Environmental Stress Testing Research Articles

Thermokinetics and reactive mechanism of lead azide (LA) in atmosphere/temperature mixed environment

To establish the influence of atmospheric and temperature factors on the stability of LA, a combined environmental stress testing device was designed to simulate reaction characteristics. Morphological characterization methods of SEM and FTIR were carried out to explore the changes of crystal structure, as the pyrolysis behavior of LA under the combined environmental stress was investigated by DSC with two isoconversional kinetic methods and thermal safety software (TSS). The research indicates that CO2 and H2O react with LA to generate basic lead carbonate in the air atmosphere, together with the stimulation of thermal stress, the synergistic effect formed microvoids to erode the crystal structure of LA. The microvoid effect reduced the apparent activation energy (Ea) from 156.47 to 29.52 kJ/mol as the order of degradation of thermal stability of LA was Air > N2 > CO2, which demonstrated that CO2 and N2 atmosphere have a particular protective effect for LA storage, transportation, and application. The pyrolysis reaction mechanism model of LA under the combined environment factors testing was the same as the original LA through the calculation of TSS, thereby the findings could contribute to a better understanding of available boundary conditions for LA.

ETFE and its Role in the Fabrication of Lightweight c-Si Solar Modules

Glass-free, lightweight, photovoltaic modules have the potential to enable new uses of solar in building integrated and vehicle integrated applications. Glass-free modules have the advantages of reduced weight, lower-cost mounting solutions, and reduced transportation costs. Ethylene tetrafluoroethylene (ETFE) is usually considered a suitable candidate to replace glass as the front cover sheet material in module fabrication. In this article, we report on its optical, chemical, self-cleaning, and morphological properties. Durability is a key issue, especially for building-integrated applications since harsh conditions are prevalent outdoors. We report on the effect of sequences of environmental stress tests (UV exposure, and Damp Heat). The module cover material is also subject to regular cleaning, which can cause surface damage. We report on the use of linear abrasion testing to assess the abrasion resistance of ETFE to a variety of abrasive materials. The results provide useful data on the advantages and disadvantages of replacing glass with a durable polymer for front sheets in solar modules.

S-14-05 Nrf2 in environmental stress and toxicity testing

S-14-05 Nrf2 in environmental stress and toxicity testing

Performance of a directly deposited optical blocking filter on x-ray CCDs: case study from the REgolith X-ray Imaging Spectrometer (REXIS) experiment

The REgolith X-ray Imaging Spectrometer (REXIS) is a soft x-ray spectrometer and the student collaboration instrument aboard NASA’s OSIRIS-REx asteroid sample return mission. REXIS utilizes MIT Lincoln Laboratory CCID-41 x-ray detectors coated with a directly deposited optical blocking filter (OBF) with a thickness of 320 nm. The aluminum coating, developed at MIT Lincoln Laboratory, is designed to block visible light from the detector, to maintain high sensitivity to soft x-rays in the presence of reflected sunlight from the surface of the target asteroid Bennu. The scientific objective for the REXIS instrument is to measure the stimulated x-ray flux fluoresced from Bennu to discern elemental abundances present on the asteroid’s surface. The coating technique applied for blocking visible light had not previously been used on the CCD-41s in an extended space flight mission. The performance of the OBF on the flight detectors was not characterized before and after environmental stress testing. Therefore, to mature the OBF to technology readiness level (TRL) 6, the flight spare detectors were tested while the instrument was on the way to the asteroid. The flight spare hardware underwent vibration and thermal environmental stress testing to test the durability and effectiveness of the OBF. This testing informed our expectations of the in-flight OBF once it reached the asteroid and helped mature the TRL level of this directly deposited OBF. We discuss the setup and results of those tests and address the performance of the flight OBF at the asteroid. We conclude that depositing an aluminum OBF onto the surface of a charge-coupled device is able to withstand stresses of launch and an extended life-mission in interplanetary space.

