measurements of membrane deflection executed at two different times and was below 10−11 mbar ⋅ l ⋅ s−1. The average bond strength ranged from 44 to 175 MPa.

Electrical, Mechanical, and Hermetic Properties of Low-Temperature, Plasma Activated Direct Silicon Bonded Joints

The electrical, mechanical, and hermeticity properties of low-temperature, plasma activated direct silicon bonds were investigated. On individual dies with a bonding area ranging from 1–4 mm2, the bonded interface was found to have a capacitance ranging from 2.62 pF/mm2–2.89 pF/mm2 at 1 kHz. Linear I-V curves showed ohmic behavior without hysteresis. A resistance around 2.2 Ω and a current density of 1.1 × 104 A/m2 was measured at DC. We speculate that the capacitive and resistive responses are related to traps that are formed during the plasma activation process. The applied bonding process resulted in hermetic sealing with 100% yield on 2 × 481 dies. The maximum leak rate of the seals was 2.4 × 10−11 mbar⋅l⋅s−1, but could be significantly lower. No gross leaks were observed following a steady-state life test, a thermal shock test, and a moisture resistance test applied on 100 dies.

Hermeticity and Reliability of Au-Au Thermocompression Bonds, Realized at Low Temperature

Hermeticity and reliability of four laminates bonded at different temperatures by Au-Au thermocompression bonding have been investigated. Laminates of diameter 150 mm were realized by bonding a wafer containing membrane structures to Si wafers with patterned bond frames. The laminates were bonded applying a bonding pressure of 8.5 MPa at temperatures of 150–300 °C for 15 minutes. The hermetic properties were estimated by measurement of membrane deflection at two different times after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. A dicing yield above 90 % was obtained for laminates bonded at or above 150 °C. Laminates bonded at 200 °C and above had significantly higher hermetic yield than the laminate bonded at 150 °C. No degradation in hermeticity was observed after the reliability tests. A maximum leak rate in the range of 10-11 mbar×l×s-1 was estimated.

Hermeticity and Reliability of Al-Al Thermocompression Wafer Bonding

Hermeticity and reliability of laminates bonded by Al-Al thermocompression bonding applying different bonding parameters have been investigated. Laminates of diameter 150 mm were realized by bonding a wafer containing membrane structures to wafers with patterned bonding frames. The laminates were bonded applying a bond force of 36 or 60 kN at temperatures ranging from 300 to 400 °C for 15, 30 or 60 minutes. The hermetic properties were estimated by optical measurement of membrane deflection after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Laminates bonded applying a bond force of 60 kN at temperatures of 350 °C or higher resulted in hermetic and reliable bonds. All the dies on the laminates survived steady-state life test and thermal shock test. Leakage was observed in some dies after exposure to moisture resistance test. Measurements of membrane deflection estimated a maximum leak rate below 10-11 mbar×l×s-1 for all tested bonding parameters.

Electrical, Mechanical, and Hermeticity Properties of Low-Temperature, Plasma Activated Direct Silicon Bonded Joints

The electrical, mechanical, and hermeticity properties of low-temperature, plasma activated direct silicon bonds were investigated. On individual dies with a bonding area ranging from 1 – 4 mm2, the bonded interface was found to have a capacitance ranging from 2.62 pF/mm2 – 2.89 pF/mm2 at 1 kHz. Linear I-V curves showing ohmic behavior without hysteresis and a resistance around 2.2 W were measured at DC voltage. We speculate that the capacitive and resistive responses are related to traps that are formed during the plasma activation process. The applied bonding process resulted in hermetic sealing with 100% yield on 2 × 481 dies. The maximum leak rate of the seals was 3.5 × 10-11 mbar×l×s-1, but could be significantly lower. No gross leaks were observed following a steady-state life test, a thermal shock test, and a moisture resistance test applied on 100 dies.

Electrical, Mechanical, and Hermeticity Properties of Low-Temperature, Plasma Activated Direct Silicon Bonded Joints

