Helium Leak Test Research Articles

Glass welding with ultra-short laser pulses and long focal lengths A process model

The welding of glasses with ultra-short laser pulses and high-NA optics has matured to a well-established process. The short focal length requires relatively thin work pieces in the order of 1-2 mm, and the short Rayleigh length requires a very precise adjustment of the laser focus relative to the interface to be welded.To make welding of thick samples possible with relaxed alignment requirements, we welded optically contacted fused silica with a focal length of 65 mm. The resulting welding seams can be as deep as 2 mm and more. It turned out, that they grow from the focal point towards the laser source with increasing pulse energy and irradiation time. A thermal model for the growth of the molten zones will be presented and compared to the process with short focal lengths. Furthermore, the results of tensile tests and helium-leakage tests of welded fused silica samples will be presented.

3D-Printed Hermetic Alumina Housings.

Ceramics are repeatedly investigated as packaging materials because of their gas tightness, e.g., as hermetic implantable housing. Recent advances also make it possible to print the established aluminum oxide in a Fused Filament Fabrication process, creating new possibilities for manufacturing personalized devices with complex shapes. This study was able to achieve integration of channels with a diameter of 500 µm (pre-sintered) with a nozzle size of 250 µm (layer thickness 100 µm) and even closed hemispheres were printed without support structures. During sintering, the weight-bearing feedstock shrinks by 16.7%, resulting in a relative material density of 96.6%. The well-known challenges of the technology such as surface roughness (Ra = 15–20 µm) and integrated cavities remain. However, it could be shown that the hollow structures in bulk do not represent a mechanical weak point and that the material can be gas-tight (<10−12 mbar s−1). For verification, a volume-free helium leak test device was developed and validated. Finally, platinum coatings with high adhesion examined the functionalization of the ceramic. All the prerequisites for hermetic housings with integrated metal structures are given, with a new level of complexity of ceramic shapes available.

Validating Container Closure Integrity with Statistically Based Tests.

Two statistically based testing procedures, a zero-failure test and a one-failure test, are proposed for demonstrating that a vial capping process has an acceptably low rate of failed seals, i.e., nonintegral container closures, or leaky vials. These tests are developed for use with the standard helium-leak test method that measures the amount of escaped helium from a capped vial. The amount of escaped helium is a continuous measurement, and a vial is said to be leaky if the measurement exceeds a threshold and not leaky if it does not. Not leaky measurements are often less than the lower limit of validation, i.e., left-censored. By using the continuous measurements that describe the extent of leaking instead of the binary measurements, leaky or not leaky, the proposed tests are able to reach similar conclusions as tests using binary measurements but with much smaller sample sizes. The proposed tests can handle any number of measurements less than the lower limit of validation.

Failure Analysis and Salvaging of Bellow-Sealed Sodium Valve

Valves with conventional gland packing seals are not suitable in high-temperature sodium systems. Bellow-sealed valves are used in sodium systems in which bellows are used as primary leak tight barrier. Bellows are made up of very thin gauge material, and hence, most of the failures in the bellow-sealed valves are due to failure of the bellows. The cost of the bellows is typically < 20% of overall cost of the valve. This paper discusses the failure analysis of the bellows in a failed bellow-sealed sodium valve and reconditioning of the same by replacing the failed bellow with new and improved bellows. Initially, sticking sodium from the internal surfaces of the valve was cleaned using alcohol. Subsequently, the failed bellows were disassembled from the valve and a detailed failure analysis was carried out. New and improved bellows were designed initially as per Expansion Joint Manufacturer’s Association (EJMA). The geometry arrived as per EJMA was further analyzed using visco-plastic constitutive model to obtain the creep–fatigue life of the bellows. The inputs from the failure analysis were considered while evolving the new and improved design of the bellows. The bellows were tested and qualified at high temperature and installed in the bellow-sealed valve. Integral testing of the valve was carried out using pressure hold testing and helium leak testing. The valve was reconditioned for further use in sodium services.