Critical processing temperature for high-performance protected silver mirrors

Silver (Ag) mirrors for astronomical telescopes consist of multiple metallic and dielectric thin films. Furthermore, the topmost surface of such Ag mirrors needs to be covered by a protection coating. While the protection coating is often deposited at room temperature and the entire mirrors are also handled at room temperature, various thin film deposition techniques offer protection coatings with improved characteristics when carried out at elevated temperatures. Thus, in this work, high-performance Ag mirrors were designed and fabricated with a new benchmark. The resulting Ag mirrors were annealed (i.e., post-fabrication annealing) at various temperatures to investigate the viability of introducing thermal processes during and/or after fabrication in improving overall optical performance and durability of protected silver mirrors. In our experiments, Ag mirror samples were deposited by electron-beam evaporation and subsequently annealed at various temperatures in the range from 60 {\deg}C to 300 {\deg}C, and then the mirror samples underwent an environmental stress test at 80 {\deg}C and 80% humidity for 10 days. While all the mirror samples annealed below 200 {\deg}C showed negligible corrosion after undergoing the stress testing, those annealed below 160 {\deg}C presented spectral reflectivity comparable to or higher than that of as-deposited reference samples. In contrast, the mirror samples annealed above 200 {\deg}C exhibited significant degradation after the stress testing. The comprehensive analysis indicated that delamination and voids caused by the growth of Ag grains during the annealing are the primary mechanisms of the degradation.

Consistent Dosing Through the Salmeterol-Fluticasone Propionate Easyhaler for the Management of Asthma and Chronic Obstructive Pulmonary Disease: Robustness Analysis Across the Easyhaler Lifetime.

Background: Easyhaler (registered trademark by Orion Corporation) is a multidose dry powder inhaler (DPI) for the treatment of asthma and chronic obstructive pulmonary disease (COPD), designed to be simple and easy to use. Salmeterol–fluticasone propionate (S-F) Easyhaler (50/250 and 50/500 μg per dose), available in several European countries, provides combined inhaled corticosteroid and long-acting beta agonist therapy for the management of asthma and COPD. A requirement of the European Committee for Medical Products for Human Use guidelines is to demonstrate product performance under conditions that mimic real-life patient use. Therefore, our aims were to assess the robustness of the S-F Easyhaler by assessing the delivered dose (DD) and fine particle dose (FPD) throughout the inhaler lifespan and under simulated environmental stress conditions.Methods: This was a noncomparative exploratory in vitro study. Two batches and six to nine inhalers per batch from both dose strengths were used to assess drug delivery performance over the inhaler lifespan (doses 1–60). For determining the impact of simulated environmental stress (tests for exposure of dropping, vibration, moisture, and freeze–thawing) on DD and FPD, one batch and three inhalers per batch from both dose strengths were used per test, respectively. Aerodynamic particle size distribution was evaluated during the simulated dropping and vibration tests.Results: DD and FPD from both dose strengths of S-F Easyhaler performance remained consistent through the inhaler lifespan and simulated environmental stress did not affect its performance. Similar DD and FPD values were observed with or without dropping, vibration, exposure to moisture, and freeze–thawing, and no inhaler breakages occurred during the simulated tests.Conclusions: The in vitro performance of S-F Easyhaler at both dose strengths suggests that reliable dosing and robustness can be achieved under real-life stress conditions; S-F Easyhaler is a durable DPI for the management of asthma and COPD.

Banks Financing the Green Economy: A Review of Current Research

Achieving the goals of sustainable development and the transition to a green economy requires significant financial resources. Banks are active participants in the financing of projects and industries with a positive environmental and social impact. In this regard, the emerging responsible banking and its regulation are of scientific and practical interest, which ensures the relevance of the study. The aim of the study is to generalize and systematize the results of scientific research on the participation of banks in financing the green economy. In the context of the historical approach, the authors apply the methods of critical analysis, logical generalization, systematization, and grouping. The research is based on scientific publications by Russian and foreign authors. As a result, the authors substantiated the correlation of the concepts “green”,“sustainable”,“responsible” bank, and identified that such green financial instruments as green bonds, in some countries — green loans, green deposits, green leasing, and green insurance are being introduced into banking practices. Responsible banking is regulated using monetary and macroprudential policy instruments; in some countries, incentive-based regulation of responsible banking is mandatory. The authors concluded that responsible banking is moving towards the transformation of classic products and services into environmentally and socially oriented ones, accompanied by the transformation of business processes, management culture, and the content of banking policy. Responsible banking contributes to ensuring financial stability, but the regulator needs to use macroprudential tools to timely identify a green credit bubble, including through climate and environmental stress testing. Prospects for further research are aimed at assessing the impact of green financial instruments on the bank’s performance, the role of responsible banking in achieving sustainable development goals, at finding the most effective monetary and macroprudential tools to stimulate responsible banking and ensure financial stability.