Low-temperature silicon direct bonding enabled by plasma activation (plasma bonding) is widely used in the fabrication of silicon-on-insulator (SOI) material. We expand the current knowledge by electrical and mechanical characterization of plasma bonded interfaces. Further, we report the first assessments on hermeticity properties of plasma bonds subjected to environmental testing. CTwo types of test laminates were prepared: hermeticity laminates (Herm) and laminates for electrical and mechanical measurements (ElMech). Cross-sectional sketches of dies of both types are shown in Figure 1. Herm wafers had 481 membranes of dimension 2500 × 2500 × 36 µm3. ElMech wafers had 169 frame structures of widths 100, 200, or 400 µm protruding 6 µm above the silicon surface. Wafer ElMech1 was boron implanted on both sides for electrical contact. Laminates were made by silicon direct bonding between Herm or ElMech wafers and plane silicon wafers, which was boron implanted for laminate ElMech1. All wafers were activated for 1 min in an O2 plasma in an AMS-200 (Alcatel) with a source power of 2500W and a bias power of 180W. After activation, the ElMech and Herm wafers were dipped in DI-water for 1 minute and dried. Laminates were bonded applying a bonding pressure of 350 mbar for 2 minutes at 50oC in an ambient pressure below 5×10-3mbar. Aluminium contacts for electrical measurements were made on both sides of laminate ElMech1.ElMech laminates were diced into individual dies. The dicing yield was recorded for each frame design. Dies from laminate ElMech1 were characterized by capacitance and I-V measurements. The deflection of individual membranes was measured by white light interferometry three times over a period of four months. Pieces containing 25 membranes were subjected to environmental testing consisting of 1000 hours of storage at 150° C, 50 cycles of thermal shock from -65° C to +200° C, and 10 cycles in 90-100% humidity from 25° C to 65°C.The dicing yield of laminates ElMech1 and ElMech2 is shown in Figure 2. Frames of width 100 µm had low yield of 17 – 30%, while frames of widths 200 and 400 µm had yield of 39 – 58%. Considering that the applied frame design is very poorly suited for the continuous propagation of a bonding wavefront [1], the dicing yield indicates that satisfactory bond strength was obtained.Capacitance values were obtained for all measured samples, corresponding to an SiO2 layer of thickness 11 – 14 nm at the bonding interface. However, the I-V measurements showed an ohmic behavior without hysteresis, showing a resistance of 2.2 W which was independent of frame width, i.e. bonding area. This result contradicts earlier results that the current is restricted at the bonded interface [2]. The calculated oxide thickness of 11 – 14 nm is in agreement with the 8 – 10 nm oxide thickness found by capacitance-voltage measurements in a previous study [2]. The same study reports a discrepancy between ellipsometry and capacitance measurements [2]. Further investigation is needed to verify the physical thickness of any SiO2at the bonding interface of our samples. In addition, the simultaneous capacitive and resistive behavior of the bonded dies must be explained.No significant change in the membrane deflection was observed over the course of 4 months. This means that the leak rate was at least below 1.54×10-11 mbar l s-1, which is agreement with earlier results [3]. Longer storage time can reveal that the actual leak rate is even lower. No visible leaks were found in any of the 2 × 25 membranes that had undergone environmental testing. The presented results indicate that the bonds are conductive, hermetic, and that they can sustain environmental stresses.[1] Q-Y.Tong, U. Gösele, Semiconductor Wafer Bonding, Wiley, 1998[2] P. Amirfeiz et al., J. Electrochem Soc 147(7) 2693, 2000[3] M.M.V. Taklo et al., Sens. Act. A 97-98, 434, 2002

Integrated electrode and high density feedthrough system for chip-scale implantable devices

High density feedthroughs have been developed which allow for the integration of chip-scale features and electrode arrays with up to 1141 stimulating sites to be located on a single implantable package. This layered technology displays hermetic properties and can be produced from as little as two laminated 200 μm thick alumina sheets. It can also be expanded to a greater number of layers to allow flexible routing to integrated electronics. The microelectrodes, which are produced from sintered platinum (Pt) particulate, have high charge injection capacity as a result of a porous surface morphology. Despite their inherent porosity the electrodes are electrically stable following more than 1.8 billion stimulation pulses delivered at clinically relevant levels. The ceramic-Pt constructs are also shown to have acceptable biological properties, causing no cell growth inhibition using standard leachant assays and support neural cell survival and differentiation under both passive conditions and active electrical stimulation.

Hermetic integration of liquids using high-speed stud bump bonding for cavity sealing at the wafer level

This paper reports a novel room-temperature hermetic liquid sealing process where the access ports of liquid-filled cavities are sealed with wire-bonded stud bumps. This process enables liquids to be integrated at the fabrication stage. Evaluation cavities were manufactured and used to investigate the mechanical and hermetic properties of the seals. Measurements on the successfully sealed structures show a helium leak rate of better than 10−10 mbarL s−1, in addition to a zero liquid loss over two months during storage near boiling temperature. The bond strength of the plugs was similar to standard wire bonds on flat surfaces.