A Chip Integrity Monitor for Evaluating Moisture/Ion Ingress in mm-Sized Single-Chip Implants

For mm-sized implants incorporating silicon integrated circuits, ensuring lifetime operation of the chip within the corrosive environment of the body still remains a critical challenge. For the chip's packaging, various polymeric and thin ceramic coatings have been reported, demonstrating high biocompatibility and barrier properties. Yet, for the evaluation of the packaging and lifetime prediction, the conventional helium leak test method can no longer be applied due to the mm-size of such implants. Alternatively, accelerated soak studies are typically used instead. For such studies, early detection of moisture/ion ingress using an in-situ platform may result in a better prediction of lifetime functionality. In this work, we have developed such a platform on a CMOS chip. Ingress of moisture/ions would result in changes in the resistance of the interlayer dielectrics (ILD) used within the chip and can be tracked using the proposed system, which consists of a sensing array and an on-chip measurement engine. The measurement system uses a novel charge/discharge based time-mode resistance sensor that can be implemented using simple yet highly robust circuitry. The sensor array is implemented together with the measurement engine in a standard 0.18 μm 6-metal CMOS process. The platform was validated through a series of dry and wet measurements. The system can measure the ILD resistance with values of up to 0.504peta-ohms, with controllable measurement steps that can be as low as 0.8M Ω. The system works with a supply voltage of 1.8V, and consumes 4.78mA. Wet measurements in saline demonstrated the sensitivity of the platform in detecting moisture/ion ingress. Such a platform could be used both in accelerated soak studies and during the implant's life-time for monitoring the integrity of the chip's packaging.

Interfacial and Cross-sectional Studies of Thermally Cycled Alumina-Monel Brazed Joint

Alumina and monel superalloy was successfully joined by active metal brazing technique using Ticusil (68.8Ag-26.7Cu-4.5Ti in wt%) filler alloy in a vacuum furnace at 910°C for 10 min under a vacuum of 5×10–6 Torr. Phase analysis of the monel-filler alloy and alumina-filler alloy interfaces was conducted by X-ray diffraction analysis. Interfacial and cross-sectional microstructural investigation and determination of elemental composition were performed by scanning electron microscopy and energy dispersive X-ray analysis. No crack was found at the joint interfaces after thermal cycling test for 100 cycles between 50° and 600°C. Microhardness was estimated by Vickers hardness tester at the cross-section of the joint after thermal cycling test. Typical brazing strength of the thermally cycled joint was above 23 MPa. Helium leak tests indicated good hermiticity of the thermally cycled brazed joints.

Progress on the manufacturing of ITER thermal shields

The role of the ITER thermal shield (TS) is to minimize the radiation heat load transferred from the warm components to the superconducting magnet operating at 4.5 K. Fabrication of the TS components is ongoing. Manufacturing of LCTS (Lower Cryostat TS) cylinder and VVTS (Vacuum Vessel TS) sector #6 was completed. The leak tightness of the cooling tubes, the on-site installation feasibility and the quality of the silver coated surfaces are main concerns during the manufacturing. Leak tightness of the cooling tubes is guaranteed by the test and the inspection. The surfaces of the cooling tube inside are inspected visually using the endoscope and the leak tightness has been qualified by the pressure and helium leak test. The on-site installation feasibilities are validated by the preassembly test at the factory. According to the qualified coating process, the TS panels are electro-plated with silver. This paper describes the manufacturing progress and the technical achievements.

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.

Fabrication and performance studies on explosively welded CuCrZr/316L bimetallic plate applied in extreme environments

In order to obtain high-quality CuCrZr/316L clad plates prepared by explosive welding (EW), theoretical analysis and numerical simulation were introduced to optimize welding parameters. The bonding properties of the achieved joints were systematically studied through multiscale interface analyses, mechanical performance tests, and evaluation of sealing properties. It was concluded that the theoretical analysis in collaboration with numerical calculations is an effective way to design parameters, because its predicted result was in good agreement with the ultrasonic test (UT) one. In both microstructure observations and mechanical tests, an excellent bonding quality of the CuCrZr/316L bimetallic plate was confirmed, where a uniform wavy morphology without defects such as voids and cracks was found at the bonding interface. The bonding strength was higher than the CuCrZr alloy. Moreover, a self-designed hydraulically pressed mold method was developed to manufacture a U-shaped CuCrZr/316L component, and the resulting sample matches well with the designed dimensions. Finally, the helium-leak test results demonstrate that the sealing property of the CuCrZr/316L bimetallic plate meets the practical requirements, indicating that the welded specimens were sound.