Deletion of Orphan G Protein-Coupled Receptor GPR37L1 in Mice Alters Cardiovascular Homeostasis in a Sex-Specific Manner.

GPR37L1 is a family A orphan G protein-coupled receptor (GPCR) with a putative role in blood pressure regulation and cardioprotection. In mice, genetic ablation of Gpr37l1 causes sex-dependent effects; female mice lacking Gpr37l1 (GPR37L1−/−) have a modest but significant elevation in blood pressure, while male GPR37L1−/− mice are more susceptible to cardiovascular dysfunction following angiotensin II-induced hypertension. Given that this receptor is highly expressed in the brain, we hypothesize that the cardiovascular phenotype of GPR37L1−/− mice is due to changes in autonomic regulation of blood pressure and heart rate. To investigate this, radiotelemetry was employed to characterize baseline cardiovascular variables in GPR37L1−/− mice of both sexes compared to wildtype controls, followed by power spectral analysis to quantify short-term fluctuations in blood pressure and heart rate attributable to alterations in autonomic homeostatic mechanisms. Additionally, pharmacological ganglionic blockade was performed to determine vasomotor tone, and environmental stress tests were used to assess whether cardiovascular reactivity was altered in GPR37L1−/− mice. We observed that mean arterial pressure was significantly lower in female GPR37L1−/− mice compared to wildtype counterparts, but was unchanged in male GPR37L1−/− mice. GPR37L1−/− genotype had a statistically significant positive chronotropic effect on heart rate across both sexes when analyzed by two-way ANOVA. Power spectral analysis of these data revealed a reduction in power in the heart rate spectrum between 0.5 and 3 Hz in female GPR37L1−/− mice during the diurnal active period, which indicates that GPR37L1−/− mice may have impaired cardiac vagal drive. GPR37L1−/− mice of both sexes also exhibited attenuated depressor responses to ganglionic blockade with pentolinium, indicating that GPR37L1 is involved in maintaining sympathetic vasomotor tone. Interestingly, when these mice were subjected to aversive and appetitive behavioral stressors, the female GPR37L1−/− mice exhibited an attenuation of cardiovascular reactivity to aversive, but not appetitive, environmental stimuli. Together, these results suggest that loss of GPR37L1 affects autonomic maintenance of blood pressure, giving rise to sex-specific cardiovascular changes in GPR37L1−/− mice.

A data fusion approach to optimize compositional stability of halide perovskites

Summary Search for resource-efficient materials in vast compositional spaces is an outstanding challenge in creating environmentally stable perovskite semiconductors. We demonstrate a physics-constrained sequential learning framework to subsequently identify the most stable alloyed organic-inorganic perovskites. We fuse data from high-throughput degradation tests and first-principle calculations of phase thermodynamics into an end-to-end Bayesian optimization algorithm using probabilistic constraints. By sampling just 1.8% of the discretized CsxMAyFA1−x−yPbI3 (MA, methylammonium; FA, formamidinium) compositional space, perovskites centered at Cs0.17MA0.03FA0.80PbI3 show minimal optical change under increased temperature, moisture, and illumination with >17-fold stability improvement over MAPbI3. The thin films have 3-fold improved stability compared with state-of-the-art multi-halide Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3, translating into enhanced solar cell stability without compromising conversion efficiency. Synchrotron-based X-ray scattering validates the suppression of chemical decomposition and minority phase formation achieved using fewer elements and a maximum of 8% MA. We anticipate that this data fusion approach can be extended to guide materials discovery for a wide range of multinary systems.