Enabling Low Temperature Copper Bonding with an Organic Monolayer

Typically, copper material is used as a bonding material in MEMs devices for its excellent mechanical, electrical and hermetic properties. Direct copper bonding, however, requires high temperature (&gt;300°C) to forge a bond due to the oxidative nature of copper. In this study, using an alternative approach based on an organic monolayer coating, we demonstrate metallurgical bonding between two copper surfaces under ambient condition at low bonding temperature below 140°C, while maintaining reliable mechanical joint integrity of 50MPa. This monolayer is believed to behave as a passivation layer, protecting the copper surface against oxidation under ambient conditions. In contrast to a bulk oxide layer, this layer can be easily displaced during mechanical deformation at the bonding interface.

Sealing of adhesive bonded devices on wafer level

Abstract In this paper, we present a low temperature wafer-level encapsulation technique to hermetically seal adhesive bonded microsystem structures by cladding the adhesive with an additional diffusion barrier. Two wafers containing cavities for MEMS devices were bonded together using benzocyclobutene (BCB). The devices were sealed by a combined dicing and self-aligning etching technique and by finally coating the structures with evaporated gold or PECVD silicon nitride. The sealing layer was inspected visually by SEM and helium leak tests were carried out. Devices sealed with silicon nitride and with known damage of the sealing layer showed a helium leak rate of about 7–14 times higher than the background level. Devices of the same size without damage in the sealing layer had a leak rate of only 1.5 times higher than the background level. Experiments with evaporated gold as cladding layer revealed leaking cracks in the film even up to a gold thickness of 5 μm. The sealing technique with silicon nitride shows a significant improvement of the hermeticity properties of adhesive bonded cavities, making this bonding technique suitable for applications with certain demands on gas-tightness.

Characterization of CVD carbon films for hermetic optical fiber coatings

Thin carbon films are being studied as hermetic coatings for optical fibers used in harsh environment applications. This work details an experimental study of pyrolytic carbon films grown in a cold walled chemical vapor deposition (CVD) reactor. The films are grown from methane, acetylene, propane and butane precursors on stationary 3-mm quartz rods. Results are presented at 15 and 600 torr, total pressure for substrate temperatures between 1050 and 1750 K. Hydrocarbon precursor gas concentrations are varied between 10 and 100% in N 2 dilutant. Auger electron spectroscopy (AES) shows mostly carbon composition, with trace levels of Cr and O 2 impurities. X-Ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) reveal small amounts of SiC at the carbon–glass interface, but could not resolve a continuous transition layer. The thickness, microstructure and surface roughness are analyzed using environmental scanning electron microscopy (ESEM). ESEM reveals an increase in deposition rate with temperature and concentration for all hydrocarbon species and a noticeable change in surface morphology with deposition temperature and hydrocarbon species. Raman spectroscopy is used to relate film microstructure to deposition conditions, providing non-intrusive evaluation of crystalline size and hermetic properties.

Fusion reactor application issues for low activation SiC/SiC composites

Silicon carbide composites are attractive for fusion applications beacuse of their low activation and afterheat properties coupled with excellent high-temperature properties. Their application will require material development and an expanded data base as well as evaluation for high-temperature stability, chemical compatibility with fusion relevant coolants, thermal conductivity, thermal fatigue and shock, hermetic properties, joining methodology and radiation stability. Preliminary data suggest that commercially available material has adequate performance for some requirements in its present form or that there are identifiable routes to improve the performance. This paper summarizes SiC/SiC behavior relative to some performance requirements and identifies areas where further research is needed.

Diffusion of Hydrogen Through Hermetic Carbon Films on Silica Fibers

AbstractRecent work has made it possible to deposit hermetic carbon coatings on optical fibers during the drawing process. These coatings are used to protect the silica portion of the fiber from undesirable loss increases and strength reductions caused by H2 and H2O, respectively. The hermetic properties of the carbon films have been evaluated using accelerated test conditions where the coated fibers are exposed to H2 at elevated temperatures and hydrogen pressures. In-situ spectral loss monitoring has made it possible to measure changes in the characteristic optical loss features associated with either molecular H2or with species such as OH which form when hydrogen reacts with defects in the silica. By using long lengths of fiber it is thus possible to optically measure the extremely small amounts of hydrogen that penetrate the carbon films during accelerated tests. At temperatures in the range of 100 to 145°C the diffusion of H2 is readily modeled using classical diffusion theories for a composite cylinder, allowing calculation of the diffusion coefficient and the solubility for H2 in the carbon. At higher temperatures the diffusing H2 is partially depleted by reaction with defects in the glass. For these conditions the inward diffusion of the H2 and its reaction at defect sites tend to balance each other, giving rise to a constant, but extremely low, concentration of H2 in the fiber.