Solder Glass Research Articles

Study on the Effects of Organic Bonding Agent and Low-Temperature Glass Solder Process on the Performance of Compact Packaged Fiber Optic Temperature Sensors

Study on the Effects of Organic Bonding Agent and Low-Temperature Glass Solder Process on the Performance of Compact Packaged Fiber Optic Temperature Sensors

Encapsulation of SiC/SiC cladding tubes with excellent mechanical performance and air tightness using a CaO-modified Y2O3–Al2O3–SiO2 glass

Currently, the encapsulation of SiC/SiC has been a key technical challenge limiting further application, and YAS-based glass offered a possible solution. In this paper, different CaO-doped Y2O3–Al2O3–SiO2 (YAS) glass solders were prepared and employed to join SiC/SiC. The joints were all structurally dense with the room temperature shear strengths higher than or equal to ∼51.7 MPa. Notably, joints containing 3.0 wt% CaO exhibited increased shear strength of ∼57.1 MPa, and the shear strength at 1200 °C was about 15.8 MPa in an air environment, meeting the requirements of the LOCA conditions. Optimal performance was achieved by using 3.0 % CaO-doped YAS glass to encapsulate SiC/SiC cladding, yielding a continuous, dense encapsulation region with predominantly small closed pores (≤1.0 mm3). Glass infiltration was found in both the end plug and cladding wall. The joints did not leak after 72h of holding pressure at 15 MPa, indicating their excellent air tightness.

Multifunctional Hybrid Material for Endoprosthetic Implants Based on Alumina-Toughened Zirconia Ceramics and Additively Manufactured TiNbTa Alloys.

Aseptic implant loosening after a total joint replacement is partially influenced by material-specific factors when cobalt-chromium alloys are used, including osteolysis induced by wear and corrosion products and stress shielding. Here, we aim to characterize a hybrid material consisting of alumina-toughened zirconia (ATZ) ceramics and additively manufactured Ti-35Nb-6Ta (TiNbTa) alloys, which are joined by a glass solder. The structure of the joint, the static and fatigue shear strength, the influence of accelerated aging, and the cytotoxicity with human osteoblasts are characterized. Furthermore, the biomechanical properties of the functional demonstrators of a femoral component for total knee replacements are evaluated. The TiNbTa-ATZ specimens showed a homogenous joint with statistically distributed micro-pores and a slight accumulation of Al-rich compounds at the glass solder-TiNbTa interface. Shear strengths of 26.4 ± 4.2 MPa and 38.2 ± 14.4 MPa were achieved for the TiNbTa-ATZ and Ti-ATZ specimens, respectively, and they were not significantly affected by the titanium material used, nor by accelerated aging (p = 0.07). All of the specimens survived 107 cycles of shear loading to 10 MPa. Furthermore, the TiNbTa-ATZ did not impair the proliferation and metabolic activity of the human osteoblasts. Functional demonstrators made of TiNbTa-ATZ provided a maximum bearable extension-flexion moment of 40.7 ± 2.2 Nm. The biomechanical and biological properties of TiNbTa-ATZ demonstrate potential applications for endoprosthetic implants.

Investigation of the Processing Behavior and Stability of Different Glass Frit Materials