Research on Wiener Degradation Model and Failure Mechanism of Interconnect Solder Joints Under Random Vibration Load

Electronic packaging solder joints are the key parts of mechanical fixation and electrical interconnection between electronic chips and printed circuit boards, which are prone to failure and lead to electronic device failures under the action of vibration environment stress. In regard to the failure characterization and degradation modeling of electronic packaging solder joints under vibration load, this paper adopts environmental stress tests, builds a vibration failure test platform, designs a vibration load excitation spectrum, and obtains solder joint degradation data under vibration stress; it uses the square root amplitude, form factors, and kurtosis factors to characterize the solder joint degradation process, which effectively identify the solder joint degradation node, and improve the data monotonicity of the solder joint degradation process; the Wiener process is used to build a solder joint multi-stage degradation model. Based on the EM algorithm, the hyperparameters of the degradation model have been optimized, and the universal test of the Wiener degradation model with multiple samples is carried out in accordance with the LB index. The analysis shows that the effectiveness of different samples is as high as 87.5%, which verifies the universality of the Wiener degradation model; Based on the crack morphology subject to the solder joint test and the features of the solder joint in the multi-stages, the paper analyzes the crack propagation behavior of the solder joint, and clarifies the failure mechanism of the solder joint.

Comprehensive Technology Qualification Process for Subsea Electronics Assemblies

Subsea production systems technologies are being developed steadily to address the technological issues associated with the deep-sea environment, primarily pressure, and temperature. To ensure the reliable operation of electrical/electronic systems for at least 25 years on the seabed, a comprehensive technology qualification program is proposed in this article. In relation to this, technology readiness level of the subsea electrical/electronics assembly is achieved after conducting devised environmental stress tests compliant to the internationally recognized standards, e.g., API, ISO, IEC, and IEEE. The comprehensive tests methods of the qualification program are explained to achieve the technology readiness level 3 of the subsea printed circuit board and subassemblies. Finally, experimental test results of a standalone subsea Ethernet switch and also functional verification with 100 m of electrical flying lead undergoing the prescribed test methods show that the subsea electronics comply with the international standards and is fit for use in the subsea environment.

Environmental Stress Testing for China’s Overseas Coal Power Investment Project

The advance of the Chinese “Belt and Road” initiative encourages increased overseas investment in coal power projects. However, it also brings about external environmental risks. In this paper, we use the approach of environmental stress testing to examine China’s overseas coal power investment projects by focusing on two countries: Indonesia and Vietnam. We first identify five key testing factors (i.e., coal price, utilization hours, exchange rate, carbon tax, and environmental protection requirements) by examining the market regulation and the environmental risks of coal power projects along the “Belt and Road” countries. Then, we observed changes in the enterprise value and internal rate of return (IRR) by setting different scenarios in which the values of the five stress factors varied. The results show that (1) the economics of coal-fired projects in Indonesia is most sensitive to exchange rate, while the economics of coal projects in Vietnam is most sensitive to coal price; (2) the pressure of nationally determined contributions (NDC) goals on environmental protection will push the “Belt and Road” countries to implement more stringent environmental regulation, which will reinforce environmental stress on overseas coal power investment. These results have important policy implications for the enterprise, industry, and Chinese government.

Strategies for failure prevention in a gas motor of launch vehicle control actuation system

Hydraulic servo actuators are employed for the thrust vector control of the liquid engines. Vane type gas motor, the prime mover of the system, is a critical subsystem with intricate dynamic elements such as rotor, bearings, vanes and speed regulator. Failure prevention of such critical systems, which is of paramount importance to the success of a launch vehicle mission, depends on making the design robust and ensuring that the critical parameters of the system hardware are within the specified range to give optimal performance. This paper addresses the strategies for achieving the design robustness through severe environmental stress testing and realisation of system hardware complying with quality requirements, which are essential for failure prevention. Towards this, critical environments for the gas motor have been identified and testing extended much beyond the system qualification levels, inducing failures. The test observations and data are analysed critically and design modifications made for broadening the operating environments. The quality systems and procedures for the system hardware are strengthened to assure reliable performance of the gas motor.