Lack of tightness analysis of concealed welded radiators

Stainless steel X2CrNi18-9 (304L) radiators were analysed. During detailed examination we proved that tube overlap fillet joint was welded incorrectly and had leaks. Wrong designed jig, incorrect robot movements and non-central tubes position let mounted parts move during welding operation. Shrinkage of the weld caused the tubes to move relative to each other with the formation of a larger gap on one side. Lack of correction of the robot arm movement and fixed stick-out created inadequate fusion into the tube with a smaller cross-section.Identification of non-compliance based on standard NDT methods such as visual inspection, liquid or dye penetrant inspection or X-ray was not possible. Also, destructive methods such as high-pressure water test was not be able to show this type of defect.Only innovative HLT helium leak testing method was able to show non-compliance of the joint. Helium is the ideal element to detect micro cracks in weld as it is an insert gas made up to tiny atoms and has low viscosity, so little atoms can travel fast. This method has a very big potential in the welding industry as a precise and fast NDT test on highest quality requirements.

Evaluation of Different Quality-Relevant Aspects of Closed System Transfer Devices (CSTDs).

Health care professionals can be exposed to hazardous drugs such as cytostatics during preparation of drugs for administration. Closed sytem transfer devices (CSTDs) were introduced to provide protection for healthcare professional against unintended exposure to hazardous drugs. The interest in CSTDs has significantly increased after USP <800> monograph was issued. The majority of the studies published so far on CSTDs have focused on their "containment" function. However, other important attributes for CSTDs with potential importance for product quality impact are not yet fully evaluated. In the current study, we evaluated four sytems from different suppliers, in combination with different container closure systems (CCS), using solutions of different viscosity and surface tension. The different CSTD / CCS combinations were tested for (a) containment (integrity) using a highly sensitive helium leak test, (b) the force required for mounting the vial adaptor, (c) contribution to visible and subvisible particles as well as (d) the hold-up volume. Results show that the majority of CSTDs may have leaks varying in size, and that some of them generated visible particles due to stopper coring and subvisible particles, both due to silicon oil and particulate contaminations of the Devices. Finally, the holdup volume was up to 1mL depending on the CSTD type, vial size and solution viscosity. These results show that there is a need to evaluate the compatibility of CSTD systems to select the best system for the intended use and that CSTDs may adversely impact product quality and delivered dose.

Hot Helium Leak Test of ITER blanket shield block

To ensure successful operation of the International Thermonuclear Experimental Reactor (ITER), the blanket shield block modules are required to demonstrate the vacuum performance by Hot Helium Leak Test (HHLT), which is performed at the relevant ITER operational conditions and is one of the Factory Acceptance Tests (FAT) of the product. A specific facility is developed in China to perform these demanding tests, which has a 10 m3 vacuum chamber to accommodate the large size of shield blocks and achieved an overall system leak detect sensitivity of 7.19 × 10−11Pa. m3/s at 235 °C. A full-scale proto-type of ITER shield block was tested in this facility, which showed maximum helium leak rate is less than 1.74 × 10-10Pa. m3/s under 4.2 MPa pure helium gas pressure at 235 °C. The HHLT was performed with cyclic pressure and temperature process and the results were given in this paper. The behavior of the background leak rate during these processes were also monitored and discussed.

Pipe-to-pipe friction welding of dissimilar Al-SS joints for cryogenic applications

In the present investigation, dissimilar materials such as AA6063 and SS304L having pipe dimensions of 60.33 mm outer diameter and 3.9 mm wall thickness were friction-welded with different conditions of process parameters. Nondestructive tests such as radiography test (RT) and liquid penetration test (LPT) were carried out on the welded pipes in order to qualify weld joint. Thermal shock test and helium leak tests were performed on the successful welded samples in order to check its ability to work with cryogenic application. The results revealed that the pipe-to-pipe configuration of dissimilar Al–SS joints was produced successfully by friction welding using continuous drive. There were no defects presented in the joint area as revealed by RT and LPT. Thermal shock test and helium leak tests have also confirmed the soundness of joints. Higher deformation of Al base material results in the huge flash formation of Al that results in the sleeve formation of Al pipe on SS pipe. The helium leak test has confirmed the soundness of joints without any defects after its testing at 1.2 psi pressure. More than 60% of joint efficiency was obtained from Al–SS friction-welded joints.