Although glass frit bonding has long been a well-established process in the industry, research and development efforts are continuously improving it for application in modern MEMS products. First, it should be mentioned that the main advantage of the glass frit bonding is easily integration of this process module into even the most complex technologies. Using screen printing, the glass frit paste can be applied in a structured manner to one of the two wafers to be bonded, no subsequent structuring (e.g., by lithography and etching) is necessary. Subsequently, the paste is transformed into a compact glass in a batch process (the organic binder is burned out in a furnace and the glass particles are melted). The bonding is performed in conventional wafer bonders. The glass frit, which is located as an intermediate layer between the wafers to be bonded, is melted, and joined by surface wetting to form a heretic seal (vacuum or defined gas pressures can be included). During cooling the glass solidifies and forms a very strong and reliable bond. Virtually all surface layers utilized in microsystems technology can be bonded. The surface roughness of the wafers does not play any role here and even rather high topographies (e.g. metal lines in the bond interface) can be well covered and sealed [1]. Related to this process flow, the glass frit bonding is very cost attractive, e.g., compared to Al-Ge eutectic bonding.The research and development activities of the last years, the requirements that led to them and the corresponding solutions are to be presented and discussed here. Bond frame width: screen printing is mostly associated with very coarse and broad structures and in fact a few years ago, the bond frame width determined the chip size. In the meantime, bond frame widths of 100 µm and smaller can be realized, which is hardly larger than with other bonding processes and allows the economical production of small chips. To realize this, special new screen materials are of key importance. Wafer layout of the Glass Frit layer: with the smaller chips, sealing rings at the wafer edge and support structures in the scribe line, the degree of coverage during screen printing increased significantly, which makes the release of the screen and thus a defined printing process much more challenging. These requirements can be achieved with the new screen materials and measures for keeping the back of the printing screen clean. Glass frit in complex manufacturing chains: Glass frit wafer bonding is not only utilized at the very end of the process to encapsulate MEMS structures; it is now also part of complex wafer level packaging technologies for realizing SoC (system on chip) solutions. After wafer bonding, many different process steps are implemented to create through-silicon-vias (TSVs) and solderable metallizations, for example. The above-mentioned sealing rings at the wafer edge are an important requirement for bonded wafers in such processes, in which mainly wet chemicals are used, therefore it is also essential that the glass frit is chemically resistant and thermally stable up to a certain temperature. This was investigated for different glass frit materials, and it can be concluded that there is a good stability against water and solvents. The resistance to bases varies from material to material and acids usually destroy the glass (Figure 1). Regarding the temperature, it can be stated that up to 50 °C below the bonding temperature, the Glass frit can be considered as solid. Lead-free glass frit materials: until now, lead in glass frit materials was exempt from the legal regulations governing their use. These exemptions will expire in the foreseeable future [2]. Therefore, the detailed evaluation of lead-free glass frits is of very high importance. These materials are currently being investigated in terms of the entire process chain in preparation for industrial application. This evaluation faces some challenges (crystallization tendency of lead-free glasses) but also advantages (e.g., significantly low bonding temperatures are possible with Te-based glass solders). Even though glass frit bonding appears at first glance to be a well-understood process that is easy to apply. There are several modern manufacturing processes, with new challenges that can be mastered by understanding the materials and the processes. However, this requires extensive research and optimization.Literature:[1] Knechtel, Roy. "Glass frit bonding: an universal technology for wafer level encapsulation and packaging." Microsystem technologies 12.1-2 (2005): 63-68.[2] DIRECTIVE 2011/65/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL Figure 1

Synergistic effect of graphene on improving laser sealing performance of inorganic glass solder

Synergistic effect of graphene on improving laser sealing performance of inorganic glass solder

Microstructure and Wettability of Glass Solder on Al2O3 Ceramic and Its Joints Properties

The borate glass 35B2O3–25SiO2–25Na2O-10ZnO3–5BaO (in wt.%) formed the basis for the glass system employed in this study. In air at various pressures and temperatures, 96 wt.% pure alumina ceramics (96 Al2O3) were brazed together using glass solder. At the same time, the wettability of the glass on the Al2O3 ceramics is researched at different temperatures and pressures. The results demonstrated that the contact angle of glass on Al2O3 ceramics was decreased with the temperature increasing, and attached 18 degrees as temperature was 580 °C with holding 120 mins. It was also concluded that the bubbles in the glass solder were changed from round to oval and the quantity was decreased with the pressure increasing. Furthermore, the thickness of the glass solder was decreased with the pressure and temperature. When the pressure was changed from 5 kPa to 20 kPa at 560 °C welding temperature, thickness of glass solder is decreased from 22.3 μm to 8.5 μm. Upon increasing the temperature at 10 Kpa, the thickness of glass solder was from 23.74 μm to 6.2 μm. The EDS analysis for Al2O3/glass/Al2O3 joints boned at 560 °C under 20 kPa and 580 °C under 10 kPa, respectively. The elements Si and O were observed in joint domain that penetrated into alumina ceramic layer forming the interface layer with ceramic substrate thoroughly.