Coal Power Environmental Stress Testing in China

The development of China’s coal power industry is accompanied by various environmental risks. In this paper, typical coal power enterprises are taken as examples to establish a tool for environmental cost internalization and environmental risk analysis under the risk constraints of energy efficiency standards, environmental protection tax, national carbon market, water resources tax, overcapacity and renewable energy substitution. The study considered the impact on the value of coal power companies under different stress scenarios and constructed a stress testing framework for environmental risks that affect financial costs. The results show that the impacts of overcapacity and carbon market on enterprise value for individual risks are the main risk drivers that most regions face in different scenarios. In the comprehensive risk stress test, the enterprise value of the 1000 MW ultra-supercritical units in each region was found to have a small difference from the corporate value of the reasonable return in the optimistic and pessimistic scenarios, while the 300 MW and 600 MW sub critical units were more likely to deviate from the reasonable return due to low energy efficiency and high operating costs. With continuous increase in the severity of environmental risks, the environmental stress test helps coal power companies and financial institutions understand the impact of environmental risks on the financial status of the company and thus influence investment decisions.

Roll-to-roll printed and assembled large area LED lighting element

Novel continuous and mass customizable light-emitting diode (LED) lighting foil system, capable to produce adequate lighting levels for general lighting, was designed, processed, and characterized. Lighting element substrate was processed by roll-to-roll (R2R) printing using silver ink and automatic bonding of LEDs and current regulators on polyethylene terephthalate (PET) substrate using isotropic conductive adhesive (ICA). Demonstrator consisting of two basic lighting elements contained 98 LEDs and produced 860 lm when running with 25 mA operational current through the LEDs when using total electrical driving power of 8.4 W. Measured power conversion efficiency of the demonstrator was 31 % and efficacy 102 lm/W. Element produced 460 lx illumination level measured by an illumination level meter at element’s central axis at distance of 1 m. At a distance of 2 m, illumination level was 110 lx, respectively. Temperature measurements with T3Ster thermal characterization instrument showed that when driving LED with maximum nominal driving current of 100 mA, LED junction temperature was about 120 °C, when lighting element was in air in room temperature. Accelerated environmental stress tests consisting of 500 cycles from −40 … +80 °C in aging oven and 1000 h in +60 °C/95 % RH climate chamber were performed to test samples without any failures. In addition, over 700 bending cycles using 20 mm bending radius were performed to test samples without any failures, so bonding of LEDs were shown reliable according to these tests. Achieved results proved that thin, flexible, and large area high luminous flux lighting elements and systems can be processed based on plastic foil manufactured using R2R silver ink printing and R2R automatic bonding of LEDs and regulator components using ICA on that foil.

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.

Large Form Factor Hybrid LGA Interconnects; Recent Applications and Technical Learning

Recent high-end server design trends have continued to challenge electronic packaging engineers to design and integrate larger form factor land grid array (LGA) attached modules within their assemblies. These trends have included the application of larger, denser, organic packaged modules whose electrical performance and postencapsulation physical characteristics have been enabled by both the continued development of hybrid LGA connectors as well as new module actuation hardware designs. In this paper, we'll discuss these recent trends, including the specific technical attributes and challenges that need to be addressed to ensure a repeatable and reliable assembly design is developed. Initially, overviews of the latest connector and module design trends, including styles and physical sizes and their implications to the module's bottom surface metallurgy (BSM) flatness requirements, etc. are provided. Pursuant to this, recent system integration trending is reviewed; including both the module quantity per system assembly as well as module to module physical placements and how each of these impact printed wiring board (PWB) design (i.e., layer count, LGA site flatness, etc.) as well as the PWB assembly's solder processing characteristics (i.e., LGA pre- and post-solder attach contact co-planarity, etc.). Completing the application portion, is a description of some recent LGA actuation hardware and module external cooling apparatus designs (e.g., air-cooled heats sinks and water-cooling cold-plates and thermal interface materials (TIMs), etc.). The remaining portion of the paper is dedicated to the description of the mechanical analysis efforts completed to provide a fundamental understanding of the design's “as-assembled” attributes and a review of the associated evaluation completed to verify the integrated assembly's reliability characteristics. From the analysis methodology perspective, both the means of including each of the integrated assembly's key attributes (e.g., module mechanical construction and as encapsulated flatness, LGA contact compliance and stiffness as well as soldered contact coplanarity, TIM stiffness, actuation hardware, heat sink and cold-plate mechanical construction, etc.) and the resulting estimation of the predicted module internal TIM and hybrid-LGA's Pb-free soldered interface strains, actuation hardware stresses and LGA contact load variation are provided. Completing the discussion is a review of the variety of testing executed to validate the design's intended reliability. Included in this is a description of the test vehicle's design, the environmental stress testing conducted (i.e., mechanical pre-conditioning, accelerated thermal cycling (ATC), mixed flowing gas (MFG) and heat aging (HA), etc.) and the resulting data.