Microwave-assisted alumina-zirconia brazed joint for microwave tubes

Alumina-zirconia joint was fabricated by microwave-assisted brazing technique at 980 °C for 15 min using TICUSIL (68.8Ag26.7Cu4.5Ti in wt%) as the brazing alloy. The brazed joints were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Vickers microhardness evaluation, brazing strength measurement, and helium leak test. X-ray diffraction analysis confirmed the formation of Ti-based compounds at the substrate-filler alloy interfaces of the brazed joints. SEM images showed the substrate-filler alloy interfaces of the brazed joints. The EDX analysis determined the elemental compositions along the joint cross-section. Vickers microhardness measurement indicated reliable joint performance for the microwave-assisted brazed joints during actual application. Brazing strength measurement and helium leak test proved the formation of sound alumina-zirconia brazed joint by both microwave and conventional heating techniques. Scratch tests were performed on the cross-sectional surfaces of the alumina-zirconia joints. Scratch test results established the strong interfacial strength of the microwave brazed joints.

Effect of Impact Velocity on Interface Characteristics of HT-9 Steel Joints Fabricated by Magnetic Pulse Welding

The weldability window in magnetic pulse welding (MPW) is proposed for the end-closure joining of HT-9 steel tubular workpieces. Based on both theoretical and experimental investigations, the impact velocity of the flyer tube at the moment of collision had a dominant effect on the bonding characteristics of the resultant joints and the optimal impact velocity was estimated to be in the range of 265–290 m/s in this alloy system. Under the optimal process conditions, no leak was detected during helium leak testing. Moreover, the integrity of the joint interface was preserved until the tube section ruptured during internal pressure burst testing. For HT-9 steel, the ductile δ-ferrite phase produced by the localized interfacial melting during MPW acted as an effective obstacle to crack propagation, thereby enhancing the fracture resistance of the joint interface. All of the results demonstrated the high integrity and durability of the HT-9 steel tube assembly fabricated by the MPW process.

Quantifying the Vial-Capping Process: Reexamination Using Micro-Computed Tomography.

A vial-capping process for lyophilization stopper configurations was previously quantified using residual seal force (RSF). A correlation between RSF and container closure integrity (CCI) was established, and component positional offsets were identified to be the primary source of variability in RSF measurements.To gain insight into the effects of stopper geometry on CCI, serum stoppers with the same rubber formulation were investigated in this study. Unlike lyophilization stoppers that passed CCI (per helium leak testing) even with RSF of 0 N owing to their excellent valve seal, serum stoppers consistently failed CCI when RSF was <15.8 N. When the plug was removed, both types of stoppers exhibited a comparable critical lower RSF limit (19-20 N), below which CCI could not be maintained. When CCI was retested at later time points (up to 6 mo), some previously failed vials passed CCI, suggesting that CCI improvement might be related to rubber relaxation (viscous flow), which can fill minor imperfections on the vial finish.To confirm component positional offsets are the primary sources of RSF variability, a novel quantification tool-micro-computed tomography (micro-CT)-was used in this study. Micro-CT provided images for quantification of positional offsets of the cap and stopper that directly correlated with RSF fluctuations. Serum stoppers and lyophilization stoppers are comparable in RSF variations, although lyophilization stoppers are more robust in CCI. The use of micro-CT provides a nondestructive and innovative tool in quantitatively analyzing component features of capped vials that would otherwise be difficult to investigate.

Sealing of glass with titanium by glass pressing at the softening point

Hermetic and mechanically strong glass-to-metal seals are required for many applications in technological fields such as aerospace engineering or medical engineering. While traditional glass-to-metal bonding technologies require melting of the glass, modern technologies such as anodic bonding use glass in its solid state. In this publication, a novel glass-to-metal bonding method with process temperatures around the softening point of the glass material is investigated. A glass window (silica based crown glass B270) in a titanium (grade 5) housing is manufactured by applying compressive force to the glass in a controlled low pressure argon atmosphere. Adherence of the glass-to-metal interface is determined with a universal testing machine. Hermeticity is measured directly with either pressure gain test or helium leak test. Experiments were performed in a full factorial design with 3 different process temperatures, 3 different process forces and 3 different methods for preparing the titanium surface. The results indicate that the bonding method is capable of producing hermetic seals with leak rates below 10−8 mbar l/s. Roughening of the metal surface generally improves both hermeticity and interface strength. Bonding strength can be further improved by increasing either processes temperature or, especially for rough surfaces, process force. For improving hermeticity either processes temperature or, especially for smooth surfaces, process force must be increased. The results indicate that successful bonding of glass and titanium with the new bonding method is influenced by the effects of mechanical interlocking and chemical reactions at the material interface.