Structural study of hermetic seal formed by water glass at low temperature when trapped between glass plates

Hermetic sealing is an important technology in applications such as packaging of MEMS, sensors and vacuum glazing. Hydrocarbon materials like cyanoacrylate “super glue” have been used for convenient sealing. However, it is known that cyanoacrylate and other hydrocarbon glues are permeable to water vapour and do not act as a hermetic seal. On the other hand, there are some hermetic sealing techniques such as anodic bonding, ultrasonic solder bonding, solder glass bonding with or without laser assistance that require high process temperatures and are of high cost. In this paper, we assess water glass for low-cost hermetic sealing of soda lime glass at low temperatures of less than 100 °C. The vacuum level in a sample encapsulation was measured by means of a spinning rotor gauge which showed no pressure increase for one year. In addition, the bonding strength was also measured, showing that the 80 °C annealing process is the best process temperature for the highest adhesion strength.

Fracture strength of monolithic and glass-soldered ceramic subcomponents of 5-unit fixed dental prosthesis.

Zirconium dioxide ceramic has been successfully introduced as a framework material for fixed dental prostheses. To reduce manufacturing constraints, joining of subcomponents could be a promising approach to increase the mechanical performance of long-span fixed dental prostheses. In this experimental study, the biomechanical behavior of monolithic and soldered framework specimens for fixed dental prostheses made of Y-TZP was investigated. Framework specimens (n = 80) of 5-unit fixed dental prostheses made of Y-TZP were prepared and divided into 10 equal groups. The specimens were monolithic or composed of subcomponents, which were joined using a silicate-based glass solder. Thereby, three joint geometries (diagonal, vertical with an occlusal cap, and dental attachment-based) were investigated. Moreover, the groups differed based on the mechanical test (static vs. dynamic) and further processing (veneered vs. unveneered). The framework specimens were cemented on alumina-based jaw models, where the canine and second molar were acting as abutments before a point-load was applied. In addition, µCT scans and microscopic fractography were used to evaluate the quality of soldered joints and to determine the causes of fracture. The determined fracture loads of the different unveneered framework specimens in static testing did not vary significantly (p = 1). Adding a veneering layer significantly increased the mechanical strength for monolithic framework specimens from 1196.29± 203.79N to 1606.85± 128.49N (p = 0.008). In case of soldered specimens with a dental attachment-based geometry, the mechanical strength increased from 1159.42± 85.65N to 1249.53± 191.55N (p = 1). Within the dynamic testing, no differences were observed between monolithic and soldered framework specimens. µCT scans and fractography proved that the dental attachment-based joining geometry offers the highest quality. Using glass soldering technology, subcomponents of 5-unit framework specimens made of Y-TZP could be joined with mechanical properties comparable to those of monolithic frameworks.

Polarization extinction ratio in polarization maintaining fiber sealed with glass solder

The paper considers the effect of sealing with glass solder a pair of optical polarization maintaining fibers with an elliptical stress cladding on the value of the polarization extinction ratio. A variant with the placement of non-working fibers in the sealing area to create the symmetry of induced mechanical stresses is proposed. An experimental study of the contribution of the induced mechanical stresses on the value of the polarization extinction ratio has been performed. The assessment of temperature effect on the coefficient of polarization extinction in the place of sealing of optical polarization maintaining fibers has been made. Sealing of fibers in a metal tube was performed using a glass solder preform and an induction heater. Evaluation of the polarization extinction ratio was obtained by white-light interferometry using the scanning Michelson interferometer. The value of the polarization extinction ratio was measured on 4 samples with a length of working fibers of 4 meters. This experiment shows that creation of isometry structure in the area of sealing by addition of non-working fibers allows decreasing the polarization extinction ratio from 0.082 dB/K to 0.035 dB/K in the temperature range from –15 °C to +70 °C. This method allows the sealing of several fibers in one tube to reduce the size of the devices. The performed research can be useful in the development of optoelectronic devices where it is required to introduce optical birefringent fibers in a sealed housing.