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

Au-Au thermocompression bonding is a reliable and space-efficient method for wafer-level sealing [1]. It is commonly performed at bond temperatures of 300 – 400 oC [1-3] and bond pressures of 0.5 – 15 MPa [1, 3]. He leak rates of 2.7 ×10-10 atm cm3 s-1 have been presented [2]. We have explored the lower temperature limits for realizing Au-Au thermocompression bonds with high yield. Further, we have investigated the reliability of the bonds when subjected to environmental stress test conditions. Test laminates were prepared by bonding bottom Si wafers to top Si wafers with 481 membranes with a nominal thickness of 36 µm and nominal dimension 2.5 × 2.5 mm2. A cross-sectional view of a single die is shown in Figure 1. Both wafers had a SiO2 layer of 7500 Å. Metal layers of 400 nm TiW and 1.2 µm Au were sputter deposited and patterned to form frames on all wafers. The nominal width of the bonding frames was 20, 40, 80, and 200 µm. The total bonding area on a 150mm wafer was 504 mm2. Top and bottom wafers were aligned and bonded in vacuum ambient in a SB6e (Suss MicroTec.) bonder applying a tool pressure of 2266 mbar for 15 minutes at temperatures ranging from 150 oC to 300 oC. The targeted bond pressure was 8.5 MPa. The bonded laminates and parameters are given in Table 1.After bonding, the inward deflection of the membranes was measured by white light interferometry. The wafers were subjected to environmental stress conditions consisting of steady-state life test (exposure to 150 °C for 1000 h), 50 cycles of thermal shock from -65 °C to +200 °C, and 10 cycles in 90 – 100 % humidity from 25 °C to 65 °C. Characterization was done by investigating the membrane deflection after each test.The hermeticity yield was defined as the percentage of membranes deflecting inwards by more than 2 µm after bonding, and is shown in Figure 1 and Table 1. An average membrane deflection was 5.5 µm. Laminates Au200 and Au250 had hermeticity yields of 65 – 75 % for all frame widths, except 200 µm wide frames on Au200. Laminate Au150 had yields of 3 – 11 % for all frame widths. Laminate Au300 appeared to be misaligned since the yield was below 2 % for frames of widths 20 – 80 µm and 54 % for 200 µm wide frames. The results indicate that at 8.5 MPa bond pressure, there seems to exist a threshold temperature for bonding between 150 oC and 200 oC. Bonding at 200 oC and 250 oC seem to be of equal quality.The membrane deflection measurements provided an estimate of the maximum air leak rate of 7.4×10-12 atm cm3 s-1. Longer storage times can reveal more accurate leak rates. No changes in membrane deflection were observed in any of the laminates after exposure to the steady-state life test, thermal shock test or moisture resistance test. The results indicate that Au-Au thermocompression bonds realized at 200 oC and 250 oC are hermetic and can withstand environmental stress test conditions.

Accelerated-stress reliability evaluation for an encapsulated wireless cortical stimulator.

In preparing a wireless cortical stimulator for use in the Intracortical Visual Prosthesis (ICVP) project at the Illinois Institute of Technology (IIT), an accelerated environmental stress test is being performed on prototype stimulator modules. Stimulator devices, containing a custom application specific integrated circuit (ASIC), and encapsulated with PDMS, were soaked in an autoclave chamber at 121°C and 100% relative humidity for more than 2200 hours with and without power supplied to the ASIC. Experimental results showed no physical degradation of the stimulator devices after soaking. Reverse telemetry that measures the stimulator internal power supply, recorded periodically over the entire test time, verified that the devices were electrically functioning, as designed, without deterioration. Taking into consideration other standard reliability test environments, the accelerated moisture resistance-biased autoclave testing duration of 2200 hours, as conducted in this study, overwhelms other less-severe test conditions and demonstrates long term stability of the proposed vision prosthesis device with proven thermo-mechanical and electrical robustness.