Experimental study for manufacturing 316L/CuCrZr hollow structural component

In this study, a multi-step welding method combining explosive welding, laser welding, and Tungsten Inert Gas (TIG) welding was developed to manufacture 316L/CuCrZr hollow structural component. The welding parameters were selected according to theoretical calculations and preliminary tests, and the bonding qualities were evaluated by microstructure analyses and mechanical tests. The results demonstrated that this method was a feasible way to manufacture hollow structural components. All the joints exhibited good quality without micropores and cracks, and the tensile shear testing confirmed that the joining section was not the weakest element of the component. Under bending load, no separation, tearing or fracture was observed at the 316L/CuCrZr interface. The helium leak test results also proved that the welded specimens were sound. In addition, a hardening phenomenon near the 316L/CuCrZr interface was revealed by microhardness tests and fractography studies on tensile specimens.

Cost-Effective Testing Solutions for Sealing Material With IR Package

Hermeticity is one of the critical issues for infrared (IR) device package since the leakage will impair the functionality of the device. In this paper, two types of tests are conducted, i.e., moisture sensitivity test and helium leakage test. Pure material moisture sensitivity test is done in the first step, for the samples are made of pure hermetic sealing material and the cost is very low. The samples are subjected to moisture sensitivity level 1 (MSL1) condition, then desorbed by isothermal thermogravimetric analysis TGA at constant temperature 85 °C, and then followed by subsequent simulations to compare void penetration time and final relative humidity for different types of materials. The results show that the simulation can extend the time of the test to the fully dry/saturated condition, so that the test time/labor cost can be greatly reduced. The test results show that epoxy-based materials are suitable for this method. The moisture diffusion data repeatability is quite good and strictly follows Fick’s law. For glass material, TGA test has limitations in sample preparation. Voids are generated in glass samples during screen printing, which will lead to inaccurate test results. Then, helium leakage test is done by using alumina substrate bottom casing hermetically sealed by a silicon filter as the testing sample. The selected sealing materials are the ones with longer penetration time in TGA test and simulation. Bonding surfaces have no surface finish considering low cost. Sample preparation is not limited to epoxy-based materials. High-temperature storage (HTS) and thermal cycling (TC) are carried out to detect the hermeticity changes. The results show that some of the glass samples have peeling issues with anti-reflective coating after reliability test, although helium leak rate is slightly better. In conclusion, the advantage of moisture sensitivity test is low cost and can identify whether the material can pass or fail MSL1 condition. However, helium leakage test has fewer limitations in sample preparation. Combined with TC and HTS, helium leakage test can detect the material degradation and bonding quality effect. TGA and helium leakage test are combined together to enhance the hermeticity of IR package in this paper.

Silica‐free sealing glass for sodium‐beta alumina battery

AbstractA CaO‐Bi2O3‐Al2O3‐B2O3 glass system was studied as a sealant for sodium‐sulfur battery. The thermal properties such as thermal expansion coefficient, glass transition, and softening temperature were determined by dilatometry and differential scanning calorimetry. Selected glasses, based on the thermal properties, were bonded with α‐alumina substrate followed by aging in air at 400°C for 100 hours and in sodium vapor at 350°C for 100 hours. The interfacial compatibility and resistance to sodium vapor corrosion of the bonded and aged samples were evaluated by structural and microstructural analysis using X‐ray diffractometer (XRD) and scanning electron microscope (SEM) attached with energy dispersive spectroscope (EDS). Helium leakage test was performed at room temperature to examine the sealing ability of the select glass. It is found that Bi2O3 increases the thermal expansion coefficient, decreases the glass transition and softening temperature, shows excellent interfacial compatibility and thermal cycling resistance, improves sealing ability, and degrades sodium corrosion resistance.