Assembly and interconnection technology for high-temperature bulk acoustic wave resonators

Abstract. A sensor based on a piezoelectric single crystal enables operation even under harsh environmental conditions. In addition to the sensor element, the packaging technology is crucial for sensor performance. In this paper, a suitable assembly and interconnection technology concept of Ca3TaGa3Si2O14 (CTGS) resonators for high-temperature applications is presented as a platform for future sensor assemblies. The concept described here has already been functionally tested as a temperature sensor (Schulz et al., 2021). The concept includes a sapphire base plate, a housing lid, and a spacer made from aluminium oxide (Al2O3). The substrate is metallised with platinum manufactured into thin film and thick film technology. The ceramic components are fused with glass solder. The connection of the resonator to the conductive tracks is realised by thermosonic bonding with 25 µm platinum wire. Initially, the stability of the metallisation must be investigated before subsequent electrical testing under high temperature. Diffusion processes play a major role in this temperature range, and the stability of the layer is a necessary condition for subsequent investigations. A suitable set of bonding parameters and the strength of the platinum bonds prior to and after thermal load is analysed. Shear tests are used to evaluate the quality of the ceramic materials fused with glass solder after thermal ageing. The dielectrical properties of sapphire and glass solder such as the isolation resistance, the relative permittivity, and the loss factor at high temperatures are evaluated using interdigital structures. The loss factor is measured on both bare interdigital structures and the samples coated with glass solder to make an estimation about the conductive behaviour up to 1000 ∘C. A ceramic lid for the sensor housing is attached by a high-temperature stable glass solder. Since platinum conductors are fed through this glass solder connection, the electrical conductivity of the glass solder is characterised at high temperature. Furthermore, the hermeticity of the assemblies is verified by means of helium leakage tests. These investigations are the basis for the implementation of an assembly and interconnection technology that is suitable for reliable operation under extreme temperature conditions. The packaging technology also offers further possibilities for pressure or chemical sensors that can withstand high-temperature loads.

Nondestructive Testing of the Integrity of Solid Oxide Fuel Cell Stack Elements by Ultrasound and Thermographic Techniques

Single planar fuel cell elements consisting of metallic interconnectors that are bonded and sealed by a thin glass solder layer form the core of a solid oxide fuel cell. For reliable operation, the bonding layer has to adhere well and must be without voids or foreign material inclusions, which might cause gas leakage, electrical shorts or mechanical weakening and structural failure. Nondestructive testing (NDT) by the high-frequency ultrasound in immersion technique and by air-coupled ultrasound was optimized to find such defects. Another technique was flash light excited thermography for detection of voids. The NDT techniques used are complementary to each other, as they are based on different physical principles. Voids and small steel platelets of different sizes were prepared in the glass solder layer before the high-temperature bonding process and then monitored by the NDT techniques through the interconnector plates. Two selected NDT techniques were then validated in a probability of detection (POD) study. The study resulted in detection limits for the two main types of defects. As a step towards production testing, a demonstrator was built combining testing by air-coupled ultrasound and that by flash thermography. During the testing steps, the cell elements were handled by a collaborative robot.

Techniques and Materials for Optical Fiber Sensors Sealing in Dynamic Environments with High Pressure and High Temperature.

We detail a study of the techniques and sealing materials for optical fiber sensors used in dynamic environments with high pressure (>300 bar) and high temperature (>300 °C). The sealing techniques and materials are the key for the robustness of sensors in harsh dynamic environments, such as large combustion engines. The sealing materials and techniques studied in this work are high-temperature epoxies, metallic polymer, metallic solders, glass solder, cement, brazing and electroless nickel plating. Because obtaining high temperature simultaneously with high pressure is very difficult in the same chamber in the laboratory, we developed a new and simple method to test sealed fibers in these conditions in the laboratory. In addition, some sensors using the materials tested in the laboratory were also field tested in real thermoelectric combustion engines. The study also discusses the methods of fabrication and the cost−benefit ratio of each method.

Artificial intelligence for defect detection in infrared images of solid oxide fuel cells

Active thermography is considered in this paper as a non-destructive testing technology to ensure the quality of solid oxide fuel cells. The acquired infrared images are automated processed by artificial intelligence methods in order to detect defects within the glass solder layer of solid oxide fuel cells. For this purpose, three supervised machine learning methods are investigated: (1) Support Vector Machine, (2) Adaptive Boosting, (3) U-Net. Among those methods, the U-Net method outperforms the other considered methods with higher accuracy and F-measure.

Wetting and joining of surface-oxidized SiC ceramic with calcium lithium aluminosilicate glass filler

A novel strategy was developed to join SiC ceramics via a two-step method (i.e., SiC surface was modified by pre-oxidation treatment before bonding) using CaO-Li2O-Al2O3-SiO2 (CLAS) glass as the joining material. The wetting behavior, joint microstructure, bonding strength, fracture characteristics, and joining mechanism were investigated. Due to the formation of the SiO2 layer on the SiC surface by the pre-oxidation, the wettability of CLAS glass solder on the SiC matrix was significantly improved and the interfacial bonding was also enhanced. The microstructure of the joint revealed that the nanoscale eutectic structure composed of wollastonite and spodumene and the rod-shaped anorthite with micron-size were the main products in the joint seam. Besides, the content and size of anorthite in the joints increased with the increase of the joining temperature. Compared with one-step joining, the two-step method can obtain more reliable SiC/SiC joints due to the strong interfacial bonding. As a result, the optimal shear strength of 127 MPa was achieved at a joining temperature of 1240 °C, which was 119% higher than that obtained by the one-step joining method.

Heat Conductivity Based Inner Cavity Pressure Monitoring and Hermeticity Monitoring for Glass Frit Wafer Bonded MEMS Devices

Hermetic sealing is important regarding functionality and reliability for MEMS components. Typically this sealing is done at the wafer level using wafer bonding, which simultaneously provides mechanical protective caps. Here, a universally usable MEMS Foundry technology for inertial sensors and the glass frit bonding to seal them are introduced. A test structure for inner cavity pressure measurement, utilizing the pressure dependence of heat transfer in gasses, which can be realized in this MEMS technology, is introduced and described for use in detailed investigations of factors, which influence the inner cavity pressure in the wafer pre-processing and wafer bonding step itself. These investigations ultimately allowed optimized wafer processing, improved process control, and reliability investigation. We show how, based on the inner cavity pressure measurements, the glass frit bond process can be set up, that side effects such as storing times of the glass frit can be understood, how fine tuning of the bond process can be done, and how both process stability and device reliability can be efficiently be proven.

Bending strength of ceramic compounds bonded with silicate-based glass solder

AbstractIn the field of dental technology, the length of ceramic pontics is limited to avoid mechanical failure. To reduce thermal-induced residual stress within the ceramic, using smaller subcomponents and subsequent bonding with silicate-based glass solder may be a favorable approach. Thus, the bending strength of zirconia compounds bonded with different silicate-based glass solders was investigated. For this purpose, rectangular specimens made of zirconia were bonded by glass solder. Parameters such as the scarf angle (45° and 90°), two different glass solders, as well as the soldering process (pressure and surface treatment) were varied. All specimens were subjected to quasi-static four-point bending tests according to DIN EN ISO 843-1. Additionally, the quality of the glass solder connection was evaluated usingμCT and fractography. In the present study, zirconia compounds were sucessful bonded of zirconia compounds using silicate-based glass solder was. No significant differences in terms of bending strength were observed with respect to the different bonding parameters analyzed. The highest bending strength of 130.6 ± 50.5 MPa was achieved with a 90° scarf angle combined with ethanol treatment of the specimens before soldering and an additional application of a pressure of 2 bars in a dental pressure pot before subsequent soldering. Nevertheless, the bending strengths were highly decreased when compared to monolithic zirconia specimens (993.4 ± 125.5 MPa).

Fiber Bragg grating accelerometer based on symmetrical tilting cantilever beams and solder glass packaging for harsh environment

A high-reliability acceleration sensor based on fiber Bragg grating (FBG) that can be used in downhole for a long time is proposed, which is aimed at solving the problem of low-reliability of existing optical fiber acceleration sensors in the field of petroleum and natural gas resources exploration. The acceleration sensor uses the inertial force generated by the mass to make the symmetrically tilting cantilever beams bend slightly to detect the vibration signal. Using solder glass to package FBG is an important method to ensure that the sensor maintains high stability in harsh environment. It can significantly reduce the creep and improve the thermal shock resistance of the sensor. Through theoretical calculation, the sensitivity formula of sensor is derived, and the size parameters that can maximize sensitivity is solved by MATLAB. After that, the performance of the sensor and the stability at high temperature are tested. Experiments show that the operating frequency range of the acceleration sensor is from 0.1 Hz to 30 Hz, the sensitivity is 290 pm/g at room temperature, and the maximum lateral interference degree is 3.6%. Most importantly, the sensor packaged by glass welding can keep excellent stability under long-term high temperature. Moreover, the sensor has a quick response to severe temperature shock and can maintain measuring accuracy after cyclic thermal shocks. Therefore, the sensor can be reliably used for micro-vibration measurement in harsh environments such as downhole.

Microstructure and properties of SiCf/SiC composite joints with CaO–Y2O3–Al2O3–SiO2 interlayer

Using CaO, Y2O3, Al2O3, and SiO2 micron-powders as raw materials, CaO–Y2O3–Al2O3–SiO2 (CYAS) glass was prepared using water cooling method. The coefficient of thermal expansion (CTE) of CYAS glass was found to be 4.3 × 10−6/K, which was similar to that of SiCf/SiC composites. The glass transition temperature of CYAS glass was determined to be 723.1 °C. With the increase of temperature, CYAS glass powder exhibited crystallization and sintering behaviors. Below 1300 °C, yttrium disilicate, mullite and cristobalite crystals gradually precipitated out. However, above 1300 °C, the crystals started diminishing, eventually disappearing after heat treatment at 1400 °C. CYAS glass powder was used to join SiCf/SiC composites. The results showed that the joint gradually densified as brazing temperature increased, while the phase in the interlayer was consistent with that of glass powder heated at the same temperature. The holding time had little effect on phase composition of the joint, while longer holding time was more beneficial to the elimination of residual bubbles in the interlayer and promoted the infiltration of glass solder into SiCf/SiC composites. The joint brazed at 1400 °C/30 min was dense and defect-free with the highest shear strength of about 57.1 MPa.

Joining of sintered SiC ceramics at a lower temperature using borosilicate glass with laser cladding Si modification layer

The silicon carbide whose surface had been modified by laser cladding silicon layer was soldered by borosilicate glass. And the borosilicate glass solder had a thermal expansion coefficient similar to that of the silicon carbide substrate. The laser cladding silicon layer significantly improved the wettability between molten glass solder and silicon carbide and could reduce the soldering temperature. A sandwich-like joining structure (SiC/Si/solder/Si/SiC) was made after the borosilicate glass slurry put on the laser cladding silicon layers. The microstructure, compositions, and interfacial properties were studied. Results showed that good adhesion between silicon carbide and the glass soldering layer was achieved. The flexural strength of the connection structure prepared at 900 °C in the air reached 110 MPa. This research provides an effective technical solution for realizing local heat treatment soldering of large silicon carbide components.

Factors influencing the performance parameters of vacuum glazed smart windows to net zero energy buildings

The progression of smart technologies such as vacuum glazed windows are considered a realistic achievement of the net energy zero buildings (NZEBs). From designers to researchers to builders, there has been an increasing concern about understanding the inter-dependencies between the parameters and influencing factors that determine the performance of vacuum glazed smart windows. This research reviews the performance parameters such as thermal transmittance (U value), thermal resistance (R value), solar transmittance (g value), visible light transmittance (tv value) and  thermal resistance of residual gas space (Rgas value). These are inter-dependent on factors such as edge seal, support pillar array, low emittance coatings, getters, and effective evacuation process. This research implicates that effective hermetic edge seal provides longevity such as fusion and solder glass edge sealed vacuum glazing could be cost-effective and energy efficient solution. Stainless steel support pillar array is an unavoidable compromise on U value. This review shows that an increase of the size of glass sheet increases support pillar array improving the overall U value. Also, an addition of low emittance coatings enhances U value whilst maintaining tv value. To improve the overall life span of the vacuum glazed smart window, an incorporation of combo-getter that absorb any gases released from the internal glass surfaces in to into the vacuum cavity from the glass surface which prevents degradation of vacuum pressure and provide long term vacuum pressure stability in the vacuum glazed smart window. A recent improvement in the understanding of evacuation process shows that hot-plate surface heat induction of 60?C improved the vacuum pressure and mitigates the pump-out hole sealing process whilst lessening the temperature induced stresses.